Solubility of Polymethyl Methacrylate in Organic Solvents(2)

Fig.2.DegreeQofPMMAdissolutionin1,4-dioxanevs.timet.Temperature(oC):(1)30,(2)40,(3)50,and(4)

70.

Fig.1.RelativelossofmassbyPMMAsamplesQvs.timetat30oCin(1)ethylacetate,(2)benzene,(3)toluene,and(4)o

-xylene.

Somewhatbetterresultswereobtainedwithanotherparameterofthesolvent,themolarvolumeVM,whichisdirectlyrelatedtothemoleculeradiusrinformula(2).Itwasshownin[11]thatthemolarvolumeisanimportantparameterforgeneralizationofdataontheswellingratesforcarbonsinvarioussolvents,withtheprocessratedecreasingasthisparameterbecomeslarger[11].Similarresultswereobtainedinthecaseinquestion.However,noclearlydefinedrelationshipcouldbeobtained,either.Therefore,weattemptedtofindoutwhetherthevaluesobtainedcanbequantitativelygeneralizedontheLFEprinciplebysimultaneouslytakingintoaccounttheinfluenceofbothparametersinaccordancewiththedependence:

1+a71,logQ=a0+a1772hVM

(3)

Fig.3.RelationshipbetweenthedegreeQofpolymer

dissolutioninvarioussolventsandtheirviscosityh(30oC,20min).(1)Benzene,(2)toluene,(3)o-xylene,(4)m-xy-lene,(5)trichloromethane,(6)1,4-dioxane,(7)cyclo-hexanone,(8)acetophenone,(9)trichloroethylene,(10)ethylacetate,(11)pentylacetate,and(12)dimethylformamide.

whereQistherelativelossofmassbythePMMA

sample(%).

Thisattemptwasunsuccessfultoo.Thus,there-sultsobtainedshowthatthedissolutionkineticsofpolymersisacomplexprocessdependentonmany

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SOLUBILITYOFPOLYMETHYLMETHACRYLATEINORGANICSOLVENTS1579

factors.Amongthem,mentionshouldbemadeoftheoppositedirectionsofthefollowingtwoprocesses.Thefirstisthepenetration(diffusion)ofasolventintothepolymer,whichismainlydeterminedbythesizeofitsmolecules.Thesecondisthatofapar-tialdissolutionofagel-likeswollensurfacelayerofthepolymer.Thisprocessismainlydependentontheviscosityoftheliquidphase,which,inaddi-tion,graduallyincreasesinthecourseofitssatura-tionwiththepolymer.Apparently,thesecondprocesswillbealsofacilitatedbyagitationoftheliquid,whichmakesitsviscosityuniformthroughoutthepolymervolumeandpreventsformationofhighlyviscouslayersofapolymersolutiononthesurfaceofpolymers.

Therefore,weattemptedtogeneralizethedataonthedegreeofpolymerdissolutionatdifferentintervalsoftime(Tables1,2)byusingthemultiple-parameterKoppel3Palmequation[12],whichtakesintoaccountdifferenttypesofsolvation,andsupplementingthisequationwithtermsthatcharacterizeself-associationofsolventsandtheirmolarvolume:

e31n231+a777logQ=a0+a1777222e+1n32+a3B+a4ET+a5

d2

+a6VM.

(4)

whichcharacterizethespecificsolvation,wealso

obtainanadequatefour-parameterequation:

logQ=3.35+(4.11+1.48)f(n)+(4.41+0.63)f(e)3(5.31+0.79)010!3d23(26.2+2.59)010!3VM,

R=0.978,S=0.109.

(6)

OnexcludingthenonsignificanttermsBandET,

Theaboveconsiderationshowsthatanincreaseinthesizeofsolventmolecules(VM)andintheirself-association(d2)deceleratesthedissolutionofpolymerinthesolvents,whichispresumablyduetothehindrancetosolventdiffusionintothepolymer.Atthesametime,thenonspecificsolvationofthechainsofapolymerbythesolventfavorsitsdissolu-tion.However,particularinterestinginthiscaseistheconclusionthatthepossiblespecificsolvationofPMMAisunimportantforthedissolutionprocess,despitethepresenceofelectron-donatingcarbonylgroupsinitsstructure.Possibly,thisisduetothefactthatwestudiednearlyexclusivelytypicalelectron-donatingsolvents,andtheelectron-acceptingtri-chloromethaneissoactiveasolventthatitcannotbeinvolvedinthecomparison.

ItshouldbenotedthatEq.(4)yieldssatisfactoryresultsonlyfortemperaturesclosetoroomtemper-ature.Apparently,theeffectofpolymerdiffusionin-totheliquid,whichstronglydependsbothonthein-creaseinviscosityuponsaturationofthesolutionwiththepolymerandontheoppositeeffectofthedecreaseintheviscosityofthemediumonraisingthetemper-ature,whichisdifficulttotakeintoaccount,willbealsotheimportantfactorsunderotherconditions.

CONCLUSION

ThedissolutionrateofpolymethylmethacrylateinvariousorganicsolventscannotbedescribedintermsoftheEinshtein3Stokesdependence.Dissolu-tionisacomplexprocessdependentonthediffusionandsolvationphenomenaoccurringinthesystem.Themaximumdissolutionrateisobservedintrichlo-romethaneandtrichloroethylene.Dissolutioninothersolventsisdetermined,ontheonehand,bythein-fluenceoftheirpolarityandpolarizability,whichfacilitatetheprocess,and,ontheother,bytheenergydensityofcohesionandthemolarvolume,whichactintheoppositedirection.

REFERENCES

1.Ueberreiter,K.andAsmussen,F.,J.Polym.Sci.,1962,vol.57,no.165,pp.1873198.

Herenandearetherefractiveindexandthedielec-tricconstantofsolvents,whichdeterminethepolar-izationandpolarityandcharacterizethecapacityofthesolventsfornonspecificsolvation;BandET,thePalmbasicityandtheReichardtelectrophilicity,whichdeterminethespecificsolvationofthesubstrate;d,Hildebrandtsolubility,whosesquareisproportionaltothecohesionenergyofthemedium;andVM,molarvolumeofthesolvent.

ItwasfoundthatEq.(4)adequatelydescribesthedependenceofthediffusioncoefficientsofsolventsintothepolymerontheirphysicochemicalproperties[9,10].Indeed,onexcludingthemostinconsistentdatafortrichloromethane,thedegreeofpolymerdissolutionattainedat30oCin20min(Table1)issatisfactorilydescribedbythefollowingsix-parameterequation

logQ=0.95+(4.31+3.54)f(n)+(2.84+1.91)f(e)

3(0.95+0.93)010!3B+(0.088+0.107)ET3(5.98+2.51)0

10!3d2

3(26.1+4.32)0

10!3V

M,

(5)

N=10,R=0.987,S=0.110.

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