TETRAMETHYLTHIURAM DISULFIDE AND 2-MERCAPTOBENZOTHIAZOLE AS BINARY ACCELERATORS IN SULFUR VULCANIZATION .1. EXCHANGE-REACTIONS BETWEEN THE ACCELERATORS AND SULFUR IN THE ABSENCE OF RUBBER

Exchange reactions between tetramethylthiuram disulfide, 2-mercaptoben zothiazole, and sulfur were studied by heating powdered mixes to vulca nization temperatures at a programmed rate in a DSC. The reaction was stopped at points along the thermal curve and the mixture was analyzed by HPLC. On dissolution, even unheated samples underao a sulfide exch ange reaction leading to a mixed accelerator, while polysulfides of th e thiuram and mixed accelerator form in low concentrations. On heating , higher concentrations of these polysulfides are formed, particularly in the presence of elemental sulfur. Dimethyl-dithiocarbamic acid, fo rmed in the exchange, influences the product spectrum if it remains tr apped in the DSC pan. Tetramethylthiourea is formed only at elevated t emperatures when dimethylamine, a degradation product of the acid, is trapped in the DSC pan. A series of reactions is proposed to explain t he product spectrum obtained under different conditions. (C) 1995 John Wiley & Sons, Inc.