rheological properties in aqueous solution for...

Research ArticleRheological Properties in Aqueous Solution forHydrophobically Modified Polyacrylamides Prepared inInverse Emulsion Polymerization

Shirley Carro1 Valeria J Gonzalez-Coronel2 Jorge Castillo-Tejas1

Hortensia Maldonado-Textle3 and Nancy Tepale2

1Facultad de Ciencias Basicas Ingenierıa y Tecnologıa Universidad Autonoma de Tlaxcala Calzada Apizaquito SN90300 Apizaco TLAX Mexico2Facultad de Ingenierıa Quımica Benemerita Universidad Autonoma de Puebla Av San Claudio y 18 SurCol San Manuel Ciudad Universitaria 72520 Puebla PUE Mexico3Centro de Investigacion en Quımica Aplicada Blvd Enrique Reyna 140 25253 Saltillo COAH Mexico

Correspondence should be addressed to Valeria J Gonzalez-Coronel valeriagonzalezcorreobuapmx

Received 6 October 2016 Revised 2 February 2017 Accepted 6 February 2017 Published 29 March 2017

Academic Editor Atsushi Sudo

Copyright copy 2017 Shirley Carro et al This 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

Inverse emulsion polymerization technique was employed to synthesize hydrophobically modified polyacrylamide polymers withhydrophobe contents near to feed compositionThree different structures were obtained multisticker telechelic and combined N-Dimethyl-acrylamide (DMAM) n-dodecylacrylamide (DAM) and n-hexadecylacrylamide (HDAM) were used as hydrophobiccomonomers The effect of the hydrophobe length of comonomer the initial monomer and surfactant concentrations on shearviscosity was studied Results show that the molecular weight of copolymer increases with initial monomer concentration and byincreasing emulsifier concentration it remained almost constant Shear viscosity measurements results show that the length of thehydrophobic comonomer augments the hydrophobic interactions causing an increase in viscosity and that the polymer thickeningability is higher for combined polymers

1 Introduction

Water-soluble associating polymers have been studied exten-sively due to their rheological characteristics in aqueoussolution These materials are structured by a water-solublebackbone where a small amount of hydrophobic groups isinserted distributed randomly or as microblocks in themain polymer chain (multisticker) at both extremes of it(telechelic) or along the macromolecular chain as well asthe chain ends (combined) [1 2] Associating polymerscan be synthesized by modifying chemically a precur-sor polymer or by free radical copolymerization of thesuitable monomers [3] For the latter method copolymersbased on acrylamide (AM) and its derivatives have beenwidely researched Different synthesis techniques have beenexplored (i) solution polymerization where the hydrophobicand hydrophilic monomers are solubilized by the addition

of a cosolvent the resultant polymer can be maintained assoluble (homogeneous polymerization) [4 5] or insoluble(precipitation polymerization) [5ndash7] in the reactionmedium(ii) heterogeneous polymerization where the water-insolublemonomer is distributed finely in the acrylamide aqueousmedium under stirring [4 8 9] (iii) micellar polymerizationwhere in presence of a surfactant due to the amphiphiliccharacter of its molecules the hydrophobic monomer issolubilized within the micelles formed [3 10ndash12] This lastmethod is the most employed because the copolymersprepared have a hydrophobic blocky distribution along thehydrophilic chain and it is possible to control the length ofsuch microblocks Besides the copolymers obtained have anexcellent thickening ability

For many applications molecular weight of associa-tive polymers is required to be sufficiently high Solution

HindawiInternational Journal of Polymer ScienceVolume 2017 Article ID 8236870 13 pageshttpsdoiorg10115520178236870

2 International Journal of Polymer Science

polymerization processes are inadequate because as con-version increases viscosity in reaction medium extremelyaugments causing mixing and heat transfer problems [13]Inverse emulsion and microemulsion polymerization havebeen also employed to synthetize acrylamide copolymers[11 14ndash16] Inverse emulsion polymerization is one of thebest methods for obtaining polymers with high molecularweight and low viscosity of the medium of reaction In theacrylamide polymerization the main locus of particle for-mation is the monomer droplets [17ndash20] however if an oil-soluble initiator is employed a certain amount of micellar orhomogeneous nucleation can be present [19] Polymerizationoccurs near the disperse phase interface monomer dropletsbecause of the formation of a contrasting boundary betweenoil and aqueous phases Consequently the copolymerizationof monomers with strongly dissimilar hydrophilicities ismore probable [21]Thus polymerization in inverse emulsionis an attractive alternative to micellar polymerization tosynthesize hydrophobically modified polyacrylamide

In this work hydrophobically modified polyacrylamideswere synthesized in inverse emulsion polymerization varyingthe surfactant and monomer concentration The microstruc-ture obtained and the reaction mechanism are proposedtaking as base the rheometric behavior of these materialsWe describe a detailed study of the rheological properties inaqueous solutions of three different structures of hydrophobi-cally modified polyacrylamides (telechelic multisticker andcombined) prepared using two different hydrophobic lineargroups of 12 and 16 carbon atoms

2 Experimental Section

21 Materials All substances were employed without addi-tional purification Acrylamide (AM Aldrich 99 purity)was used as hydrophilic monomer and n-dimethyl acry-lamide (DMAM Aldrich 99 purity) n-dodecyl acry-lamide (DAM) and n-hexadecyl acrylamide (HDAM) ashydrophobic comonomers 441015840-Azobis(4-cyanovaleric acid)(ACVA Aldrich 99 purity) was used as initiator and SPAN80 (nonionic emulsifier sorbitan monooleate Aldrich) assurfactant DAM and HDAM were prepared according to[22] For telechelic and combined polymers hydrophobi-cally modified initiator ACVA12 or ACVA16 was used thesynthesis of these initiators was previously reported [2]Toluene (Aldrich) and acetonitrile (Aldrich) were employedas organic phase in emulsion and solution polymerizationrespectively In Figure 1 a schematic representation of thesynthesized copolymers is presented

22 Polymerization Batch copolymerization processes werecarried out at 80∘C using a constant temperature water bathin a 500ml glass reactor equipped with mechanical stirrerFor solution polymerization monomers 3 wt (99 molAM and 1 mol hydrophobic comonomer) were dissolvedin acetonitrile For emulsion polymerization the continu-ous phase (51 wt) was prepared dissolving the hydropho-bic comonomer and surfactant (45 or 36wt relative tomonomer feed) in toluene Dispersed phase 49wt was

prepared dissolving AM in deionized and distilled waterand added to organic phase Total monomer concentrationwas varied [1198720] 15 or 4wt Molar monomer relationwas maintained as in solution polymerization Stirrer wasadjusted at 600 rpm After homogenization once reachingtemperature reaction the mixture was purged with nitrogenat least 20 minutes before adding initiator 0002M that hadbeen previously dissolved in the continuous phase tolueneor acetonitrile and heated to the temperature reaction Thereactions were carried out for 1 h The nitrogen atmospherewas maintained during the polymerization

