The presence of nanopores in mesophase of syndiotactic polystyrene estimated from gas sorption behaviour

Effect of encaged aromatic guests on the shape and connectivity of molecular cavity in crystalline polystyrene evaluated by molecular simulations

The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.

Gas Solubility in and Foamability of Various Forms of Syndiotactic Polystyrene

A high pressure microbalance was used to measure solubility of CO2 at 35°C and pressures to 55 atm in amorphous, meso, and α-crystalline forms of syndiotactic polystyrene, sPS. Diffusion coefficient of CO2 in the various samples were derived from sorption kinetics. When normalized with respect to 100% amorphous content, the solubility and diffusivity of CO2 was found to be highest in the semi-crystalline α-form, followed by the meso and the amorphous forms. This rather unusual observation was attributed to the existence of microvoids in α-sPS and meso-sPS, and due to the finite solubility of gas in the rigid amorphous phase associated with these two forms. All three forms of sPS were foamed at various temperatures in the range 50 to 295°C to give microcellular structures. The cell walls in foams obtained from amorphous sPS showed unusual, starburst type structure. The density of meso-sPS foams first decreased and then increased with foaming temperature due to the transformation of the mesophase to the α-phase with increasing temperature. The microvoids in α-sPS and meso-sPS are conjectured to serve as the nucleating sites rather than the often suggested phenomenon of heterogeneous nucleation induced by the crystallites.