phosphonyl/hydroxyl hydrogen bonding–induced miscibility of poly(arylene ether phosphine...

Phosphonyl/Hydroxyl Hydrogen Bonding–InducedMiscibility of Poly(arylene ether phosphine oxide/sulfone)Statistical Copolymers with Poly(hydroxy ether)(Phenoxy Resin): Synthesis and Characterization

SHENG WANG, QING JI, C. N. TCHATCHOUA, A. R. SHULTZ, AND J. E. MCGRATH,

Department of Chemistry and NSF Science and Technology Center: High Performance Polymeric Adhesives andComposites, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0344

Received 23 September 1998; revised 18 February 1999; accepted 18 February 1999

ABSTRACT: High molecular weight bisphenol A or hydroquinone-based poly(aryleneether phosphine oxide/sulfone) homopolymer or statistical copolymers were synthesizedand characterized by thermal analysis, gel permeation chromatography, and intrinsicviscosity. Miscibility studies of blends of these copolymers with a (bisphenol A)-epichlo-rohydrin based poly(hydroxy ether), termed phenoxy resin, were conducted by infraredspectroscopy, dynamic mechanical analysis, and differential scanning calorimetry. Allof the data are consistent with strong hydrogen bonding between the phosphonylgroups of the copolymers and the pendent hydroxyl groups of the phenoxy resin as themiscibility-inducing mechanism. Complete miscibility at all blend compositions wasachieved with as little as 20 mol % of phosphine oxide units in the bisphenol A poly-(arylene ether phosphine oxide/sulfone) copolymer. Single glass transition tempera-tures (Tg) from about 100 to 200°C were achieved. Replacement of bisphenol A byhydroquinone in the copolymer synthesis did not significantly affect blend miscibilities.Examination of the data within the framework of four existing blend Tg compositionequations revealed Tg elevation attributable to phosphonyl/hydroxyl hydrogen bondinginteractions. Because of the structural similarities of phenoxy, epoxy, and vinylesterresins, the new poly(arylene ether phosphine oxide/sulfone) copolymers should findmany applications as impact-improving and interphase materials in thermoplasticsand thermoset composite blend compositions. © 1999 John Wiley & Sons, Inc. J Polym Sci B:Polym Phys 37: 1849–1862, 1999Keywords: bisphenol A poly(arylene ether phenylphosphine oxide); poly(hydroxyether); blends; phosphonyl; hydrogen bonding; FTIR; DMA; DSC

INTRODUCTION

Polymer matrix composite materials can be de-signed to have very good mechanical properties.1

Epoxy and dimethacrylate vinylester resins arewidely used as crosslinked polymer matrix resins.However, some matrices exhibit marginal adhe-

sion among the polymer matrix and reinforcingfibers. The adhesion can be improved by introduc-ing an interphase material among the matrix andfibers. An interphase with a finite thickness hasbeen shown to drastically alter the mechanicalperformance of various composite systems.2 It isproposed that an interphase material should bemiscible with the polymer matrix and exhibit ex-cellent adhesion to the fibers.

Miscible polymer blends often require sometype of specific interaction between the two com-ponents to provide a negative enthalpy of mix-

Correspondence to: J. E. McGrath (E-mail: [email protected] of Polymer Science: Part B: Polymer Physics, Vol. 37, 1849–1862 (1999)© 1999 John Wiley & Sons, Inc. CCC 0887-6266/99/151849-14

1849

ing.3 One very important specific interaction ishydrogen bonding, which may have bond energiesof about 13–25 kJ/mol.4 The formation of hydro-gen bonds requires proton-donating groups, suchas hydroxyl, carboxyl, amine, or amide groups,and proton-accepting groups, such as carbonyl,ether, hydroxyl group oxygen atoms,or amine andheterocyclic compound nitrogen atoms. Examplesof miscible blends fostered by such strong specificinteractions include (1) phenoxy with poly(buty-lene/terephthalate),5 poly(2-vinylpyridine), andpoly(4-vinylpyridine)6; (2) poly(4-vinylphenol)with vinylacetate,7 poly(arylate)s,8 or poly(vi-nylpyrrolidone)9; and (3) poly(benzimidazole)with polyimides or poly(bisphenol-A carbonate).10

Hydrogen bonding is believed to be responsiblefor the miscibility of these polymer blends, as wellas crucial for the strengthening of polymer–poly-mer interfaces.11

Several aryl phosphine oxides–containing poly-(arylene ether) have been reported to be toughthermoplastic fire-retardant materials.12 Intro-duction of the polar phosphonyl group into thepolymer chain also allows the preparation of mis-cible blends with certain other polymers.

