Transition temperatures and molecular structures of poly(methyl methacrylate) thin films by principal component analysis: comparison of isotactic and syndiotactic poly(methyl methacrylate)

This study determines the glass transition temperatures of isotactic and syndiotactic poly(methyl methacrylate) (PMMA) thin films and provides plausible molecular origins by principal component analysis (PCA). Principal components (PCs) are calculated for reflection-absorption FTIR spectra of isotactic and syndiotactic PMMA thin films in two spectral regions, 1000-1800 and 1100-1300 cm−1. The glass transition temperature is assigned to the highest peak (or the lowest valley) in the PC score plot. The glass transition temperatures of isotactic and syndiotactic PMMA thin films thus determined are 60 and 110-120 °C, respectively, which are consistent with existing results obtained by other techniques. The PC loadings indicate that the carbonyl groups giving rise to bands in the range of 1700-1750 cm−1 affect the thermal properties and the flattened structure in the isotactic PMMA thin film but not in the syndiotactic PMMA thin film.