Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene (PS) with sec-butyl and proton-terminated end groups atroom temperature. In the case of the number-average molecular weight

Mn

less than ca. 4.0×104

the surface was in a glass-rubber transition state even though the bulk glass transition temperature

Tg was far above room temperature

meaning that the surface molecular motion was fairly active compared with that in the bulk.LFM measurements of the monodisperse PS films at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to the surface mechanical relaxation behavior and also that the surface glass transition temperature

Tg

was depressed in comparison with the bulk one even though the magnitude of MN was fairly high at 1.40×105.The surface molecular motion of monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanning viscoelasticity microscopy (TDSVM).The tgσs for the PS films with Mn of 4.9 × 103 to 1.45×106 measured by TDSVM were smaller than those for the bulk one

with corresponding Ms

and the Tgσs for Mns smaller than ca.4.0 ×104 were lower than room temperature (293 K).The active thermal molecular motion at the polymeric solid surface can be interpreted in terms of an excess free volume near the surface region induced by the surface localization of chain end groups.In the case of Mn=ca.5.0×104

the Tgσs for the α

ω-diamino-terminated PS(α

ω-PS(COOH)2) films were higher than that of the PS film.The change of Tgσ for the PS film with warious chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region depending on the relative hydrophobicity.