Conformational behaviour of poly (β-aspartate) with n-alkyl side chains in the solid state as studied by 13C-CP/MAS-NMR spectroscopy

Abstract

13C cross-polarization/magic-angle-spinning NMR experiments were carried out for poly (β-aspartate) with long n-octadecyl side chains as a function of temperature, in order to elucidate the conformational feature in the solid state. From the experimental results it was found that the conformational change in the main chain from the right-handed α-helix to the left-handed α-helix occurs within the temperature range 23.5–100°C, while long n-octadecyl side chains take on an all- trans zig-zag conformation in the crystalline state at room temperature and are in a mobile state above 40°C. It is suggested that such a conformational change of the main chain leads to the prevention of the formation of thermotropic liquid crystals in the above temperature range. The main-chain and side-chain conformations of poly (β-aspartate) with n-alkyl side chains of various lengths at room temperature are discussed.