Abstract
In our previous paper1) of this series the properties of styrene-butadiene rubber vulcanizates in tensile fracture was discussed. In this paper the properties of three copolymer vulcanizates in tensile fracture are studied, namely isoprene-butadiene, styrene-isoprene and methyl methacrylate-isoprene, and the following conclusions have been obtained.
(1) The fracture in the vulcanizates of these copolymers compounded with carbon black is mainly due to scission in the molecular chains of polymer, and there is almost no scission in the bonds between the rubber molecules and the surface of the carbon black.
(2) The temperature which affords the maximum value of ultimate elongation depends entirely on the transition temperature Tg, though the rubbers used may vary in average molecular weights per piece, in the network chain densities and in the combined sulfur structure.
(3) The ultimate elongation at reduced temperature is little affected by the composition of two copolymers that do not differ markedly in Tg of homopolymer, as in the isoprene-butadiene system, while the elongation is thought to be decreasing with the increasing variance between the two component copolymers in Tg of homopolymer. For instance the elongation of styrene-isoprene copolymer decreases with increased content of styrene.
