Mesomorphic properties of liquid crystalline polysiloxanes and elastomers based on a tri-vinyl crosslinker

A series of crosslinked liquid crystalline polymers and the corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization; their liquid crystalline properties were characterized by DSC, POM and X-ray measurements. The results show that the crosslinking obtained in the isotropic state leads to a reduction of the clearing point (T-c) of the crosslinked polymers, as compared with the corresponding uncrosslinked polymers. The crosslinked polymers with low crosslinking density (P-1-P-7) exhibit nematic mesogenic phases, as do the uncrosslinked polymers. In contrast, a high crosslinking density leads to the crosslinked polymers P-8 and P-9 losing their thermotropic liquid crystalline phases; they instead exhibit stress-induced orientation.