Surface Molecular Motion of Monodisperse α,ω-Diamino-Terminated and α,ω-Dicarboxy-Terminated Polystyrenes

Abstract

Surface glass transition behaviors of monodisperse α,ω-diamino-terminated and α,ω-dicarboxy-terminated polystyrenes (α,ω-PS(NH2)2 and α,ω-PS(COOH)2) were studied by scanning force microscopy and were compared with the results of proton-terminated polystyrene (PS−H). All surface glass transition temperatures, Tgs, of PS−H, α,ω-PS(NH2)2, and α,ω-PS(COOH)2 were discernibly lower than each corresponding bulk glass transition temperature, Tgb. However, the magnitude of Tgs was strongly dependent on the chemical structure of chain end groups, because the surface concentration of chain ends varied with the surface free energy difference between the main chain part and the chain end portion, via the surface segregation or surface depletion of chain ends. This result makes it clear that chain end chemistry is one of determining factors on the magnitude of Tgs. On the basis of the time−temperature superposition principle applied to the scanning rate dependence of lateral force as a function of temperature, the appa...