Structure and rheology of model side-chain liquid crystalline polymers with varying mesogen length

We probed the structural transitions and rheological properties of norborne ne-based polymeric liquid crystals with attached side mesogenic groups of v arying length. Whereas the short side chain liquid crystals (C5) formed a n ematic mesophase, the long ones (C9) formed a smectic-A solid. The degree o f polymerization of the main backbone affected the isotropic-mesophase tran sition temperatures, but did not influence the change of the mesophase dyna mics from the isotropic to the anisotropic state. The temperature dependenc e of the shift factors obtained from the time-temperature superposition wer e divided into three regions, namely isotropic, mesophase, and transition, all exhibiting Arrhenius behavior except for the nematic fluid, which follo wed a WLF dependence. A remarkable strain hardening observed in both nemati c and smectic samples was attributed to the dynamic coupling of the main ch ain and the mesogenic side groups. By applying large amplitude oscillatory shear, macroscopic alignment was achieved; the long recovery times upon flo w cessation suggested a very slow structural reorganization, which was much longer in the smectics compared to the nematics, possibly due to the invol vement of smaller length scales in the former case.