research article keggin-type heteropolyacid for ring...
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Research ArticleKeggin-Type Heteropolyacid for Ring-Opening Polymerizationof Cyclohexene Oxide Molecular Weight Control
Ahmed Aouissi1 Zeid Abdullah Al-Othman1 and Abdurrahman Salhabi2
1Department of Chemistry College of Science King Saud University PO Box 2455 Riyadh 11451 Saudi Arabia2King Abdulaziz City for Science and Technology PO Box 6086 Riyadh 11442 Saudi Arabia
Correspondence should be addressed to Ahmed Aouissi aouissedyahoofr
Received 20 April 2015 Accepted 7 June 2015
Academic Editor Jose Ramon Leiza
Copyright copy 2015 Ahmed Aouissi et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Polymerization of 12-cyclohexene oxide (CHO) in dichloromethane was catalyzed by 12-tungstophosphoric acid(H3PW12O40sdot13H2O) as a super solid acid The effect of polymerization parameters such as reaction time temperature and
catalyst amount was investigated The effect of acetic anhydride as a ring-opening agent was also investigated The resultingpoly(12-cyclohexene oxide) (PCHO) was characterized by Fourier transform infrared (FTIR) nuclear magnetic resonancespectroscopy (1HNMR) gel-permeation chromatography (GPC) and differential scanning calorimetry (DSC) It has been foundthat the PCHO prepared over H
3PW12O40sdot13H2O has a stereoregularity higher than that prepared over clay and Aluminium
alkoxide catalysts The 119879g value obtained is due to the microstructure but not to molecular weight The yield and the molecularweight of the polymer depend strongly on the reaction conditions Molecular weights can be readily controlled by changingreaction temperature reaction time and catalyst amount Contrary to most polymerization reactions the molecular weightincreases with the temperature increase Addition of acetic anhydride to the reaction medium increased the yield threefold
1 Introduction
Due to their high polarizability and flexibility polyethersconstitute a very important soft segment for producingthermoplastic elastomers Many of these polymers have beensynthesized by ring-opening polymerization (ROP) of cyclicether monomers [1] Among cyclic monomersrsquo ring-openingpolymerization that of cyclohexene oxide (epoxide) intopolycyclohexene oxide (polyether) has been the subject ofa large number of papers [2ndash5] This is due to the fact thatcyclohexene oxide (CHO) polymers are useful materials Infact they are used in the synthesis of various alicyclic targetmaterials including pesticides pharmaceuticals perfumeryand dyestuffs ROP of cyclic ethers could be initiated byelectrophilic agents such as Broslashnsted acids (HCl H
2SO4
HClO4 etc) and Lewis acids (AlCl
3 BF3OEt2 TiCl
4 etc)
However the protonic acid catalysts used are corrosive andnot recoverable and the Lewis acids required great amountto achieve acceptable polymer yields Because of increasing
environmental concerns in recent years a more effectivecatalytic process has been sought In this respect researchershave conducted studies on the development of solid acidsso that aggressive and dangerous homogeneous acids can bereplaced to overcome the problem of separating the catalystsfrom the products and from the disposal of solidliquidwasteSolid Broslashnsted acids with super acidic character such asthe Keggin-type heteropolyacids are known as highly activecatalysts [6ndash8] Due to their strong acidity these ldquosuperacidsrdquo catalyze various reactions much more effectively thanthe conventional protonic acids [9 10] In recent yearsheteropolyacids have been used as catalysts to induce thepolymerization of various monomers such as cyclic ethersstyrene acetals polyalcohols and lactones [11ndash13] In aprevious paper [14] we have reported the polymerization oftetrahydrofuran catalyzed by a series of heteropolyacids Ithas been found that H
3PW12O40was the efficient catalyst of
the series of heteropolyacids tested This fact prompted us toinvestigate the cationic ring-opening polymerization of CHO
Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015 Article ID 826512 6 pageshttpdxdoiorg1011552015826512
2 International Journal of Polymer Science
by this catalyst The effect of reaction temperature reactiontime catalyst amount and acetic anhydride proportion onthe polymerization was investigated
2 Materials and Methods
21 Catalyst Preparation H3PW12O40was prepared accord-
ing to a now well-known method [15] that is 100 g ofNa2WO4sdot2H2O was dissolved in 100mL of warm distilled
water and then successively 85 H3PO4(5mL) and 375
HCl (22mL) were added slowly to the solution The mixturewas concentrated to three quarters of its initial volume byheating and then after that it was cooled to room temperatureThe cooled mixture was extracted with diethyl ether inhydrochloric acid medium The product formed with etherwhich settled down at the bottom was separated from theaqueous phaseThewhite crystals ofH
3PW12O40sdot13H2Owere
dried at room temperature
22 Polymerization Procedure Polymerization reactions ofCHO were carried out in dichloromethane in a glass reactorfitted with a condenser The temperature of the reactor wasadjusted by a heating jacket Typically a fixed amount ofH3PW12O40
as catalyst was added to CHO (10mL) anddichloromethane (4mL) mixture under stirring at a desiredtemperature Polymerization was terminated with additionof a saturated NaOH aqueous solution and still stirred for5min At the end of the reaction the resulting PCHOpolymer was precipitated in methanol and then filtrated offfor characterization and molecular weight measurements
23 Catalyst and Polymer Characterization The Kegginstructure of the catalyst (H
3PW12O40) was checked by means
of FTIR IR spectrum was recorded with an infrared spec-trometer GENESIS II FTIR (4000ndash400 cmminus1) as KBr pellets
The polymer was characterized by using FTIR spec-troscopy NMR spectroscopy differential scanning calorime-ter (DSC) and molecular weight measurements 1H NMRspectra were recorded on a Bruker Avance 400MHz spec-trophotometer using 5mm NMR tubes using deuteratedacetone-D6 as solvent DSC model DSC-60 made by Shi-madzu was utilized here The specimens weigh about 12mgeach Each specimen was placed in aluminum pan The panwas placed in the DSCrsquos oven in air at atmospheric pressureSpecimens were heated at a constant heating rate of 5∘Cminto 300∘C Molecular weight measurements were determinedby means of a HT-GPC Model 430 Viscotek Houston TXUSA gel-permeation chromatograph (GPC) with CLM6210column
3 Results and Discussion
31 Characterization of the Catalyst Infrared spectrum of 12-tungstophosphoric acid H
3PW12O40sdot13H2O (abbreviated as
H3PW12O40) is shown in Figure 1 According to [16] the
main characteristic features of the Keggin structure observedat 1080ndash1060 cmminus1 (]as P-Oa) at 990ndash960 cm
minus1 (]as Mo-Od)
20
16
12
8
4
Tran
smitt
ance
()
