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 formation oiʹdienes and trienes from model 1,5-polyolefins. It has been found that in the presence of dioxygen and at high temperatures model l,5-po!yoletins are oxidized to yield allylic alcohols or hydroperoxides. These structures subsequently dehydrate lo tonn dienes and trienes, a reaction which was found to be calalyzed by bis(dimeihyldithiocarbamalo)zinc(ll) (ZDMC) and bis(mercaptobenzothiazolato)zinc(II) (ZMBT), but not by zinc stearate. The observed dehydration reaction has been established to occur exclusively via a 1,2-dchydration pathway; whereas 1,4-dehydration was not observed. In addition, the present paper reports that NBCI, a model compound For the anti-reversion agent 1,3-bis(citraconimidomethy])benzene (BCIMB), reacts completely within 2 h with squalene at 170 C in the absence of vulcanization curatives, which can be attributed to this oxidation/dehydration mecharnsn). The combined results suggest that the occurrence of dienes and trienes in vulcanized rubber may in part be caused by oxidation of the rubber backbone and subsequent dehydration.