Structure of Highly Disordered Chains in Polymers by Vibrational Spectroscopy

本研究是用振动光谱法研究聚合物体系的构象紊乱。无序在决定高分子材料的性质方面起着重要的作用，这激发了许多旨在表征和理解其复杂性质的活动。由于缺乏一种通用但实用的理论来提供构象统计与无序链分子系统的红外或拉曼光谱之间的定量关系，振动光谱学对无序的适用范围受到了严重限制。作者的工作导致了一个模型，该模型可以在无序链的结构和光谱之间建立一般关系。该模型是基于发现无序链的振动具有一定的有序链的远程相干性。在一个简单系统上的初步结果表明，用该模型计算的红外波段形状再现了观测到的主要特征。这个模型将被修改以使其更广泛地适用。对这个问题的第二种方法也将被追求，其中通过对每个组成构象计算的光谱求和，以数值方式生成无序链系的光谱。以这种方式获得的光谱将用于开发与光谱和无序相关的模型，并用于测试已提出的各种聚合物的构象模型。此外，振动光谱学和其他可用的技术，包括非弹性中子散射，将用于研究各种无序聚合物体系。特别强调将致力于系统存在于非平衡状态和链单层，液晶，液晶聚合物。

This research is a study of conformation disorder in polymer systems by vibrational spectroscopy. Disorder plays an important role in determining the properties of polymeric materials, and this has stimulated much activity aimed at characterizing and understanding its complex nature. The range of applicability of vibrational spectroscopy to disorder has been seriously limited by the absence of a general, but practical, theory that can be used to provide quantitative relations between the conformational statistics and the infrared or Raman spectrum of a system of disordered chain molecules. Work by the authors has led to a model that enables general relations to be established between the structure and spectra of disordered chains. The model is based on the finding that the vibrations of disordered chains have some of the long-range coherence of ordered chains. Preliminary results on a simple system show that infrared band shapes calculated with this model reproduce the main features of those observed. This model will be modified to make it more widely applicable. A second approach to this problem will also be pursued in which the spectra of ensembles of disordered chains are generated numerically by summing the spectra computed for each constituent conformer. Spectra obtained in this way will be used to develop models that relate spectra and disorder, and to test conformational models that have been proposed for various polymers. In addition, vibrational spectroscopy and other available techniques, including inelastic neutron scattering, will be used to study a variety of disordered polymer systems. Special emphasis will be devoted to systems that exist in nonequilibrium states and to chain monolayers, liquid crystals, and liquid crystal polymers.