Surface molecular motion in polyolefin single crystals

In order to study an effect of underneath crystalline phase on surface molecular motion, lateral force on an isotactic polypropylene (iPP) single crystal was examined as a function of temperature. Single crystals of iPP were prepared by isothermal crystallization from a 1-chloronaphthalene solution with the concentration of 4×10 ^-3 wt% at 383 K for 24 h. Thermal molecular motion for a bulk iPP sample prepared by a melt-quenching method was also examined by dynamic mechanical analysis, hi the case of the single crystal surface, α _a-relaxation process arisen from the segmental motion was observed at approximately 260 K, which was lower than the corresponding bulk value by about 30 K. This result indicates that surface molecular motion in the single crystal is more active than that in the bulk although the surface located on the crystalline phase is quite thin.