One major objective of this article was to de-velop an attractive interphase between a reinforc-ing fiber and a polymer matrix (e.g., epoxies andvinylester resins), as the mechanical properties ofthe composites can be strongly influenced by theinterphase.2 Because phenoxy resin [poly(hy-droxy ether)] is a thermoplastic with a structuresimilar to those of epoxy and vinylester precur-sors of thermosetting polymer matrix composites,it should be an appropriate model polymer. Pre-liminary research showed that a bisphenol A (BA)poly(arylene ether phenylphosphine oxide) with aMn of 20,000 g/mol was miscible with phenoxyresin.13 FTIR showed a band shift of the phospho-nyl group stretching mode, indicating specific in-teractions (hydrogen bonding) between the phos-phonyl group of the poly(arylene ether phe-nylphosphine oxide) and the hydroxyl group ofthe phenoxy resin repeat unit.13 However, de-tailed studies of the magnitude of the band shiftas a function of copolymer composition were notpursued. It was noted that bisphenol A–basedcommercial poly(arylene ether sulfone) was notmiscible with phenoxy resin. It is of interest fromboth a scientific and technological point of view toimprove miscibility by incorporating phosphonylgroups into the poly(arylene ether sulfone) mainchain. The present study has focused on furtherinvestigation of the miscibility of phenoxy resin

with poly(arylene ether phosphine oxide) andwith poly(arylene ether phosphine oxide/sulfone)statistical copolymers as a function of the phos-phine oxide content. The structures of poly-(arylene ether phosphine oxide/sulfone) copoly-mer; phenoxy, epoxy, and dimethacrylate (i.e., vi-nylester) resin; and related structures are shownin Scheme 1.

EXPERIMENTAL

Materials

Materials included PAPHENTM phenoxy resinPKHHTM with Mn of about 20,000 g/mol (20K)(Phenoxy Associates, Inc., Rock Hill, SC), bisphe-nol-A (Dow Chemical Company, Midland, MI),hydroquinone (Eastman Chemical Company,Kingsport, TN), and 4,49-dichloro diphenyl sulfone(DCDPS) monomer (AMOCO Chemical Company).The 4,49-bis(fluorophenyl) phenylphosphine oxide(BFPPO) and 4,49-bis(fluorophenyl) methyl phos-phine oxide (BFPMPO) were synthesized in ourlaboratory.12 All monomers were of high purity,as judged by melting behavior and H-NMR.

Scheme 1. Structures of BA–poly(arylene ether phe-nylphosphine oxide/sulfone)s, phenoxy resin, and re-lated systems.

1850 WANG ET AL.

Synthesis of BA-Based Poly(arylene etherphenylphosphine oxide/sulfone)

All of the polymers were synthesized via aromaticnucleophilic substitution reactions by using 1 : 1stoichiometry and no monofunctional end-cap-ping agents. Typically, a 250-mL, four-neckround-bottom flask equipped with an overheadstirrer, nitrogen inlet, and Dean–Stark trap witha reflux condenser was used for all of the poly-merizations. As an example, 0.03300 mol of bis-phenol A were reacted with 0.03300 mol of mix-tures of BFPPO and DCDPS. The molar ratio ofBFPPO/DCDPS was varied to achieve desiredtarget compositions of the copolymer. A 15 mol %excess of potassium carbonate was also chargedas the weak base for the nucleophilic reaction. A70/30 (140/60 mL) volume ratio of dimethylacet-amide/toluene was used as the reaction medium.The reaction was initially performed at 135°Creflux for 4 h in a nitrogen atmosphere to dehy-drate the system. Then most of the toluene wasremoved, and the reaction temperature was keptat 160°C for 16 h to achieve high molecularweight. The viscous liquid was allowed to cool toroom temperature and then was diluted withmore solvent, filtered, and acidified with aceticacid to protonate any phenolate end groups. Thepolymer was precipitated into methanol, redis-solved in chloroform, again precipitated intomethanol, filtered, and dried in a vacuum oven at150°C for 24 h.

Synthesis of Hydroquinone-Based Poly(aryleneether phosphine oxide/sulfone) Copolymers

The procedure described in the preceding sectionwas also followed for hydroquinone-based poly-mer synthesis. By using hydroquinone in placeof bisphenol A, various mixtures of BFPPO andDCDPS or BFPMPO and DCDPS were used toprepare copolymers with desired target composi-tions.

