Molecular Organization of Amorphous Polymers

Abstract

The rapid advance in materials in modern times has resulted largely from the detailed comparison of properties and behavior with the microstructure. For polymers we usually know the atomic sequence along the chain, the bond distances, and, roughly, the bond anglcs. But since it is the nature of the amorphous state to lack regularity, the rotational conformations about backbone bonds and the nature of the packing of the chains vary from point to point and are largely unknown. One would expect that if more were known about the molecular arrangements, better control could be exerted over the behavior and properties of polymers. This review is confined to mainly single phase homopolymers in equilibrium conformations. This means, for example, that the amorphous content of crystalline polymers will not be dealt with, though considerable information concerning the structure of the amorphous content has come to light recently, and its structure is very important for the properties and behavior of crystalline polymers. We are concerned with the molecular organization in undeformed polymer melts, lightly crosslinked elastomers, and unoriented polymer glasses. Aside from the crosslinks, polymer melts and elastomers are virtually the same. The molecules in polymer glasses, though not in conformational equilibrium at the ambient tempetature, are thought to have conformations characteristic of equilibrium at some higher temperature near that of the glass transition. Thus the structures of the glass and melt are thought to be only infinitesmally different. The plan of this review is to examine the data concerning molecular organization that has been obtained from various sources and attempt to evaluate its significance. The more direct or traditional measurements are considered first, followed by those that are less so. The review concludes by attempting to draw the information together for a best current estimate of the nature of the organization.