Thermal and Viscoelastic Behavior of Hydrogenated Polystyrene

Fully saturated hydrocarbon polymers often exhibit superior stability toward thermal, oxidative, and radiation-induced degradation. Recent improvements in catalyst technology allow for the convenient synthesis of the saturated hydrocarbon poly(cyclohexylethylene) (PCHE) from polystyrene (PS) by heterogeneous catalytic hydrogenation. The focus of this report was to prepare nearly monodisperse samples of polystyrene by anionic polymerization and to fully saturate those materials by catalytic hydrogenation. The thermal and viscoelastic properties of these materials were then evaluated using differential scanning calorimetry and dynamic mechanical spectroscopy. On the basis of these experimental results, the glass transition temperature of PCHE has been found to approach 148 °C at high molecular weight. Relationships between the zero shear viscosity, steady-state compliance, and rubbery plateau modulus of PCHE with respect to molecular weight have been determined, and entanglement spacing and packing length have been calculated from these data. PCHE shows an entanglement spacing ( M e ) of 40 200 g/mol, compared to 18 700 g/mol for the starting material PS. This increase in glass transition temperature and entanglement length can be attributed to the increase in steric bulk of the cyclohexyl substituent compared to the phenyl ring present in the starting material.