Investigations of crosslinking in the emulsion polymerization of butadiene

A study of the dilution effect of four hydrocarbons (biallyl, hexane, 3‐methyl‐1‐butene, and isopentane) on the rate of polymerization of butadiene and on the characteristics of the resulting polymer has shown that chain transfer of the following type is an unimportant reaction in butadiene polymerization: magnified image The above result is consistent with the kinetic treatment of crosslinking as developed by Flory. The results of a comparison of the emulsion polymerization of 2,2′‐azobisisobutyronitrile‐ and of persulfate‐catalyzed butadiene are adequately accounted for without considering the effect of the catalysts on branching or crosslinking. As previously suggested, the differences noted between 2,2′‐azobisisobutyronitrile‐ and persulfate‐catalyzed polybutadienes are probably due to a different molecular‐weight distribution. This difference in molecular‐weight distribution is partly produced by a large difference in r values for the two systems. The unmodified emulsion polymerization of butadiene with 2,2,‐azobisisobutyronitrile in an oxygen‐and peroxide‐free system produces a highly crosslinked polymer.