A reconsideration of polymer crystallization theory

Abstract

Two polymer crystallization theories are reviewed and discussed against the background of a revision of general nucleation theory, given in a preceding paper. Since crystallization nuclei, as usually defined, do not exist, the free energy of formation of a nucleus, such as it is applied for the calculation of nucleation frequency or rate of crystal growth, is a misleading concept. The latter quantities must be described as functions of parameters governing the attachment of polymer segments to, and their separation from, the growing crystal. The crystallization of polymers is supposed to proceed via attachment of segments of one or a few polymer repeating units rather than by steps of a whole “fold length” at once. Chain folding as aprerequisite for crystallization must be rejected as being highly improbable; it may be theresult of crystallization. One cannot decide from data on polymer-crystallization kinetics alone which theory is right or wrong, since it is the derived interfacial free-energy parameters that are actually the adjustable parameters of the theory.