Preparation of Polymer Blends

The poly(arylene ether) copolymers and phenoxyresin were separately dissolved in chloroform as7.5 wt % solutions. These solutions were thenmixed to achieve the desired compositions. Thepolymer mixtures were isolated by precipitatingthe cosolutions in methanol, and the precipitateswere dried in a vacuum oven for 24 h at 150°C.Films for FTIR measurements were prepared by

casting blend solutions onto glass slides or saltplates and drying in a vacuum oven in a similarmanner. The films used for dynamic mechanicalanalysis (DMA) measurements were obtained bymelt pressing the precipitates between metalplates for about 3 min at temperatures rangingfrom 160°C for the phenoxy resin to 260°C for thepoly(arylene ether phenylphosphine oxide). Themelt-pressed samples were allowed to cool to am-bient temperature between the metal plates.

Characterization

Intrinsic viscosities of the homopolymers and co-polymers were measured in chloroform at 25°C.GPC measurements were performed at 60°C in aWaters 150C instrument to characterize the mo-lecular weights and molecular weight distribu-tions of the poly(arylene ether phosphine oxide)sand phenoxy resin. N-methyl pyrrolidone (NMP)containing 0.02M phosphorus pentoxide was thesolvent. A differential refractive index detectorand a Viscotek differential viscometer connectedin parallel permitted calculation of absolute mo-lecular weights and molecular weight distribu-tions by application of the universal calibrationprinciple.

FTIR measurements utilized a Nicolet Impact400 instrument at a resolution of 2 cm21 with anaverage of 256 scans. FTIR measurements at var-ious temperatures were performed after the sam-ples were allowed to approach equilibrium for 5min.

The Tg of the poly(arylene ether phosphine ox-ide/sulfone)/phenoxy resin blends was measuredwith a Perkin–Elmer DSC-7 differential scanningcalorimeter at a heating rate of 10°C/min. All ofthe results reported in this article were obtainedduring a second heat after cooling from 250°C.The midpoint temperature of the specific heattransition during the second heat was taken asthe value of Tg. A Perkin–Elmer DMA-7e instru-ment was used for DMA measurements in anextension mode at a frequency of 1 Hz and aheating rate of 5°C/min.

RESULTS AND DISCUSSION

The compositions, molecular weights, and intrin-sic viscosities for four BA-based polymers and forthe phenoxy resin are shown in Table I. The com-positions, molecular weights, and intrinsic viscos-ities of the hydroquinone-based homopolymers

HYDROGEN BONDING–INDUCED MISCIBILITY OF COPOLYMERS 1851

and copolymers are shown in Table II. The resultsconfirm that high molecular weight homopoly-mers and copolymers were obtained under thechosen reaction conditions. The Tg of BA–Px/PHEblends are presented in Table III. The blend vari-ables include both the weight percentage of thepoly(arylene ether) and the poly(arylene ether)composition.

Hydrogen Bonding

FTIR has been widely used to study hydrogenbonding in polymer blends. The specific interac-

tion (hydrogen bonding) generally affects theFTIR bandwidths and positions of the interactinggroups.3 Hydrogen bonding between phosponylgroups of poly(arylene ether phosphine oxide) andphenoxy resin hydroxyl groups has previouslybeen measured on the basis of the shift of thephosphonyl group stretching vibration.13 Furthercharacterization of the specific interaction be-tween phosphonyl groups of poly(arylene etherphosphine oxide) and hydroxyl groups of phenoxyresin was achieved by observation of the hydroxylstretching region. In the present study, the effectof copolymer composition and blend composition

Table I. GPC and Intrinsic Viscosity Characterization of Bisphenol A–Based Poly(arylene etherphenylphosphine oxide/sulfone) Homo- and Copolymers and Phenoxy Resin

SampleaBFPPO : DCDPS

(mol %)

GPC [h] (dL/g)b [h] (dL/g)

Mn 1023 Mw 1023 Mw/Mn NMP (60°C) CHCl3 (25°C)

BA-P100 100/0 39 74 1.9 0.43 0.42BA-P50 50/50 70 159 2.3 0.76 0.73BA-P20 20/80 44 85 1.9 0.51 0.62BA-P10 10/90 39 67 1.7 0.43 0.55Phenoxy — 20 46 2.3 0.38 —

a BA, bisphenol A; P- represents the mole percent of 4,49-bis(fluorophenyl) phenylphosphine oxide used as the activated halide.b From GPC/differential viscometric measurements.

Table II. GPC and Intrinsic Viscosity Characterization of Hydroquinone-Based Poly(arylene ether phenyl ormethylphosphine oxide/sulfone) Homo- and Copolymers

SampleBFPPO : DCDPS

(mol %)

GPC [h] (dL/g)b [h] (dL/g)

Mn (K) Mw (K) Mw/Mn NMP (60°C) CHCl3 (25°C)

HQ-BFPPO1a 50/50 32 62 1.9 0.45 0.53HQ-BFPMPO1 100/0 48 74 1.8 0.63 0.85HQ-BFPMPO2 50/50 59 149 2.5 1.00 1.39

1852 WANG ET AL.

on the phosphonyl group and hydroxyl groupstretching vibrations are examined by FTIR.

