FACTORS CONTROLLING THE DISTRIBUTION OF ORGANICALLY MODIFIED CLAYS BETWEEN POLYBUTADIENE-RICH AND POLYSTYRENE-RICH PHASES IN THE SYNTHESIS OF HIGH IMPACT POLYSTYRENE

Abstract

This work investigates the effect of kinetic factors and the surface chemistry of the particles on the dispersion and distribution of clays in heterogeneous system containing polystyrene (PS) and  polybutadiene  (PB).  It was carried out in 2 stages.  In the  first  stage,  an isothermal system without copolymer was investigated; that involved simple blends of the mentioned homopolymers, of commercially- modified clays, and of styrene (St) as solvent. In these soft blends, phase demixing was not spontaneous observed, but was induced by centrifugation. After demixing, the composition of the isolated phases was determined by calcination/infrared spectroscopy (FTIR); and in  some  phases,  the  clay  dispersion  was  analyzed  by  X-ray  diffraction  (XRD).  In  the  second  stage,  in  situ  and  nitroxide-mediated polymerizations of the St-containing blends were carried out. The incorporation of the organo-clay particles into the different phases and morphology  of  the  rubbery  particles  of  the  resulting  high-impact  polystyrenes  (HIPS’s),  were  observed  by  transmission  electronic microscopy, TEM. The distribution of silicates between the phases was analyzed by calcination/FTIR. In all the samples (i.e., in those of simple  blends  and  in  those  with  polymerization),  the  clay  was  mainly  incorporated  into  the  PB-rich  phase,  due  to  the  high  affinity between PB and the clay modifiers. In the case of the soft blends, demixing was prevented by the increased stability introduced by the clay; and several mechanisms were proposed to explain such behavior. In the case of the synthesized HIPS’s, their thermal resistances were increased by the presence of the modified clays and by increasing the degree of dispersion of the clay in the polymer.