23 Characterization Samples were withdrawn periodicallyfrom the reactor for the conversion and molecular weightanalysis The samples were short-stopped with a hydro-quinone solution (04 wt) As polymerization progressesthe polymer obtained appeared as a viscous solution or agel (for the highest monomer contents) In order to removeunreacted monomers and surfactant samples and final poly-mer were precipitated and washed into a methanolacetonemixture (50 50 volvol) Finally samples were dried toconstant weight in oven at 50∘C Conversion was followed bygravimetric technique

231 Hydrophobic Monomer Composition The hydrophobicmonomer composition in the copolymers was determinedby 1H-NMR spectroscopy at room temperature in a JEOL300MHz spectrometer D2O-DMSO (85ndash15 wt) was usedfor associative polymers This kind of characterization hasbeen performed for associative polymers elsewhere [23ndash26]

232 Molecular Weight The hydrophobic copolymers can-not be characterized by size exclusion chromatography (SEC)in water due to the association of the hydrophobic groupsas it has occurred elsewhere [1] However molecular weightof the homopolymer from AM prepared under identicalexperimental conditions was measured in a Hewlett PackardHPLC series 1100 equipped Calibration was carried outwith standards of polyethylene glycol and polyethylene oxideand a buffer solution at pH = 7 as eluent to a flow rateof 1mLmin 119872119899 was 520000 with a polydispersity index119872119908119872119899 of 20Viscometricmolecularweightwas determinedand reported as a valid approximation as it has been doneelsewhere [27ndash30] The viscosity-average molecular weight119872V of copolymers was calculated from

[120578] = 631 times 10minus311987208V (mLsdotgminus1) (1)

Parameters in (1) are proper for AM [31] nevertheless theywere used to estimate the copolymers 119872V value Limitingviscosity number [120578] was determined with an Ubbelohdeviscometer in distilled deionized water at 25∘C

233 Rheological Measurements Samples preparation wasperformed as follows a specific amount of polymer wasdissolved in deionized water These solutions were put intoagitation during 48 hours More concentrated solutionscontaining polymers with a larger hydrophobic chain were

International Journal of Polymer Science 3

On

CN

O

O

O

CN

O

CH3

CH3

NH2

(a)

CN

CN On

O

O

O

O

1111

CH3

CH3

NH2

(b)

CN

CN

11

O O

HN

n

O

O

O

O

CH3

CH3

NH2

nminus1

(c)

CN

CN

1111

11

HN

O On

OO

O

O

CH3

CH3

NH2

nminus1

(d)

Figure 1 Schematic representation of the synthesized hydrophobic polymers (a) homopolymer (b) telechelic (c) multisticker and (d)combined

stirred until they were homogeneous Interval concentrationstudied was 01 to 10 wt

Solutions were measured in two rheometers dependingon the concentration of the sampleThemore diluted sampleswere analyzed in a rotational rheometer Rheolab QC usinggeometry double-walled cylinder (DG42) and more con-centrated samples at the Physica UDS200 controlled stressrheometer equipped with a cone and plate (angle 2 anddiameter 50mm) at 25plusmn005∘CThe zero-shear viscosity (120578119900)was obtained by extrapolation of the apparent viscosity

Sample Code The name assigned to the polymers is accord-ing to hydrophobic monomer and initiator For example

PAM-co-DAM12 relates to the copolymer poly(acrylamide-co-dodecilacrylamide) synthesized by copolymerizing acry-lamide and the hydrophobic monomer dodecylacrylamideusing hydrophobically modified initiator ACVA12 Thiscopolymer corresponds to a combined type

3 Results and Discussion

In order to demonstrate that inverse emulsion polymerizationis a suitable technique to obtain associative polymers resultsfor multisticker copolymers are compared with solutionpolymerization Viscosity results intend to show the advan-tage of obtaining higher molecular weight with emulsion


Table 1 Viscometric molecular weight for the different polymers synthetized

Method Solution Emulsion EmulsionMonomer concentrationlowast wt 3 150 4

Polymer Molecular weight (gmol)Viscometric Viscometric SEC Viscometric

PAM 55933 216520 119872119899 = 137500119872119908 = 506490 466029

PAM-co-DAM 80879 239777 mdash 492249PAM-co-DMA mdash mdash mdash 514452PAM-co-HDAM mdash mdash mdash 350763lowastMonomer concentration is related to total weight of reaction mixture

0 15 30 45 60000

025

050

075

100

SolutionEmulsion

Frac

tiona

l con

vers

ion

Time (min)

Figure 2 Evolution of fractional conversion for the PAM synthe-sized by emulsion and solution polymerization

polymerization Also the effect of the hydrophobicmonomerlength and surfactant concentration is presented The studyfor the rheological properties includes telechelicmultistickerand combined copolymers

31 Effect of the Hydrophobic Monomer Length A compar-ison for the evolution of conversion between solution andemulsion AM homopolymerization is presented in Figure 2As it can be seen maximum conversion for emulsionpolymerization is reached at really low time (20min) incomparison with solution polymerization Also molecularweight is higher (Table 1) even though a smaller percentageof monomer is used in comparison with solution (15 versus3wt) This behavior is expected because of compart-mentalization of the reaction loci [32] Results show thatthe conditions employed provide an emulsion system 119872Vobtained by the homopolymers and copolymers are presentedin Table 1 As it can be seen119872V value for PAM is between119872119899and119872119908 obtained by SEC then results for119872V or copolymerscan be used as an approximation

An interesting observation is that an increase in mono-mer concentration causes an increase in 119872V for emulsion

polymerization This behavior has been observed in styreneemulsion polymerization and was attributed to limited par-ticle coagulation causing an apparent change in radicalconcentration leading to bimolecular termination [33 34] Inour case for an increase in initial monomer concentration[1198720] a greater number in droplets is expected howeverfor the same surfactant concentration droplet degradationcan take place via coalescence or particle coagulation occursbecause of a lack of surfactant to stabilize the system Asa consequence a minor number of bigger droplets areobtained Taking into consideration that in inverse emulsionpolymerization monomer droplets are the sites of particleformation [17] more radicals can coexist leading to bimolec-ular termination In this sense the number and size ofreaction loci can be manipulated taking into considerationthe stability system to influence molecular weight Highermonomer concentrations were tried however the viscosityof the medium reaction was too high that a gel was rapidlyformed

The difference in the polymer molecular weight isreflected in rheological behavior (Figure 3(a)) An increasein molecular mass results in a larger coil and more chainentanglements which can be seen as increase in viscosityNotice that when AM homopolymer is prepared by emulsionpolymerization its viscosity is three orders of magnitudegreater than the polymer obtained by solution even whenthe totalmonomer concentration is lower than that employedin solution polymerization Thus viscosity of these kindsof materials synthesized by inverse emulsion polymerizationcan be manipulated by adjusting the initial polymerizationloci Notice that a diminution in viscosity is observed asshear rate is increased for AM homopolymer synthesized byemulsion technique at higher monomer concentration Thisbehavior is typical for polymers with high molecular weightAlso the behavior of multisticker copolymers synthesized bydifferentmethods is presented (Figure 3(b)) As it can be seenthe copolymer has a higher viscosity for all polymerizationprocesses and again molecular weight plays an importantrole the larger the value for 119872V the higher the solutionviscosity

