Homogeneous zinc(II) catalysis in accelerated vulcanization II. (Poly)olefin oxidation, dehydration, and reaction with anti-reversion coagents

This paper establishes a new and previously unrecognized pathway for the fo rmation of dienes and trienes from model 1,5-polyolefins. It has been found that in the presence of dioxygen and at high temperatures model I,S-polyol efins are oxidized to yield allylic alcohols or hydroperoxides. These struc tures subsequently dehydrate to form dienes and trienes, a reaction which w as found to be catalyzed by bis(dimethyldithiocarbamato)zinc(II) (ZDMC) and bis(mercaptobenzothiazolato)zinc(LI) (ZMBT), but not by zinc stearate. The observed dehydration reaction has been established to occur exclusively vi a a 1,2-dehydration pathway; whereas 1,4-dehydration was not observed. In a ddition, the present paper reports that NBCI, a model compound for the anti -reversion agent 1,3-bis(citraconimidomethyl)benzene (BCIMB), reacts comple tely within 2 h with squalene at 170 degrees C in the absence of vulcanizat ion curatives, which can be attributed to this oxidation/dehydration mechan ism. The combined results suggest that the occurrence of dienes and trienes in vulcanized rubber may in part be caused by oxidation of the rubber back bone and subsequent dehydration.