4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers (cmminus1)
Figure 1 IR spectrum of H3PW12O40
3500 3000 2500 2000 1500 1000 500
110
100
90
80
70
60
50
40
30
20
CH2
C O
Tran
smitt
ance
()
O
Wavenumber (cmminus1)
Figure 2 IR spectrum of poly(CHO) Polymerization catalyzed by02 g of H
3PW12O40at 40∘C during 3 hours in CH
2Cl2
at 900ndash870 cmminus1 (]a Mo-Od-Mo) and at 810ndash760 cmminus1 (]asMo-Oc-Mo) were obtained
32 Polymer Characterization The cationic ring-openingpolymerization of cyclohexene oxide was catalyzed byH3PW12O40
solid super acid catalyst in dichloromethane at40∘C (Scheme 1)
The IR spectrum of PCHO is shown in Figure 2 Thebands present at 2932 (120574as CH2) 2859 (120574s CH2 120574 CH) 1449(120575 CH
2) 1366 (120575 CH
2) 1158 1090 (C-O-C antisymmetric
stretching) 895 850 and 756 (120575 CH out-of-plane) Theseassignments for PCHOagree well with those of Yahiaoui et al[2] and Suga and Aoyama [17] for the PCHO prepared withan acid-exchanged montmorillonite clay catalyst
Figure 3 shows different peaks the methylene groups(cyclohexane CH
2-) at 10ndash20 ppm and methine groups
(CH2-CHO) at 32ndash36 ppm The signal of the methine
protons appears in the form of two peaks (328 and 333 ppm)which we attribute respectively to triads isotactic (mm) andheterotactic (mr and rm)These assignments for PCHO agreewell with those of Ling et al [5] for the PCHO prepared overrecyclable scandium triflate in room temperature ionic liquidcatalyst
International Journal of Polymer Science 3
O
Olowast
lowast
nH3PW12O40
40∘C CH2Cl2
Scheme 1 Reaction scheme for the synthesis of PCHO by ring-opening polymerization of CHO over H3PW12O40catalyst
40 20 030 1050 minus10
ab
c
nO c2
b2
c1
b1mm
mr + rm
lowast
120575 (ppm)
Figure 3 1HNMR spectrum of PCHO Polymerization catalyzed by02 g of H
3PW12O40sdot13H2O at 40∘C during 3 hours in CH
2Cl2
10 20 30 40 50 60 700
5
10
15
20
25
30
35
40
45
50
Yiel
d (
)
3500
4000
4500
5000
5500
6000
6500
Temperature (∘C)
Mw
(gm
ol)
Figure 4 Yield and Mw of PCHO as a function of reaction tem-perature Polymerization catalyzed by 02 g of H
3PW12O40during 3
hours in CH2Cl2
33 Effect of Reaction Temperature The effect of the reactiontemperature on the yield molecular weight and 119879g of thePCHO was investigated The reactions were carried out in atemperature ranging from 15∘C to 70∘C in dichloromethanesolvent Figure 4 shows the effect of the temperature onthe yield and on the molecular weight It can be seen thatboth the yield and the molecular weight increased withthe increase of the temperature This result is in agreementwith that reported in the literature [2] The increase of theyield with temperature is an expected result but the increaseof the molecular weight is unexpected In fact in mostpolymerization reactions the molecular weight decreases
Hea
t flow
(Wg
)
Temperature (∘C)000 5000 10000
70∘C
60∘C
50∘C
40∘C
30∘C
35∘C
25∘C
20∘C
Figure 5 Typical DSC thermograms of the prepared PCHOobtained at a heating rate of 20∘Cmin Polymerization catalyzed by02 g of H
3PW12O40during 3 hours in CH
2Cl2
with the increase of the temperature owing to the fact that thetemperature accelerates the rate of chain transfer reactionswhich in turn decreases themolecular weight [18] In the caseof CHO polymerization the increase of the molecular weightcan be explained by the fact that the HO- group bound to arigid cyclohexene ring cannot approach sufficiently close tothe oxygen atom to allow for the interchange reaction [19]
The effect of the temperature reaction on the PCHO 119879gis shown in Figure 5 It can be seen that the 119879g values areranging between 23 and 37∘C These 119879g values are differentfrom that observed by Yahiaoui et al (119879g = 7523∘C) overa clay catalyst [2] As for the PCHO prepared by Zevacoet al over Aluminium alkoxides catalyst [20] the authorsreported that they have not observed a clear glass transitiontemperature but a broad endotherm between 66 and 100∘C(max at 70∘C) which they have attributed to a melting pointof their resulting polymer The difference in the 119879g valuebetween our polymer and that of Yahiaoui et al and Zevacoet al might be due to the difference in the microstructureof the prepared polymer Indeed our PCHO which wasprepared by a super acid (Keggin heteropolyacid) has adifferent stereoregularity than that prepared by these authorsIn fact the 1H NMR spectrum of our PCHO showed onlytwo peaks (328 and 333 ppm) for the signals of the methine
4 International Journal of Polymer Science
001 002 003 004 0050
10
20
30
40
50
60
70
80
90
Yield
Catalyst amount (g)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
10000
Mw
(gm
ol)
Mw
Figure 6 Effect of catalyst amount on the molecular weight andyield for the polymerization of CHO in CH
2Cl2at 40∘C over
H3PW12O40
protons which we have attributed respectively to triadsisotactic (mm) and heterotactic (mr and rm) whereas theNMRof the PCHOprepared by Yahiaoui et al [2] and Zevacoet al [20] showed three peaks (33 34 and 35 ppm) and(366 378 and 388 ppm) respectively which they attributerespectively to triads isotactic (mm) heterotactic (mr andrm) and syndiotactic (rr)
34 Effect of Catalyst Amount To investigate the effect of theamount of catalyst on the polymerization yield andmolecularweight we carried out the polymerization reaction of CHO(10mL) in dichloromethane (4mL) at 40∘C during 3 hoursThe results obtained are reported in Figure 6 It can beseen that the polymer yield increases as the mass of thecatalyst increases whereas the molecular weight decreasesThe highestmolecular weight (9100 gmolminus1) was obtained forthe lowest amount used of catalyst (10mg) The inverse pro-portionality between themolecular weight and the amount ofcatalyst can be explained by the fact that when the amount ofthe catalyst increased the number of initiating active respon-sible sites (H+) for inducing polymerization increased andconsequently the number of chains increased which is obvi-ously at the expense of the length of the chains The decreaseinmolecular weightmight be due also to the increase in waterwhich increased with the increase of catalyst amount
35 The Effect of Reaction Time Effect of reaction time onthe yield and the molecular weight of the polymer wereexamined The polymerization reactions were catalyzed by002 g of catalyst at 40∘C in dichloromethane solvent Theresults (Figure 7) show that both the yield and molecularweight of the polymer increase with increasing reaction timeThe increase of the yield and the molecular weight was rapidfor short reaction times whereas for long time reactions aslight variation is observed A yield of 64 and a molecular
0 4 8 12 16 20 24 280
10
20
30
40
50
60
70
Yield
Time (h)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
Mw
(gm
ol)
Mw
Figure 7 Effect of reaction time on the conversion and molecularweight of PCHO in CH
2Cl2at 40∘C over H
3PW12O40
000 005 010 015 020 025 030 035 040 045 05020