Figure 1 shows typical infrared spectra of theBA-P100/PHE polymer blends recorded at roomtemperature in the hydroxyl [Fig. 1(a)] and phos-phonyl [Fig. 1(b)] stretching regions. The spec-trum of the phenoxy resin in the hydroxyl stretch-ing region shows a small peak at 3570 cm21,attributed to free hydroxyl groups, with a majorbroad shoulder at about 3445 cm21, attributed tohydrogen-bonded OH dimers and multimers.6

When the phenoxy was blended with sample BA-P100, the intensities of these two bands decreasedsignificantly. The free hydroxyl group absorptionpeak wave number remains at 3570 cm21. How-ever, an obvious band shift of the dimer and mul-timer hydroxyl stretching vibrations was ob-served with 20 wt % of BA-P100. A blend of 40 wt% of BA-P100 leads to a shift of the broad dimerand multimer OH group stretching vibrationpeak absorbance down to 3300 cm21. The stretch-ing vibration of free phosphonyl groups in BA-P100 was observed at 1196 cm21 [Fig. 1(b)].13

However, with the addition of 20 wt % phenoxyresin, the band shifted to 1194 cm21, and therelative intensity decreased significantly. In-creased amounts of phenoxy resin lead to largerband shifts of the phosphonyl group absorbancepeak. More critical analysis of the band shifts hasbeen realized by subtraction of the spectra of phe-noxy and BA-P100 from the spectrum of theirblend. Thus, if there is no interaction between thetwo components, then the spectra of the blendsshould be the weight-averaged sum of the spectraof the two components. In contrast, interactionbetween the two components may lead to bandshifts in the blends, as shown in Figure 2. Thedifference spectrum in Figure 2(b) shows that thestretching band of phosphonyl group shifts about

25 cm21. The shift of both hydrogen-bonded hy-droxyl group and phosphonyl group absorptionssuggests a strong hydrogen bonding between thetwo groups. Although quantitative correlationsare difficult in this region of the spectrum becauseof the effects of the associated environment, theresults are consistent with reasonably strong hy-drogen bonding.14

When the amount of phosphine oxide in thecopolymer was reduced to 50 mol %, strong hy-drogen bonding of the phosphonyl group couldstill be observed in the polymer blends. In con-trast to the BA-P100/PHE, very broad bands inthe hydroxyl stretching vibration region were ob-served, as illustrated in Figure 3. Some self-asso-ciated hydrogen bonds remained in all the poly-mer blends within the studied composition region.Only with 80 wt % BA-P50 can one observe twoseparate hydroxyl stretching bands. Coleman etal. recently proposed a concept of accessibility offunctional groups that may aid understandingthis phenomenon.15 Because phosphonyl groupsare randomly dispersed in the copolymer chains,not all of the hydroxyl groups can form intermo-lecular hydrogen bonding with phosphonylgroups, because of space accessibility limitations.High amounts of self-associated hydrogen bond-ing among hydroxyl groups leads to a high wavenumber, because not all of the hydroxyl groupsare readily available for hydrogen bonding tophosphonyl groups. If the hydroxyl groups arestrongly diluted by BA-P50, then more hydroxylgroups have opportunities to form intermolecularhydrogen bondings. Meanwhile, hydrogen bond-ing between hydroxyl groups and phosphonylgroups shifts the band of hydroxyl group stretch-ing vibrations to a lower wave number. Also, var-ious environments of hydrogen bonding lead todifferent stretching frequencies. A combination of

Table III. Influence of Phosphine Oxide Concentration on the Composition Dependency of the Glass TransitionTemperature (°C) for Various Polymer Blends

Blend

Wt % of BA–Px in the Blends

0 20 40 50 60 80 100

Tg (°C)

BA-P100/PHE 93 123 145 153 163 182 200BA-P50/PHE 93 121 138 149 159 180 204BA-P20/PHE 93 106 120 129 141 161 186BA-P10/PHE 93 99 102,138 102,140 140a 160 183

a Very broad glass transition.


these three factors results in a fairly broad bandof hydroxyl group stretching vibrations.

