The effect of ZnO and bis(2-mercaptobenzothiazole)zinc(II) [Zn(mbt)(2)] on 2-bisbenzothiazole-2,2 ＇-polysulfide (MBTP) formation in 2-bisbenzothiazole-2,2＇-disulfide (MBTS) and MBTS/sulfur, in the absence of rubber, was studied by heating mixes isothermally for various times and analyzing products by HPLC. Both compounds accelerate MBTP formation but do not affect equilibrium concentrations. It is proposed that ZnO induces opening of the sulfur ring, permitting more rapid sulfuration of benzothiazole radicals (BtS), while with Zn(mbt)(2), exchange between sulfurated Zn(mbt)(2) and BtS radicals promotes their sulfuration. MBTP of lower sulfur rank form first and in the highest concentrations, while MBTP of higher sulfur rank form sequentially and form from MBTP of immediately lower sulfur rank. The concentrations of MBTP of lower sulfur rank pass through a maximum before equilibrating at lower concentrations. Reaction mechanisms to account for MBTP formation and the role of ZnO and Zn(mbt)(2) in accelerating the reactions are proposed. (C) 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1405-1412, 2000.