Abstract
4-Propargyloxy benzoic acid, 6-propargyloxy-2-naphthoic acid and 4′-propargyloxybiphenyl-4-carboxylic acid were synthesized from the corresponding hydroxy acids and converted into the acid chlorides. Diesters were then prepared by the reaction of these acid chlorides with diphenols such as hydroquinone, methylhydroquinone n-octylthiohydroquinone and phenylhydroquinone. Most of these diesters form an enantiotropic nematic melt but some diesters form a monotropic liquid crystal phase. Cholesteric phases were observed for diesters of (S)-2-methylbutylthiohydroquinone. Diesters derived from 6-propargyloxy-2-naphthoic acid begin to crosslink above 200 °C with an optimum cure temperature of 240–250 °C. The crosslinking of the 4′-propargyloxybiphenyl-4-carboxylic acid derivatives occurs at a temperature 60 °C higher. Several diesters crosslink in the nematic state, but most of them undergo isotropization before completion of the crosslinking process. Numerous cholesteric blends of nematic diesters and chiral diesters of isosorbide were studied and Grandjean textures with bright colours were found. Thermal crosslinking in the cholesteric phase was feasible in several cases.
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