30
40
50
60
70
80
90Yi
eld
()
Acetic anhydride (volume ratio)
Figure 8 Effect of acetic anhydride proportion on PCHO yieldReaction conditions T = 40∘C reaction time = 3 h
weight of 8300 gmolminus1 are reached after 21 hours of reactionThe stagnation of the molecular mass may be due to the factthat at higher yields and higher molecular weights theviscosity of the medium increased and therefore the reactionbecame kinetically slow So there was a stagnation of themolecular weight and yield
36 Effect of Acetic Anhydride Proportion Acetic anhydridehas been used for the ring-opening of many heterocycliccompounds and it has been found that the yield of thepolymer depends on its used proportion [21ndash23] That is whywe have tried to study its effect on the ring-opening of CHOTo achieve this different volumes are added to the solutionCHOCH
2Cl2 The reactions were carried out at 40∘C for
three hours The results obtained (Figure 8) showed that theyield of the polymer depends strongly on the acetic anhydrideproportion In fact when the volume ratio varies from 0 to
International Journal of Polymer Science 5
C
O
OO
CH3CO H2PW12O40 +
+CH3CO H2PW12O40 + H2PW12O40
CH3COOH
CH3
(CH3CO)2O + H3PW12O40
Initiation
Propagation
Termination
O OC
O
C
O
O
O
CH3 CH3 lowast
n
n
O O C
O
C
O
+
H2PW12O40
H3PW12O40CH3COOHCH3 CH3
n + 1
Scheme 2 Mechanism for the ring-opening polymerization of cyclohexene oxide in the presence of acetic anhydride over H3PW12O40
catalyst
030 the yield increased by 20 to 60 This shows that theinitial value has tripled When the volume ratio of the aceticanhydride added is beyond 03 the yield decreased Thedecrease of the yield at high acetic anhydride volume ratiomight be due to consumption of heteropolyacid protons bythe acetic anhydride leading to acetic acid (a weak acid) or toan increase in the number of methyl groups at the extremitiesof the chains that block the growth of polymer chains In factlarge addition of acetic anhydride to themixture creates chainends unable to take part in polymerization
37 Polymerization Mechanism The ring-opening polymer-ization of PCHO can be achieved by addition of aceticanhydride via a cationic pathway According to the obtainedresults we propose a cationic mechanism for the poly-merization initiated by protons provided by H
3PW12O40
(Scheme 2) Initiation The first stage is the protonation ofacetic anhydride by H
3PW12O40 leading to the formation
of acetyl polyoxometalate salt Then there is a nucleophilicattack of the oxygen of cyclohexene oxide on the carbon atomof the acetyl species The formed oxonium ion undergoes anucleophilic attack on the carbon by the oxygen of the cyclo-hexene oxide of the chains in growth Propagation In thisstage the protonated oxonium ion undergoes a nucleophilic
attack by a molecule of cyclohexene oxide Termination Thelast stage is a nucleophilic attack of the oxygen of the aceticacid formed in the first stage on the carbon in alpha ofpositively charged oxygen of the chains in growth
4 Conclusions
From the results it can be concluded that Keggin-type het-eropolyacid (H
3PW12O40) is an effective catalyst of the ring-
opening polymerization of cyclohexene oxide owing to itsstrong Broslashnsted acidity
The microstructure of the resulting PCHO is differentfrom that prepared over clay and alumina alkoxide catalystsThe low119879g value of the PCHO is due to themicrostructure butnot to molecular weight Contrary to most polymerizationreactions the molecular weight and the yield increase withthe increase of the temperature
The decrease in the molecular weight with the increaseof the amount of catalyst might be due to the increase ofthe amount of water which increased with the increase ofcatalyst amount or to the increase of the number of initiatingactive sites (H+) which increases the number of chains at theexpense of the length of the chains
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
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Journal ofNanomaterials
2 International Journal of Polymer Science
by this catalyst The effect of reaction temperature reactiontime catalyst amount and acetic anhydride proportion onthe polymerization was investigated
2 Materials and Methods
21 Catalyst Preparation H3PW12O40was prepared accord-
ing to a now well-known method [15] that is 100 g ofNa2WO4sdot2H2O was dissolved in 100mL of warm distilled
water and then successively 85 H3PO4(5mL) and 375
HCl (22mL) were added slowly to the solution The mixturewas concentrated to three quarters of its initial volume byheating and then after that it was cooled to room temperatureThe cooled mixture was extracted with diethyl ether inhydrochloric acid medium The product formed with etherwhich settled down at the bottom was separated from theaqueous phaseThewhite crystals ofH
3PW12O40sdot13H2Owere
dried at room temperature
22 Polymerization Procedure Polymerization reactions ofCHO were carried out in dichloromethane in a glass reactorfitted with a condenser The temperature of the reactor wasadjusted by a heating jacket Typically a fixed amount ofH3PW12O40
as catalyst was added to CHO (10mL) anddichloromethane (4mL) mixture under stirring at a desiredtemperature Polymerization was terminated with additionof a saturated NaOH aqueous solution and still stirred for5min At the end of the reaction the resulting PCHOpolymer was precipitated in methanol and then filtrated offfor characterization and molecular weight measurements
23 Catalyst and Polymer Characterization The Kegginstructure of the catalyst (H
3PW12O40) was checked by means
of FTIR IR spectrum was recorded with an infrared spec-trometer GENESIS II FTIR (4000ndash400 cmminus1) as KBr pellets
The polymer was characterized by using FTIR spec-troscopy NMR spectroscopy differential scanning calorime-ter (DSC) and molecular weight measurements 1H NMRspectra were recorded on a Bruker Avance 400MHz spec-trophotometer using 5mm NMR tubes using deuteratedacetone-D6 as solvent DSC model DSC-60 made by Shi-madzu was utilized here The specimens weigh about 12mgeach Each specimen was placed in aluminum pan The panwas placed in the DSCrsquos oven in air at atmospheric pressureSpecimens were heated at a constant heating rate of 5∘Cminto 300∘C Molecular weight measurements were determinedby means of a HT-GPC Model 430 Viscotek Houston TXUSA gel-permeation chromatograph (GPC) with CLM6210column
3 Results and Discussion
31 Characterization of the Catalyst Infrared spectrum of 12-tungstophosphoric acid H
3PW12O40sdot13H2O (abbreviated as
H3PW12O40) is shown in Figure 1 According to [16] the
main characteristic features of the Keggin structure observedat 1080ndash1060 cmminus1 (]as P-Oa) at 990ndash960 cm
minus1 (]as Mo-Od)
20
16
12
8
4
Tran
smitt
ance
()
4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers (cmminus1)
Figure 1 IR spectrum of H3PW12O40
3500 3000 2500 2000 1500 1000 500
