Analytic expressions for grafting and crosslinking of PBD (Polybutadiene) during the bulk thermal polymerization of HIPS(High Impact Polystyrene) were derived by use of the moments of the distribution function. The chain transfer ratio term, f $k_5/k_3$, was determined by the linear correlation between GE (Grafting Efficiency) and ln 1/(1-X), which was found to independent of temperature. The crosslinkings drastically increased at the high temperature, 190℃, and high conversion, about 95%. These formulas can be also applied for the polymerization initiated by initiators with some modifications.
In order to control the particle size distribution of PBD, PS was added at initial solution(homogeneous adding, A series), shortly after phase inversion(heterogeneous adding, B series) and bimodal molecular weight distribution PBD(series C) was tried instead of unimodal one. Particle size distribution obtained was the abnormal distribution in series B and shifted distribution to the large particle size in series A. But series C gave us usual Gaussian distributions. Heterogeneous adding of PS had relatively high gloss and impact resistance to normal HIPS(A-1) sample, which was shown bimodal distribution HIPS, although homogeneous adding of PS had high impact resistance and low gloss, which was shown normal distribution HIPS. The tensile properties and dynamic viscosty at the low frequency were largely influenced by adding PS. Therefore, in order to obtain both high gloss and impact resistance, heterogeneous adding PS at shortly after phase inversion is desirable.