The 1H NMR spectra of the (a) homopolymer (b)multisticker polymer PAM-co-DAM (c) telechelic polymerPAM12 and the (d) combined polymers are presented inFigure 4The chemical shifts are presented in part permillion


Table 2 Percentages of hydrophobic monomer incorporated for emulsion polymers 4 solids contents

Type Polymer [119867] ( mol) Conversion 119872V (gmol)Homopolymer PAM 96 466029

Multisticker PAM-co-DAM 080 94 492249PAM-co-HDAM 085 97 350763

Telechelic PAM12 96 522211PAM16 89 mdash

Combined PAM-co-DAM12 085 90 531107PAM-co-HDAM16 082 92 mdash

10 100 100001

1

10

100

1000

10000

Shear rate (1s)

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(a)

Shear rate (1s)001 01 1 10 100 1000

01

1

10

100

1000

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(b)

Figure 3 Influence of the polymerization method in the viscosity as a function the shear rate for (a) PAM and (b) HDAM-AM Polymerconcentration 5wt for aqueous solutions Noncrossed symbols correspond to AM homopolymer [1198720] = initial monomer concentration

3 2 1 0

(d)

(c)

(b)

(ppm)

(a)

Figure 4 1HNMR spectra of the polymers (a) homopolymer PAMin D2O (b) multisticker PAM-co-DAM (c) telechelic PAM12 and(d) combined PAM-co-DAM12 in D2O-DMSO (85ndash15)

downfield from the internal TMS standard or with respectto a solvent resonance line The ratio of the two monomersin the copolymer was determined by integrating the signalsof the methyl proton (lowast08 ppm) and of the ethylene protonattached to the backbone (11ndash18 ppm) the ratio was foundto be around 080mol with respect to the feed compositionfor multisticker and 085mol for combined polymers Asit can be observed in the spectra for telechelic polymer thecorresponding signal to the hydrocarbon chain is not visiblebecause of its low concentration in the polymer chain Due tothe low concentration of hydrophobicmonomer the signal inthe spectrum is very tenuous However an approximation onthat area can be carried out and properly be integrated [23ndash26]

Table 2 shows the percentages of hydrophobic monomerincorporated for different copolymer structures It also showsthe obtained values for 119872V Notice that they are greaterthan those observed in similar polyacrylamides synthesizedby solution polymerization and the reported molecular


0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)

Figure 5 Influence of hydrophobic monomer length in (a) specific viscosity and (b) shear viscosity Polymer concentration is indicated inthe figure Water viscosity is shown as reference

weight for them was 200000 gmol approximately [2 35]Results show that hydrophobe contents are near to thefeed composition These results demonstrate that inverseemulsion polymerization is a suitable technique to synthetizehydrophobically modified polyacrylamide polymers

The behavior for specific viscosity 120578sp for themultistickercopolymers prepared by emulsion polymerization is shownin Figure 5(a) Results correspond to [1198720] = 40 wt Theintention of using 120578sp instead of shear viscosity is to comparethe behaviors of the copolymers in a very dilute aqueoussolutionNotice that as the length of hydrophobic alkyl chainsincreases an augment in solutions viscosity is observed evenwhen the concentration of hydrophobic comonomer is low(1 mol) Because of this low comonomer concentrationmolecular weight does not change significantly comparedwith homopolymer (Table 1)However the augment observedin 120578sp for the copolymer PAM-co-HDAMsuggests hydropho-bic associations For the copolymer PAM-co-DAM 120578sp isslightly depressed because of the well-known phenomena ofcontraction at this dilute regimen of concentration due tointramolecular associations [36 37] At low solution con-centrations the possibility of interaction between differenthydrophobic groups in polymer molecules is small Intra-aggregation associations predominate which results in areduced coil size [36] Therefore at such concentrations thespecific viscosity of copolymers is often lower than theirunmodified homopolymers

Figure 5(b) shows the effect of polymer concentration inthe steady-state viscosity 120578 as a function of shear rate and 120574for themultisticker copolymers at different aqueous solutionsconcentration For the lowest polymer solution concentrationtested (1) the behavior is Newtonian this is there is novariation in viscosity with 120574 but as concentration augments

120578 increases drastically and the solutions exhibit a shear-thinning behavior

As it can be observed variation between 120578 values cor-responding to copolymers and homopolymer is not largeThis behavior has previously been observed for comonomerswith low hydrophobic length [38 39] however HDAMhas a longitude of 16 carbons Besides it was found thatcopolymers PAM-co-HDAM were water insoluble whichwas not our case A possible explanation in behavior for thepolymers synthetized here and in otherworks is the differencein reaction sites In the micellar copolymerization processthe hydrophobic monomer is solubilized within surfactantmicelles whereas the hydrophilic monomer is dissolved inthe aqueous continuous phase This situation contrasts withthe inverse emulsion process where the hydrophobe ispresent in the continuous phase and the hydrophile in thedispersed phase In the first case blocks of hydrophobiccomonomer are inserted along the hydrophilic chain Assurfactant concentration increases the hydrophobic blockslength decrease and consequently viscosity diminishesbecause of the ldquodilutionrdquo of hydrophobic monomer in amayor number of micelles In inverse emulsion the initiatingradicals are formed by the decomposition of the hydrophobicinitiatorThese radicals cannot enter the hydrophilic polymerparticles however they can addmonomer units from theAMdissolved in the continuous phase When radicals becomemore hydrophilic they can enter the droplets and polymerize[40] Besides it has been suggested that AM is presentin the droplets surface behaving as cosurfactant [41 42]then oligoradicals can reach this monomer at the surfaceand be adsorbed Also as in micellar process at the sametime hydrophobic comonomer and AM dissolved in thecontinuous phase are polymerized in a solution process


Water soluble monomerHydrophobic monomer

Figure 6 Schematic representation of the inverse emulsion poly-merization

then a random distributed copolymer is obtained [4] Inaddition due to the low concentration of the hydrophobiccomonomer (1 mol solved in the continuous phase) itseems difficult to form blocks Therefore inverse emulsionprocess provides long AM chains which are formed withinmonomer droplets with both ends formed by a block of ahydrophobic-hydrophilic copolymer randomly distributedpolymerized in the continuous phase (Figure 6)

If 120578 in Newtonian plateau is analyzed the effect of thehydrophobic monomer length is clear viscosity increasesas hydrophobicity does PAM lt DMA lt DAM lt HDAMFor solutions at 1 wt this effect is not appreciable but forsolutions with 5wt of polymer the effect is perceptible

