Viscoelastic properties of immiscible telechelic polymer blends : effect of acid-base interactions

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Macromolecules, 25, 10, pp. 2651-2656, 1992-05-01

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Viscoelastic properties of immiscible telechelic polymer blends : effect

of acid-base interactions

Charlier, Pascal; Jerome, Robert; Teyssie, Philippe; Utracki, L. A.

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1992, 25,

Viscoelastic

_{Properties of Immiscible Telechelic Polymer}

Blends:

Effect of

Acid-Base Interactions

Pascal

Charlier,f

Robert _Jéróme,*and

_Philippe

Teyssié

Laboratoryof Macromolecular Chemistryand Organic Catalysis, University ofLiége,

Sart-Tilman B6,B-4000 Liége,Belgium L. A.

Utracki

Industrial MaterialsResearchInstitute, NationalResearch Council ofCanada, Boucherville,

Québec, CanadaJ4B6Y4

ReceivedOctober7, 1991;Revised_ManuscriptReceived_January27, 1992

ABSTRACT: Whenatelechelic polyisoprene(PIP)end-cappedwithtertiaryamine groupsisblendedwith

an immiscible telechelic polystyrene (PS) terminated with either sulfonicor _carboxylicacid functions, a

proton transferoccurs fromthe acid to the amine end groups. Viscoelastic propertiesoftheseblendssupport theformation of eitherammonium sulfonateor _{ammonium carboxylate linkages between}PSandPIP ina manner _{analogous to block copolymerization. Due to the lowstability of}ammonium carboxylates, the related

polyblendshave been_{investigated up to}100°CandtheyshowTeofeachpolymeric partner. WhenPSand

PIPchainendsare associatedthroughmore _thermallystableammonium sulfonates, thethermal

depend-ences of_storageandloss shearmodulishowtwoadditional relaxationprocessesat leastinsome _rangeof

PSandPIPmolecular weights. Byanalogywith SAXSanalysisof similarpolyblends, these relaxationshave been assignedtoaclassicorder-disordertransition similartothatseen in.traditional blockcopolymers and totheirreversible dissociationofthesulfonate salts at higher temperatures, respectively. Theseadditional transitionswhich involvea_changein_{phasemorphology}havebeenconfirmedby the“Cole-Cole”logG"vs

logG' plots.

Introduction

Nowadays,thefinetailoring ofmultiphase polymersis

one ofthe most efficient ways to generate new _organic materials ofhighperformance.1"9 That opportunityhas been _{highlighted for the}first time by the

poly(styrene-b-diene-b-styrene) triblock copolymers which behave as thermoreversibly cross-linked rubbersand are commer-cializedas_{thermoplastic}elastomers.4 Comparedto block copolymerization, melt blending of available polymers

usingtraditionalprocessingequipmentis a more conve-nientway to producemultiphasepolymericmaterials.1"3,5^

Although inthese systemseachofthepartners retains its own _{properties, the overall physicomechanical behavior}

is _{only satisfactory when} two _demanding structural

requirements are _{met: (i)} a controlled _microphase sep-arationinrelation to a_proper interfacialtension and/or appropriate processing conditions; (ii) an _interphase

adhesionstrongenough toassimilatestressesandstrains

without_{disruption of}theestablished morphology. Several strategies have been proposedwiththe viewofreaching

these targets.5 Creating a _practically irreversible mor-phology either in the polymerizationprocess itself(e.g.,

HIPS andABS resins)10 or in the blending _processis a

first _{possible approach.5·7·8} A more _{general strategy}

consistsofusingdiblockcopolymersoftailored structure and_{molecular weight}asinterfacial_{agents.1·5·11"24} These

polymeric additivescan lead toexcellent propertiesofthe finalmaterialseven when usedinratherlowamounts(ca. 1-2 wt %). Mutual interaction of functional groups

randomly attached,one on each_{immiscible polymer}ofa binary blend, isanothermeans of controlling interfacial tensionandinterphaseadhesion. Severaltypes of inter-action can be promoted, e.g., acid-base, dipole-dipole,

ion-ion,andion-dipoleinteractions, hydrogen bonding,

* _{Towhom correspondence shouldbeaddressed.}

1_{Present address: Machelen Chemical Technology Center,Exxon} ChemicalInternationalInc.,2,NieuweNijverheidslaan,B-1831

Ma-chelen,Belgium.

