| Abstract: | Side-chain liquid crystalline polymers with poly(silphenylene-siloxane) backbones and 4,4′-biphenyl-containing pendant mesogenic groups have been prepared and characterized. Polymers with spacers having only three methylene groups were not liquid crystalline, LC, but those with spacers having eight methylene groups or more and a long terminal substituent were LC as indicated by an isotropization peak on the shoulder of the melting peak in the DSC thermogram and the appearance of a Schlieren texture on examination by polarized light microscopy. However, the LC behavior could not be confirmed by wide-angle X-ray diffraction, WAXD, because the crystalline pattern apparently remained up to the isotropization temperature, presumably because the melting transition and isotropization are too close. In contrast, polymethylsiloxanes with the same mesogenic side-chains revealed the presence of well-defined smectic phases by WAXD as well as by polarized light microscopy. |
