Molecular orientation of aromatic polycarbonates containing fluorene side chains by polarized infrared spectroscopy and birefringence analysis

The molecular orientation of an aromatic polycarbonate containing fluorene side chains was investigated by polarized infrared spectroscopy and birefringence analyses. The copolymers were synthesized from 2,2-bis(4-hydroxyphenyl)propane (BPA), 9,9-bis(4-hydroxy-3-methylpheny)fluorene (BMPF), and phosgene by interfacial polycondensation. The 1449-cm−1 band of the uniaxially oriented films, stretched at the glass-transition temperature (Tg) plus 5 °C, was assigned to various combinations of CC stretching and CH in-plane bending vibrations in the fluorene ring, and the transition moment angle was estimated to be 90°. The intrinsic birefringence of aromatic polycarbonate films with BMPF molar ratios ranging from 0.5 to 1 was obtained with the 1449-cm−1 band. The copolymer was estimated to show zero intrinsic birefringence at the BMPF molar ratio of 0.75, and the BMPF homopolymer showed negative intrinsic birefringence. A linear relationship between the volume fraction of BMPF units and the intrinsic birefringence indicated that the two monomer units of BPA and BMPF in each copolymer were not independent, and an intrinsic birefringence could be defined even in the copolymer. The sign of the photoelastic coefficient in the homopolymer with BMPF units was positive. The different signs of the photoelastic coefficient and the intrinsic birefringence suggest that the fluorene side-chain orientation induced by stress in the glass state is quite different from the orientation of the uniaxially oriented films stretched at Tg + 5 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1554–1562, 2003