In micellar copolymerization it has been proved thatas surfactant concentration increases the viscosity of theaqueous solutions for the hydrophobic copolymers decreasesdue to a decrease in hydrophobic block length The samemonomer concentration is distributed in more micellesHowever for the copolymers obtained here when a minorconcentration of surfactant is employed viscosity is higherIt could be attributed to the localization of the hydropho-bic groups As it was suggested in the continuous phasecopolymerization like solution process is performed Then astatistical copolymer AM-HDAM is added to a large blockof PAM (Figure 6) If reaction sites are decreased thenmolecular weight inside the site of polymerization (monomerdroplets) is increased this block becomes larger and thehydrophobic groups are far from each other In this case theAM blocks can bend and the HB groups can associate easilyIn this sense the effect of initial surfactant concentration wasinvestigated

10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0

Figure 7 Influence of initial tensioactive concentration on shearviscosity

Capek [32] found that the AIBN-initiated polymeriza-tion 119877119901 and molecular weight decrease at higher emulsifierconcentrations He argued that the decrease in the polymer-ization rate with increasing the emulsifier concentration isexpected because monomer concentration at the particleloci (diluted by the emulsifier molecules) diminishes Onthe other hand when a water-soluble initiator (ammoniumpersulfate) is used [43] themolecularweight of PAM is nearlyindependent of surfactant concentration It is attributed to anincreased number of polymer particles which is followed bythe decreased termination rate Barari et al [44] found thatthe molecular weight of final polymer increases by increasingthe emulsifier concentration up to 5wt and then remainedalmost constant beyond this value In this work dependenceof molecular weight on emulsifier concentration was notfound explaining why 120578 is almost the same for differentsurfactant concentration (Figure 7)

32 Steady-Shear Flow Measurements The flow viscositiesfor the polymer solutions in water at 25∘C are depicted inFigures 8ndash12 Polymers characteristics correspond to Table 2Figure 8 shows steady-shear viscosities for homopolymerPAM at various concentrations in water as a function ofthe shear rate It is apparent that the viscosity increases aspolymer concentration does All curves exhibit a behaviorpredominantly Newtonian

Figure 9 plots the viscosity against shear rate at differentconcentrations for multisticker PAM-co-DAM As it canbe seen at low concentrations shear viscosity does notexhibit significant changes with respect to the homopoly-mer behavior however after 4 wt in the flow curvesa Newtonian plateau is observed followed by a drop inviscosityThe behavior for the copolymer PAM-co-HDAM issimilar the viscosity curves are not shown but were used toobtain the zero-shear rate viscosity Notice that for the same


01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)

Figure 8 Variation of the viscosity as a function the shear rate forvarious concentrations of PAM

0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10

Figure 9 Variation of the viscosity as a function the shear rate forvarious concentrations of PAM-co-DAM

solution concentration copolymers viscosity is significantlyhigher than that for homopolymer confirming hydrophobicincorporation

For the telechelic copolymer PAM12 only at low con-centrations a completely Newtonian behavior is observed(see Figure 10) and from 05 a slight shear-thinning is

0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa

middots)Figure 10 Variation of the viscosity as a function the shear rate forvarious concentrations of PAM12

observed At high concentrations it clearly shows a decreaseof Newtonian plateau followed by a pronounced shear-thinning however the traditional shear-thickening behavioris not observed It is reported for telechelic polymers inaqueous solution that they have a shear-thickening effectbecause the end groups form micelles such as flowers due tothe increase in shear rate they connect each other throughthe end groups of other polymer chains (bridges) Thisgenerates aggregates with a larger hydrodynamic volumeaffecting the solution viscosity Finally these aggregates breakat higher shear rate and a shear-thinning is observed In ourcase shear-thickening effect is not observed although thestructure is of telechelic type It is possible that the shearrate employed does not promote the formation of bridgesbetween micellar flowers and thus the viscosity increase isnot presented

This behavior can be thought of as if hydrophobic groupswere not incorporated In that case micellar flowers shouldnot be formed nevertheless viscosity reached is really higherthan that for homopolymer indicating that the hydrophobecomonomer is incorporated and the telechelic structure isreached Polymer behavior for PAM16 is similar to PAM12

Themechanisms of association according to the viscositybehavior as a function of the shear rate can be observed in thenonlinear rheology Typically it is observed that the viscosityremains constant at a short interval at low shear rate and athigh shear rates the viscosity decreases In our case a New-tonian plateau is not observed for the combined polymers(see Figure 11) A shear-thickening behavior followed by anabrupt decrease in viscosity is noticed This behavior variesdepending on the concentration kind of associative polymerand hydrophobic group As mentioned many authors agreethat the shear-thickening effect is due to the shear stress


0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4

Figure 11 Variation of viscosity in terms of the shear rate for theaqueous solutions for combined copolymers PAM-co-DAM12

that promotes associations because more bridges are formedthis implies that the transient network formed has a greaterhydrodynamic volume so that the viscosity of the solutionincreases In our case bridges are not formed by micellarflower but a direct network for hydrophobic groups betweenand at the end of the chains Finally due to increased shearrate these bridges break and the polymer chains are quicklyoriented with the flow [45]

It is clear that the structure plays an important roleAs it can be seen shear viscosity increases according tothe different structure obtained for the copolymers mul-tisticker telechelic and combined It can be explained asfollows For telechelic copolymers as it has been mentionedthe main chain bends easily for the hydrophobic groupslocated at the end can associate then the loops formedincrease viscosity However for multisticker copolymersthe hydrophobic groups are randomly distributed along thechain therefore it is difficult for the chain to bend and form aloopHydrophobic associations occurwhen the groups are faraway from each other and intermolecular interactions give asmaller size for the aggregates as it has been demonstrated bymolecular simulations [46] For combined copolymers dueto the hydrophobic end groups the formation of loops canoccur and also the intramolecular hydrophobic groups canpromote a net formation explaining why a higher viscosity isobserved (Figure 12)

The viscosity variation as function the polymer concen-tration was analyzed according to the hydrophobic groupposition the viscosity was extrapolated to zero-shear rateexcept for combined polymers which was measured at lowshear rate

To analyze the results it is necessary to indicate the mainproperties of rheological behavior for unmodified polymers

which present three regimes dependent on concentration [3847ndash49]

(I) At very low concentrations dilute regime 119862 lt 119862120578where the rheological behavior is primarily controlledby intramolecular associations is observed Clustersof small size are formed so that the viscosity of themodified polymer is lower than unmodified polymer119862120578 is the critical concentration at which intermolec-ular associations form

(II) A semidilute untangled regime is observed at 119862120578 lt119862 lt 119862119879 This regime is characterized by a rapidviscosity increase This depends on the molecularweight of the polymer the nature concentration andlength of the hydrophobic group 119862119879 is equivalentto Ce (for homopolymers) which represents theconcentration at which the entanglements becomeelastically effective

(III) A semidilute entangled regime 119862 gt 119862119879 is observedIt can be safely assumed that in the concentrationrange considered the density of entanglements ismuch larger than that of hydrophobic associations

