Cooperative Molecular Motions in Glassy Polymers

玻璃聚合物的二次力学松弛与其力学性能之间存在很强的相关性。以前的动态力学研究并没有得到关于力学松弛的性质和起源的精确信息。先进的核磁共振技术提供了某些分子运动的详细信息，但这些运动不一定代表DMS检测到的那些。与机械变形最直接相关的分子运动可能是高度合作的。聚碳酸酯共聚物中的协同分子运动将通过系统地改变可移动和不可移动重复单元的序列来研究。链内相关距离将通过动态力学测量来确定。通过测量动态体弛豫，可以评估与这些协同运动相关的分子间相互作用的程度。通过测量屈服应力和屈服后冷拔对温度和应变速率的依赖，可以建立分子结构、分子协同性和力学性能之间的相关性。通过将聚合物的机械性能与聚合物的结构和分子运动联系起来，这项研究可能最终导致聚合物的机械性能得到改善。

Strong correlations exist between secondary mechanical relaxations in glassy polymers and their mechanical properties. Previous dynamic mechanical studies have not yielded precise information on the nature and origin of the mechanical relaxations. Advanced NMR techniques have provided detailed information on certain molecular motions, but these motions are not necessarily representative of those detected by DMS. Molecular motions most directly relatable to mechanical deformations are likely to be highly cooperative. Cooperative molecular motions in copolymers of polycarbonates will be studed by systematically varying sequences of mobile and less mobile repeat units. The in-chain correlation distance will be determined using dynamic-mechanical measurements. By measuring dynamic bulk relaxation, one can assess the extent of intermolecular interaction associated with these cooperative motions. By measuring the yield stress and post yield cold drawing dependence on temperature and strain rate, one can establish correlations between molecular architecture, molecular cooperativity, and mechanical properties. This research could ultimately lead to polymers with improved mechanical properties by relating those propertes with the structure of the polymers and their molecular motions.