Use of perbenzoic acid in analysis of unsaturated compounds. III. Results of determinations of external double bonds in synthetic rubbers

Abstract

AbstractEmulsion polybutadiene and emulsion copolymers of butadiene and styrene (e.g., GR‐S) contain about 20% external double bonds. A systematic study has been made of the effects of temperature, type of “catalyst,” percentage conversion, microgel formation, and varying styrene content of emulsion copolymers of butadiene and styrene. None of these variables affects the amount of external double bonds. Copolymers of butadiene with styrene and a small amount of acrylonitrile, and of butadiene with various monochlorostyrenes and dichlorostyrene, all prepared by emulsion polymerization, were found to contain the same amount of external double bonds. Emulsion polyisoprene and the emulsion copolymers of isoprene and styrene (75:25) were found to contain only 13 and 5%, respectively, external double bonds. Polybutadiene, butadiene—styrene copolymer, and polyisoprene, all prepared by sodium—catalyzed, bulk polymerization at 50°C., contain 50–60% external double bonds. The amount of external double bonds in sodium polybutadiene is strongly dependent on temperature of polymerization. More external double bonds are formed at low temperatures than at high temperatures. The amount of external double bonds in sodium butadiene—styrene copolymer and in sodium polyisoprene is nearly independent of temperature in the range 30–50°C. A sample of sodium polyisoprene was found to contain 36% internal double bonds and 64°C external double bonds. From an analysis of the reaction—rate curve it was concluded that approximately 40% (absolute percentage) of the external double bonds were formed by 3,4 addition and 24% by 1,2 addition. The rates of reaction of the cis—and trans—forms of natural rubber are very nearly the same, the cis—form reacting slightly more rapidly.