Crystallization of polymers from the melt and the structure of bulk semicrystalline polymers

Abstract

Despite the abundance of experimental observations recorded in the literature on specific aspects of the morphology of polymers crystallized from the melt, there still remain wide gaps in our knowledge, particularly when it comes to giving proper weight to these observations in attempting to synthesize an accurate over-all picture of the structure of bulk polymers. Two stages in crystallization can be recognized: the first unmistakably gives rise to spherulites composed of chain-folded lamellar crystals; the second probably to a diversity of morphological forms (including both chain-folded and extended-chain crystals) which grow in interstices within the spherulites. Crystals of these various kinds are connected both by tie molecules and by more substantial intercrystalline links, and between them there are disordered regions arising both from irregular folds at crystal surfaces and from polymer whose crystallization has been impeded by entanglements. However, inter-relations between these various components of the bulk polymer are not as yet well understood, and their elucidation poses problems of considerable difficulty. Nevertheless, an understanding of macroscopic properties in terms of underlying structure depends upon their solution.