梳形支化聚苯乙烯中运动单元的松弛行为

Relaxation Behavior of Motion Units for Comb-Like Branched Polystyrene

使用差示扫描量热仪和旋转流变仪测定梳形支化聚苯乙烯(cPS)的玻璃化转变温度(Tg)及动态黏弹性,并与线型聚苯乙烯(lPS)对比,研究了梳形支化聚苯乙烯中运动单元的松弛行为。结果表明,cPS的Tg高于与其重均相对分子质量相当的lPS,在cPS主链长度相当的情况下,随着侧链长度或侧链数目的增加,cPS的Tg逐渐升高。cPS中与主链运动相对应的松弛过程发生在低频区,在高频区会出现与侧链解缠结相关的侧链松弛,侧链对主链的松弛起延缓作用。随着侧链长度的增加,cPS主链特征松弛时间与侧链特征松弛时间均延长;随着侧链数目的增加,cPS主链特征松弛时间延长而侧链特征松弛时间不变。梳形支化聚苯乙烯橡胶平台的缺失归因于其主链周围密集排列的侧链,侧链的密集排列削弱了大分子链之间的缠结,侧链缠结对橡胶平台影响不大。侧链的存在延缓了cPS大分子链的松弛过程,导致cPS黏流态下的储存模量(G')大于与其重均相对分子质量相当的lPS。

The glass transition temperature（Tg） and dynamic viscoelasticity of comb-like branched polystyrene（cPS） compared with linear polystyrene（lPS） were measured by DSC and rotational rheometer.The relaxation behavior of motion units for cPS was investigated.The results show that the Tgfor cPS is higher than that of lPS with the same weight average molecular weight.When the cPS samples own equal backbone lengths,Tgincreases as the side chain length or degree of branching is improved.Relaxation corresponding to backbone and side chain motion of cPS occurs in low and high frequency region,respectively,and the side chains delay the relaxation of the backbone.With side chain length increasing,the characteristic relaxation time of backbone and side chain becomes longer.With degree of branching increasing,the characteristic relaxation time of backbone turns longer and the characteristic relaxation time of side chain remains unchanged.The absence of the rubber plateau in these comb-like branched polystyrenes is ascribed to the side chains of high density around the backbone,which weaken the entanglement among the macromolecular chain.The entanglement among the side chains has little impact on rubber plateau.The existence of the side chains delays the relaxation process of the macromolecular chain of cPS,and leads to the storage modulus G＇of cPS at viscous flow state higher than that of lPS with the same weight average molecular weight.