Rheological and mechanical properties of ABS plastics prepared by bulk polymerization

A series of ABS plastics prepared by bulk polymerization was studied. The test samples contained almost equal amounts of PB but mostly differed in the molecular mass of a styrene-acrylonitrile copolymer. It was shown that the molecular mass of the copolymer strongly affects the rheological and mechanical properties of ABS plastics. An increase in molecular mass leads to a rise not only in the non-Newtonian viscosity of plastics but also in their yield point, storage modulus under periodic steady-state shear flow in the low-frequency plateau region, and impact strength. Quantitative correlations between these rheological and mechanical characteristics of the copolymers and their M _w values were established. As opposed to homophase polymer systems, a marked increase in the shear stress has no effect on viscosity in relation to the molecular mass of ABS plastics. In the case of melts, the influence of the M _w of the styrene-acrylonitrile copolymer on the rheological behavior of ABS plastics is apparently related to a change in the interaction of PB particles with the copolymer that controls the structural framework of the system. The relationship between the impact strength of the copolymer and its M _W may be explained by the fact that the latter parameter influences orientational effects in crazes that arise during steady-state shear flow of ABS plastics in the solid state.