聚甲基乙烯基醚的局部构象

采用低能构象方法和构象扫描方法,在Dreiding力场下,对含有3种不同侧基取向的PVME的全同二单元体和间同二单元体进行全松弛优化.通过统计平均得到PVME各种构象状态的几何参数和构象能.由统计平均的结果确立了包含侧基所有可能取向信息的PVME链的RIS模型,并利用MontCarlo方法计算了PVME链的特征比,结合实验数据讨论了侧基取向行为的影响.

Effect of Transesterification on High-pressure Crystallization Behaviour of PET/PC Blend System

Effect of transesterification on high-pressure crystallization behaviour of PET/PC blend system was investigated by torque rheometer, DSC, SEM and WAXD measurements. The crystallized samples of 20%PC in PET/PC blends mixed at 30 r/min and 523, 533 and 553 K for 15 min were obtained at 300 MPa and 613 K for 6 h with a self-made piston-cylinder high-pressure apparatus. SEM observation revealed that transesterification during mixing profited a quick thickening of extended-chain crystals and enhanced ester interchange at a high pressure. Wedge-shaped and bending extended-chain crystals found in these samples indicated that chain-sliding diffusion and transesterification contributed to the growth of such polyester crystal. With transesterification extent rising, the result of WAXD profile deconvolution and WA/FT showed that the total crystallinity letted up, the mean crystallite size and micro-strain of PET increased and decreased respectively and crystallite distribution for PET widened correspondingly. The result obtained suggests that under certain conditions two procedures, i.e. crystallization-induced reaction and reaction-induced crystallization can concur for such copolymer wholly composed of crystallizable units.