Crystalline order and melting behavior of isotactic polypropylene (α form)

Abstract

Abstract Samples of isotactic polypropylene in the α form may have different degrees of order in the up and down positioning of the chains. By suitable programming of the crystallization history of unoriented samples it is possible to show, from DSC and WAXS data, that a strict correlation exists between the melting behavior and the degree of ordering of the chains. The process of ordering at annealing temperatures above 150°C may lead to a “continuum” of modifications of the α form from less ordered to highly ordered ones; correspondingly we observe an increase in the melting point by as much as 15°C.