A note on single crystals in polymers: Evidence for a folded chain configuration

Abstract

The morphology and orientation of a number of polymers as crystallized from solution was studied with the electron microscope combined with selected area electron diffraction. In the course of this work single crystals could be prepared which were most striking in the case of straight chain polyethylenes. There is evidence among others, that the fibrillar (sheaf-type, spherulitic) crystallization, characteristic of polymers, develops through formation of flat single crystals. The single crystals contain screw dislocations and grow by spiral terraces. The observed orientation and the minimum thickness of the crystals leads to the inescapable conclusion that the molecules must bend sharply back on themselves forming a regular folded configuration. Accordingly the strength of the dislocation, consequently the height of growth step, would correspond to the distance between successive bends. Various other observations are consistent with this new concept.