Silica retards radial growth of spherulites in isotactic polystyrene

Abstract

We recently reported the retardation of the rate of crystallization, measured calorimetrically, in isotactic polystyrene (iPS) nucleated with silica (Cab-O-Sil) that had been treated with trimethylsilane¹. The loading of the nucleant was 5 g per 100 g of polymer or two parts per hundred (p.p.h.) by volume, of polymer. From microscopic observations it was known that the number of nuclei present in the nucleated system was at least double that present in the pure polymer in identical cooling conditions². The only rationale available for the retardation effect seemed to be that the nucleant was inhibiting the growth of the crystals and thus the overall rate of crystallization. However, previous workers have reported spherulitic growth rates to be unaffected by the presence of nucleants in systems with loadings up to 3 p.p.h. (refs 3–6). To clarify this apparent paradox the measurement of the radial growth rates of spherulites in the system iPS–silica by photomicrography was undertaken. Here we confirm that silica does retard the rate of growth of such spherulites.