Nonequilibrium Molecular Characteristics of Glassy Polymers

简介：玻璃聚合物在低于玻璃化转变温度Tg的化学和物理老化和/或退火过程中发生的瞬态结构和性能变化是当前的研究热点。这种依赖于时间的行为，也被称为体积或焓弛豫（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化或部分玻璃化聚合物材料在其使用寿命内的“初始”行为和实际性能的控制因素。研究总结：在本研究中，pi研究了受控（和加速）化学和物理老化和/或再生对一种精心挑选的具有重要商业意义的玻璃状聚合物（聚对苯二甲酸乙二醇酯）可达到的屏障性能水平的影响。这将通过在Tg以下的温度范围内用小分子渗透剂（在高化学势下）与小片段区域相互作用来调节聚合物来实现。最重要的是，通过监测控制聚合物节段构象分布的异构化反应动力学，将首次直接测量和识别专门控制吸附和扩散中传输参数行为的微观结构变化。该研究将通过结合气体透射和傅立叶变换红外光谱的实验，以及焓弛豫研究来完成。意义:这项工作的结果将有力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，用于生产玻璃状聚合物，这些聚合物在包装应用中具有优异的性能，作为保护涂层，并用于气体混合物的节能分离中作为过选择膜。这里只举几个例子。此外，将在本研究中获得关于运输和机械性能变化（可以通过自由体积及其分布相互关联）的知识。预计将发现具有显著提高性能水平和使用寿命的新型聚合物微观结构状态。

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.