110
100
90
80
70
60
50
40
30
20
CH2
C O
Tran
smitt
ance
()
O
Wavenumber (cmminus1)
Figure 2 IR spectrum of poly(CHO) Polymerization catalyzed by02 g of H
3PW12O40at 40∘C during 3 hours in CH
2Cl2
at 900ndash870 cmminus1 (]a Mo-Od-Mo) and at 810ndash760 cmminus1 (]asMo-Oc-Mo) were obtained
32 Polymer Characterization The cationic ring-openingpolymerization of cyclohexene oxide was catalyzed byH3PW12O40
solid super acid catalyst in dichloromethane at40∘C (Scheme 1)
The IR spectrum of PCHO is shown in Figure 2 Thebands present at 2932 (120574as CH2) 2859 (120574s CH2 120574 CH) 1449(120575 CH
2) 1366 (120575 CH
2) 1158 1090 (C-O-C antisymmetric
stretching) 895 850 and 756 (120575 CH out-of-plane) Theseassignments for PCHOagree well with those of Yahiaoui et al[2] and Suga and Aoyama [17] for the PCHO prepared withan acid-exchanged montmorillonite clay catalyst
Figure 3 shows different peaks the methylene groups(cyclohexane CH
2-) at 10ndash20 ppm and methine groups
(CH2-CHO) at 32ndash36 ppm The signal of the methine
protons appears in the form of two peaks (328 and 333 ppm)which we attribute respectively to triads isotactic (mm) andheterotactic (mr and rm)These assignments for PCHO agreewell with those of Ling et al [5] for the PCHO prepared overrecyclable scandium triflate in room temperature ionic liquidcatalyst
International Journal of Polymer Science 3
O
Olowast
lowast
nH3PW12O40
40∘C CH2Cl2
Scheme 1 Reaction scheme for the synthesis of PCHO by ring-opening polymerization of CHO over H3PW12O40catalyst
40 20 030 1050 minus10
ab
c
nO c2
b2
c1
b1mm
mr + rm
lowast
120575 (ppm)
Figure 3 1HNMR spectrum of PCHO Polymerization catalyzed by02 g of H
3PW12O40sdot13H2O at 40∘C during 3 hours in CH
2Cl2
10 20 30 40 50 60 700
5
10
15
20
25
30
35
40
45
50
Yiel
d (
)
3500
4000
4500
5000
5500
6000
6500
Temperature (∘C)
Mw
(gm
ol)
Figure 4 Yield and Mw of PCHO as a function of reaction tem-perature Polymerization catalyzed by 02 g of H
3PW12O40during 3
hours in CH2Cl2
33 Effect of Reaction Temperature The effect of the reactiontemperature on the yield molecular weight and 119879g of thePCHO was investigated The reactions were carried out in atemperature ranging from 15∘C to 70∘C in dichloromethanesolvent Figure 4 shows the effect of the temperature onthe yield and on the molecular weight It can be seen thatboth the yield and the molecular weight increased withthe increase of the temperature This result is in agreementwith that reported in the literature [2] The increase of theyield with temperature is an expected result but the increaseof the molecular weight is unexpected In fact in mostpolymerization reactions the molecular weight decreases
Hea
t flow
(Wg
)
Temperature (∘C)000 5000 10000
70∘C
60∘C
50∘C
40∘C
30∘C
35∘C
25∘C
20∘C
Figure 5 Typical DSC thermograms of the prepared PCHOobtained at a heating rate of 20∘Cmin Polymerization catalyzed by02 g of H
3PW12O40during 3 hours in CH
2Cl2
with the increase of the temperature owing to the fact that thetemperature accelerates the rate of chain transfer reactionswhich in turn decreases themolecular weight [18] In the caseof CHO polymerization the increase of the molecular weightcan be explained by the fact that the HO- group bound to arigid cyclohexene ring cannot approach sufficiently close tothe oxygen atom to allow for the interchange reaction [19]
The effect of the temperature reaction on the PCHO 119879gis shown in Figure 5 It can be seen that the 119879g values areranging between 23 and 37∘C These 119879g values are differentfrom that observed by Yahiaoui et al (119879g = 7523∘C) overa clay catalyst [2] As for the PCHO prepared by Zevacoet al over Aluminium alkoxides catalyst [20] the authorsreported that they have not observed a clear glass transitiontemperature but a broad endotherm between 66 and 100∘C(max at 70∘C) which they have attributed to a melting pointof their resulting polymer The difference in the 119879g valuebetween our polymer and that of Yahiaoui et al and Zevacoet al might be due to the difference in the microstructureof the prepared polymer Indeed our PCHO which wasprepared by a super acid (Keggin heteropolyacid) has adifferent stereoregularity than that prepared by these authorsIn fact the 1H NMR spectrum of our PCHO showed onlytwo peaks (328 and 333 ppm) for the signals of the methine
4 International Journal of Polymer Science
001 002 003 004 0050
10
20
30
40
50
60
70
80
90
Yield
Catalyst amount (g)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
10000
Mw
(gm
ol)
Mw
Figure 6 Effect of catalyst amount on the molecular weight andyield for the polymerization of CHO in CH
2Cl2at 40∘C over
H3PW12O40
protons which we have attributed respectively to triadsisotactic (mm) and heterotactic (mr and rm) whereas theNMRof the PCHOprepared by Yahiaoui et al [2] and Zevacoet al [20] showed three peaks (33 34 and 35 ppm) and(366 378 and 388 ppm) respectively which they attributerespectively to triads isotactic (mm) heterotactic (mr andrm) and syndiotactic (rr)
34 Effect of Catalyst Amount To investigate the effect of theamount of catalyst on the polymerization yield andmolecularweight we carried out the polymerization reaction of CHO(10mL) in dichloromethane (4mL) at 40∘C during 3 hoursThe results obtained are reported in Figure 6 It can beseen that the polymer yield increases as the mass of thecatalyst increases whereas the molecular weight decreasesThe highestmolecular weight (9100 gmolminus1) was obtained forthe lowest amount used of catalyst (10mg) The inverse pro-portionality between themolecular weight and the amount ofcatalyst can be explained by the fact that when the amount ofthe catalyst increased the number of initiating active respon-sible sites (H+) for inducing polymerization increased andconsequently the number of chains increased which is obvi-ously at the expense of the length of the chains The decreaseinmolecular weightmight be due also to the increase in waterwhich increased with the increase of catalyst amount
35 The Effect of Reaction Time Effect of reaction time onthe yield and the molecular weight of the polymer wereexamined The polymerization reactions were catalyzed by002 g of catalyst at 40∘C in dichloromethane solvent Theresults (Figure 7) show that both the yield and molecularweight of the polymer increase with increasing reaction timeThe increase of the yield and the molecular weight was rapidfor short reaction times whereas for long time reactions aslight variation is observed A yield of 64 and a molecular
0 4 8 12 16 20 24 280
10
20
30
40
50
60
70
Yield
Time (h)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
Mw
(gm
ol)
Mw
Figure 7 Effect of reaction time on the conversion and molecularweight of PCHO in CH
2Cl2at 40∘C over H
3PW12O40
000 005 010 015 020 025 030 035 040 045 05020
30
40
50
60
70
80
90Yi
eld
()
Acetic anhydride (volume ratio)
