Solid phase radical reactions and the mechanism of carbon chain polymer oxidations

Abstract

The oxidation of polymers in the solid state, like the liquid phase oxidation of hydrocarbons, has a spontaneously initiated chain reaction mechanism with a bimolecular chain termination. The following are the characteristic differences between the solid and liquid phase oxidations. The radical reactions are slower in the polymer matrix than in the liquid phase; the lower the molecular mobility in the former, the more difficult will be the elementary act of segmental orientation. The free valency travels in the polymer sample in the shape of alkyl and peroxide radicals by a relay mechanisms, ile. due to a segmental shift and the elementary acts: P + PH → PH + P, and PO 2 + PH → POOH + P. In constrast to the liquid, the solid polymer is non-homogeneous and therefore oxidizes irregularly; the less dense amorphous phase in PE and PP oxidizes earlier than the crystalline phase. The alkyl radicals react more slowly with oxygen in the polymer and various reactions take place in addition to P + O 2 → PO 2 ., especially an isomerization; the latter results in PP in the conversion of the absorbed O 2 into alcohol groups, with the exception of the hydroperoxide which reacts with ROOH and causes its induced decomposition and a reaction with the CH bonds of adjacent segments. This can be seen in PP on the ratio of single to block hydroperoxide groups. the decomposition of the macro-radicals, which still has a relatively unexplored mechanism, plays an important part in the oxidation of polymers.