Taking into consideration the applications the three differentarchitectures were studied in order to compare the effectsthat structure has on viscosity The Newtonian viscosityvalues are considered as the parameters to evaluate thethickening efficiency of the prepared associative polymersFigures 13 and 14 show the variation of the zero-shearviscosity (1205780) as a function of the polymer concentration[119862] for the telechelic multisticker and combined polymerssynthesizedwith differentmonomer length on the alkyl chain[C12 (Figure 10) and C16 (Figure 11)] These copolymersare compared with the homopolymer Three regimes canbe identified for different homopolymer concentration Theaggregation concentration 119862lowast is presented in 03 and thestart concentration of crosslinking Ce in 17 For associa-tive polymers for series 12 a short dilute regime is observedbecause of their high molecular weight and hydrophobiccontributions so intramolecular associations are generatedat lower concentrations Semidiluted nonentangled regime isdescribed by the model of reptation 119862119879 for combined andtelechelic polymers is presented at the same concentration(4) while 119862119879 of multisticker polymer is shifted at 6 Thisbehavior is the result of combined and telechelic polymersgenerating a net with a hydrodynamic radius greater at lowerconcentrations than the multisticker polymer Series 16 had asimilar behavior A diluted regime is observed in this case119862119879 for combined and telechelic polymers is presented at4 while the multisticker polymer 119862119879 is shifted to 5 Avalue near to four for the slope in the semidiluted entangledregimen curve is also observed which is representative forassociative polymers The slope curves of the semidiluteregime varies depending on the hydrophobic groups andtheir localization [23ndash26]

Intramolecular hydrophobic associations occur atlow polymer concentration and cause contraction ofmacromolecular spheres In dilute regime the viscosity ofhydrophobicallymodified polymer is generally less than their


(a) (b) (c)

Figure 12 Schematic representation of the hydrophobic associations for the copolymers synthesized (a) telechelic (b) multisticker and (c)combined

01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405

Figure 13 Variation of zero-shear viscosity (1205780) as a function ofpolymer concentration (119862) for the synthesized polymers using thelinear C12 hydrophobic group

unmodified counterpart When the polymer concentrationincreases and is greater than119862lowast the viscosity of the modifiedpolymer becomes higher than the unmodified polymerIn this stage the intermolecular interactions becomedominant with respect to intramolecular interactions hencea thickening effect is observed In general the concentrationof the modified polymer 119862lowast is less than Ce of the modifiedpolymerThe increase in viscosity from119862lowast is more importantwhen the polymer concentration is high The thickeningeffect is moved towards smaller shear rates by the differencein viscosity between several orders of associative polymerand the unmodified counterpart When intermolecularhydrophobic interactions are strong enough they canreach the gel formation Determining the value for 119862lowast is ofparamount importance for the description of the rheologicalproperties of associative polymers

PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)


The following mentioned values of 1205780 from aqueoussolutions at 1 approximately of hydrophobically modifiedpolyacrylamides which were synthesized by different meth-ods of polymerization Wever et al [50] reported viscositiesup to 14mPasdots for polyacrylamides comb line and star witha molecular weight of 230000 Cram et al [25] reportedspecific viscosities values up to 1 for hydrophobically modi-fied polyacrylamides synthesized bymicellar polymerizationwith a molecular weight of 96000 Penott-Chang et al [27]reported 1205780 up to 1 times 103mPasdots for hydrophobically modi-fied polyacrylamides synthesized bymicellar polymerizationwith a molecular weight of 4200000 Lu et al [24] reported1205780 up to 1 times 106mPasdots for hydrophobically modified poly-acrylamides synthesized by micellar polymerization with amolecular weight of 340000 Zhu et al [23] reported 1205780up 800mPasdots for hydrophobically modified polyacrylamides


synthesized by micellar polymerization with a molecularweight of 2300000

It is clearly known that viscosity of these polymersdepends on several factors including molecular weighthydrophobic content type and location method of poly-merization and polymer concentration however the resultspresented show that inverse emulsion polymerization is asuitable technique to synthesize these kinds of polymers

4 Conclusions

Hydrophobic copolymers derived from acrylamide were sat-isfactorily synthesized by inverse emulsion polymerizationThe hydrophobe content was limited to 1mol and theincorporation level determined by 1H-NMR spectroscopywas close to the alimentation monomer feed In order toanalyze the influence of the length of the hydrophobe groupin the rheological properties homopolyacrylamide was alsosynthesized as reference

The results showed that molecular weight of the finalpolymer increased by increasing emulsifier concentrationand then remained almost constant without further increaseThe data show that the molecular weight of final polymer isincreased as monomer concentration increases This aspectinfluences the behavior of viscosity of aqueous solutionbecause shear viscosity increases as the length of AM blocksis increased

The viscosity of aqueous solutions is function of thepolymeric structure that is polymers having higher viscosityare combined followed by the telechelic and finally combinedpolymers Multisticker solutions and telechelic polymersexhibit a Newtonian plate in viscosity as function of theshear rate followed by a decrease in viscosity For telechelicpolymers neither the plate nor the shear-thickening behavioris observed Only two regimes dependent on concentrationwere determined according to intra- and intermolecularassociations of the different synthesized structures Rheo-logical behavior could not be observed in dilute regimedue to high viscosities of polymers solutions even at lowconcentrations

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

The authors thank the financial support from PRODEPunder Grant no PROMEP1035122116 and Judith Cabello-Romero forNMRdeterminations S Carro thanks Erick Lunaand Victor Amador for experimental assistance

References

[1] E J Jimenez-Regalado G Cadenas-Pliego M Perez-Alvarezand Y Hernandez-Valdez ldquoStudy of three different families ofwater-soluble copolymers synthesis characterization and vis-coelastic behavior of semidilute solutions of polymers prepared

by solution polymerizationrdquo Polymer vol 45 no 6 pp 1993ndash2000 2004

[2] V J Gonzalez-Coronel and E J Jimenez-Regalado ldquoSynthesischaracterization and rheological properties of three differentmicrostructures of water-soluble polymers prepared by solutionpolymerizationrdquo Polymer Bulletin vol 62 no 6 pp 727ndash7362009

[3] F Candau and J Selb ldquoHydrophobically-modified polyacry-lamides prepared by micellar polymerizationrdquo Advances inColloid and Interface Science vol 79 no 2-3 pp 149ndash172 1999

[4] A Hill F Candau and J Selb ldquoProperties of hydrophobicallyassociating polyacrylamides influence of themethod of synthe-sisrdquoMacromolecules vol 26 no 17 pp 4521ndash4532 1993

[5] W D Emmons and T E Stevens ldquoAcrylamide copolymerthickener for aqueous systemsrdquo US Patent 4 395 524 1982

[6] S A Ezzell and C L McCormick ldquoWater-soluble copoly-mers 39 Synthesis and solution properties of associativeacrylamido copolymers with pyrenesulfonamide fluorescencelabelsrdquoMacromolecules vol 25 no 7 pp 1881ndash1886 1992

