由乙烯高效催化聚合而得的超高分子量聚乙烯的研究

本工作系研究以高效催化聚合获得的超高分子量聚乙烯的结构和性能。用扫描电子显微镜观察了高效催化剂及初生聚乙烯的形态。透射电子显微镜观察了初生聚乙烯粉未,发现毛遂边缘的超分子原纤维状织态结构。用偏光显微镜观察了不同分子量聚乙烯粉末的熔融和冷却结晶过程,生成的球晶随分子量增大而增大。用X-射线衍射、差热分析、倒换气相色谱测定了初生聚乙烯的结晶度随分子量而增大;用X-射线衍射、差热分析及密度梯度法测定经退火或热压制的聚乙烯样品的结晶度均随分子量增大而下降。X-射线衍射测定其晶粒尺寸亦随分子量增大而减小。差热分析和倒换气相色谱测定超高分子量聚乙烯粉末的结晶熔点温度(T_m)要比普通分子量聚乙烯高8-12℃。不同分子量聚乙烯的热形变曲线表明,超高分子量聚乙烯在熔融温度后出现明显的橡胶态。此外,还用差热与热重分析研究了超高分子量聚乙烯的热老化行为。测定了超高分子量聚乙烯的优异抗冲强度和沙浆磨耗量。并用扫描电镜对比观察了常规分子量和超高分子量聚乙烯试样的冲击断面的织态结构。

STUDIES ON THE ULTRAHIGH MOLECULAR WEIGHT POLYETHYLENE FROM HIGHLY ACTIVE CATALYTIC POLYMERIZATION OF ETHYLENE

The physical properties of ultrahigh molecular weight of polyethylene (UMWPE) obtained from highly active polymerization of ethylene have heen studied-with various instrumental methods.The morphology of initial polymer was observed by scanning electron microscope.The transmitting electron micrograph shows morphology of supermolecular fibrillar fringe of polymer.The melting and cooling crystallization processes of initial (nascent) polyethylene powder of various molecular weight were studied by the aid of polarimetric microscope with the result that the spherulite size increases with molecular weight.The crystallinity of initial polyethylene powder or its annealed heat molded specimen increases with increasing molecular weight (by X-ray diffraction,DTA,inverse gas chromatographic and density determination),while the crystallite size decreases with it.The crystalling melting temperature T_m(determined by DTA and inverse gas chromatographic method) of UMWPE initial powder is about 8-12℃ higher than that of PEwith ordinary molecr.lar weight (M_W≌10×10⁴).The thermomechenical curves show that above T_mthe UMWPE molded specimens present a nonflowing rubery elastic state untill the higher viscoflowing temperature is reached.The oxidation degradation behavior has been investigated with DTAand TGmethods.Besides,the extinguished impact strength and anti-abrassion properties of UMWPEspecimens have been determined.The scanning electron micrographs for the textures of the cross-section cleavage surfaces of impacted molded specimen of polyethylene with M_W=10×10⁴and M_W=126×10⁴were interpreted from the viewpoint of molecular chain aggregation.