Kinetics of natural rubber （NR） vulcanization by lanthanum O, O＇-diisopropyldithiophosphate [ La（DiPDP）3 ] was studied. La（DiPDP）3 had remarkable accelerating effect on the vulcanization of NR. The rate constant k6 of the reaction that turned polysulphidic cross-links into the modified main chain was higher than that of desulfuration reaction of polysulfidic cross-links （k3 ）. The activation energies （Ea2, Ea3, and Ea6） of the formation, desulfuration, and decomposition of polysulfidic cross-links were 87.57,102.34, and 95.01 kJ · mol^-1, respectively. Activation energy （Eas） of the reaction that turned the cross-link precursors into the modified main chain was 82.67 kJ · mol^-1. It could be concluded that the proportion of polysulphidic cross-links was higher than mono- and di- sulphidic cross-links during induction and curing periods, mono- and di- sulphidic cross-links increased as curing temperature rose. In the temperature range of 140 - 160 ℃, the amounts of polysulphidic cross-links were similar. However, over 160℃, mono- and di- sulphidic cross-links increased rapidly. Moreover, cross-link density of the vulcanizates was determined from the equilibrium-swelling data. A chemical probe detected the concentration of polysulphidic cross-links of vulcanizates. The change trend of the results predicated from equation corresponded to that of the experimental results.