Figure 4 displays FTIR spectra in the hydroxylstretching region of 50/50 weight compositionblends of BA-Px/PHE with various compositions(x) of phosphine oxide in the copolymers. As ex-

pected, decreased amounts of phosphine oxide inthe copolymer reduces the amount of hydrogenbonding between the two components. For BA-P20/PHE, the hydrogen bonding was barely ob-servable for a 50/50 polymer blend. For BA-P10/PHE, no hydrogen bonding between the hydroxyland phosphonyl groups could be observed withinthe sensitivity limit of the FTIR measurement.

To study qualitatively the strength of the hy-drogen bonding, temperature measurements of

Figure 2. FTIR spectra of (a) BA-P100; (b) phenoxy;(c) 50/50 wt % blend, and (d) difference spectra of theblend and the components in the hydroxyl stretchingregion (a) and in the phosphonyl stretching region (b).

Figure 1. FTIR spectra of BA-P100/phenoxy blendsat various weight compositions recorded at room tem-perature in the hydroxyl stretching region (a) and thephosphonyl stretching region (b).

1854 WANG ET AL.

the FTIR spectra were performed. Figure 5 showsthe temperature dependency of hydrogen bondingof BA-P100/phenoxy (50/50). No significantchange of intensity and shift of band were ob-served until the temperature reached 180°C.When the temperature was raised to 230°C, the

band of OH stretching vibration shifted slightlyand became broader. Its intensity decreased butstill remained fairly strong. No significant bandshift of the phosphonyl stretching vibration wasobserved. In contrast, the hydrogen-bonded hy-droxyl groups were highly dissociated at 160°C forthe pure phenoxy control, as shown in Figure 6.

Figure 3. FTIR spectra of BA-P50/phenoxy blends atvarious weight compositions recorded at room temper-ature in the hydroxyl stretching region.

Figure 4. FTIR spectra recorded at room tempera-ture in the hydroxyl stretching region for 50/50 BA-Px/PHE blends for various phosphonyl composition (x) inthe copolymers. (a) BA-P100; (b) BA-P50; (c) BA-P20;(d) BA-P10.

Figure 5. FTIR spectra of blend BA-P100/PHE 50/50wt % in the hydroxyl stretching region recorded atvarious temperatures.

Figure 6. FTIR spectra of PHE in the hydroxylstretching region recorded at various temperatures.


The temperature dependency of hydrogenbonding of BA-P50/phenoxy (50/50) showed a sim-ilar behavior as that of BA-P100/phenoxy (50/50),as illustrated in Figure 7. However, when thetemperature was raised to 180°C, significant dis-sociation of the hydrogen-bonded OH group wasobserved. At 230°C, the hydrogen bonding wassharply decreased. Although the Tg of the poly-mer blends BA-P100/phenoxy (50/50) and BA-P50/phenoxy (50/50) are changed only slightly,the strength of the hydrogen bonding is quitedifferent. This is due in part to the dissociation ofself-associated hydroxyl groups. Although it isdifficult to quantitatively analyze the data, wequalitatively conclude that the strength of hydro-gen bonding among the hydroxyl groups andphosphonyl groups is higher than that of self-associated hydroxyl groups, which no doubt en-hances miscibility.

It has been suggested to the authors that thephenoxy hydroxyl groups should also be able toform hydrogen bonds with the ether groups in thearylene ether homopolymers and copolymers ofthis study. This is a reasonable possibility. Suchhydroxyl–ether group hydrogen bonding shouldbe considerably weaker than hydroxyl–hydroxyland hydroxyl–phosphonyl hydrogen bonding. Inblends of phenoxy resin with poly(arylene ethers),the effect of such hydroxyl–ether group hydrogenbonding on miscibility is greatly mitigated by the

fact that these groups are present in both poly-mers in the blends. The phenoxy resin arylene–oxygen–methylene structure and the poly(aryleneether) arylene–oxygen–arylene structure shouldprovide a slight difference in hydroxyl–ether hy-drogen bonding strength.

Phase Behavior of Polymer Blends

A polymer blend that exhibits a sharp single Tgmay be considered a miscible blend. Partially mis-cible or incompatible blends display two or moreTg.16,17 The poly(arylene ether phosphine oxide)homopolymer and the poly(arylene ether phos-phine oxide/sulfone) copolymers used for thisstudy and phenoxy resin are amorphous materi-als. When a poly(arylene ether phosphine oxide/sulfone) copolymer with high phosphine oxidecontent and number-average molecular weight(Mn) of 20K was blended with phenoxy resin, theblends were found to be miscible, on the basis thatsolvent-cast well-dried films from these blend so-lutions were transparent and displayed a singleTg.13 The miscible blends utilized high molecularweight phenoxy resin with poly(arylene etherphenylphosphine oxide/sulfone) copolymers. Thefilms prepared by blending the polymer BA-P100,PA-P50 with phenoxy were transparent. DSCshows a single Tg for blends of high molecularweight phosphine oxide containing polymer andphenoxy resins, within the studied compositionrange from 20/80 to 80/20 weight ratio. From theprevious FTIR analysis, the miscibility was as-cribed to hydrogen bonding. These results suggestthat homogeneous polymer blends can be ob-tained with the component polymers, even at highmolecular weights.

