SOLID-STATE C-13 NMR-STUDIES OF ELASTOMERS .11. N-T-BUTYL BENZOTHIAZOLE SULFENIMIDE ACCELERATED SULFUR VULCANIZATION OF CIS-POLYISOPRENE AT75 MHZ

The network structure of TBSI-accelerated vulcanization of cis-polyiso prene was studied using C-13 solid-state NMR. The initial crosslink pr oducts consisted of A1c (cis) and A2c (cis) polysulfides. As the perce nt cure is increased, the A1c and A2c structures reduce in rank to mon osulfides, and polysulfidic B1c (cis) and B1t (trans) structures are f ormed. During the maturation period C1c (cis) polysulfidic structures are also formed. The percent of sulfurization was shown to vary direct ly with sulfur concentration, while the efficiency of sulfurization (c rosslink/cyclic-structure ratio) was shown to vary with accelerator co ntent. TBSI-accelerated vulcanization was found to be more inefficient (lower crosslink/cyclic-structure ratio) than TBBS-accelerated vulcan ization during the initial cure region. However, this results in short er sulfur chains, which decreases the reactivity of TBSI vulcanizates as compared to TBBS vulcanizates during the reversion regime.