Study of the transition temperatures and acid-base properties of poly (methyl methacrylate) adsorbed on alumina and silica, by using inverse gas chromatography technique

The study of phenomena transitions in polymers is of vital importance in material sciences and more particularly when polymers are adsorbed on oxides. In a previous study, we determined the glass transition temperatures of poly (methyl methacrylate) (PMMA) adsorbed on alumina, by using the inverse gas chromatography (IGC) at infinite dilution. This technique proved to be an excellent technique to determine not only the glass transitions, but also beta -transition and liquid-liquid transitions of polymers adsorbed on solid substrates. In this paper, we also used the IGC technique to determine the second order transitions of the systems PMMA/SiO2 and PMMA/Al2O3, at various covered surface fractions and for various tacticities of the polymer (atactic, isotactic and syndiotactic). The maxima of the dispersive component of the surface energy gamma (d)(s) of our two systems, obtained by IGC at infinite dilution, indicated clearly the presence of transition temperatures (glass or local transitions). In general, we observed with PMMA, three principal maxima that reflect the changes in motions leading to reorganisation and rearrangement of the various groups or chain segments of the polymer. The change in the retention mechanism of the probes at the transition temperatures is attributed to an increased molecular mobility of the polymer segments, allowing for the penetration of the probes into the polymer layer. The study of the chemical physical properties of PMMA/SiO2 and PMMA/Al2O3, revealed an important difference in the acidic and basic behaviour, in Lewis terms, of oxide covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the acidic basic character of PMMA adsorbed on oxides. (C) 2001 Elsevier Science B.V. All rights reserved.