When the amount of phosphine oxide in thecopolymer was decreased to 20 mol %, DSC mea-surements still showed a single Tg for the BA-P20/PHE blends, as illustrated in Figure 8. Thisis still presumed to be due to hydrogen bonding,although FTIR measurements do not show anobvious band shift. To further confirm the conclu-sions from the DSC results, the blend componentsand the BA-P20/PHE blends in the entire compo-sition range were subjected to DMA. Generally,the segmental motions responsible for mechanicalloss peaks are considered to be related to smallerdomains than those of the molecular processesresponsible for the heat capacity discontinuitymeasured by DSC.18,19 The temperature at amaximum of mechanical loss tangent (tan d) wastaken as the Tg. These results for the BA-P20/

Figure 7. FTIR spectra of blend BA-P50/PHE 50/50wt % in the hydroxyl stretching region recorded atvarious temperatures.

1856 WANG ET AL.

PHE blends are shown in Figure 9; note that asingle tan d peak was observed for each blend.The Tg of the blends, like those of the parent PHEand BA-P20, are sharp and increase monotoni-cally with the BA-P20 concentration. No low- tem-

perature transitions near the Tg of the phenoxyresin were observed, again suggesting that theblends are homogeneous.

The effect of annealing on the phase behaviorof a blend of BA-P20 and PHE was studied usinga 50/50 (w/w) blend of BA-P20/PHE. The samplewas quenched from 250°C to 180°C and furthercooled to 70°C at a rate of 0.13°C/min; then, aDSC measurement was performed at a heatingrate of 10°C/min. Again, only a single Tg wasobserved. This result showed that high-tempera-ture annealing under the experimental conditionsdid not lead to a phase separation. One couldreasonably expect a lower critical solution tem-perature (LCST) behavior for the hydrogen bond-ing blend system. However, if an LCST exists forthe BA-P20/PHE blends, it is above the tempera-tures investigated.

One notes in Figure 10 that a decrease in theamount of phosphine oxide to 10 mol % in thecopolymer resulted in DSC curves showing two Tgof blends with 40/60, 50/50, and 60/40 BA-P10/PHE (w/w) compositions. However, blends of BA-P10/PHE with 20/80 and 80/20 blends still appearto be homogeneous. DMA measurements revealedrather broad tan d transitions for the 40/60, 50/50,and 60/40 blends but single, well-defined peaksfor the 20/80 and 80/20 blends, as shown in Figure11. These results are consistent with the DSCdata that showed partial miscibility in the inter-

Figure 8. DSC thermograms of BA-P20/PHE blendsat various weight compositions.

Figure 9. Mechanical loss tangents of BA-P20/PHEblends at various weight compositions.

Figure 10. DSC thermograms of BA-P10/PHE blendsat various weight compositions.


mediate blend compositions and miscibility forthe 20/80 and 80/20 w/w blends. Stoelting et al.observed a similar phenomenon in a different sys-tem.18 The partial miscibility behavior is ascribedto a compromise of the repulsion and the attrac-tion between the two components. Because purebisphenol A–polysulfone is not miscible with phe-noxy resin,13 sulfone units do not promote misci-bility with the phenoxy resin. Phosphonyl groupsand hydroxyl groups provide hydrogen bondingand thus promote miscibility. The limited amountof hydrogen bonding between BA-P10 and PHEthus afforded only partial miscibility.

In a 50/50 (w/w) blend of BA-P10/PHE an-nealed by the same procedure as BA-P20/PHE,the two Tg were more distinct but not shifted fromthose in the nonannealed blend, as illustrated inFigure 12. Further study of the phase behaviorsof blends of phenoxy resin with copolymers withphosphine oxide unit concentrations slightlyabove 10 mol % could give a blend system with anobservable LCST and phase boundaries in thevicinity of the LCST.

Effect of Copolymer Structure on Miscibility

An obvious question is to what extent does thearylene ether portion of the polymer backbonestructure affect the molecular interaction? To ad-

dress this question, hydroquinone-based poly-(arylene ether phenylphosphine oxide/sulfone) co-polymer–phenoxy blends were also studied.Again, only a single Tg was observed. The hydro-quinone poly(arylene ether methyl phosphine ox-ide) copolymer was blended with phenoxy resin;DSC results still showed a single Tg, as illus-trated in Figure13. These results indicate thatthe arylene ether portion of the backbone struc-ture does not play a major role in miscibility, atleast in the case of hydroquinone versus the BA-based system. Further studies with fluorinatedsystems are in progress.

