Conformation and orientation analysis of modified polyglutamates in thin films by ATR infrared spectroscopy

Abstract The molecular conformation and orientation in solution cast films of poly(-methyl l -glutamate) x -co-( γ - n -octadecyl l -glutamate) y ), a coplymer of the ‘hairy rod’ type, was investigated by ATR FTIR spectroscopy. The influence of a structured interface on the molecular order of the polymer film was studied by introducing mechanical grooves in the surface of the solid support (ATR crystal). The resulting preferential orientation of the ‘hairy rods’ was quantified by recording polarized IR-spectra and yielded an order parameter of S = 0.8. A necessary condition for orientation was a high enough mobility of the molecules, which could be obtained by a swelling of the film in solvent vapor. Temperature dependent measurement revealed the influence of the molecular composition, i.e. the mole fraction y of the long side chain, on the phase state of the ‘hairy rod’ molecules. Our results are in agreement with the model by Tsujita et al. [Y. Tsujita, R. Ojika, K. Tsuzuki, A. Takizawa, T. Kinoshita, J. Polym. Sci., Part A: Polym. Chem. 25 (1987) 1041], proposing a glassy phase state of the long side chains for small mole fractions and a partly crystalline phase for high mole fractions.