2,3-Dimethyl-2-butene (TME) was used as a model for polyisoprene in studying the formation of crosslinks in tetramethylthiuram disulfide (TMTD)-accelerated sulfur vulcanization. Mixtures of TME with TMTD, sulfur, and ZnO were heated in sealed tubes at 130 degrees C for various times and the contents analyzed by HPLC. In the absence of ZnO crosslinking is delayed until most of the TMTD has been consumed. Crosslinking results from the interaction of thiuram and dimethylammonium pendent groups, tetramethylthiourea being formed as a byproduct. In the presence of ZnO two crosslinking reactions occur, viz (1) disproportionation between thiuram pendent groups, which gives TMTD as a byproduct; and (2) a zinc dimethyldithiocarbamate-catalyzed reaction between pendent groups and the olefin.