Glass Transition Temperatures

One of the most important ways of characterizingmiscible polymer blends is the determination ofthe composition dependencies of their Tg. Becauseour aim was to study the effect of phosphine oxideon blend miscibilities, Tg data (Table III) wereexamined in the context of four existing blend Tgweight fraction composition equations.

Three of these equations were derived on thebasis of free-volume additivity [Fox eq (1)],20 free-volume additivity corrected for thermal expan-sion coefficient differences [Gordon–Taylor eq(2)],21 and a pseudo–second-order thermodynamictransition combination of entropic changes in the

Figure 11. Mechanical loss tangent of BA-P10/PHEblends at various weight compositions.

Figure 12. DSC thermogram of BA-P10/PHE blendat 50/50 wt % composition. (a) not annealed; (b) an-nealed.

1858 WANG ET AL.

constituent polymers at their respective Tg[Couchman eq (3)].22 The fourth equation [Kweieq (4)]23 is an empirical equation of the Gordon–Taylor form to which a term representing specificinteraction contributions has been added. A re-cent derivation similar in protocol to that ofCouchman, but from an enthalpic approach andincorporating an enthalpy of mixing, has yieldedan equation of the Kwei form but expressed inpolymer unit mole fractions.24

Fox:1

Tgm

5wA

TgA

1wB

TgB

(1)

Gordon–Taylor: Tgm 5wATgA 1 kGTwBTgB

wA 1 kGTwB(2)

Couchman: ln Tgm 5wAln TgA 1 kCwBln TgB

wA 1 kCwB(3)

Kwei: Tgm 5wATgA 1 kKwBTgB

wA 1 kKwB1 qwAwB (4)

The Fox equation contains only the weight frac-tion compositions of the prepared blends and theexperimentally determined Tg of the constituentpolymers. From the derivation of the Gordon–Taylor equation, kGT5(alB

2agB)/(alA

2agA) is a

compression constant involving the ratio ofthe thermal expansion coefficient changes ofthe constituent polymers at their respectiveTg. The Couchman equation derivation giveskC5(ClB

2CgB)/(ClA

2CgA), the ratio of the specific

heat increases of the constituent polymers attheir respective Tg. The empirical Kwei equation,which has the form of the Gordon–Taylor equa-tion plus an arbitrary interaction contributionterm, could logically be applied by setting kKequal to the theoretical kGT and using q as anadjustable parameter. In Tg data analyses of thecomposition dependencies of miscible polymerblends, kGT and kC are often treated as adjust-able, curve-fitting parameters that contain a com-bination of the individual constituent contribu-tions and specific interaction contributions.Adopting such an empirical curve-fitting ap-proach to the present Tgw

data, we obtained theparameter values shown in Table IV. Rather thansetting kK equal to the theoretical kGT as sug-gested earlier, we set kK equal to the theoreticalkC in calculating the q values listed in Table IV.The increases in heat capacity at Tg that wereused in the theoretical Couchman kC and in theKwei equations are 0.23 J/gz°C21 for the phos-phine oxide–containing polymers and 0.41J/gz°C21 for the phenoxy resin.

Figure 14 presents the observed Tg of bisphe-nol A–poly(arylene ether phosphine oxide/sul-fone)/phenoxy resin blends plotted against theweight fraction of bisphenol A–poly(arylene etherphosphine oxide/sulfone). The elevation of theblend Tg relative to the Fox equation prediction(broken line) is greatest for the phosphine oxidehomopolymer blends (BA-P100/PHE), decreasesas the copolymer phosphine oxide content de-creases to 50 mol % (BA-P50/PHE), and becomesslightly negative as the phosphine oxide contentdecreases to 20 mol %. These observations areconsistent with a free-volume decrease with re-sultant increased Tg in the blends because of fa-vorable (exothermal, densifying) phosphonyl/hy-droxyl group interactions. Fitting of the data to

Table IV. Empirical Constants Determined for theTg/Composition Equations of BA–P/PHE Blends

Blend kGT kC q (°C)

BA-P100/PHE 1.2 1.4 93BA-P50/PHE 0.89 1.0 68BA-P20/PHE 0.69 0.78 14

Figure 13. DSC thermogram of HQ-BFPMPO-2/PHEblends at various weight compositions.


