Effect of end group chemistry on surface molecular motion of monodisperse polystyrene films

The surface molecular motion of monodisperse polystyrene (PS) with various chain end groups was investigated on the basis of temperature‐dependent scanning viscoelasticity microscope (TDSVM). The surface glass transition temperatures, Tgss for the proton‐terminated PS (PS‐H) films with number‐average molecular weight, Mn of 4.9k–1,450k measured by TDSVM measurement were smaller than those for the bulk one, with corresponding Mns, and the Tgss for Mn smaller than ca. 50k were lower than room temperature (293 K). In the case of Mn = ca. 50k, the Tgss for the α,ω‐diamino‐terminated PS (α,ω‐PS(NH2)2) and α,ω‐dicarboxy‐terminated PS (α,ω‐PS(COOH)2) films were higher than that of the PS‐H film. On the other hand, the Tgs for the α,ω‐perfluoroalkylsilyl‐terminated PS (α,ω‐PS(SiC2CF6)2) film with the same Mn was much lower than those for the PS films with all other chain ends. The change of Tgs for the PS film with various chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region.