Antioxidative stabilization of poly(vinyl chloride)

Halogenated resins such as poly(vinyl)chloride undergo rapid degradation when exposed to heat. Such degradation is significantly increased by oxygen, and it is believed that the induction of the process of decomposition is caused by autoxidation of the polymer, followed by extensive dehydrohalogenation. Sulfur‐containing peroxide decomposers allow primary stabilization of PVC with organic compounds which are not HCl acceptors but prevent free radical cross‐linking of the polymer. This implies a discolored polymer melt (due to loss of HCl and formation of polyenes) which nonetheless exhibits good long term stability (no cross‐linking). The stabilization of labile chlorine atoms results from the oxidation of various chain irregularities, and thus the elimination of the early discoloration can be achieved by the use of small quantities of monohydrocarbyltin co‐stabilizers. The relative performance of various antioxidant systems are reported and possible stabilization mechanisms are discussed.