charge-transfercomplexes, andmetal-ligand coordination

complexes.25

The beneficial effectofmutual acid-base interactions on themaincharacteristicsof_polyblendshas been_reported

in the scientificliterature.25"30 Forinstance,ionic cross-interactionsbetweenoriginallyimmiscible polymers are

generatedbya_{proton transfer fromacid groups}attached

to one _{polymer to amino groups present} on the second

polymer. For that transfer to be _{quantitative,}pKa’sof

theacid andamino_{groups have}tobedifferentby atleast

3units.25 This isthe reason _{why sulfonic acid/aromatic} amine_(ApKa 4) isa_commonlyusedacid/basepair. The effect promoted by the mutually interacting groups dependson theirconcentration. Belowacriticalvalue₍₅ mol%withrespect to the monomericunitsofthemodified

polymer),polystyrene/poly(ethylacrylate) and polystyrene/

polyisoprene blends are opaque and show two _Tg’s, although theirmechanicalpropertiesare _improved. Above the critical ionic content, blends are _transparent and exhibita_uniqueTgwhichis,however, observedasabroad relaxation_peakby mechanicalmeasurements, suggesting that miscibilitydoesnot existat ascale smallerthan 10

nm.25 _{Spectroscopic}andmechanicalstudieson blendsof sulfonicacid_{containing polystyrene}andpolyurethanealso showthata_{proton transfer}takes placefrom the sulfonic

acid groups to the urethanemoieties.31"33 _{Interestingly} enough, when used at a rate ofatleast 13 mol %, car-boxylic acid and pyridineunitsare ableto promote the

miscibility of poly(methyl methacrylate) (PMMA) and poly(butyl acrylate).34 A positive effect of hydrogen

bonding has also been reported forblends of

poly(2-vi-nylpyridine) and poly(ethylene-co-methacrylic acid).35 Finally,carboxylic acid-urethane interactions are _likely

to occur sincemechanical propertiesof polystyrene/poly-urethane blendsare _improvedwhen_polystyreneis mod-ified by carboxylicacidgroups.36·37

Proton transfer fromacid end groupsofone telechelic polymerto _{dimethylamine end groups}ofan immiscible

0024-9297/92/2225-2651$03.00/0 © 1992American Chemical Society

2652 Charlieret al. Macromolecules, Vol. 25, No. 10, 1992 telechelic partnerhasbeeninvestigatedas a_{model system}

for the more _{complex situation in which intermolecular} ionic bonding or _{hydrogen bonding} is promoted by interactive moieties distributed at random _along the polymericbackbones.38-42 Since _{the spontaneous}trend

oftheblendedpolymers to demixiscounterbalancednow

by cross-interactions between the chain ends of each

polymeric component, these mixtures are _expected to mimicclosely thephasemorphologyand general properties

ofthecorrespondingmultiblockcopolymers. Thatanalogy hasbeen substantiated byseveral_techniques. IR

spec-troscopy38·41 supports the occurrence of_{proton transfer} from carboxylicacid to dimethylamine end groupswith

theformationof “interchain”ammonium carboxylate ion pairs (eq 1). Optical microscopy shows that the phase

-PA—COOK + _R2N~^PB«

-PA—COO R2NH*~PB- (1)

separationofPA and PB is _{controlled by the ion pairs}

bridging the chain extremities toalevelthatdepends(i) on the nature ofPA and PB and their intrinsic

immis-cibility,(ii)on the ion pair content, in relation to

molec-ular weightofPAand_PB,and(iii)on the strengthofthe

ion_pairs, ammonium sulfonatesbeing more effectivein

fightingthe_{immiscibility of}PAandPB than ammonium

carboxylates.41 Tgmeasurementsare in qualitative agree-ment with the general pattern reported for multiphase block_{polymers.38·41} The_{solution viscosity}ofPA andPB telechelic polymerblendsina_{common, apolar solvent}is

significantly modified by the ionic bondingbetweenthe polymers and the possible dipolar interactions of the bridging ion pairs.41 Finally a temperature-dependent

small-angle X-ray scattering study has shown that the morphology ofthe_{polyblendsclosely resembles}thatseen in covalentlybonded blockcopolymers.39 When ammo-nium sulfonate ion pairsare concernedanddependingon themolecular weightofPAand PB,aclassicorder-disorder

transitionisobserved andeven _{possibly followed by the} effectofacriticalsolution temperature. This_{paper deals}

withthe viscoelastic properties ofblends of a,w-bis(di-methylamino)polyisoprene [PIPfNRzk] and

,

-dicar-boxy-or _{-disulfopolystyrene [PS(COOH)2}or _PS(S03H)2]. The effectofthebridging ion pairsandtheir_strengthand

content willbeconsidered, andthe dynamic mechanical behaviorwillberelatedasmuchas_possibletothephase

morphologypreviously investigated by SAXS.

