Regulation of molecular weight of styrene–butadiene rubber. II. Influence of variation of polymerization recipe on the regulating efficiency of diisopropyl xanthogen disulfide

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Abstract
The influence of kind and amount of an anionic emulsifier, pH of water phase, addition of free rosin, and content of conjugated structures in rosin on the regulation efficiency of diisopropyl xanthogen disulfide in emulsion copolymerization of butadiene with styrene at +5°C. was studied. The apparent chain transfer constant C decreased in the order: Li+ > Na+ > K+, for the cations with the hydrolysis of rosin soap. This soap is replaceable with other anionic emulsifiers, C being dependent on the absorption area of one soap molecule. With increasing amount of soap the value of C decreased. With the decreasing pH of the water phase, the value of C increases. This fact can be explained by the increase in hydrolysis of carboxylic groups of rosin and oleate soaps and an increase in the permeability of the monomer–polymer particle surface to molecules of regulator. This tendency does not exist in the case of sulfonate‐type soaps. After addition of free rosin to the monomer phase, a similar increase in C is noted. The value of C increased also with an increase in the content of conjugated structures characterized by a value δ, which is related to the retardation of polymerization. The standard polymerization recipe at pH 10.8 is suitable from the point of view of using diisopropyl xanthogen disulfide as a molecular weight regulator.