Amorphous Polymers

Abstract

Amorphous is used as a description of the structure of a material and it implies that there is no long-range order such as that found in crystalline or liquid crystalline substances. Such disordered arrangements are found in melts. In this case the arrangement of polymer molecules will normally be that of randomly arranged, entangled molecules that are mobile. The same structural arrangement might exist as a solid in which there is no long-distance mobility of a molecule due to thermal motion. This is characteristic of a ‘glassy’ material. Materials that can be cooled from a melt sufficiently rapidly that they do not have the opportunity to reorganise to a regular structure in the form of a crystal will form glassy or amorphous solids. The usual thermodynamic equilibrium state of most materials will be a crystal at sufficiently low temperatures. Many polymers are never observed as crystalline or semi-crystalline solids. This is either as a consequence of the very low gain in free-energy on crystallisation or of the high viscosity near the melting point. Polymers with bulky sidegroups and irregular tacticity are particularly likely to form amorphous solids (see Crystallinity, Glass Transition).