Experimental

Section

SamplePreparation. Telechelic polymers were _prepared

by anionicpolymerization. Pure andcarefully driedmonomers

and solventswere used. _{Isoprene and styrene}were driedover

CaH2atroom _{temperature and}distilledunder reduced pressure justbefore use. Isoprene andstyrene were mixed with rc-bu-tyllithiumandlithium fluorenyl, respectively, and againdistilled before_{polymerization.}

Polymerization was _performed in _{previously flamed and}

nitrogen-purged flasks equippedwith rubberseptums. Hypo-dermicsyringesandstainless-steel capillarieswere usedtohandle

liquidproducts undera_nitrogenatmosphere. a,o)-Bis(dimeth-ylamino)polyisoprenewas _anionicallypreparedinTHF,at-78 °C, using sodium naphthaleneas adifunctional initiator, ,

-Disulfopolystyrenewas _{prepared under the}same _experimental

conditions exceptforthe counterionoftheactivespecieswhich

was Li insteadofNa. Theinitiatorsresultedfromthereaction ofnaphthalenewitha _slightexcess oftheappropriate alkaline metalinTHF at room _temperature.

The living macrodianions were deactivated by anhydrous

carbondioxide,43 1,3-propane sultone,44and l-chloro-3-(dime-thylamino)propane45withtheformation of ,

-dicarboxypoly-TableI

Molecular Characteristics of Telechelic Polymers

sample M„,X10"3 _{Mw/Mn Mt,°}X10"3 Z6 PIP(NMe2)218K 18.0 1.2 19.5 1.85 PIP(NMe2)238K 38.4 1.3 41.5 1.86 PS(COOH)213K 13.2 1.4 13.5 1.96 PS(S03H)29K 9.1 1.3 10.0 1.82 PS(S03H)215K 14.6 1.2 15.8 1.85

0_Mt= _{molecular weight determined by}titration_{oftheend groups.37}

b_f = _{functionality}= _2MJMt.

TableII

Compositions andCodeNamesof Blends of Telechelic Polymers

blends0 codename

PIP(NMe2)238K-PS(COOH)213K M38-13C PIP(NMe2)238K-PS(S03H)2 9K M38-9S PIP(NMe2)238K-PS(S03H)215K M38-15S PIP(NMe2)218K-PS(COOH)213K M18-13C PIP(NMe2)218K-PS(S03H)2 9K M18-9S PIP(NMe2)218K-PS(S03H)215K M18-15S “PIP/PS= _{1/1 (mol/mol).}

styrene [PS(COOH)2], , -disulfopolystyrene [PS(S030H)2], and a,ü>-bis(dimethylamino)polyisoprene [PIP(NMe2)2],

respec-tively.

The microstructure ofthe polyisoprene was found to be a

mixture of1,2/3,4inaratio of_35/65. Molecularweightsofthe telechelicswere controlled_byadjustingthemonomer toinitiator molar ratio. The molecular weight and polydispersity ofthe telechelic polymerswere _{measured by size-exclusion}

chroma-tography(SEC),as_reportedelsewhere.45 Thefunctionalitywas

calculatedfrom theM„value (SEC) and from thepotentiometric

titration ofthe end groups. Dimethylamino groups and acid groups (COOH and S03H)were titratedwith perchloricacid and tetramethylammoniumhydroxide, respectively,ina9/1toluene/ methanolmixture. Polyisoprenewas _carefullystabilized byan

antioxidant(1wt % of_Irganox1010).

The main molecular characteristicsoftelechelic polymersare

reported in Table I.

Polymer blendswere _{prepared by}means of_{solvent-casting}

techniques. Separate solutionsofeach_polymerina9/1toluene/ methanolmixturewere prepared. Afterhaving mixed the proper volumesofeachsolution(sothatthe acid/amine molarratiowas

1), the solutions were allowed to stir for24 h before casting. Filmswere _preparedbyaslow_{evaporation of}thesolvent followed byvacuum _{dryingto constant weight at} 70 °C (ca. 1 _month).

Samplesfordynamic mechanical measurementswere _prepared

by compressionmoldingat2MPaand140°Cfor20min. Table II summarizesthe compositionsofthe blends investigated in this_{study together}with theircodenames.

Differential Scanning Calorimetry(DSC). DSC thermo-gramswere _recorded, from-40 _{up to +200 °C. Samples}were

previously annealed at200°Cfor15min. APerkin-Elmer

DSC-4 was usedata_{heating rate}of20°C/minunderaconstantflow ofdrynitrogen.

Dynamic MechanicalMeasurements. A Rheometrics

me-chanical spectrometer (RMS 605S) was used with a

parallel-plate geometry. The 25-mm-diameter specimenin a 1.4-mm-wide _gap was tested under a constant flow _{of dry nitrogen.} Measurementwere carried out ata_{constant frequency}(t-= _1Hz)

and a constant heating/cooling rate of2 °C/min. Isothermal frequencyscans atfrequenciesfrom0.016to16Hzwere conducted forM38-13C and M18-15S blends.