the Gordon–Taylor equation (solid curves inFig.14) by an adjustable kGT is fairly successful.Figure 15 indicates that the kGT values required

for the best fits of the datasets increase linearlywith increasing mol % phosphine oxide units inthe copolymer. Because the compression con-stants for the three blend systems should notdiffer greatly, the rather marked increase of kGTwith increasing phosphine oxide may reasonablybe attributed to favorable (exothermal, densify-ing) interactions of the phosphonyl groups withthe PHE hydroxyl groups. Such attribution of kGTassociation with specific interaction contributionsin other blend systems has been proposed.25

Figure 16 presents the same blend Tg datapresented in Figure 14. The broken-line curvescorrespond to the Couchman equation in which kCvalues were calculated from the individual con-stituent polymer-specific heat changes at their Tg.The solid curves represent the fit by using adjust-able kC values. The increased Tg elevation, rela-tive to the theoretical Couchman equation predic-tion, with increased phosphine oxide content isconsistent with favorable (exothermal, densify-ing) phosphonyl/hydroxyl group interactions. Fig-ure 17 presents the blend Tg data, the Tg valuespredicted by the theoretical Gordon–Taylor equa-tion (with kGT 5 kC; broken-line curves), and theempirical Kwei equation fit (solid curves) of the

Figure 14. Fit of experimental Tg versus compositiondata to the curves predicted by the Fox equation (bro-ken line) and the Gordon–Taylor equation with empir-ical adjusted kGT (solid line). (a) BA-P100/phenoxy; (b)BA-P50/phenoxy; (c) BA-P20/phenoxy.

Figure 15. Effect of the amount of phosphine oxide inthe copolymer on the kGT coefficient of the Gordon–Taylor equation.

Figure 16. Fit of experimental Tg values to those pre-dicted by Couchman with kC as the ratio of the heatcapacity increases of the components at their Tg (brokenline) and with empirical kC values (solid line). (a) BA-P100/phenoxy; (b) BA-P50/phenoxy; (c) BA-P20/phenoxy.

1860 WANG ET AL.

data. Fitting the blend Tg data by the Kwei equa-tion with q as an adjustable interaction parame-ter gives very good fits (solid curves), with q val-ues increasing with increasing copolymer phos-phine oxide content. The parameter q is 14, 68,and 93°C for blends containing 20, 50, and 100mol %, respectively, phosphonyl units in the co-polymer (Table IV). This trend of enhanced Tg bythe qwAwB term is definitely consistent with afavorable, hydrogen-bonding interaction betweenthe phosphonyl group of the copolymer and thehydroxyl group of the phenoxy resin.

CONCLUSIONS

High molecular weight, tough, film-forming amor-phous poly(arylene ether phenylphosphine oxide/sulfone) homopolymers and copolymers of variouscompositions have been successfully prepared.Blends prepared via solution mixing of these poly-mers with phenoxy resin exhibited specific inter-action (hydrogen bonding) between the phospho-nyl groups of poly(arylene ether phosphine oxide)and hydroxyl groups of the phenoxy resin. Thiswas confirmed by observation of the band shift of

the hydrogen-bonded hydroxyl group stretchingmode from around 3445 cm21 to 3300 cm21 and ofthe phosphonyl group stretching mode from 1196cm21 to 1170 cm21. The miscibility of the blendsdepends on the mole ratio of phosphine oxide tosulfone in the copolymer. BA-based copoly-mers form miscible blends with phenoxy resineven when the phosphine oxide monomer used toprepare the copolymer is decreased to 20 mol %.However, a further decrease of the amount ofphosphine oxide in the copolymer to 10 mol %results in multiphase blends. These results pro-vide good evidence of the importance of hydrogenbonding to the miscibility of the polymer blends.Various empirical equations have been used todescribe the composition dependency of Tg. Theelevation of Tg with increased phosphonyl groupconcentration can be attributed to the hydrogenbonding specific interaction between the copoly-mer phosphonyl groups and the phenoxy resinhydroxyl groups. Replacement of BA by hydroqui-none in the copolymers did not significantly affecttheir miscibility with phenoxy resin, confirmingthe important role of the phosphorus–oxygenbond in this specific interaction. The study alsoprovides evidence that these copolymers may beuseful to provide interphase materials in severalcomposite structures and in the important field ofpolymer blends.

The authors appreciate support from the NSF-STC(DMR-91004) and the Office of Naval Research(N00014-91-J-1037). Generous support from GenCorpFoundation is also appreciated.

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Figure 17. Fit of experimental Tg values to thosepredicted by the Gordon–Taylor part term of the Kweiequation with kK 5 kC (broken line) and the full form ofKwei equation (solid line). (a) BA-P100/phenoxy; (b)BA-P50/phenoxy; (c) BA-P20/phenoxy.


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