Figure 8 Effect of acetic anhydride proportion on PCHO yieldReaction conditions T = 40∘C reaction time = 3 h
weight of 8300 gmolminus1 are reached after 21 hours of reactionThe stagnation of the molecular mass may be due to the factthat at higher yields and higher molecular weights theviscosity of the medium increased and therefore the reactionbecame kinetically slow So there was a stagnation of themolecular weight and yield
36 Effect of Acetic Anhydride Proportion Acetic anhydridehas been used for the ring-opening of many heterocycliccompounds and it has been found that the yield of thepolymer depends on its used proportion [21ndash23] That is whywe have tried to study its effect on the ring-opening of CHOTo achieve this different volumes are added to the solutionCHOCH
2Cl2 The reactions were carried out at 40∘C for
three hours The results obtained (Figure 8) showed that theyield of the polymer depends strongly on the acetic anhydrideproportion In fact when the volume ratio varies from 0 to
International Journal of Polymer Science 5
C
O
OO
CH3CO H2PW12O40 +
+CH3CO H2PW12O40 + H2PW12O40
CH3COOH
CH3
(CH3CO)2O + H3PW12O40
Initiation
Propagation
Termination
O OC
O
C
O
O
O
CH3 CH3 lowast
n
n
O O C
O
C
O
+
H2PW12O40
H3PW12O40CH3COOHCH3 CH3
n + 1
Scheme 2 Mechanism for the ring-opening polymerization of cyclohexene oxide in the presence of acetic anhydride over H3PW12O40
catalyst
030 the yield increased by 20 to 60 This shows that theinitial value has tripled When the volume ratio of the aceticanhydride added is beyond 03 the yield decreased Thedecrease of the yield at high acetic anhydride volume ratiomight be due to consumption of heteropolyacid protons bythe acetic anhydride leading to acetic acid (a weak acid) or toan increase in the number of methyl groups at the extremitiesof the chains that block the growth of polymer chains In factlarge addition of acetic anhydride to themixture creates chainends unable to take part in polymerization
37 Polymerization Mechanism The ring-opening polymer-ization of PCHO can be achieved by addition of aceticanhydride via a cationic pathway According to the obtainedresults we propose a cationic mechanism for the poly-merization initiated by protons provided by H
3PW12O40
(Scheme 2) Initiation The first stage is the protonation ofacetic anhydride by H
3PW12O40 leading to the formation
of acetyl polyoxometalate salt Then there is a nucleophilicattack of the oxygen of cyclohexene oxide on the carbon atomof the acetyl species The formed oxonium ion undergoes anucleophilic attack on the carbon by the oxygen of the cyclo-hexene oxide of the chains in growth Propagation In thisstage the protonated oxonium ion undergoes a nucleophilic
attack by a molecule of cyclohexene oxide Termination Thelast stage is a nucleophilic attack of the oxygen of the aceticacid formed in the first stage on the carbon in alpha ofpositively charged oxygen of the chains in growth
4 Conclusions
From the results it can be concluded that Keggin-type het-eropolyacid (H
3PW12O40) is an effective catalyst of the ring-
opening polymerization of cyclohexene oxide owing to itsstrong Broslashnsted acidity
The microstructure of the resulting PCHO is differentfrom that prepared over clay and alumina alkoxide catalystsThe low119879g value of the PCHO is due to themicrostructure butnot to molecular weight Contrary to most polymerizationreactions the molecular weight and the yield increase withthe increase of the temperature
The decrease in the molecular weight with the increaseof the amount of catalyst might be due to the increase ofthe amount of water which increased with the increase ofcatalyst amount or to the increase of the number of initiatingactive sites (H+) which increases the number of chains at theexpense of the length of the chains
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
International Journal of Polymer Science 3
O
Olowast
lowast
nH3PW12O40
40∘C CH2Cl2
Scheme 1 Reaction scheme for the synthesis of PCHO by ring-opening polymerization of CHO over H3PW12O40catalyst
40 20 030 1050 minus10
ab
c
nO c2
b2
c1
b1mm
mr + rm
lowast
120575 (ppm)
Figure 3 1HNMR spectrum of PCHO Polymerization catalyzed by02 g of H
3PW12O40sdot13H2O at 40∘C during 3 hours in CH
2Cl2
10 20 30 40 50 60 700
5
10
15
20
25
30
35
40
45
50
Yiel
d (
)
3500
4000
4500
5000
5500
6000
6500
Temperature (∘C)
Mw
(gm
ol)
Figure 4 Yield and Mw of PCHO as a function of reaction tem-perature Polymerization catalyzed by 02 g of H
3PW12O40during 3
hours in CH2Cl2
33 Effect of Reaction Temperature The effect of the reactiontemperature on the yield molecular weight and 119879g of thePCHO was investigated The reactions were carried out in atemperature ranging from 15∘C to 70∘C in dichloromethanesolvent Figure 4 shows the effect of the temperature onthe yield and on the molecular weight It can be seen thatboth the yield and the molecular weight increased withthe increase of the temperature This result is in agreementwith that reported in the literature [2] The increase of theyield with temperature is an expected result but the increaseof the molecular weight is unexpected In fact in mostpolymerization reactions the molecular weight decreases
Hea
t flow
(Wg
)
Temperature (∘C)000 5000 10000
70∘C
60∘C
50∘C
40∘C
30∘C
35∘C
25∘C
20∘C
Figure 5 Typical DSC thermograms of the prepared PCHOobtained at a heating rate of 20∘Cmin Polymerization catalyzed by02 g of H
3PW12O40during 3 hours in CH
2Cl2
with the increase of the temperature owing to the fact that thetemperature accelerates the rate of chain transfer reactionswhich in turn decreases themolecular weight [18] In the caseof CHO polymerization the increase of the molecular weightcan be explained by the fact that the HO- group bound to arigid cyclohexene ring cannot approach sufficiently close tothe oxygen atom to allow for the interchange reaction [19]
The effect of the temperature reaction on the PCHO 119879gis shown in Figure 5 It can be seen that the 119879g values areranging between 23 and 37∘C These 119879g values are differentfrom that observed by Yahiaoui et al (119879g = 7523∘C) overa clay catalyst [2] As for the PCHO prepared by Zevacoet al over Aluminium alkoxides catalyst [20] the authorsreported that they have not observed a clear glass transitiontemperature but a broad endotherm between 66 and 100∘C(max at 70∘C) which they have attributed to a melting pointof their resulting polymer The difference in the 119879g valuebetween our polymer and that of Yahiaoui et al and Zevacoet al might be due to the difference in the microstructureof the prepared polymer Indeed our PCHO which wasprepared by a super acid (Keggin heteropolyacid) has adifferent stereoregularity than that prepared by these authorsIn fact the 1H NMR spectrum of our PCHO showed onlytwo peaks (328 and 333 ppm) for the signals of the methine
4 International Journal of Polymer Science
001 002 003 004 0050
10
20
30
40
50
60
70
80
90
Yield