Results and Discussion

Effect of

Strength

of the Ion Pairs and of Their Mutual Interactions. _{Figures 1-3}illustratethethermal

dependenceofthe_storage(GOandloss(G")shearmoduli,

measured ata_{frequency of}1rads-1forblendscontaining PIP(NR2)2 38K (where 38K refers to molecular weight)

associated to PS (SOsH^ 15K, PS(S03H)2 9K, and PS (COOH)2 13K, respectively.

Macromolecules, Vol.25, 10,

Figure 1. _Storage(GOandloss(G") shearmodulivs

temper-ature (1 Hz) for theM38-15S blend (TableII).

Figure2. Storage(GOandloss (G'O shearmodulivs

temper-ature (1 Hz)for theM38-9Sblend (TableII).

Figure3. Storage (GOandloss(G") shearmodulivs

temper-ature (1 Hz)for theM38-13Cblend (TableII).

All

theG"curves showamaximumin the temperature

rangeof 70-80 °C. Such arelaxationhas been assigned totheglasstransitionof polystyrene(orpolystyrene-rich)

phases. Abovethat transitiontemperature, the material clearly starts to flow. That interpretationassumes that the investigated blends are _{phase separated.} This has beenconfirmed elsewhere41and shown in this study by

differential_{scanningcalorimetry}(DSC). Indeed,two_Tg’s

are _{reported (Table}

III)

which_comparedto_Tgofthe_parent PIP and PS are characteristicof_phasesof that nature.

The difference in the _Tg’sforeach type ofphase isalso

mentioned inTableIII. _ATgis_{smaller by}ca. 10°Cwhen

Viscoelastic Properties Telechelic Polymer Blends TableIII

Tg’sof Telechelic PolymersandBinaryBlends

sample Tgi, °C Tg2,°C ATtb

PIP 18K“ 3 PIP38K° 17 PS9K“ 95 PS13K“ 97 PS15K 98 M38-13C 17 112 95 M38-15S 20 108 88 M38-9S 19 107 88 M18-13C 14 113 99 M18-15S 18 106 88 M18-9S 18 105 87 a

Polymerfreefromfunctionalend groups.6

ATf= “

T$l.

Figure4. _Comparisonofthe log G'vs_temperaturecurve (1Hz) forM38-15S and M38-13C blends (TableII).

thechainendsare held together through ammonium

sul-fonate ion pairs rather _{than carboxylate} ones. This indicatesthatan increaseinthe strengthofthe bridging ion pairs is in favor of an _{improved miscibility, all} the other conditions_{being unchanged.}

Figure4 comparesthe G' curves fortwo blends M38-15SandM38-13C which essentiallydifferon thenature

oftheacid end groups.

The_{intermediate plateau below}70-80°Cextendsover a_{largertemperaturerange, and G'}of that_plateauishigher

when PSis _end-cappedbyasulfonicacid. These

obser-vations mean that ammonium sulfonates are _stronger dipoles than theircarboxylatecounterpartsandthattheir

mutual interactions stabilize a _{stronger chain network.} Indeed_{the telechelic polymer}blendsunder investigation can be _{depicted not only} as an _ionically bonded block copolymerbutalsoas a_{two-component}(PS andPIP) ion-omer ofthe_{sulfonic type.} In this_regard,itiswell-known

thatthemutualassociationofsulfonateion pairs improves

the_{high-temperature properties of}theionomer muchmore effectively than carboxylate dipoles do.46

At

70_{°C, theM38-13C blend starts to flow rapidly which} reflectsthe fast _{disruption of}themutual association of

theammonium carboxylate ion pairsand mostlikelythe thermalrupture oftheion pairsthemselveswith release of_{the carboxylic}acid and dimethylamineend groups.It is_{worth pointing}outthata_{PS(COOH)213Ksample}has beenpreviously neutralizedwith triethylamineandthen

heatedat130°Cundervacuum. Theback_{proton transfer}

has been observed as _{supported by the quantitative} elimination oftriethylamine47,48 (eq 2). Incontrastto

M38-130°C

PS(COO~ +HNR3)2 —

PS(COOH)2+ 2NR3 (2)

2654 Charlieret al. Macromolecules, Vol._25, No. 10, 1992

TableIV

MolarandWeightCompositionsofBinaryBlendsof Telechelic Polymers

pip_

ps _so3-n+:

codename mol%< wt % mol %° wt % mol%°

M38-15S 79.3 71.7 20.4 28.3 0.28

M38-9S 86.3 80.9 13.4 19.1 0.31

M18-15S 64.4 54.5 35.1 45.5 0.49

M18-9S 74.9 66.7 24.5 33.3 0.57

0_{Onthebasisofthemonomer content.}

Figure5. _{Storage (G') and}loss (G")shearmodulivs

temper-ature(1 Hz) for theM18-15S blend (TableII).

