Relaxations and Molecular Motions in Polymers

9972225Boy本研究采用平行或相伴的方法来阐明松弛机制。第一个涉及精心选择的系统的仔细实验表征，第二个涉及分子运动的原子水平模拟。介电弛豫谱是使用的主要实验工具，因为它允许在非常宽的时间范围内进行测量。分子动力学(MD)模拟产生原子在时间轨迹上的位置，用于研究与实验研究相同的系统中的分子运动。需要解决的具体问题涉及以下几个方面。芳香族聚酯聚对苯二甲酸乙二酯(PET)在玻璃化转变下有明显的松弛。它背后的分子运动尚不清楚。它的近亲聚萘酸乙二酯(PEN)有两个这样的过程，因此人们对其了解更少。要对聚合物及其共聚物进行亚玻璃化过程和玻璃化转变区域的彻底介电表征。特别要注意的是高频、短时间区域，在那里可以与相同系统上的MD模拟进行直接比较。另一个要研究的系统是直线型脂肪族聚酯共聚物。亚玻璃化过程和玻璃化过渡区，在那里可以直接与相同系统上的MD模拟进行比较。另一个要研究的系统是直线型脂肪族聚酯共聚物。亚玻璃化过程和玻璃化转变区域都将被研究。将进行相伴的MD模拟。液晶全芳香族聚酯的模拟工作也将继续进行。在所有这些领域，人们将更详细地了解松弛过程和分子运动是如何联系在一起的。美国的化学工业是国家经济的重要组成部分。它是继续在国际贸易中贡献正平衡的部分之一。它的支柱是聚合物的制造和加工。这些材料已经交织到日常生活的方方面面。它们的行为，以及对特定应用的特定材料的选择，敏感地依赖于松弛过程的存在。后者是明确定义的温度和时间区域，属性随其变化，通常是戏剧性的。这些过程的存在是由于各种类型的分子运动随着温度的升高而开始的。为了合理地调整现有材料以适应新的应用和设计新的材料，重要的是尽可能在最基本的水平上理解松弛。这需要了解潜在的分子运动。实现这一认识是聚合物科学的一个重要目标。

9972225BoydThe present research deals with parallel or companion approaches to elucidation of relaxation mechanisms. The first involves careful experimental characterization of well chosen systems and the second invokes atomistic level simulations of molecular motions. Dielectric relaxation spectroscopy is the principal experimental tool to be employed as it allows measurements over an extremely broad temporal range. Molecular dynamics (MD) simulations, which generate atom positions over a time trajectory are to be used to study molecular motions in the same systems as studied experimentally. The specific probems to be addressed concern the following. The aromatic polyester poly(ethylene terephthalate) (PET) has prominent relaxation below it glass transition. The molecular motions underlying it are not understood. Its close relative poly(ethylene naphthylate) (PEN) has two such processes and thus is even less understood. Thorough dielectric characterization of both the subglass processes and the glass transition region is to be carried out on both polymers and their copolymers. Special attention is to be given to the high frequency, short time region where direct comparisons with MD simulations on the same systems can be made. Another system for study will be linear aliphatic polyester copolymers. Both the subglass processes and glass transition region where direct comparisons with MD simulations on the same systems can be made. Another system for study will be linear aliphatic polyester copolymers. Both the subglass processes and glass transition region will be investigated. Companion MD simulations are to be made. Simulation efforts on liquid crystalline wholly aromatic polyesters will be continued as well. In all of these areas a considerably more detailed understanding of how relaxation processes and molecular motions are connected will evolve.The chemical industry of the United States is an important segment of the nation's economy. It is one of the segments that continues to contribute a positive balance in international trade. Its backbone is the manufacture and processing of polymers. These materials have become interwoven into every aspect of everyday life. Their behavior, and hence the choice of a given material for a given application, depends sensitively on the presence of relaxation processes. The latter are well defined regions of temperature and time over which properties change, often dramatically. The presence of the processes is due to the onset of various types of molecular motions with increasing temperature. In order to rationally tailor existing materials for new applications and design new ones, it is important that relaxations be understood at the most fundamental level possible. This requires understanding of the underlying molecular motions. Achieving this insight is an important goal of polymer science.