INSTANTANEOUS SHAPE AND SEGMENTAL DENSITY OF INDIVIDUAL FLEXIBLE LINEAR MACROMOLECULES .4. TAGGED IN UNTAGGED CRYSTALLIZABLE POLYMERS

Monomolecular dispersions of iodine-tagged high molecular weight isotactic polystyrene (TiPS) in untagged isotactic polystyrene (iPS) were prepared. By means of transmission electron microscopy through the microtomed bulk, and microdensitometry across imaged molecules, it was found that the amorphous TiPS molecules are neither spherical nor have a smooth bell-shaped segmental distribution. The shape is irregular and the segmental density reveals 100 to 250 Å size submolecular domains of high segmental density intermixed with regions of lower density. In solution cast films and in annealed molded films, nascent crystallization of the TiPS was observed. Small crystallites and minute lamellae are initially formed within the confines of the parent molecules. The indication is that incipient crystallization occurs within the molecule and involves one or more of the higher density submolecular domains. Then, co-crystallization with domains belonging to other macromolecules takes place. Such crystallization requires no large scale intermolecular disentanglements or long-range molecular transport. It also leaves the radius of gyration of the molecule unchanged upon going from the melt to the semicrystalline solid. Observations on bromine-tagged ultra-high molecular weight polyethylene in untagged polyethylene lead to similar conclusions. © 1979, American Chemical Society. All rights reserved.