13C, the occurrence ofthe flow_regime is_delayed in the M38-15SblendandthedecreaseinG'atincreasing tem-peratureismuchslower. For_instance,the_{complex shear} modulusofM38-15Sis_{easily measured at} 150°C _(Figure

1)whereasitis_{already too small to}be_{measured accurately} at100°Cfor theM38-13Cmixture_(Figure3). Thisisthe

consequence of the highest thermal stability of the ammonium sulfonate ion pairscomparedto the

carbox-ylate ones.47’48

Effect

oftheIon

Pair

Content. Inthe previous blends, the _{molecular weight of PStSOsHh} associated to

PIP-(NH2)2 38K was changed from 15K to 9K and no substantialmodificationintheviscoelasticbehaviorwas noted(seeFigures1and_2). It_{must,however,}bestressed

thatthe_{ion pair content remained essentially unaffected}

ascalculatedinTableIV. Thisisthereason _whyasecond

seriesofblendswas_preparedinwhich the molecularweight

of PIP(NH2)2 was made to decrease by a factor of 2. Accordingly, the ion pair content was increased _by ca.

80% withrespecttosamplesofthefirstseries(TableIV). Figures5and6showtheG' andG"curves forthe

M18-15Sand M18-9S mixtures whichare _basically different from those _reported for the related blends containing PIP(NR2)2ofa twice as _{high molecular weight (Figures}

1and_{2). Actually, two additional transitions}are observed on the high-temperature side. In order _{to assign} the relaxationprocessesobservedin the investigated temper-ature range, it is worth_referringto _TgdataofTable II. Inspiteofasubstantialincreaseintheion_paircontent, the telechelic polymer blends are still _{phase separated}

and the _Tg of each phase as measured _by DSC is not significantly modified. According to the G" curves of Figures 5 and 6,the first maximumon the low-temper-ature sideisobservedat 65°C andthenext one at

120-130°C. Oneofthesemaxima shouldbeattributedtothe Tgofpolystyrene-rich phases. The decrease in the PIP molecular weight together withthe increasein thecontent oftheion_{pairs which}haveto accumulateintheinterfacial

regionis_expectedtoenhance_{the polymermiscibility}and

TEMPERATURE ( C!

Figure6. Storage (G') andloss(G") shearmodulivs

temper-ature (1 Hz) forthe M18-9S blend (TableII).

Figure7. Schematic_phasediagramofblendsofPIP(NR2)2 and PS(COOH)2or _PS(S03H)2.35

move _Tg’s closer _together. On that _basis, the _glass

transitionofthePS-rich_phasesshouldbeat_{the origin}of

therelaxation at65°C. If thisisso,dynamic mechanical

measurements conclude to a decrease in _Tg ofthe _rigid

phaseswhenthePIP molecular weightisdecreasedfrom 38K to18K. The apparent contradictionwithDSCdata (Table

III)

will be discussed later.

Theadditionalrelaxations observed at 120-130 and 160-180°C, respectively, have_somethingto dowiththe

sul-fonateion pairsandtheir association, sincepolystyrene

ionomers_{of the sulfonic type} exhibitan ionicrelaxation inthat _range oftemperature.49 It is,however, ofgreat

significancetorefernow toa_{previousstudy}on thethermal

dependence ofthe SAXS profile of blends comprising PIP(NR2)218Kanda,w-disulfopoly(a-methylstyrene)of

various molecular_weights.39 Fromthatstudy, the general phasediagramschematizedin Figure7hasbeen proposed whereUCSTistheuppercriticalsolution temperature of

the constituent telechelic polymers, MST is the

mi-crophase-separationtemperatureoftheionic_copolymers, Tgistheglasstransitionofthehardphases,andT¡ isthe

25, Viscoelastic Properties Telechelic Polymer Blends

block _copolymers are _disrupted. T¡ depends on the strengthoftheionpairs, theintrinsic immiscibility ofthe

polymerpair,andthe molecular weightofeachofthem.

When Tiisaboveboth _TgandtheMSTcurve (represen-tativesystemA),anorder-disordertransitionoccurs when

the microphase-separated system goes across the MST curve and a uniform melt is observed. At _higher tem-peratures, i.e.,greater thanT¡,the effectivehomogeneous

copolymer melt is _{broken up} into the constituent

ho-mopolymersand phaseseparationofthe homopolymers occurs. The two additional relaxation mechanisms of Figures5and6couldnow beaccounted for. The maximum

in G" at 120-130 °C should _correspond to the classical

order-disordertransitionseen in_covalentlybondedblock

copolymers. In the investigated blends (M18-15S and

M18-9S), that transition is _{actually triggered by the}

relaxationofthe ion_pairassociation.50"53 Inotherwords,

themutual interactionsoftheammonium sulfonate ion pairs are unable to stabilize a _{microphase-separated} morphology at temperatureshigher than120-130 °C. As

longasthe ion pairsare stable, chainsretaina _“blocky” structure and the system remains homogeneous at the microscopiclevel. At_{higher temperatures(160-180 °C)}

thethermal_breakupoftheammonium sulfonate ion pairs occurs _togetherwithareleaseofsulfonic acid and_tertiary amine end groups,resulting ina _{macrophase separation.}

