Nonequilibrium Molecular Characteristics of Glassy Polymers

前言：玻璃化聚合物在玻璃化转变温度Tg以下的化学和物理老化和/或退火过程中发生的瞬时结构和性能变化是当前研究的热点。这种依赖时间的行为，也被称为体积或热焓松弛(或恢复)，起源于玻璃态的非平衡性质。从应用的角度来看，这一现象显然是预测玻璃态或部分玻璃态聚合物材料在使用寿命期间的“初始”行为和实际性能的控制因素。研究摘要：在这项研究中，PI探查了受控(和加速)化学和物理老化和/或再生对精心挑选的具有重大商业意义的玻璃聚合物(聚对苯二甲酸乙二醇酯)可实现的阻隔性能水平的影响。这将通过在低于Tg的一定温度范围内使用小分子渗透剂(在高化学势下)与小片段区域相互作用来实现。最重要的是，通过监测控制聚合物链节构象分布的异构化反应动力学，将首次直接测量和识别具体控制吸附和扩散过程中传输参数行为的微观结构变化。这项研究将通过利用气体传输和傅里叶变换红外光谱的组合实验，以及热焓松弛研究来完成。意义：这项工作的结果将极大地促进全面分子理论的发展，这可能导致设计各种新的和/或改进的工艺，以生产在包装应用中具有优异性能的玻璃聚合物，作为保护涂层，并作为渗透选择膜用于气体混合物的节能分离，仅举几个例子。此外，在这项研究中还将获得有关运输和力学性质变化的知识(这两个变化可以通过自由体积及其分布相互关联)。预计将发现具有显著增强的性能水平和应用寿命的新型聚合物微结构状态。

Introduction: The transient structure and property changes that occur in glassy polymers during chemical and physical aging and/or annealing below the glass-transition temperature Tg are of great current research interest. This time-dependent behavior, also referred to as volume or enthalpy relaxation (or recovery), originates from the nonequilibrium nature of the glassy state. From an application point of view, it is apparent that this phenomenon is the controlling factor in predicting the "initial" behavior as well as the practical performance of glassy or partially glassy polymeric materials during their useful lifetimes. Research Summary: In this research, the PIs probe the effects of controlled (and accelerated) chemical and physical aging and/or rejuvenation on achievable barrier property levels in a carefully selected glassy polymer of major commercial significance (polyethylene terephthalate). This will be accomplished by conditioning the polymer over a range of temperatures below Tg with small molecule penetrants (at high chemical potentials) which are interactive with small segment regions. Most importantly, the microstructural changes which specifically control the behavior of transport parameters in sorption and diffusion will be directly measured and identified for the first time, via monitoring of the kinetics of the isomerization reaction which governs the distribution of polymer segmental conformers. The research will be accomplished through combined experiments utilizing gas transmission and Fourier Transform I.R. Spectroscopy, together with enthalpy relaxation studies. Significance: The results of this work will contribute strongly to the development of a comprehensive molecular theory which may lead to the design of a variety of new and/or improved processes for the production of glassy polymers with superior properties in packaging applications, as protective coatings, and for use as permselective membranes in energy-efficient separations of gaseous mixtures, to cite only a few examples. Also, knowledge of both transport and mechanical property variations (which can be interrelated through free volume and its distribution) will be acquired in this research. It is anticipated that novel polymer microstructural states with significantly enhanced property levels and application lifetimes will be discovered.