热分析法研究超高分子量聚乙烯的热熔性质

Thermal Melting Behavior of the Ultra High Molecular Weight Polyethylene Studied by Thermal Analysis

本文采用差热分析(DTA)、差示扫描量热法(DSC)研究了一系列以高效催化聚合而得的初生态超高分子量(M_w=70—315×10^(4))聚乙烯粉的热熔行为,还研究了在接近熔化或部分熔化的温度下恒温热处理对晶体性质的影响.

The thermal properties, of various initial ultra-high molecular weight polyethy-lcne(UMWPE Mw = 70-315×10^(4)) powders obtained from highly active catalytic polymerization of ethylene have been studied by differential thermal analysis and differential scanning calorimetry. By plotting the ratio of △ H1 to △H_(2) against molecular weight of polymer, a linear correlation is given by Y = 0.95 + 0.28× 10^(-6)Mw, where Y = △H_(1)/△H_(2) and △H1 and △H2 are the heat of fusion of nascent polyethylene and cooling specimen of melted polyethylene respectively.The double melting endotherms of UMWPE can be observed when the samples crystallized from polymerization were annealed in proper condition. The melting peak of the high temperature can convert into the melting peak of the low temperature inconvertibly with different annealing time and temperature. It is reasonable to say that when the molecular weight of polyethylene formed in the polymerization system is very high (Mw≥70 × 10^(4)), the crystal chain conformation of nascent polyethylene is mainly extended and after being melted and then recrystallized on cooling, it can be converted into less extended or partially folded conformation with more crystalline deficiency.