PHOTO-OXIDATION OF POLYPROPYLENE - SOME EFFECTS OF MOLECULAR ORDER

Fractional crystallization was used to separate a commercial, predominatly isotactice, unstabilized polypropylene into fractions of relatively low and relatively high atacticity, but of similar molecular weight. IR spectroscopy was used to follow the photo‐oxidations of films formed from these fractions during irradiation in air with light of wavelengths greater than 3000 À. The major oxidation products included hydrogenbond hydroperoxides and carbonyl compounds. Films of constant tacticity, but varying morphology were prepared by quenching from the melt. No distinct correlation was found between sample photostability and morphology, as indicated by film density. Films of low atactic content were found to undergo faster photo‐oxidation than films of high atactic content, irradiated under identical conditions. This effect is believed to be due to the occurrence of a stereo‐dependent step (or steps) in the oxidative chain, and not due to differences in sample morphology. The possible nature of the stereo‐dependent steps is considered in terms of well‐established oxidative chain processes. The effects of polypropylene polymorphism on oxygen permeability are briefly considered. Copyright © 1969 John Wiley & Sons, Inc.