Heterogeneous Polymer Systems. IV. Mechanism of Rubber Particle Formation in Rubber Modified Vinyl Polymers

Abstract

Abstract Polymerization of a solution of a rubber in a vinyl monomer consists of two stages. In the first stage (0–40 per cent conversion), in which the system is liquid, a polymeric oil-in-oil emulsion is formed, and the size of the rubber particles is established. In the second stage (40–100 per cent) this polymeric oil-in-oil emulsion hardens gradually to a solid dispersion of rubber particles in a matrix of the vinyl polymer, whereby the structure of the emulsion is retained and no significant morphological changes occur. The rubber particles are formed in the phase inversion which occurs in the first stage of polymerization. After the manuscript of this paper had been completed, a publication appeared, in which the dispersion of rubber by a phase inversion was also described. Bender's observations are in agreement with the observations presented in this paper and in the first paper in this series.) At the phase inversion point, the rubber phase is dispersed in the form of droplets in the vinyl polymer. Formation of multiple emulsions can occur at this point. The droplets of the rubber phase harden gradually by polymerization of the monomer and by crosslinking of the rubber and become finally solid rubber particles. The rubber particles contain irregularly shaped, tiny occlusions of vinyl polymer caused by polymerization of the portion of the monomer which was the solvent in the rubber phase. In addition, the rubber particles can contain larger occlusions with round peripheries stemming from multiple emulsions formed at the phase inversion point. Since the high viscosity of rubber solutions has an impeding effect on phase inversion, agitation is necessary in the first phase of the polymerization in order to overcome the inertia of the system and achieve inversion before the emulsions can solidify in the uninverted state.