Gas solubility and foamability of various forms of syndiotactic polystyrene

A high pressure microbalance was used to measure solubility Of CO2 at 35 de greesC and pressures to 55 atm in amorphous, meso, and alpha -crystalline f orms of syndiotactic polystyrene, sPS. Diffusion coefficient of CO2 in the various samples were derived from sorption kinetics. When normalized with r espect to 100% amorphous content, the solubility and diffusivity of CO2 was found to be highest in the semi-crystalline alpha -form, followed by the m eso and the amorphous forms. This rather unusual observation was attributed to the existence of microvoids in alpha -sPS and meso-sPS, and due to the finite solubility of gas in the rigid amorphous phase associated with the-s e two forms. All three forms of sPS were foamed at various temperatures in the range 50 to 295 degreesC to give microcellular structures. The cell wal ls in foams obtained from amorphous sPS showed unusual, starburst type stru cture. The density of meso-sPS foams first decreased and then increased wit h foaming temperature due to the transformation of the mesophase to the alp ha -phase with increasing temperature. The microvoids in alpha -sPS and mes o-sPS are conjectured to serve as the nucleating sites rather than the ofte n suggested phenomenon of heterogeneous nucleation induced by the crystalli tes.