Catalyst amount (g)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
10000
Mw
(gm
ol)
Mw
Figure 6 Effect of catalyst amount on the molecular weight andyield for the polymerization of CHO in CH
2Cl2at 40∘C over
H3PW12O40
protons which we have attributed respectively to triadsisotactic (mm) and heterotactic (mr and rm) whereas theNMRof the PCHOprepared by Yahiaoui et al [2] and Zevacoet al [20] showed three peaks (33 34 and 35 ppm) and(366 378 and 388 ppm) respectively which they attributerespectively to triads isotactic (mm) heterotactic (mr andrm) and syndiotactic (rr)
34 Effect of Catalyst Amount To investigate the effect of theamount of catalyst on the polymerization yield andmolecularweight we carried out the polymerization reaction of CHO(10mL) in dichloromethane (4mL) at 40∘C during 3 hoursThe results obtained are reported in Figure 6 It can beseen that the polymer yield increases as the mass of thecatalyst increases whereas the molecular weight decreasesThe highestmolecular weight (9100 gmolminus1) was obtained forthe lowest amount used of catalyst (10mg) The inverse pro-portionality between themolecular weight and the amount ofcatalyst can be explained by the fact that when the amount ofthe catalyst increased the number of initiating active respon-sible sites (H+) for inducing polymerization increased andconsequently the number of chains increased which is obvi-ously at the expense of the length of the chains The decreaseinmolecular weightmight be due also to the increase in waterwhich increased with the increase of catalyst amount
35 The Effect of Reaction Time Effect of reaction time onthe yield and the molecular weight of the polymer wereexamined The polymerization reactions were catalyzed by002 g of catalyst at 40∘C in dichloromethane solvent Theresults (Figure 7) show that both the yield and molecularweight of the polymer increase with increasing reaction timeThe increase of the yield and the molecular weight was rapidfor short reaction times whereas for long time reactions aslight variation is observed A yield of 64 and a molecular
0 4 8 12 16 20 24 280
10
20
30
40
50
60
70
Yield
Time (h)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
Mw
(gm
ol)
Mw
Figure 7 Effect of reaction time on the conversion and molecularweight of PCHO in CH
2Cl2at 40∘C over H
3PW12O40
000 005 010 015 020 025 030 035 040 045 05020
30
40
50
60
70
80
90Yi
eld
()
Acetic anhydride (volume ratio)
Figure 8 Effect of acetic anhydride proportion on PCHO yieldReaction conditions T = 40∘C reaction time = 3 h
weight of 8300 gmolminus1 are reached after 21 hours of reactionThe stagnation of the molecular mass may be due to the factthat at higher yields and higher molecular weights theviscosity of the medium increased and therefore the reactionbecame kinetically slow So there was a stagnation of themolecular weight and yield
36 Effect of Acetic Anhydride Proportion Acetic anhydridehas been used for the ring-opening of many heterocycliccompounds and it has been found that the yield of thepolymer depends on its used proportion [21ndash23] That is whywe have tried to study its effect on the ring-opening of CHOTo achieve this different volumes are added to the solutionCHOCH
2Cl2 The reactions were carried out at 40∘C for
three hours The results obtained (Figure 8) showed that theyield of the polymer depends strongly on the acetic anhydrideproportion In fact when the volume ratio varies from 0 to
International Journal of Polymer Science 5
C
O
OO
CH3CO H2PW12O40 +
+CH3CO H2PW12O40 + H2PW12O40
CH3COOH
CH3
(CH3CO)2O + H3PW12O40
Initiation
Propagation
Termination
O OC
O
C
O
O
O
CH3 CH3 lowast
n
n
O O C
O
C
O
+
H2PW12O40
H3PW12O40CH3COOHCH3 CH3
n + 1
Scheme 2 Mechanism for the ring-opening polymerization of cyclohexene oxide in the presence of acetic anhydride over H3PW12O40
catalyst
030 the yield increased by 20 to 60 This shows that theinitial value has tripled When the volume ratio of the aceticanhydride added is beyond 03 the yield decreased Thedecrease of the yield at high acetic anhydride volume ratiomight be due to consumption of heteropolyacid protons bythe acetic anhydride leading to acetic acid (a weak acid) or toan increase in the number of methyl groups at the extremitiesof the chains that block the growth of polymer chains In factlarge addition of acetic anhydride to themixture creates chainends unable to take part in polymerization
37 Polymerization Mechanism The ring-opening polymer-ization of PCHO can be achieved by addition of aceticanhydride via a cationic pathway According to the obtainedresults we propose a cationic mechanism for the poly-merization initiated by protons provided by H
3PW12O40
(Scheme 2) Initiation The first stage is the protonation ofacetic anhydride by H
3PW12O40 leading to the formation
of acetyl polyoxometalate salt Then there is a nucleophilicattack of the oxygen of cyclohexene oxide on the carbon atomof the acetyl species The formed oxonium ion undergoes anucleophilic attack on the carbon by the oxygen of the cyclo-hexene oxide of the chains in growth Propagation In thisstage the protonated oxonium ion undergoes a nucleophilic
attack by a molecule of cyclohexene oxide Termination Thelast stage is a nucleophilic attack of the oxygen of the aceticacid formed in the first stage on the carbon in alpha ofpositively charged oxygen of the chains in growth
4 Conclusions
From the results it can be concluded that Keggin-type het-eropolyacid (H
3PW12O40) is an effective catalyst of the ring-
opening polymerization of cyclohexene oxide owing to itsstrong Broslashnsted acidity
The microstructure of the resulting PCHO is differentfrom that prepared over clay and alumina alkoxide catalystsThe low119879g value of the PCHO is due to themicrostructure butnot to molecular weight Contrary to most polymerizationreactions the molecular weight and the yield increase withthe increase of the temperature
The decrease in the molecular weight with the increaseof the amount of catalyst might be due to the increase ofthe amount of water which increased with the increase ofcatalyst amount or to the increase of the number of initiatingactive sites (H+) which increases the number of chains at theexpense of the length of the chains
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
4 International Journal of Polymer Science
001 002 003 004 0050
10
20
30
40
50
60
70
80
90
Yield
Catalyst amount (g)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
10000
Mw
(gm
ol)
Mw
Figure 6 Effect of catalyst amount on the molecular weight andyield for the polymerization of CHO in CH
2Cl2at 40∘C over
H3PW12O40
protons which we have attributed respectively to triadsisotactic (mm) and heterotactic (mr and rm) whereas theNMRof the PCHOprepared by Yahiaoui et al [2] and Zevacoet al [20] showed three peaks (33 34 and 35 ppm) and(366 378 and 388 ppm) respectively which they attributerespectively to triads isotactic (mm) heterotactic (mr andrm) and syndiotactic (rr)
