GB751630A - Production of vulcanized rubber of improved resistance to cracking and compounds for use therein - Google Patents

Abstract

Vulcanized synthetic rubber with improved resistance to cracking under exposure is obtained by incorporating into a sulphur-vulcanizable synthetic rubber stock a vulcanizing agent and an N-alkyl-N1-phenyl-paraphenylene diamine in which the alkyl group contains at least six but not more than ten carbon atoms (see Group IV (b)) and maintaining the mixture at a vulcanizing temperature until vulcanization is effected. Between 0.2 and 5 per cent by weight of the phenylene diamine based on the weight of the rubber may be used. Specified synthetic rubbers include polymers of aliphatic conjugated dienes such as butadiene, isoprene, piperylene, dimethyl butadiene and ethyl butadiene and their copolymers with olefins containing a vinyl group such as styrene, a -methyl styrene, mono- and dichlorostyrene, vinyl naphthalene, divinyl benzene, vinyl diphenyl, vinyl carbazole, 2-vinyl-5-ethyl-pyridine, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid and esters thereof and methyl vinyl ketone. The effect of the N-alkyl - N1 - phenyl - para - phenylene diamine compounds is shown by admixing the N-n-hexyl- or N-n-decyl-compounds with a butadiene-1 : 3-styrene copolymer composition containing the usual vulcanizing agents, vulcanizing and evaluating the cured compositions by exposure under dynamic conditions in an atmosphere of ozone. Similar compositions containing copolymers of butadiene-1 : 3-acrylonitrile copolymer or isobutylene-isoprene copolymer are described. The vulcanized rubbers so treated are also resistant to flex cracking and to ageing due to exposure to air or oxygen, even when the vulcanized rubber contains copper.ALSO:The invention comprises N-alkyl-N1-phenyl-para-phenylene diamines in which the alkyl groups contain at least six but not more than ten carbon atoms. The compounds are incorporated into sulphur-vulcanizable natural (see Group V) or synthetic (see Group IV (a)) rubber stocks and improve the resistance to cracking under exposure of the vulcanized rubber. In Example (1) a mixture of n-hexyl alcohol and N - phenyl - para - phenylene diamine are refluxed together in the presence of a nickel catalyst with concurrent removal of water, the reaction mixture extracted with ether and distilled to give N-hexyl-N1-phenyl-para-phenylene diamine; (2) as in (1) but using n-decanol and crystallizing the reaction mixture from heptane to yield N-n-decyl-N1-phenyl-para-phenylene diamine.ALSO:Vulcanized natural rubber with improved resistance to cracking under exposure is obtained by incorporating into a sulphur-vulcanizable natural rubber stock a vulcanizing agent and an N-alkyl-N1-phenyl-para-phenylene diamine in which the alkyl group contains at least six but not more than ten carbon atoms (see Group IV(b)) and maintaining the mixture at a vulcanizing temperature until vulcanization is effected. Between 0.2 and 5 per cent by weight of the phenylene diamine based on the weight of rubber may be used. The effect of the N-alkyl-N1-phenyl-para-phenylene diamine compounds is shown by admixing the N-n-hexyl-compound with a rubber composition containing the usual vulcanizing agents and fillers, and then vulcanizing and evaluating the cured compositions by exposure under dynamic conditions in an atmosphere of ozone. The antioxidant action of the N-n-hexyl-compound is also shown in cured compositions containing copper.