Effect of side chain structure on the liquid crystalline properties of polymers bearing cholesterol, dihydrocholesterol and bile acid pendant groups

Four methacrylate derivatives of steroid molecules, namely cholic acid methyl ester, lithocholic acid methyl ester, cholesterol and dihydrocholesterol, were synthesized. A 10-carbon spacer separates the rigid core and the polymerizable methacrylate group. These monomers and their corresponding polymers were characterized for their liquid crystalline properties by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. It was found that only the compounds bearing the planar cholesterol-based moieties, and not those bearing the esterified bile acid groups, possess liquid crystalline phases. A detailed X-ray study showed that the dihydrocholesterol polymer possesses the same two mesophases as the cholesterol polymer, but with reduced thermal stability.