The effect of modification of supermolecular structure on the properties of polymers

Abstract

The properties of polymers depend on their chemical composition and physical structure. Preparation of the new practically useful polymers by modification of their chemical composition is limited by the availability of pure monomers and the complexity of the polymerization reactions; consequently, a lot of work is currently devoted to the change of their properties by modyfying their physical structure. It is shown that controlled modification of supermolecular structures by thermal treatment (rate of cooling) and drawing of low density polyethylene results in materials with different viscoelastic and electrical properties. Aspecial spinning technique consisting in simultaneous streching and twisting yields polypropylene fibres with highly modified properties. Finally it is shown that the kind and perfection of spherulitic structures in polypropylene films influence their thermal oxidative degradation. These four examples show that a detailed knowledge of the relationships between morphological structure and properties of semicrystalline polymers leads to progress in controlled modification of the properties of this important class of high molecular weight substances by physical treatment