Effect of the length of the substituents on the phase structure and transition behavior of a series of laterally attached side-chain liquid-crystal line polynorbornenes

A series of polynorbornenes (PNBEs) with 1,4-bis[(3'-fluoro-4'-n-alkoxyphen yl)ethynyl]benzene mesogens (n = 1-12, where n is the number of methylene u nits in the substituents of the mesogens) laterally attached to polymer bac kbones through a one-carbon spacer were previously synthesized by the ring- opening metathesis polymerization of the corresponding norbornene-based mon omers. Differential scanning calorimetric results showed that the first-ord er transition temperatures exhibit an odd-even alternation, especially when PNBEs have lower values of n. PNBE (n = 8), similar to the previously stud ied PNBEs (n = 9-12), shows a smectic C (S-C) phase at room temperature (Ki m, Pugh, and Cheng, Macromolecules, 33, 8983, 2000.) According to one- and two-dimensional wide-angle X-ray scattering experiments, PNBEs (n = 2-7) ex hibit a nematic (N) phase with S-C fluctuations, whereas for PNBE (n = 1), only an N phase is observed. (C) 2001 John Wiley & Sons, Inc.*.