The Melting of Crystalline Polymers

Abstract Polymer molecules are characterized by the unique structural feature of being composed of a large number of chain units covalently linked together. Despite this complexity of structure macromolecular systems still retain the ability to exist in different states, a property common to all substances. Two of the states of matter observed for monomeric substances, the liquid and crystalline states, are also found in polymeric substances. The liquid or amorphous state is characterized by the fact that, because of the freedom of rotation about the bonds connecting the chain atoms, a single polymer molecule can assume a large number of configurations. In this state, therefore, the chain units of different molecules are arranged in a random, disoriented array uncoordinated with one another. Under appropriate thermodynamic conditions, however, a spontaneous ordering of portions of the chain molecules can occur, and in contrast there results a state of configurational order, the freedom of rotation being l...