Synthesis and characterization of novel side-chain liquid crystalline polycarbonates .3. Dynamic mechanical analysis of the secondary relaxation processes

The dynamic mechanical properties of two homologous series of sidechain liquid crystalline polycarbonates were studied. One series with oxynitro-stilbene mesogenic groups and alkyl spacers of different lengths and another series with phenyl benzoate mesogenic groups with alkoxy tails of different lengths. The influence of spacer length and tail length on the low temperature relaxation processes was investigated. For the polymer with an undecyl spacer also the influence of side group crystallinity on the secondary relaxations was analyzed. A gamma-relaxation could be ascribed to motions of either the spacer or the alkoxy tail. Three different beta-relaxations could be ascribed to the carbonate groups in the backbone and to the mesogenic groups in the frozen liquid crystalline state and in the crystalline state, respectively. The alpha-relaxation, corresponding to the glass transition, showed a strong shift to lower temperatures with increasing spacer length but was hardly influenced by the tail length.