[7] J J Effing I J McLennan and J C T Kwak ldquoAssociativephase separation observed in a hydrophobically modifiedpoly(acrylamide)sodium dodecyl sulfate systemrdquo Journal ofPhysical Chemistry vol 98 no 10 pp 2499ndash2502 1994

[8] J Bock D B Siano D N Schulz S R Turner and S-LValint Jr ldquoHydrophobically associating polymersrdquo PolymericMaterials Science and Engineering vol 55 article 355 1986

[9] J Bock P L Valint Jr S J Pace D B Siano D N Schulz andS R Turner ldquoHydrophobically associating polymersrdquo inWater-Soluble Polymers for Petroleum Recovery G A Stahl and D NSchulz Eds pp 147ndash160 Plenum Press 1988

[10] S R Turner D B Siano and J Bock ldquoAcrylamide-Alkylacrylamide Copolymersrdquo US Patent 4520 182 1985

[11] S R Turner D B Siano and J Bock ldquoMicellar Process for theProduction of Acrylamide-Alkylacrylamide Copolymersrdquo USPatent 4528 348 1985

[12] S Evani ldquoWater Dispersible Hydrophobic Thickening AgentrdquoUS Patent 4432 881 1984

[13] D Hunkeler ldquoSynthesis and characterization of high molecularweight water-soluble polymersrdquo Polymer International vol 27no 1 pp 23ndash33 1992

[14] F Stanley Jr ldquoWater-In-Oil Emulsions of Hydrophobe Associ-ation Polymersrdquo US Patent 4524 175 1985

[15] M Pabon J-M Corpart J Selb and F Candau ldquoSynthesis ininverse emulsion and associating behavior of hydrophobicallymodified polyacrylamidesrdquo Journal of Applied Polymer Sciencevol 91 no 2 pp 916ndash924 2004

[16] S R Turner D B Siano and J Bock ldquoMicroemulsion Processfor Producing Acrylamide-Alkyl Acrylamide Copolymersrdquo USPatent 4521 580 1985

[17] J W Vanderhoff E B Bradford H L Tarkowski J BShaffer and R M Wiley ldquoInverse emulsion polymerizationrdquoin Polymerization and Polycondensation Processes vol 34 ofAdvances in Chemistry pp 32ndash51 American Chemical SocietyWashington DC USA 1962

[18] J W Vanderhoff D L Visioli and M S El-Aasser ldquoInverseemulsion polymerization of acrylamide anomalous behaviorof tetronic 1102 emulsifierrdquo in Polymeric Materials Science andEngineering vol 54 pp 375ndash380 1986

[19] C Graillat C Pichot A Guyot and M S El Aasser ldquoInverseemulsion polymerization of acrylamide I Contribution to the


study of some mechanistic aspectsrdquo Journal of Polymer SciencePart A Polymer Chemistry vol 24 no 3 pp 427ndash449 1986

[20] J Hernandez-Barajas and D J Hunkeler ldquoInverse-emulsionpolymerization of acrylamide using block copolymeric surfac-tants mechanism kinetics andmodellingrdquo Polymer vol 38 no2 pp 437ndash447 1997

[21] E Kobitstaya Synthesis of hydrophobically modified polyacry-lamide in inverse miniemulsion [Thesis] Universitat UlmMoscu Russia 2008

[22] P L Valint Jr J Bock and D N Schulz ldquoSynthesis and char-acterization of hydrophobically associating polymersrdquo in Poly-meric Materials Science and Engineering vol 57 p 482 1987

[23] Z Zhu O Jian S Paillet J Desbrieres and B Grassl ldquoHydro-phobically modified associating polyacrylamide (HAPAM)synthesized by micellar copolymerization at high monomerconcentrationrdquo European Polymer Journal vol 43 no 3 pp824ndash834 2007

[24] C LuW Li Y Tan et al ldquoSynthesis and aqueous solution prop-erties of hydrophobically modified polyacrylamiderdquo Journal ofApplied Polymer Science vol 131 no 18 pp 40754ndash40761 2014

[25] S L Cram H R Brown G M Spinks D Hourdet and C Cre-ton ldquoHydrophobically modified dimethylacrylamide synthesisand rheological behaviorrdquo Macromolecules vol 38 no 7 pp2981ndash2989 2005

[26] S Hietala P Mononen S Strandman et al ldquoSynthesis andrheological properties of an associative star polymer in aqueoussolutionsrdquo Polymer vol 48 no 14 pp 4087ndash4096 2007

[27] E K Penott-Chang L Gouveia I J Fernandez A J Muller ADıaz-Barrios and A E Saez ldquoRheology of aqueous solutionsof hydrophobically modified polyacrylamides and surfactantsrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 295 no 1-3 pp 99ndash106 2007

[28] F Bezzaoucha P Lochon A Jonquieres A Fischer A Brem-billa and D Aınad-Tabet ldquoNew amphiphilic polyacrylamidessynthesis and characterisation of pseudo-micellar organisationin aqueousmediardquo European Polymer Journal vol 43 no 10 pp4440ndash4452 2007

[29] Q Ye X Ge H Liu H Jia W He and Z Zhang ldquoFormationof monodisperse polyacrylamide particles by dispersion poly-merization I Synthesis and polymerization kineticsrdquo Journal ofMacromolecular SciencemdashPure and Applied Chemistry vol 39no 6 pp 545ndash556 2002

[30] Y Li and J C T Kwak ldquoRheology and binding studies inaqueous systems of hydrophobically modified acrylamide andacrylic acid copolymers and surfactantsrdquo Colloids and SurfacesA Physicochemical and Engineering Aspects vol 225 no 1-3 pp169ndash180 2003

[31] J Klein G Hannemann and W-M Kulicke ldquoZum Flieszligver-halten niedermolekularer Polyacrylamide in einem weitenKonzentrationsbereichrdquo Colloid and Polymer Science KolloidZeitschrift amp Zeitschrift fur Polymere vol 258 no 6 pp 719ndash732 1980

[32] I Capek ldquoInverse emulsion polymerization of acrylamideinitiated by oil- and water-soluble initiators effect of emulsifierconcentrationrdquo Polymer Journal vol 36 no 10 pp 793ndash8032004

[33] J Herrera-Ordonez O Rivera H Maldonado-Textle and J CRamirez ldquoKinetics of styrene emulsion polymerization abovethe critical micelle concentration effect of the initial monomerconcentration on the molecular weightrdquo Journal of PolymerScience Part A Polymer Chemistry vol 43 no 9 pp 1963ndash19722005

[34] S Carro J Herrera-Ordonez and J Castillo-Tejas ldquoOn theevolution of the rate of polymerization number and sizedistribution of particles in styrene emulsion polymerizationabove CMCrdquo Journal of Polymer Science Part A PolymerChemistry vol 48 no 14 pp 3152ndash3160 2010

[35] V J Gonzalez Coronel and E J Jimenez-Regalado ldquoRheologicalproperties of three different microstructures of water-solublepolymers prepared by solution polymerizationrdquo Polymer Bul-letin vol 67 no 2 pp 251ndash262 2011

