冷冻升华制备的超高分子量聚乙烯寡链、多链晶体的凝聚态

Condensed State of Pauci or Multi-chain Crystals of Ultra High Molar Mass Polyethylene by Freeze-drying

在 1 0 - 3～ 1 0 - 5g/ m L浓度范围内 ,用冷冻升华法制备了超高分子量聚乙烯 (UHPE)单链、寡链、多链的折叠链晶聚集体 .长达几万纳米的 UHPE分子链可以以不同的片晶参与结晶 ,或自身形成数个晶粒 ,即形成单链多晶 .DSC研究结果表明 ,随着溶液浓度的降低 ,冷冻升华样品的熔点和结晶度均降低 .由熔点估算了晶粒的体积和晶粒中包含的链数 ,它们亦随溶液浓度降低而降低 .冷冻升华得到的小晶粒中链的缠结少 ,晶体具有较高的完善性 .用 WAXD测试晶粒的 (1 1 0 )和 (2 0 0 )面的法向尺寸 ,由此计算晶粒的平均体积 。

Aggregates of single-, a few- and multi-chain crystals with folded-chain structure were prepared by a freeze-drying procedure from dilute solution of ultra-high molar mass polyethylene in para-xylene with mass concentration ranged from 10 -3 to 10 -5 g/mL. The chains in UHPE are very long (10 4 nm); they can form several lamellae themselves or enter many lamellae to crystallize together with other chains. By means of DSC, the thermal analysis of the freeze-dried samples indicated that their melting temperature and crystallinity decreased as the solution concentration decreased. Average crystal volume and the number of chain per crystal were estimated according to the melting point of samples, and also they decreased with the decrease of the solution mass concentration. Because of lower entanglement concentration in the freeze-dried samples, the resulted crystals would have a higher perfection. Crystal dimensions normal to (110) and (200) were measured by using WAXD, and the average crystal volume was estimated on the basis of the measured dimensions and it is in agreement with the data from the DSC measurement.