Study of the activity of some sulfur compounds in the modification of vulcanizates by vinyl monomers

The kinetics of the bulk polymerization of styrene in the presence of tetramethylthiu-ramdisulfide ([TMTD]; 2.11 × 10−4-1.67 × 10−1 mole/1., and some other sulfur compounds at 80, 95, 115, 130, and 140°C, were studied. The rate of polymerization has been measured as a function of the concentration of the studied compound. The formal order of reaction (n) was determined with respect to the concentration of TMTD, which varies with the increase of the concentration of TMTD and temperature of polymerization in the range 0 < n < 0.5 and it is possible to express by the relation: n = d In Rp/d In [I] = n0(1 − C[I]2)/(1 + B[I] + C[I]2). The decrease of the polymerization rate compared with the rate arising from the simple reaction scheme is caused by the participation of radicals on the termination reactions: (P' + RS', RS' + RS'), which permits us to solve this type of polymerization as a retardation polymerization: Rp − A[I]1/2 /(I + B[I] + C[I]2)1/2. (A, B, and C are complex constants dependent on temperature.) The calculated values of the fraction of primary radicals taking part in the termination reaction (assuming the neglect of the reaction (RS' + RS') grow with the increase of the concentration TMTD and temperature. The relatively high values of complex transfer constants Ci'-(0.57–0.98) and the observed decrease of values of effective activation energies with an increasing concentration of TMTD are in accordance with the given reaction scheme. The observation of other sulfur compounds (zincdiethyldithiocarbamate, dibenzothiazolyldisulfide, dipentamethylenthiuramtetrasulfide, and N-cyclohexyl-2-benz-thiazylsulfenamide) showed that they had a considerably smaller influence on the polymerization of styrene than did TMTD.