Thisis_{supported by the elsewhere-reported observation} that ammonium sulfonates attached at the end of a polystyrene chainare unstable above 180 °C.47,48 Since

it

iswell-knownthat_{aliphatic sulfonic}acidsare unstable at such _{high temperatures, the ionic block copolymer}

structureis_irreversiblylost.

It

isnow worth_mentioning

thatthe samples analyzedbyDSCinthis studyhave been

previouslyannealedat200°Cin order tomakethemfree

from any residual solvent. That _{pretreatment might}

explain the discrepancy inTgvaluesdetermined byDSC anddynamic mechanicalmeasurements. Whenthe high-temperaturepretreatmentisnot applied, data provided bythe two methodsare consistent.41 TheG' andG"curves reported inFigures1-3can alsoberationalizedbyreferring to thephase diagram ofFigure 7 where B is the repre-sentativesystem. Since T¡ is below _{Tg, as soon as Tg is} reached, the components ofthe ionic block copolymer behaveas individualhomopolymer moleculesbelow the UCSTandcoarse _{phaseseparation}ensues. _Thus,above Tg of the rigid PS phases, no additional relaxation is expectedtooccur,asis_actuallyobserved. _Figure8 sche-matizes the three main phase situations which can be observed when ion pairs associate the chain ends of immiscible telechelic _polymers.

Transitions observed at 120-130 and 160-180 °C in

Figures5and6havebeenassigned torelaxationprocesses thatinvolvea_changein the_{phasemorphology:} an order-disorder transition and a _{macrophase separation} of a

homogeneous system. Very interestingly, Han etal.54-56

have proposedamethodwhichhasprovento be

fruitful

in giving prominence to the order-disordertransitionin poly(styrene- -isoprene-b-styrene) copolymers.57 The

methodconsistsof first_{recording the isothermal}

depend-ence ofG'andG"on _frequencyandthen_plottinglogG" versus _logG'. _{These graphs}are _{actually Cole-Cole plots} on a _log-log scale. As long as the morphology remains

unchanged in the investigated temperature range,

iso-thermallogG"vs_logG'curves _superimposewithformation

ofa_single“mastercurve”.54 Incontrast,whenthephase

morphology is _{modified, the superposition fails}at least until it _{becomes again}temperature independent. Onthe

basis_{of that criterion, the}Cole-ColeplotofFigure9shows thatthemorphology oftheM38-13Cmixtureis_preserved

from40_{up to}ca. 100_{°C,i.e.,up to theorigin}oftheviscous

'·...I-Figure8. Representationofthemain_phasesituationsobserved in blends of immiscible telechelic polymers, where

sche-matizesan_{ammonium carboxylate (~COO"R2+NH-)}or sulfonate

(-SC>3"R2+NH-) ion pair. 7 6 4 3 2 3 4 5 6 7 logG' (Pa)

Figure9. logG'vs_logG"curves fortheM38-13Cblend (Table

II). 6 , 4 3 2 2 3 4 5 6 logG' (Pa)

Figure 10. Cole-Cole_{plot for}the M18-15S blend (Table II). flowregime. Thus,as _longas _TgofthePS_{phases is}not

exceeded, the two-phase structure is stabilized by that rigid PS componentinagreement with Figure7 (repre-sentative _system B). When the M18-15S blend is

con-cerned,thesituationradicallychanges, as illustrated_by Figure10. The superpositionof_{the log}G"vs_logG'curves

does not fit in two temperature ranges. The first one

extends_{approximately from} 115to 155 °C,which

corre-sponds satisfactorily to the second relaxation seen in Figure5. The Cole-Coleplotgivesaccordingly credit to

2656 Charlier etal.

the _assignment ofan order-disorder transition to that relaxation. The same conclusion can be drawn for the

secondtemperaturerangein which superpositionofthe

Cole-Cole_plotdoesnotwork(i.e.,aboveca. 165°C),since it fits the third relaxation observed in the viscoelastic

curves of_Figure5 andsubstantiates the attribution ofa

macroscopicphase demixing.

