Novel atropisomeric binaphthol containing comb-shaped copolymers forming chiral nematic phases

Novel comb-shaped liquid crystalline acrylic copolymers consisting of nematogenic methoxy-phenylbenzoate acrylic monomers (A) together with novel chiral binaphthol (BN) methacrylic monomers (MB-m) were synthesized in this study. The prepared copolymers differ in spacer lengths of MB-m (m = 3, 5, 11) and in their compositions. The homopolymers of the three new chiral BN monomers MB-m were also prepared. Copolymers with a low concentration of BN monomeric units (less than 16 mol %) display a cholesteric mesophase. The induced chirality in the polymers is due to atropisomerism (chirality due to hindered rotation around single bonds) of the BN molecules. The helical twisting power β (HTP) caused by the atropisomeric units in the synthesized copolymers was shown to decrease significantly on heating. The unusually high negative temperature coefficient of HTP observed above the glass transition temperature (T_g) could be explained in terms of conformational changes of the BN molecules in the copolymers.