[36] J Bock D B Siano P L Valint Jr and S J Pace ldquoStructureand properties of hidrophobically associated polymersrdquo inPolymeric Materials Science and Engineering vol 57 pp 487ndash491 1987

[37] E Volpert J Selb and F Candau ldquoAssociating behaviour ofpolyacrylamides hydrophobically modified with dihexylacry-lamiderdquo Polymer vol 39 no 5 pp 1025ndash1033 1998

[38] E Volpert J Selb and F Candau ldquoInfluence of the hydrophobestructure on composition microstructure and rheology inassociating polyacrylamides prepared by micellar copolymer-izationrdquoMacromolecules vol 29 no 5 pp 1452ndash1463 1996

[39] W Xue I W Hamley V Castelletto and P D OlmstedldquoSynthesis and characterization of hydrophobically modifiedpolyacrylamides and some observations on rheological proper-tiesrdquo European Polymer Journal vol 40 no 1 pp 47ndash56 2004

[40] L Ouyang L Wang and F J Schork ldquoSynthesis and nucleationmechanism of inverse emulsion polymerization of acrylamidebyRAFTpolymerization a comparative studyrdquoPolymer vol 52no 1 pp 63ndash67 2011

[41] F Candau Y S Leong andG J Pouyet ldquoInversemicroemulsionpolymerization of acrylamide Characterization of the water-in-oil microemulsions and the final microlatexesrdquo Journal ofColloid and Interface Science vol 114 no 2 pp 167ndash183 1984

[42] F Candau Z Zekhnini and J P Durand ldquoCopolymerization ofwater-soluble monomers in nonionic bicontinuousmicroemul-sionsrdquo Journal of Colloid and Interface Science vol 114 no 2 pp398ndash408 1986

[43] I Capek L Fialova and D Berek ldquoOn the kinetics of inverseemulsion polymerization of acrylamiderdquo Designed Monomersand Polymers vol 11 no 2 pp 123ndash137 2008

[44] M BarariM Abdollahi andMHemmati ldquoSynthesis and char-acterization of highmolecular weight polyacrylamide nanopar-ticles by inverse-emulsion polymerizationrdquo Iranian PolymerJournal vol 20 no 1 pp 65ndash76 2011

[45] C Chassenieux T Nicolai and L Benyahia ldquoRheology ofassociative polymer solutionsrdquo Current Opinion in Colloid andInterface Science vol 16 no 1 pp 18ndash26 2011

[46] J Castillo-Tejas O Castrejon-Gonzalez S Carro V Gonzalez-Coronel J F J Alvarado andOManero ldquoAssociative polymersPart III shear rheology frommolecular dynamicsrdquoColloids andSurfaces A Physicochemical and Engineering Aspects vol 491pp 37ndash49 2016

[47] M Camail A Margaillan I Martin A L Papailhou and J LVernet ldquoSynthesis of N-alkyl- and N-arylalkylacrylamides andmicellar copolymerization with acrylamiderdquo European PolymerJournal vol 36 no 9 pp 1853ndash1863 2000

[48] V Castelletto I W Hamley W Xue C Sommer J S Pedersenand P D Olmsted ldquoRheological and structural characterizationof hydrophobically modified polyacrylamide solutions in thesemidilute regimerdquoMacromolecules vol 37 no 4 pp 1492ndash15012004


[49] A A Abdala W Wu K R Olesen R D Jenkins A ETonelli and S A Khan ldquoSolution rheology of hydrophobicallymodified associative polymers effects of backbone compositionand hydrophobe concentrationrdquo Journal of Rheology vol 48 no5 pp 979ndash994 2004

[50] D A Z Wever F Picchioni and A A Broekhuis ldquoBranchedpolyacrylamides synthesis and effect of molecular architectureon solution rheologyrdquo European Polymer Journal vol 49 no 10pp 3289ndash3301 2013

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of



polymerization processes are inadequate because as con-version increases viscosity in reaction medium extremelyaugments causing mixing and heat transfer problems [13]Inverse emulsion and microemulsion polymerization havebeen also employed to synthetize acrylamide copolymers[11 14ndash16] Inverse emulsion polymerization is one of thebest methods for obtaining polymers with high molecularweight and low viscosity of the medium of reaction In theacrylamide polymerization the main locus of particle for-mation is the monomer droplets [17ndash20] however if an oil-soluble initiator is employed a certain amount of micellar orhomogeneous nucleation can be present [19] Polymerizationoccurs near the disperse phase interface monomer dropletsbecause of the formation of a contrasting boundary betweenoil and aqueous phases Consequently the copolymerizationof monomers with strongly dissimilar hydrophilicities ismore probable [21]Thus polymerization in inverse emulsionis an attractive alternative to micellar polymerization tosynthesize hydrophobically modified polyacrylamide

In this work hydrophobically modified polyacrylamideswere synthesized in inverse emulsion polymerization varyingthe surfactant and monomer concentration The microstruc-ture obtained and the reaction mechanism are proposedtaking as base the rheometric behavior of these materialsWe describe a detailed study of the rheological properties inaqueous solutions of three different structures of hydrophobi-cally modified polyacrylamides (telechelic multisticker andcombined) prepared using two different hydrophobic lineargroups of 12 and 16 carbon atoms

2 Experimental Section

21 Materials All substances were employed without addi-tional purification Acrylamide (AM Aldrich 99 purity)was used as hydrophilic monomer and n-dimethyl acry-lamide (DMAM Aldrich 99 purity) n-dodecyl acry-lamide (DAM) and n-hexadecyl acrylamide (HDAM) ashydrophobic comonomers 441015840-Azobis(4-cyanovaleric acid)(ACVA Aldrich 99 purity) was used as initiator and SPAN80 (nonionic emulsifier sorbitan monooleate Aldrich) assurfactant DAM and HDAM were prepared according to[22] For telechelic and combined polymers hydrophobi-cally modified initiator ACVA12 or ACVA16 was used thesynthesis of these initiators was previously reported [2]Toluene (Aldrich) and acetonitrile (Aldrich) were employedas organic phase in emulsion and solution polymerizationrespectively In Figure 1 a schematic representation of thesynthesized copolymers is presented

22 Polymerization Batch copolymerization processes werecarried out at 80∘C using a constant temperature water bathin a 500ml glass reactor equipped with mechanical stirrerFor solution polymerization monomers 3 wt (99 molAM and 1 mol hydrophobic comonomer) were dissolvedin acetonitrile For emulsion polymerization the continu-ous phase (51 wt) was prepared dissolving the hydropho-bic comonomer and surfactant (45 or 36wt relative tomonomer feed) in toluene Dispersed phase 49wt was

prepared dissolving AM in deionized and distilled waterand added to organic phase Total monomer concentrationwas varied [1198720] 15 or 4wt Molar monomer relationwas maintained as in solution polymerization Stirrer wasadjusted at 600 rpm After homogenization once reachingtemperature reaction the mixture was purged with nitrogenat least 20 minutes before adding initiator 0002M that hadbeen previously dissolved in the continuous phase tolueneor acetonitrile and heated to the temperature reaction Thereactions were carried out for 1 h The nitrogen atmospherewas maintained during the polymerization

