Phase structures, transition behavior, and surface alignment in polymers containing rigid-rod backbones with flexible side chains. 4. Solid-state C-13 NMR studies of molecular motions in PEFBPs(n) (n=10 and 11)

摘要

"Combined" main-chain/side-chain liquid crystalline (LC) polyesters have been investigated using carbon-13 nuclear magnetic resonance (C-13 NMR), based on the polycondensation of 2,2'-bis(trifluoromethyl)-4,4'-biphenyldicarbonyl chloride with 2,2'-bis{omega-[4-(4-cyanophenyl)phenyoxy]-n-alkoxycarbonyl]}-4,4'-bipheny l diol, abbreviated as PEFBP(n). Variable-temperature cross polarization/magic angle spinning and Bloch decay techniques have been applied to detect the rigid and mobile components of the different ordered structures of PEFBPs(n) (n = 10 and 11). Upon heating, PEFBP(10) possesses a smectic A (S-A) phase at low temperatures followed by a nematic (N) phase, and finally, the isotropization. PEFBP(11) exhibits a low-temperature crystalline (K-O) phase, two high-temperature crystalline (K-T1 and K-T2) phases, and a N phase prior to isotropization. The NMR analyses indicate that the backbones and side-chain mesogens are involved in both the formation of the N phases and the construction of the smectic and crystalline structures. The detectable gauche conformations of the methylene units in the side chains provide experimental evidence that both the side-chain mesogens and the backbones parallel align and pack into one crystal lattice or LC phases. The proton spin-lattice relaxation in the rotating frame (T-H(1 rho)) and spin-spin relaxation (T-H(2)) experiments show single-exponential decays of intensities with respect to the spin lock time or delay time in both the S-A phase of PEFBP(10) and the crystalline phases of PEFBP(11), indicating that the systems have uniform dynamics. The side chains and the backbones are not; separated into individual domains on a scale of several nanometers in the S-A phase of PEFBP(10) and the crystalline K-T2 phase of PEFBP(11). [References: 39]