链缠结对聚合物结晶行为的影响

链缠结是聚合物分子链相互作用的一种形式 ,它主要影响分子链的长程运动 .自链缠结的概念被提出以来 ,人们对聚合物粘弹性、流变行为和网络平衡力学等进行了理论研究和实验验证 .然而 ,在聚合物结晶领域 ,链缠结对结晶过程的影响一直存在着很大的争论 .Flory等 1] 认为 ,聚合物结晶时分子链根本没有足够的时间进行构象调整 ,分子链进入晶格后 ,使大量的缠结链段被挤入非晶区 ,并由此建立了聚合物结晶“插线板”模型 .Hoffman等 2 ]根据单根分子链从过冷熔体“卷饶”到晶体前沿所需的时间进行估算 ,结果比 Flory预言的快约 3～ 5个数量级…

Influence of Intermolecular Entanglements on Crystallization Behavior of Macromolecules

Ultra-high molar mass polyethylene(UHPE) or HDPE was melted at various temperatures or at a constant temperature for various time, and then crystallization from the melt was investigated. The crystallization behavior of UHPE was found to be different from those of HDPE. It was found that the crystallization temperature decreased as the heating time or heating temperature increased. During the melting process, thermal motion of the chains leads to a change of chain conformation from parallel-extended chains to interpenetrated random coils, accompanied by the occurrence of entanglements. As a result, the crystallization temperature shifts to a lower temperature. In addition, the samples of UHPE with less entanglement were prepared by a freeze-drying procedure from dilute solution was proved the effect of entanglements on crystallization behavior of macromolecules. A preliminary study on the crystallization of the samples indicates that entanglements have a pronounced effect on the crystallization behavior of macromolecules.