Preparation and Properties of Rubberlike High Polymers. II. Polymerization of Mixtures in Bulk

Mixtures of butadiene and dimethylbutadiene with varying quantities of styrene and acrylonitrile were copolymerized under various catalytic conditions at 100° C. The formation of cyclic dimers from dienes and vinyl compounds is, in some cases, much more pronounced than the dimerization of the dienes alone. Since the latter is also a kind of Diels-Alder reaction, a series with increasing dienophilic properties can be established from a comparison of the yields of cyclic dimers. From solubility and swelling experiments it is evident that the polymers prepared from butadiene and the vinyl compounds and those from dimethylbutadiene and acrylonitrile are true copolymers. The mechanical properties of the copolymers from butadiene and increasing amounts of a vinyl compound change gradually from those of a rubber to those of the polyvinyl compound. The copolymers from a mixture containing 30 per cent styrene or acrylonitrile are very similar to Buna-S and Perbunan, respectively. Copolymers of the same composition from dimethylbutadiene and acrylonitrile, on the other hand, form a new class of thermoplastics with a much higher temperature of elasticity.

Preparation and Properties of Rubberlike High Polymers. III. Polymerization of Mixtures in Emulsion

The copolymerization in emulsion of butadiene with varying proportions of styrene and acrylonitrile and of dimethylbutadiene with the latter vinyl compound was studied on a laboratory scale. An essential difference between polymeric vinyl compounds and polydienes is the olefinic character of the latter, which leads to typical secondary changes in the polymers originally formed during the completion of the reaction. Such changes are of fundamental importance for the ultimate mechanical properties of polymers and copolymers based on dienes. After a brief discussion of the general theoretical line of thought serving as a base for our experiments, the influence of various factors on the rate of polymerization is pointed out and demonstrated by experiments. The changes in the nitrogen content of copolymers from acrylonitrile and the yields as a function of the reaction time also were studied. From an investigation of some physical properties, such as solubility and swelling, the existence of true. Copolymers (of unknown irregularity) is established. Copolymers from dimethylbutadiene and acrylonitrile represent a new class of olefinic thermoplastics resembling gutta-percha.

Preparation and Properties of Rubberlike High Polymers. I. Polymerization of Dienes and Vinyl Compounds in Bulk

The 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 per cent 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 dienes. The catalytic effect of benzoyl peroxide on the polymerization of dienes is, on the contrary, 10,000–100,000 times smaller than on that of vinyl compounds. This difference can be understood by the assumption that the catalyst is quickly used up by oxidizing the dienes and their polymers. Whereas 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).