Emulsion polymerization of butadiene, 1. The effects of initiator and emulsifier concentration

Abstract

AbstractThe kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′‐azobis‐(4‐cyanopentanoic acid) and 2,2′‐azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene‐polymerizations. The polymerization rate in interval II, Rpol, was found to be highly insensitive to changes in the initiator concentration (Rpol ∝ [I]0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. Rpol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.