简介:Thephotopolymerizationoftwokindsofprepolyesterscontainingconjugateddiacetylene(PDA-6andPDA-12)wasinvestigatedusingDSC.BymeasuringtheendothermicenthalpyoftheprepolymersafterdifferentUV-irradiationtimes,thepolymerizationswerefoundtofollowthefirst-orderratelawwhichagreedwiththeresultsofotherinvestigatorsusingadifferentmethod.TheendothermicenthalpymeasurementsofPDA-6andPDA-12beforeUV-irradiationprecludedthepossibilitythatthedecreaseofendothermicenthalpywascausedbythermalpolymerization.
简介:Themolecularstructureofpolyethylene(PE)sampleswithvariouscomonomersincludingpropylene,1-buteneand1-hexenewasinvestigatedbyDSCand13C-NMRtechniques.Thedensityofthesamplesvariesfrom0.948g/cm3to0.917g/cm3,andthemolecularweightdeterminedbytheGPCmethodisintherangeof1~2×105.Thebranchpointcontentofthesampleswasdeterminedby13C-NMRmeasurementsandwasfoundtobelessthan20per1000Catomsalongthemainchain.CrystallizationsegregationDSCtechnique(CSDSC)wasusedtocharacterizethebranchpointdistributionorthesegmentlengthdistributionofPEs.Thecrystallizationsegregationwasperformedinasuccessiveannealingprocessatdecreasingtemperatures.Theintervaloftwosuccessiveannealingtemperatureswas6K,andthetimelengthofeachannealingstepwas2.5h.TheCSDSCresultsclearlyindicatethatallthePEsamplesused,includingsomemetallocenePEs,moreorlessexhibittheirnon-uniformityinsegmentlengthdistribution,andbimodalormultimodalCSDSCcurveswereusuallyobserved.ForquantitativecharacterizationoftheCSDSCcurvesandthesegmentlengthdistributiontwoparameters,theaveragemeltingpoint,TmAV,andtheroot-mean-squaredeviationofmeltingtemperature,(ΔTmAV2)1/2,wereproposed.TmAViscorrespondingtotheaveragesegmentlengthduetobranchingand(ΔTmAV2)1/2givesinformationaboutthewidthofthesegmentlengthdistribution.Experimentalresultsshowthatboththedegreeofaveragemeltingtemperaturedepressionandthewidthofthedistributionseemtoincreasewithincreasingthebranchingcontentandaredependentonthetypeofcomonomers.VerygoodreproducibilityandadditivityoftheCSDSCmethodwereevidencedexperimentally.ItwasconcludedthattheCSDSCtechniqueisasensitiveandconvenientmethodforcharacterizingthesegmentlengthdistributionofbr