New Polymer Syntheses 87. Thermosetting Nematic or Cholesteric Diesters Having Propargyl Endgroups

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.

Synthesis and Properties of a Liquid Crystalline Thermoset Epoxy Resin Containing 1,3,4-Oxadiazole Groups

“…The LCT concept is compatible with a wide variety of mesogens and crosslinking end groups. Mesogens with epoxy [7][8][9][10], acrylate and methacrylate [11][12][13] and nadimide [14][15][16][17][18], vinyl [19,20], isocyanate and cyanate ester [21][22][23][24], and ethynyl [25][26][27] end groups have been investigated. Studies have examined the effect of molecular architecture on the liquid crystalline phases in the monomers [15,[24][25][26][27][28], cure reactions in ordered phases [29][30][31][32][33], mechanical properties [9,[34][35][36][37][38][39], diffusion behavior [9,40,41], alignment by external fields [11,37,[42][43][44]…”

Liquid Crystalline Bispropargyl Thermosets

“…This is the same general scheme that has been used previously to prepare LCTs with a wide variety of cross-linking end groups. 8,10,11,27 The end-capping reagent was synthesized by the reaction of propargyl chloride with methyl-4-hydroxybenzoate under Williamson ether synthesis conditions. The methyl ester thus obtained was hydrolyzed under basic conditions in aqueous methanol and converted to the acid chloride using oxalyl chloride.…”

“…Only one other publication in addition to our previous report has described propargyl LCTs. 26,27 However, where their interest was in developing cholesteric materials with unique optical textures, we have focused on understanding the phase behavior during cure.…”

Non-symmetrical liquid crystal dimers armed with azobenzene and 1,2,3-triazole-cholesterol

“…[40] 4-Hydroxybenzoic acid (3 g, 21.7 mmol) was dissolved in a solution of KOH (2.3 g, 43.4 mmol) in 15 ml water. The solution of propargylbromide (3.8 g, 32.6 mmol) in 10 ml of ethanol was added dropwise to the earlier prepared mixture and refluxed with stirring for 20 hours.…”