Analysis of the Mechanism of N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene

Abstract

Results of previously published work involving network analysis and accelerator intermediate analysis of cis-polyisoprene were compared to help correlate and rationalize network/chemistry relationships. Both classical chemical probe network analysis and further NMR measurements (DEPT analysis) were used as necessary to verify NMR peak assignments. Furthermore, samples of the conventional formulation were vulcanized in the absence of zinc oxide and stearic acid to help elucidate the role of zinc in the vulcanization process. Polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic substituted cis-polysulfides both with and without double bond migration, while zinc polysulfidic dibenzothiazole accelerator intermediates were proposed to produce allylic cis and trans polysulfides substituted structures with no double bond migration. Polysulfidic substitution on the isoprene methyl carbon was shown to result from exchange reactions during network maturation. The network-chemistry relationships were compared with earlier mechanistic studies and several points of agreement were noted.

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

“…For benzothiazolesulfenamide accelerators, 2-bisbenzothiazole-2-2'-disulfide (MBTS) plays a major role, since MBTS reacts with sulfur to form 2-bisbenzothiazole-2-2'-polysulfides (MBTPs); and, MBTPs, or the zinc/amine complexes of MBTPs, are a key sulfurating intermediate. 2,[20][21][22][23][34][35][36][37][38] Since MBS is the accelerator of primary interest, we will discuss: (i) the formation of MBTS from MBS, which is the first step in the vulcanization process; followed by (ii) the mechanism for sulfur pick-up by MBTS to form MBTPs; and finally (iii) the exchange reactions that MBTPs can undergo. Finally, we will review the affect of ZnO on the formation of zinc-accelerator complexes of Type I, II and III.…”

“…The proposed concerted mechanism is shown below, where the precursor is formed via an eight-membered transition state and MBT is the by-product of this reaction. 20,21,34,95 (R.34)…”

“…For MBS accelerated systems, the source of MBT is the initial decomposition of MBS, but for MBTS accelerated systems, there is a disagreement regarding the origin of MBT. Many researchers 2,34,81,94,95 believe that MBT is created during the formation of crosslink precursors via R.34. However, Gradwell et al 33 dispute this conclusion, since they did not observe any MBT during crosslink precursor formation and thus associate the formation of MBT with the crosslinking step.…”

“…85 Skinner's work suggests that the presence of an accelerator enables an efficient substitution in allylic position, which agrees with the conclusions of Bateman et al 2 , Lautenschlaeger 86-88 and Kresja and Koenig. 34,81 In the 1960s a radical mechanism that did not include crosslink precursors was advocated for the conversion of accelerator polysulfides into crosslinks; [89][90][91][92][93] specifically,…”

Enhanced morphology and mechanical characteristics of clay/styrene butadiene rubber nanocomposites

“…The proposed concerted mechanism (Fig. 1) is where the cross linked precursor, which are rubber (SBR) bound intermediates (structure VI) is formed via an eight-membered transition state (structure V), and Mercaptobenzothiazole gets regenerated at the end as the reaction proceeds (Coran, 1964a(Coran, ,1964b(Coran, , 1983Kresja et al, 1994). The cross-link precursor reacts with another SBR chain with the same concerted mechanism and generate a cross linked structure as in VII.…”