No abstract

The mechanism reviewed in some detail here appears adequate to explain substantially all that is now known about vulcanization with TMTD. It has predicted accurately the stoichiometric relationships between the reagents entering into the vulcanization reaction and the known products formed. It presumes that vulcanization is a primary consequence of the interaction of rubber, TMTD, and zinc oxide and not an incidental result. It is not, however, fully established by the evidence now available. In particular the studies by Scheele and coworkers (as exemplified by Reference 33). on the reaction of zinc oxide with thiuram disulfides suggest the interesting possibility that primary attack during vulcanization is on the oxide rather than the hydrocarbon, as assumed in this discussion. There is at present no experimental basis on which to eliminate either of these two alternatives. The success of the mechanism reviewed here in delimiting stoichiometry of the reaction makes it a convenient framework from which to develop a complete understanding of the reaction.

No abstract

Three recent attempts to formulate a reaction mechanism for scission during the oxidation of rubber have been evaluated with respect to their predictions concerning the formation of formic acid and the step at which scission occurs. Two do not account directly for formic acid as a principal product or for the failure of antioxidants to influence scission yield. The third, while consistent with available evidence, does not predict the observed product distribution as a necessary consequence of decomposition of the postulated intermediate.

synopsisAcetic and formic acids and acetone are products of the oxidation of propylene and ethylene polymers and copolymers. The two-and three-carbon products can be accounted for as the result of intramolecular attack by radicals, leading to &oxidation. A high proportion of scissions in polypropylene involves multiple intmmolecular attack.This papcr reports some observations pcrtincnt to the mechanism of oxidation of polyethylene and polypropylene. A number of previous investigations have dealt with other aspects of the oxidation process, including effects of temperature, crystallinit~y, and other external conditions. '-I8