MOLECULAR-STRUCTURE AND GLASS-TRANSITION TEMPERATURE OF SURFACE-LAYERS OF POLYMETHYL METHACRYLATE FILMS FROM THE DATA OF IR-SPECTROSCOPY

Features of the molecular structure of surface layers of PMMA films have been studied and T(g) has been determined by the IR-spectroscopy method. Near the interface the PMMA macromolecules are characterized by the enhanced content of the high-energetic tg-conformers and by the decrease of the fraction of the energetically more advatageous tt-conformers. The concentration of tg-conformers monotonicaly increases with decrease of the thickness of a polymer film d, beginning from d = 10 mcm. For d < 4 mcm the strengthening of the intermolecular interactions between side fragments of the chain is observed. The complicated (nonmonotonic) character of the change of T(g) has been detected. T(g) decreases with decrease of the film thickness beginning from 10 mcm and attaines the minimum at d = 3.5 mcm, then T(g) begins to enhance. Such change of T(g) is explained in the framework of the Gibbs-DiMarcio theory of the glass transition relating T(g) with turn-isomeric characteristics of a polymer chain.