Inconclusion, thereisa_{verygood agreement between}

the viscoelastic properties of blendsof

a,o>-bis(dimeth-ylamino)polyisopreneand , -dicarboxy-or

-disulfopoly-styrene and the phase morphology which has been

determined by SAXSfor analogousblends.39 The relative positions of Tg of the PS phases, the order-disorder transitiontemperatureofthe_{bridging ion pairs}(T¡), and the MST curve _play a _{key role.} That situation can interestinglybe_{controlled by (i) the}intrinsicstrengthof theion pairs(ammoniumcarboxylates against sulfonates)

whichaffectsthepartial

miscibilitity

ofPSandPIP (thus Tgof thePS phase),the strength of themutual ion pair

association (thus theMSTvalue), andT¡and by (ii) the molecular weight of the telechelic polymers, i.e., the

thermodynamic repulsion of PS and PIP which acts adversely onto the electrostatic interactions of the am-monium cation andsulfonate (or carboxylate) anion, as wellas on theirmutualassociation. Asa_result,itis_quite possible togothroughthe whole phasediagramshownon Figure7andtochangedeeply theviscoelasticbehaviorof the polyblends.

Acknowledgment. P.C., R.J., andPh.T.are _{very much} indebted to the “Servicedela_{Progranimation}dela Poli-tique Scientifique” and the “Fonds National de la Re-cherche_{Scientifique” (FNRS) for financial support.} P.C. is _{very much indebted to} IMRI for the _{opportunity of}

spendinga 3-month_stayintheir facilities. Theskillful technical assistanceofP. Sammut (IMRI) for dynamic mechanicalmeasurementsis_verymuchappreciated.P.C. also thanks the

“Instituí

pour l’Encouragement de la RechercheScientifiquedansl’lndustrieet _{Agriculture”} (IRSIA)fora_{fellowshipand the FNRS for having awarded} him a _{grant to} visit the Industrial Materials Research

Institute (IMRI) ofMontreal. Referencesand Notes

(1) Teyssié, Ph.;Fayt,R.;Jéróme, R.Makromol. Chem.,

Macro-mol. Symp. 1988, 16, 41.

(2) Utracki, L.A.Int. Polym.Process. 1987, 2, 3.

(3) Schreiber, P.;Latham,J.Polym.News 1987, 13,19.

(4) Legge,N.R.,Holden,G., Schroeder, . E., Eds.Thermoplastic Elastomers;Hanser: Munich,1987.

(5) Paul, D. R., Newman, S., Eds. Polymer Blends; Academic Press: NewYork,1978;Vols.1 and2.

(6) Olabisi,0.; Robeson, L. M.; Shaw, . T. Polymer-Polymer

Miscibility;Academic Press: NewYork, 1979.

(7) Walsh, D. J.; Higgins,J.S.PolymerBlendsand Mixtures;

Ma-connachie,A., Ed.; NATOAdvancedStudyInstituteSeries;

MartinusNijhoff: Dordrecht, The Netherlands,1985. (8) Utracki, L.A._{Polymer Alloys and}Blends,Thermodynamics

andRheology; Hanser: Munich, 1989.

(9) Utracki, L.A., Weiss,R.A., Eds.MultiphasePolymers: Blends

andlonomers; ACS Symposium Series395;AmericanChemical Society: Washington,DC,1989.

(10) Bucknall,C.B. Toughened Plastics;AppliedScience: London,

1977.

(11) Fayt,R.;Jéróme, R.; Teyssié, Ph.J. Polym.Sci.,Polym. Lett.

1981, 19,79; 1986, 24, 25.

(12) Fayt,R.; Jéróme, R.; Teyssié, Ph.J. Polym.Sci., Polym. Phys. Ed.1981, 19, 1269; 1982,20, 2209; 1989, 27, 775.

(13) Fayt,R.;Jéróme, R.; Teyssié, Ph.Makromol.Chem. 1986,187, 837.

Macromolecules, Vol. 25,No. 10, 1992 (14) Fayt, R.; Jéróme,R.;Teyssié, Ph. Polym.Eng. Sci.1987,27,

328.

(15) Fayt, R.; Jéróme, R.; Teyssié, Ph. J.Appl.Polym. Sci. 1986,32, 5647.

(16) Fayt,R.; Teyssié, Ph. Macromolecules 1986, 19, 2077. (17) Ouhadi,T.; Fayt,R.;Jéróme, R.; Teyssié, Ph.J. Polym.Sci.,

Polym.Phys. Ed. 1986,24, 973.

(18) Ouhadi,T.; Fayt,R.;Jéróme, R.; Teyssié, Ph. Polym. Commun. 1986, 27, 212.

(19) Ouhadi,T.; Fayt,R.;Jéróme,R.;Teyssié, Ph. J.Appl. Polym.

Sci. 1986,32, 5647.

(20) Heuschen, J.; Vion,J. M.;Jéróme, R.; Teyssié, Ph. Polymer

1990,31, 1473.

(21) Barlow,J. W.; Paul, D. R.Polym.Eng. Sci.1984,24, 525. (22) Anastasiadis,S.H.; Gancarz,I.; Koberstein,J.T.

