Preparation and properties of rubberlike high polymers. I. Polymerization of dienes and vinyl compounds in bulk

Abstract

AbstractThe polymerization of dienes under the influence of heat, of diazoaminobenzene, and of benzoyl peroxide, has been studied. Diazoaminobenzene probably acts as a slow, but continuous, source of free radicals giving quantitative yields of methyl rubber of good quality from dimethylbutadiene after a few days to a few weeks at 100–125°C. The effect of diazoaminobenzene on butadiene is the same, but the rate of the uncatalyzed dimerization of butadiene at 100°C. is as fast as that of dimethylbutadiene at 150°C. and, therefore, dimerization interferes much more strongly with the polymerization of butadiene. Only 60% of polybutadiene has been obtained. A few experiments with isoprene showed its position between the two other dienes. The effect of benzoyl peroxide on the polymerization of the dienes appeared to be much smaller than was expected from its known catalytic action on the polymerization of vinyl compounds, e.g., styrene, for in this case its activity is about 100–1000 times greater than that of diazoaminobenzene. It is assumed that a larger number of radicals, produced by the fast decomposition of benzoyl peroxide, causes this difference. Diazoaminobenzene has about the same effect on the polymerization of styrene and acrylonitrile as on that of the dienes. The catalytic effect of benzoyl peroxide on the polymerization of the dienes is, on the contrary, 10,000–100,000 times smaller than on that of the vinyl compounds. This difference can be understood by the assumption that the catalyst is quickly used up by oxidizing the dienes and their polymers. While methyl rubber and the polyisoprene resemble raw natural rubber, polybutadiene, prepared under comparable conditions, is hard, swells moderately, and has a tendency to become brittle as a result of oxidation (aging). Abbreviations used are DAB (= diazoaminobenzene) and BP (= benzoyl peroxide).