Glass transition temperature and conformational changes of poly(methyl methacrylate) thin films determined by a two-dimensional map representation of temperature-dependent reflection-absorption FTIR spectra

Abstract

Temperature-dependent reflection-absorption Fourier transform infrared spectra of poly(methyl methacrylate) (PMMA) thin films were measured. From these spectra, two-dimensional (2D) maps of the first derivative of the absorbance with respect to temperature over the space of wavenumber and temperature were constructed. These maps were used to determine the glass transition temperature and to investigate the subtle temperature dependence of the population of trans and gauche conformers in three PMMA thin films with different stereoregularities. The glass transition temperatures determined from the 2D maps for isotactic, syndiotactic, and atactic PMMA thin films were approximately 61,111, and 106 degreesC, respectively. Calculations of the fraction of gauche conformation from the conformational energy showed an abrupt increase in the population of the gauche conformer above the glass transition temperature. The temperature dependence of the fraction of gauche conformation was well reflected in our 2D maps. Furthermore, it was found that molecular reorganization of PMMA occurs even below the glass transition temperature.