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
简介:谁说时尚的卡片式数码相机只能在年轻人面前独占鳌头?这次,我们就带着Sony最新推出的Cyber-shotDSC-N2,造访了圈内小有名气的摄影爱好者——北京老郑。有着多年拍摄经验的老郑,在刚拿到N2的时候并没有马上将它与“专业”画上等号,但在几分钟的试用中,老郑却连连露出惊喜,看来N2的表现果然是非同凡响啊!先让我们来了解一下这款N系列最新产品的实力:1/1.7英寸、1010万像素CCD,最高分辨率3648×2736像素,3倍光学变焦的卡尔·蔡司天塞镜头,最小光圈可以达到F16,23万像素,3英寸的触摸屏幕,可重复充电电池,内置约25MB内存,并具备音乐串片秀功能。