GB806905A - Copolymer-oil modified synthetic rubber - Google Patents

Abstract

A vulcanizable composition comprises a mixture of a rubber, obtained by copolymerizing a major proportion of a C4-C7 iso-olefine and a minor proportion of a C4-C14 conjugated multi-olefine, with a minor proportion, with respect to the rubber, of an oily copolymer of a C4-C14 conjugated multi-olefine and a vinyl aromatic hydrocarbon. The rubber is preferably a butyl rubber obtained by copolymerizing 85-99.5 per cent of isobutylene with 15-0.5 per cent of isoprene, butadiene, dimethyl butadiene, myrcene, piperylene or allo-ocimene. The oily copolymer is preferably one prepared by copolymerizing 60-90 per cent of butadiene with 40-10 per cent of styrene in the presence of 0.1-10 parts by weight of sodium per 100 parts of monomer at 20-100 DEG C. in a hydrocarbon solvent. Other dienes include isoprene, 2,3-dimethyl butadiene, piperylene and 2-methyl pentadiene-1,3; other vinyl aromatic compounds include the ring-alkylated styrenes methyl-, dimethyl-, ethyl-, and diethyl-styrenes. The mixture preferably contains 51 to 99 parts by weight of the rubber and correspondingly 49 to 1 parts by weight of the oily copolymer to give 100 parts of the mixture which may be vulcanized with sulphur and preferably 1 to 30 parts by weight of a lead compound containing oxygen, 1 to 50 parts by weight of zinc oxide and an ultra accelerator such as zinc dithiocarbamate or tellurium diethyl dithiocarbamate. The lead compound preferably contains at least 25 per cent available lead oxide and may be PbO, Pb2O3, Pb3O4, PbO2 or lead stearate. Curing may be carried out at 120-200 DEG C. (250-400 DEG F.) for a time of 10-120 minutes which preferably gives a vulcanizate having a tensile strength of at least 1500 p.s.i.