Macromol-ecules 1989, 22, 1449.

(23) Shull, K. R.; Kramer, E. J.; Hadziioannou, G.; Tang, W. Macromolecules 1990,23, 4780.

(24) Cho, K.; Brown, H. R.;Miller, D. C. _{J. Polym.}Sci.,PartB;

Polym.Phys. 1990,28, 1699.

(25) Smith, P.; Kara, M.;Eisenberg, A. A Review ofMiscibility Enhancement via Ion-Ion and _{Ion-Dipole Interactions.} Current_{Topicsin Polymer}Science; Hanser: NewYork,1987; Vol.2,Part6.

(26) Eisenberg, A.;Smith,P.;Zhou,Z.L.Polym.Eng. Sci. 1982,22, 1117.

(27) Smith,P.;Eisenberg, A.J. Polym.Sci., Polym.Lett.Ed.1983, 21, 223.

(28) Zhou, Z. L.; Eisenberg, A. J. Polym. Sci.,Polym. Phys. Ed. 1983,21, 595.

(29) Bazuin,C.G.;Eisenberg, A.J. Polym.Sci.,Polym.Phys. Ed. 1986,24, 1021.

(30) Murali,R.; Eisenberg, A. J.Polym. Sci.,Polym.Phys. Ed.1988, 26, 1385.

(31) Rutkowska,M.;Eisenberg, A.Macromolecules 1984,17,821. (32) Tannenbaum,R.;Rutkowska,M.;Eisenberg, A. J.Polym. Sci.,

Polym.Phys. Ed. 1987,25, 663.

(33) Natansohn, A.; Murali,R.; Eisenberg, A. Makromol. Chem.,

Makromol. _Symp. 1988, 16, 175.

(34) Jo, W.H.;Lee,S. C.;Lee,M.S.Polym.Bull. 1989, 21, 183. (35) Lee,J.Y.;Painter,P. C.;Coleman, . M. Macromolecules1988,

21, 954.

(36) Hsieh,K. H.; Wu,M. L. J.Appl.Polym.Sci. 1989, 37, 347. (37) Hsieh,K. H.;Chou,L. M.;Chiang, Y.C.Polym. J. 1989,21,1. (38) Horrion,J.;Jéróme, R.;Teyssié, Ph.J. Polym. Sci., Polym.

Lett.Ed. 1986,24, 69.

(39) Russel, T. T.;Jéróme, R.; Charlier, P.; Foucart, M.

Macro-molecules 1988,21, 1709.

(40) Horrion, J.; Jéróme, R.; Teyssié, Ph.; Vanderschueren, J.; Corapci,M. Polym.Bull. 1989,21, 627.

(41) Horrion,J.;Jéróme, R.; Teyssié, Ph. J. Polym. Sci., Polym.

Chem.Ed.1990,28, 153.

(42) Charlier, P.;Jéróme, R.; Teyssié, Ph.;Utracki, L. A._Polym.

Networks Blends 1991,1,27.

(43) Broze, G.;Jéróme,R.;Teyssié, Ph. Macromolecules1982,15, 920.

(44) Foucart, M.Ph.D. Thesis,University ofLiége,Belgium,1988. (45) Charlier,P.;Jéróme, R.; Teyssié, Ph. Macromolecules 1990,23,

1831.

(46) Lundberg,R.D.;Makowski, H.S.Adv.Chem.Ser. 1980,187, 21.

(47) Charlier,P.Ph.D. Thesis,University ofLiége,Belgium,1990. (48) Charlier,P.;Jéróme, R.;Teyssié, Ph.;Prud’homme,R. E., to

bepublished.

(49) Bazuin,C. G.;Eisenberg, A.Ind.Eng. Chem. Prod.Res.Dev. 1981 20 271

(50) Chung,C.I.;Lin, . I.J. Polym.Sci.,Polym.Phys. Ed.1978, 16, 545.

(51) Widmaier,J._{M.; Meyer,}G. C.J. Polym.Sci.,Polym. Phys. Ed. 1980, 18, 2217.

(52) Roe,R.J.;Fishkis,M.;Chang,J. C.Macromolecules 1981,14, 1091.

(53) Kraus,G.;Hashimoto,T.J.Appl.Polym.Sci.1982,27, 1745. (54) Han,C.D.; Kim,J.J.Phys. Sci.,Polym.Phys. Ed. 1987,25,

1741.

(55) Kim,J.;Han,C.D.J. Polym.Sci.,Polym.Phys. Ed.1988, 26, 677.

(56) Han,C._D.;Kim,J.;Kim,J.K.Macromolecules1989,22, 383. (57) Han,C.D.; Back, D.M.;Kim,J.K. Macromolecules1990,23,