Evidence for Distinct Sectors in Polymer Single Crystals

Abstract

IT was reported earlier that long-chain polymers could form single crystals in which the molecules have a regularly folded configuration^1,2. Polyethylene in particular can have a paraffin-like crystal habit consisting of thin lozenge-shaped layers with each segment of the folded molecular chain normal, or approximately normal, to the plane of these layers. It was suggested³ that the molecules might fold in the plane of the growing faces, which are of the {110} type in the purely lozenge-shaped crystals. This implies that in the four different quadrants the chains are folded along four different <110> directions, and hence that the apparent single crystal consists in fact of four structurally distinct sectors in twin relation. So far as we know, this situation is unprecedented in crystalline substances.