CrystallizationPropertiesandPolymorphicBehaviorofIsotacticPoly(1-Butene)fromMetalloceneCatalysts:TheCrystallizationofFormIfromtheMelt

摘要

Astudyofthecrystallizationfromthemeltandofthepolymorphicbehaviorofisotacticpoly(1-butene)(iPB)preparedwithmetallocenecatalystsispresented.Samplesofisotacticpolybuteneofdifferentstereoregularity,containingdifferentconcentrationsofstereodefects(rrtriadsdefects)andregiodefects(4,1units)havebeenpreparedwithdifferentC2-andC1-symmetricmetallocenecatalysts.Theconcentrationofdefectsandthemolecularmassarecontrolledthrougharationalchoiceofthecatalyststructureandconditionsofpolymerization.Highlyisotacticsampleswithconcentrationofrrstereodefectslowerthan2mol%,crystallizefromthemeltinthemetastableformII.ThisisacommonpolymorphicbehaviorobservediniPBsamplespreparedwithZiegler-Nattacatalystsandextensivelyreportedintheliterature.MorestereodefectiveiPBsamples,containingconcentrationofstereodefectshigherthan2mol%,crystallizeformthemeltasmixturesofformIIandformI,thefractionofcrystalsofformIincreaseswithincreasingconcentrationofdefectsanddecreasingcoolingratefromthemelt,andsampleswithconcentra-tionofrrdefectsof3-4mol%crystallizefromthemeltinthepureformIatlowcoolingrates.ThisisthefirstexperimentalobservationofthecrystallizationofthestabletrigonalformIofiPBfromthemeltatatmosphericpressure.ThisresultmaybeofinterestbecausethecrystallizationofthemetastableformIIfromthemeltandthespontaneoustransformationatroomtemperatureofformIIintothestableformIhasbeenconsideredforlongtimeanunavoidableproblemthatstandsinthewayoftheindustrialdevelopmentoftheZiegler-NattaiPB.