Structure of neoprene. V. Viscosity‐conversion relationships in sulfur‐modified polychloroprenes

The solution properties, i.e. , gel content and intrinsic viscosity, of sulfur‐modified polychloroprenes were examined at monomer conversions ranging from 5 to 95% to obtain information about the mechanism of action of the sulfur modifier and other factors influencing the polymerization. Sulfur‐modified polymers isolated at conversions beyond 10–40%, depending upon the polymerization temperature, were found to be insoluble before treatment with tetraethylthiuram disulfide. These results, in confirmation of earlier results with radiosulfur, indicate that sulfur in chloroprene polymerization does not act as a chain transfer agent. The intrinsic viscosity‐conversion relationships for sulfur‐modified, tetraethylthiuram disulfide‐treated polychloroprenes show two viscosity maxima. The first maximum, at 15–20% conversion, appears to be the result of a change in polymer structure and, therefore, a change in the molecular weight‐intrinsic viscosity relationship. The second maximum appears at high conversion, 85–90%, and is caused by the formation of relatively tight gel that cannot be solubilized by the tetraethylthiuram disulfide scission reaction. The less pronounced decrease in viscosity beyond this peak is caused by removal of high molecular weight polymer by gelation, leaving relatively lower molecular weight sol polymer.