Thermal and viscoelastic behavior of hydrogenated polystyrene

Fully saturated hydrocarbon polymers often exhibit superior stability towar d thermal, oxidative, and radiation-induced degradation. Recent improvement s in catalyst technology allow for the convenient synthesis of the saturate d hydrocarbon poly(cyclohexylethylene) (PCHE) from -polystyrene (PS) by het erogeneous catalytic hydrogenation. The focus of this report was to prepare nearly monodisperse samples of polystyrene by anionic polymerization and t o fully saturate those materials by catalytic hydrogenation. The thermal an d viscoelastic properties of these materials were then evaluated using diff erential scanning calorimetry and dynamic mechanical spectroscopy. On the b asis of these experimental results, the glass transition temperature of PCH E has been found to approach 148 degreesC at high molecular weight. Relatio nships between the zero shear viscosity, steady-state compliance,and rubber y plateau modulus of PCHE with respect to molecular weight have been determ ined, and entanglement spacing and packing length have been calculated from these data. PCHE shows an entanglement spacing (M-e) of 40 200 g/mol, comp ared to 18 700 g/mol for the starting material PS. This increase in glass t ransition temperature and entanglement length can be attributed to the incr ease in steric bulk of the cyclohexyl substituent compared to the phenyl ri ng present in the starting material.