Abstract
Poly(fumarate)s possess rigid main-chain moieties originating from the steric hindrance of densely packed side-chains. Besides such rigid characteristics, one of the most important features of poly(fumarate)s is the capability to vary the number and nature of side-chain functionality especially when mesogenic groups are anchored. Fumarate monomers carrying two mesogenic groups (abb. Bis-F) can be polymerized to afford the polymethylenes with the doubled mesogen density as compared to the ordinary α-olefin polymers, leading to a facile appearance of liquid crystal phase. Polymerization of fumarate monomers carrying an isopropyl and a mesogenic group (abb. Mono-F) similarly provides the corresponding rigid polymethylenes with the same mesogen density as α-olefin polymers. Copolymerization of Bis-F and Mono-F yields the polymethylenes with the intermediate mesogen density. In this paper, the phase transition behaviors of a series of novel poly(fumarate)s with different cyanobiphenyl mesogen density were studied. Although poly(Bis-F) exhibited the smectic phase, copoly(Bis/Mono-F) showed the nematic phase and poly(Mono-F) did not display any liquid crystalline phases. Moreover, the liquid crystalline temperature range was very wide for poly(Bis-F). These results clearly suggest that higher mesogen density is more advantageous for realization of well-ordered liquid crystalline phases, such as smectic phase, in side-chain liquid crystalline polymers.
