短支链对双峰聚乙烯链结晶过程影响的分子动力学模拟  

Effect of Short-chain Branching on the Crystallization Process of Bimodal Polyethylene:Molecular Dynamics Simulation

作　　者：胡艳玲 何雪莲[1] 刘柏平 HU Yan-ling;HE Xue-lian;LIU Bo-ping(Shanghai Key Laboratory of Multiphase Material Chemical Engineering,East China University of Science and Technology,Shanghai 200237,China;College of Materials and Energy,South China Agricultural University,Guangzhou 510642,China)

机构地区：[1]上海市多相结构材料化学工程重点实验室,华东理工大学,上海200237 [2]材料与能源学院,华南农业大学,广州510642

出　　处：《高分子通报》2020年第8期55-66,共12页Polymer Bulletin

基　　金：国家自然科学基金项目(51573048)。

摘　　要：采用分子动力学模拟研究了短支链(short-chain branching,SCB),特别是短支链浓度、支链分布和亚甲基序列长度对于双峰聚乙烯链结晶过程的分子机理。构建了两种不同支链分布且接近于工业双峰聚乙烯管材的双峰聚乙烯模型链:短支链全部均匀地分布在长链上或者是在短链上。模拟结果表明,在双峰聚乙烯链早期结晶过程中,存在反式构象富集现象。支链分布在长链上相比支链分布在短链上,对于诱导期前驱体的形成具有阻碍作用。双峰聚乙烯链的结晶机理取决于支链浓度:低浓度下(<5 SCB/1000C),体系的结晶过程是处于成核过程和晶体生长过程相互竞争的状态;高浓度下(>5 SCB/1000C),体系的结晶过程是由晶体生长过程控制。亚甲基序列长度增加,体系的反式构象含量也会增加。当支链浓度超过5 SCB/1000C时,支链分布在短链上体系的相比支链分布在长链上的体系具有更高的反式构象含量。Molecular dynamics simulations were conducted on bimodal polyethylene(BPE)in order to reveal the molecular mechanism of short-chain branching(SCB),especially the effects of branch content(BC),short-chain branching distribution(SCBD)and methylene sequence length(MSL)on BPE crystallization.This paper built two types of BPE models which were closer to the normal industrial BPE:SCBs evenly distributed on the long chain or on the short chains.Tran-rich phenomenon was observed during the early stage of crystallization.SCB placed on the long chain provoke a delay to the formation of precursor during the induction period as compared with the case of SCB placed on the short chains.The crystallization mechanism of BPE was dependent on the BC.When BC was lower than 5 SCB/1000 C,the crystallization state was a competitive state of nucleation process and crystal growth process.However,when BC was higher than 5 SCB/1000 C,the crystallization state was a crystal growth controlled state.The trans state population of BPE models was increased with the increase of MSL.Above 5 SCB/1000 C,BPE models with SCB incorporated in the short chains show higher trans state population as compared with those with SCB incorporated in the long chain.

关 键 词：短支链分布 双峰聚乙烯 分子动力学模拟 晶体成核 

分 类 号：TQ325.12[化学工程—合成树脂塑料工业]