34 Effect of Catalyst Amount To investigate the effect of theamount of catalyst on the polymerization yield andmolecularweight we carried out the polymerization reaction of CHO(10mL) in dichloromethane (4mL) at 40∘C during 3 hoursThe results obtained are reported in Figure 6 It can beseen that the polymer yield increases as the mass of thecatalyst increases whereas the molecular weight decreasesThe highestmolecular weight (9100 gmolminus1) was obtained forthe lowest amount used of catalyst (10mg) The inverse pro-portionality between themolecular weight and the amount ofcatalyst can be explained by the fact that when the amount ofthe catalyst increased the number of initiating active respon-sible sites (H+) for inducing polymerization increased andconsequently the number of chains increased which is obvi-ously at the expense of the length of the chains The decreaseinmolecular weightmight be due also to the increase in waterwhich increased with the increase of catalyst amount
35 The Effect of Reaction Time Effect of reaction time onthe yield and the molecular weight of the polymer wereexamined The polymerization reactions were catalyzed by002 g of catalyst at 40∘C in dichloromethane solvent Theresults (Figure 7) show that both the yield and molecularweight of the polymer increase with increasing reaction timeThe increase of the yield and the molecular weight was rapidfor short reaction times whereas for long time reactions aslight variation is observed A yield of 64 and a molecular
0 4 8 12 16 20 24 280
10
20
30
40
50
60
70
Yield
Time (h)
Yiel
d (
)
4000
5000
6000
7000
8000
9000
Mw
(gm
ol)
Mw
Figure 7 Effect of reaction time on the conversion and molecularweight of PCHO in CH
2Cl2at 40∘C over H
3PW12O40
000 005 010 015 020 025 030 035 040 045 05020
30
40
50
60
70
80
90Yi
eld
()
Acetic anhydride (volume ratio)
Figure 8 Effect of acetic anhydride proportion on PCHO yieldReaction conditions T = 40∘C reaction time = 3 h
weight of 8300 gmolminus1 are reached after 21 hours of reactionThe stagnation of the molecular mass may be due to the factthat at higher yields and higher molecular weights theviscosity of the medium increased and therefore the reactionbecame kinetically slow So there was a stagnation of themolecular weight and yield
36 Effect of Acetic Anhydride Proportion Acetic anhydridehas been used for the ring-opening of many heterocycliccompounds and it has been found that the yield of thepolymer depends on its used proportion [21ndash23] That is whywe have tried to study its effect on the ring-opening of CHOTo achieve this different volumes are added to the solutionCHOCH
2Cl2 The reactions were carried out at 40∘C for
three hours The results obtained (Figure 8) showed that theyield of the polymer depends strongly on the acetic anhydrideproportion In fact when the volume ratio varies from 0 to
International Journal of Polymer Science 5
C
O
OO
CH3CO H2PW12O40 +
+CH3CO H2PW12O40 + H2PW12O40
CH3COOH
CH3
(CH3CO)2O + H3PW12O40
Initiation
Propagation
Termination
O OC
O
C
O
O
O
CH3 CH3 lowast
n
n
O O C
O
C
O
+
H2PW12O40
H3PW12O40CH3COOHCH3 CH3
n + 1
Scheme 2 Mechanism for the ring-opening polymerization of cyclohexene oxide in the presence of acetic anhydride over H3PW12O40
catalyst
030 the yield increased by 20 to 60 This shows that theinitial value has tripled When the volume ratio of the aceticanhydride added is beyond 03 the yield decreased Thedecrease of the yield at high acetic anhydride volume ratiomight be due to consumption of heteropolyacid protons bythe acetic anhydride leading to acetic acid (a weak acid) or toan increase in the number of methyl groups at the extremitiesof the chains that block the growth of polymer chains In factlarge addition of acetic anhydride to themixture creates chainends unable to take part in polymerization
37 Polymerization Mechanism The ring-opening polymer-ization of PCHO can be achieved by addition of aceticanhydride via a cationic pathway According to the obtainedresults we propose a cationic mechanism for the poly-merization initiated by protons provided by H
3PW12O40
(Scheme 2) Initiation The first stage is the protonation ofacetic anhydride by H
3PW12O40 leading to the formation
of acetyl polyoxometalate salt Then there is a nucleophilicattack of the oxygen of cyclohexene oxide on the carbon atomof the acetyl species The formed oxonium ion undergoes anucleophilic attack on the carbon by the oxygen of the cyclo-hexene oxide of the chains in growth Propagation In thisstage the protonated oxonium ion undergoes a nucleophilic
attack by a molecule of cyclohexene oxide Termination Thelast stage is a nucleophilic attack of the oxygen of the aceticacid formed in the first stage on the carbon in alpha ofpositively charged oxygen of the chains in growth
4 Conclusions
From the results it can be concluded that Keggin-type het-eropolyacid (H
3PW12O40) is an effective catalyst of the ring-
opening polymerization of cyclohexene oxide owing to itsstrong Broslashnsted acidity
The microstructure of the resulting PCHO is differentfrom that prepared over clay and alumina alkoxide catalystsThe low119879g value of the PCHO is due to themicrostructure butnot to molecular weight Contrary to most polymerizationreactions the molecular weight and the yield increase withthe increase of the temperature
The decrease in the molecular weight with the increaseof the amount of catalyst might be due to the increase ofthe amount of water which increased with the increase ofcatalyst amount or to the increase of the number of initiatingactive sites (H+) which increases the number of chains at theexpense of the length of the chains
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
International Journal of Polymer Science 5
C
O
OO
CH3CO H2PW12O40 +
+CH3CO H2PW12O40 + H2PW12O40
CH3COOH
CH3
(CH3CO)2O + H3PW12O40
Initiation
Propagation
Termination
O OC
O
C
O
O
O
CH3 CH3 lowast
n
n
O O C
O
C
O
+
H2PW12O40
H3PW12O40CH3COOHCH3 CH3
n + 1
Scheme 2 Mechanism for the ring-opening polymerization of cyclohexene oxide in the presence of acetic anhydride over H3PW12O40
catalyst
030 the yield increased by 20 to 60 This shows that theinitial value has tripled When the volume ratio of the aceticanhydride added is beyond 03 the yield decreased Thedecrease of the yield at high acetic anhydride volume ratiomight be due to consumption of heteropolyacid protons bythe acetic anhydride leading to acetic acid (a weak acid) or toan increase in the number of methyl groups at the extremitiesof the chains that block the growth of polymer chains In factlarge addition of acetic anhydride to themixture creates chainends unable to take part in polymerization
37 Polymerization Mechanism The ring-opening polymer-ization of PCHO can be achieved by addition of aceticanhydride via a cationic pathway According to the obtainedresults we propose a cationic mechanism for the poly-merization initiated by protons provided by H
