Dislocations Caused by Chain Ends in Crystalline Polymers

The molecular arrangement in the immediate vicinity of a chain end in a crystalline polymer such as 66 nylon is considered. It is shown that four simple kinds of line defect can be generated by such a chain end. One of these, called a coupled-screw dislocation, is unique to long chain structures and has not been proposed before. The remaining three are (1) vacant chain site or coupled-edge dislocation, (2) and (3) the more conventional screw and edge dislocations. These dislocations run from one chain end to another and create a three-dimensional defect network, possibly explaining the anomaly of weak x-ray diffraction intensity from (010) planes. If the ends are randomly distributed, the network may disorder the structure sufficiently to make it appear ``amorphous'' to x rays. When sufficient segmental mobility exists, it is probable that this network will rearrange itself into a more ordered substructure of lower energy. Such a substructure might include: (a) clusters of chain ends and associated defects, (b) chain ends which are condensed into line defects, (c) boundaries between adjacent misaligned crystalline regions.