23 Characterization Samples were withdrawn periodicallyfrom the reactor for the conversion and molecular weightanalysis The samples were short-stopped with a hydro-quinone solution (04 wt) As polymerization progressesthe polymer obtained appeared as a viscous solution or agel (for the highest monomer contents) In order to removeunreacted monomers and surfactant samples and final poly-mer were precipitated and washed into a methanolacetonemixture (50 50 volvol) Finally samples were dried toconstant weight in oven at 50∘C Conversion was followed bygravimetric technique

231 Hydrophobic Monomer Composition The hydrophobicmonomer composition in the copolymers was determinedby 1H-NMR spectroscopy at room temperature in a JEOL300MHz spectrometer D2O-DMSO (85ndash15 wt) was usedfor associative polymers This kind of characterization hasbeen performed for associative polymers elsewhere [23ndash26]

232 Molecular Weight The hydrophobic copolymers can-not be characterized by size exclusion chromatography (SEC)in water due to the association of the hydrophobic groupsas it has occurred elsewhere [1] However molecular weightof the homopolymer from AM prepared under identicalexperimental conditions was measured in a Hewlett PackardHPLC series 1100 equipped Calibration was carried outwith standards of polyethylene glycol and polyethylene oxideand a buffer solution at pH = 7 as eluent to a flow rateof 1mLmin 119872119899 was 520000 with a polydispersity index119872119908119872119899 of 20Viscometricmolecularweightwas determinedand reported as a valid approximation as it has been doneelsewhere [27ndash30] The viscosity-average molecular weight119872V of copolymers was calculated from

[120578] = 631 times 10minus311987208V (mLsdotgminus1) (1)

Parameters in (1) are proper for AM [31] nevertheless theywere used to estimate the copolymers 119872V value Limitingviscosity number [120578] was determined with an Ubbelohdeviscometer in distilled deionized water at 25∘C

233 Rheological Measurements Samples preparation wasperformed as follows a specific amount of polymer wasdissolved in deionized water These solutions were put intoagitation during 48 hours More concentrated solutionscontaining polymers with a larger hydrophobic chain were


On

CN

O

O

O

CN

O

CH3

CH3

NH2

(a)

CN

CN On

O

O

O

O

1111

CH3

CH3

NH2

(b)

CN

CN

11

O O

HN

n

O

O

O

O

CH3

CH3

NH2

nminus1

(c)

CN

CN

1111

11

HN

O On

OO

O

O

CH3

CH3

NH2

nminus1

(d)












PAM 55933 216520 119872119899 = 137500119872119908 = 506490 466029


0 15 30 45 60000

025

050

075

100

SolutionEmulsion

Frac

tiona

l con

vers

ion

Time (min)














10 100 100001

1

10

100

1000

10000

Shear rate (1s)

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(a)

Shear rate (1s)001 01 1 10 100 1000

01

1

10

100

1000

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(b)


3 2 1 0

(d)

(c)

(b)

(ppm)

(a)





0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)













10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



On

CN

O

O

O

CN

O

CH3

CH3

NH2

(a)

CN

CN On

O

O

O

O

1111

CH3

CH3

NH2

(b)

CN

CN

11

O O

HN

n

O

O

O

O

CH3

CH3

NH2

nminus1

(c)

CN

CN

1111

11

HN

O On

OO

O

O

CH3

CH3

NH2

nminus1

(d)












PAM 55933 216520 119872119899 = 137500119872119908 = 506490 466029


0 15 30 45 60000

025

050

075

100

SolutionEmulsion

Frac

tiona

l con

vers

ion

Time (min)














10 100 100001

1

10

100

1000

10000

Shear rate (1s)

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(a)

Shear rate (1s)001 01 1 10 100 1000

01

1

10

100

1000

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(b)


3 2 1 0

(d)

(c)

(b)

(ppm)

(a)





0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)













10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of






PAM 55933 216520 119872119899 = 137500119872119908 = 506490 466029


0 15 30 45 60000

025

050

075

100

SolutionEmulsion

Frac

tiona

l con

vers

ion

Time (min)














10 100 100001

1

10

100

1000

10000

Shear rate (1s)

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(a)

Shear rate (1s)001 01 1 10 100 1000

01

1

10

100

1000

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(b)


3 2 1 0

(d)

(c)

(b)

(ppm)

(a)





0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)













10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of








10 100 100001

1

10

100

1000

10000

Shear rate (1s)

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(a)

Shear rate (1s)001 01 1 10 100 1000

01

1

10

100

1000

Visc

osity

(mPa

middots)

Emulsion [M0] = 15

Emulsion [M0] = 40

Solution [M0] = 30

(b)


3 2 1 0

(d)

(c)

(b)

(ppm)

(a)





0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)













10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



0002 0004 0006 0008 0010

300

600

900

1200

1500

C (gml)

AMAM-co-DMA

AM-co-DAMAM-co-HDAM

120578spC

(a)

001 01 1 10 100 1000 1000001

1

10

100

1000

AM-HDAMAM-DAMAM-DMA

AMWater

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

1E minus 3

(b)













10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of








10 100 10001

10

100

1000

Shear rate (1s)

Visc

osity

(mPa

lowasts)

5wt

3wt

1wt

8S0S0






01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



01 1 10 100 1000

1

10

100

1000

Shear rate (1s)

C (wt)01030507123

45678910

Visc

osity

(mPa

middots)


0001 001 01 1 10 100 1000

100

1000

10000

100000

C (wt)0103050713

456789

Shear rate (1s)

Shear rate (1s)

Visc

osity

(mPa

middots)

Visc

osity

(mPa

middots)

200

400

600

800

1000

1

10




0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

C (wt)0103050712

345678

Shear rate (1s)

Visc

osity

(mPa






0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



0001 001 01 1 10 100 10001

10

100

1000

10000

100000

1000000

1E7

Shear rate (1s)

Visc

osity

(mPa

middots)

C (wt)010305071

23456

1E minus 4













(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



(a) (b) (c)


01 1 1001

1

10

100

1000

10000

100000

1000000

1E7

Concentration ( wt)

PAMPAM-co-DAM

PAM12PAM-co-DAM12

1205780

(mPa

middots)

CT(12DAM)

CT(DAM)

CT(12)

Ce(PAM)Clowast(PAM)

m = 405



PAM PAM-co-HDAM

PAM16 PAM-co-HDAM16

01 1 1001

1

10

100

1000

10000

100000

1000000

Concentration ( wt)

1205780

(mPa

middots)

Ce(PAM)Clowast(PAM)

m = 405

CT(16HDAM)

CT(HDAM)

CT(16)






4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of





4 Conclusions






Acknowledgments


References






























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


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