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ABSTRACT
Prevulcanization inhibitors (PVI) provide an important delay in the curing reactions that occur in accelerated sulfur vulcanization. In this study, the reactions of N-(cyclohexylthio)phthalimide (CTP) with other curatives (excluding zinc oxide) were investigated in the presence and absence of rubber. The CTP has been shown to react very readily with 2mercaptobenzothiazole (MBT) and this reaction has previously been credited with the delay observed. However, recent studies have shown that MBT is not formed until crosslinking has started. In a 2-bisbenzothiazole-2,2'-disulfide (MBTS) accelerated sulfur cure, CTP was shown not to delay the onset of crosslinking, but once crosslinking began, with the concurrent formation of MBT, the CTP reacted with the MBT inhibiting further polysulfide formation, pendent group formation and thus crosslinking. Crosslinking continues after the CTP has been consumed.
INTRODUCTION
The ability to delay the onset of vulcanization to allow sufficient time for processing is an important factor in formulations. The most common compounds used for improving processing safety are the prevulcanization inhibitors (PVI). A PVI is used to increase the induction time before crosslinking, while still retaining the good rate of cure of the accelerator system. A number of PVIs are commercially available, the most commonly used one being N-(cyclohexylthio)phthalimide (CTP). The importance of the S-N bond...