Dispirations,disclinations, dislocations,and chain twist in polyethylene crystals

It is proposed that the twist in polyethylene chains that can result from crystallization and subsequent deformation aggregates at boundaries and becomes a template for further reorganization that results in the long period observed in polyethylene fibres. The observed lower density at the boundaries requires the transport of free volume to the twist boundaries. Dispirations, disclinations and dislocations are crystallographic defects that are involved in the necessary transport mechanism. Twist and bend, derived from the Eulerian angles which are computed from the sets of chain internal coordinates, relate the orientation of different segments of a chain. Twist and bend are useful for the characterization of both crystallographic defects and arbitrary conformations of polymer chains. Defects, along with folds, chain ends, and ordinary edge and screw dislocations provide a basis for interpretation of structure-property relationships in solid polyethylene.