3PW12O40
(Scheme 2) Initiation The first stage is the protonation ofacetic anhydride by H
3PW12O40 leading to the formation
of acetyl polyoxometalate salt Then there is a nucleophilicattack of the oxygen of cyclohexene oxide on the carbon atomof the acetyl species The formed oxonium ion undergoes anucleophilic attack on the carbon by the oxygen of the cyclo-hexene oxide of the chains in growth Propagation In thisstage the protonated oxonium ion undergoes a nucleophilic
attack by a molecule of cyclohexene oxide Termination Thelast stage is a nucleophilic attack of the oxygen of the aceticacid formed in the first stage on the carbon in alpha ofpositively charged oxygen of the chains in growth
4 Conclusions
From the results it can be concluded that Keggin-type het-eropolyacid (H
3PW12O40) is an effective catalyst of the ring-
opening polymerization of cyclohexene oxide owing to itsstrong Broslashnsted acidity
The microstructure of the resulting PCHO is differentfrom that prepared over clay and alumina alkoxide catalystsThe low119879g value of the PCHO is due to themicrostructure butnot to molecular weight Contrary to most polymerizationreactions the molecular weight and the yield increase withthe increase of the temperature
The decrease in the molecular weight with the increaseof the amount of catalyst might be due to the increase ofthe amount of water which increased with the increase ofcatalyst amount or to the increase of the number of initiatingactive sites (H+) which increases the number of chains at theexpense of the length of the chains
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
6 International Journal of Polymer Science
Controlled low molecular weight of the PCHO overH3PW12O40can find various applications It can be used for
preparing soft segments for thermoplastic elastomersThe use of H
3PW12O40
as a solid acid catalyst insteadof the usual soluble inorganic acids is a contribution to areduction of waste
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors extended their appreciation to the Deanship ofScientific Research at King Saud University for funding thework through the research group Project no RGP-VPP-116
References
[1] O Nuyken and S D Pask ldquoRing-opening polymerization-anintroductory reviewrdquo Polymers vol 5 no 2 pp 361ndash403 2013
[2] A Yahiaoui M Belbachir J C Soutif and L Fontaine ldquoSynthe-sis and structural analyses of poly (1 2 cyclohexene oxide) oversolid acid catalystrdquoMaterials Letters vol 59 no 7 pp 759ndash7672005
[3] Y Zhang D Wang K Wurst and M R Buchmeiser ldquoRing-opening polymerization of cyclohexene oxide by a novel dica-tionic palladium catalystrdquo Designed Monomers and Polymersvol 8 no 6 pp 571ndash588 2005
[4] H Yasuda and E Ihara ldquoLiving polymerizations of polar andnonpolar monomers by the catalysis of organo rare earth metalcomplexesrdquo Bulletin of the Chemical Society of Japan vol 70 no8 pp 1745ndash1767 1997
[5] J Ling L You Y Wang and Z Shen ldquoRing-opening poly-merization of cyclohexene oxide by recyclable scandium triflatein room temperature ionic liquidrdquo Journal of Applied PolymerScience vol 124 no 3 pp 2537ndash2540 2012
[6] L A Allaoui and A Aouissi ldquoEffect of the Broslashnsted acidity onthe behavior of CO
2methanol reactionrdquo Journal of Molecular
Catalysis A Chemical vol 259 no 1-2 pp 281ndash285 2006[7] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemical
Reviews vol 98 no 1 pp 199ndash217 1998[8] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-
ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998
[9] E F Kozhevnikova and I V Kozhevnikov ldquoA calorimetricstudy of the acidity of bulk and silica-supported heteropoly acidH3PW12O40rdquo Journal of Catalysis vol 224 no 1 pp 164ndash169
2004[10] M Misono I Ono G Koyano and A Aoshima ldquoHeteropoly-
acids Versatile green catalysts usable in a variety of reactionmediardquo Pure and Applied Chemistry vol 72 no 7 pp 1305ndash13112000
[11] Y Chen G L Zhang and H Z Zhang ldquoControl of molecularweight in tetrahydrofuran polymerization initiated by het-eropolyacidrdquo Journal of Applied Polymer Science vol 82 no 2pp 269ndash275 2001
[12] A Aouissi ldquoCationic polymerization of 23 Dihydro-4H pyranusing H
3PW12O40
as a solid acid catalystrdquo Journal of AppliedPolymer Science vol 117 no 3 pp 1431ndash1435 2010
[13] Q Wu L Li Y Yu and X Tang ldquoThe linear relations andliving feature in cationic ring-opening copolymerization ofepoxyTHF systemrdquo Colloid and Polymer Science vol 286 no6-7 pp 761ndash767 2008
[14] A Aouissi S S Al-Deyab and H Al-Shehri ldquoCationic ring-opening polymerization of tetrahydrofuran with Keggin-typeheteropoly compounds as solid acid catalystsrdquo Chinese Journalof Polymer Science vol 28 no 3 pp 305ndash310 2010
[15] C Rocchiccioli-Deltcheff M Fournier R Franck and RThouvenot ldquoVibrational investigations of polyoxometalates 2Evidence for anion-anion interactions in molybdenum(VI)and tungsten(VI) compounds related to the keggin structurerdquoInorganic Chemistry vol 22 no 2 pp 207ndash216 1983
[16] C Rocchiccioli-Deltcheff and M Fournier ldquoCatalysis by poly-oxometalates Part 3mdashinfluence of vanadium(V) on the ther-mal stability of 12-metallophosphoric acids from in situ infraredstudiesrdquo Journal of the Chemical Society Faraday Transactionsvol 87 no 24 pp 3913ndash3920 1991
[17] S Suga and H Aoyama ldquoFree-radical-induced polymerizationof epoxides in the presence of maleic anhydriderdquo Journal ofPolymer Science Part A-1 Polymer Chemistry vol 7 no 5 pp1237ndash1245 1969
[18] E J Goethals ldquoCyclic oligomers in the cationic polymerizationof heterocyclesrdquo Pure and Applied Chemistry vol 48 no 3 pp335ndash341 1976
[19] P Kubisa and S Penczek ldquoCationic activated monomer poly-merization of heterocyclic monomersrdquo Progress in PolymerScience vol 24 no 10 pp 1409ndash1437 1999
[20] T A Zevaco J K Sypien A Janssen O Walter and E Din-jus ldquoSynthesis structural characterisation of new oligomericalkyl aluminium (221015840-methylene-p-chloro-bisphenoxides) andapplication as catalysts in polymerisation reactions involvingcyclohexene oxiderdquo Journal of Organometallic Chemistry vol692 no 10 pp 1963ndash1973 2007
[21] A Aouissi S S Al-Deyab and H Al-Shahri ldquoThe cationicring-opening polymerization of tetrahydrofuran with 12-tungstophosphoric acidrdquoMolecules vol 15 no 3 pp 1398ndash14072010
[22] M I Ferrahi and M Belbachir ldquoPreparation of poly(oxybuty-leneoxymaleoyl) catalyzed by a proton exchanged montmoril-lonite clayrdquoMolecules vol 9 no 11 pp 968ndash977 2004
[23] T Diao X Sun R Fan and J Wu ldquoUnexpected ring-openingreaction of aziridine with acetic anhydride in DMFrdquo ChemistryLetters vol 36 no 5 pp 604ndash605 2007
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials