Thermal Characterization of PMMA Thin Films Using Modulated Differential Scanning Calorimetry

Modulated differential scanning calorimetry was used to probe the thermal behavior of poly(methyl methacrylate) (PMMA) adsorbed onto silica from solution and subsequently dried. Changes in the glass transition were studied as a function of the adsorbed amount and solvent system used to deposit the polymer. The glass transition temperature (Tg) of PMMA was found to increase from 108 °C for the bulk polymer to 136 °C for the polymer adsorbed on silica from toluene (1.0Am). For the polymer adsorbed at approximately half that amount (0.6Am), the glass transition temperature increased to 158 °C. The breadth of the transition also increased from 11 °C for bulk to 61 and 58 °C for the 1.0Am and 0.6Am samples, respectively. when PMMA was adsorbed from a mixed solvent system (5:1 benzene/acetonitrile solution), the transition temperature and its breadth increased even further. For a sample with 0.5Am adsorbed amount from the mixed solvent system, the Tg was increased to 167 °C and the width of the transition was increased to 65 °C. The change in thermal behavior was attributed to polymer chain confinement, resulting in a distribution of segmental mobilities different from that of the bulk polymer. Upon aging for 328 days from the original analysis date, the polymer chains in the 0.6Am sample adsorbed from toluene rearranged, resulting in thermal behavior which was more like that of the 0.5Am sample adsorbed from the mixed solvent system