Synthesis and Crosslinking of a Series of Dimeric Liquid Crystalline Epoxy Resins Containing Imine Mesogens

Abstract

Eight aromatic imine liquid crystalline (LC) diepoxides with dimeric architecture from readily available commercial reagents were synthesized and characterized by spectroscopic techniques. We characterized their liquid crystalline mesophases by differential scanning calorimetry (DSC), hot‐stage polarized‐light optical microscopy (POM) and wide‐angle X‐ray diffraction (WAXS). The mesomorphism of the products was related to their structure, which varies in the length of the central spacer. Odd‐membered spacer mesogens lead to the formation of smectic C mesophases, whereas even‐membered samples of this series lead to the formation of smectic A and/or nematic mesophases. By relating the calculated molecular parameters to the layer spacings obtained by WAXS, we deduced the organization of the mesogens in the smectic phases, since the dimeric compounds present a variety of possible arrangements. Liquid crystal thermosets (LCTs) were obtained from these monomers by isothermal curing with equimolar amounts of 2,4‐diaminotoluene (DAT). The curing process was studied by calorimetry and their thermal stability was evaluated by thermogravimetry (TGA). Most monomers produced nematic‐like networks, but in one case a smectic C mesophase was also locked.

Novel Triaromatic Ester Mesogenic Liquid Crystalline Epoxy Resin Containing Both Methyl Substituent and Ethoxy Flexible Spacer: Synthesis and Curing

“…[17,28] Various authors have observed that the introduction of a flexible spacer that decouples the reactive end-functional group from the rigid-rod mesogenic group can also lower the melting temperature and increase the mesophase stability of LCER in most cases. [4,5,23,25,[29][30][31][32][33][34][35][36][37] Galià and co-workers have synthesized phenylhydroquinine bis-6-[6-(glycidyloxy)hexyloxy]-2-naphthoate (Gly A) from 6-hydroxy-2-naphthoic acid. A nematic mesophase was observed between 109 and 123 8C on heating and between 123 8C and room temperature on cooling.…”

Synthesis and improved mechanical properties of twin‐mesogenic epoxy thermosets using siloxane spacers with different lengths

“…LC epoxy thermosets contain rigid mesogenic groups in their backbone moiety of network chains, such as biphenyl, [9][10][11][12] stilbene, [13][14][15][16][17][18][19][20][21] azomethine, [22][23][24][25][26][27] ester, [28][29][30][31][32][33] azo, 34,35 and other, 36 which show excellent mechanical and thermal properties. LC epoxy thermosets contain rigid mesogenic groups in their backbone moiety of network chains, such as biphenyl, [9][10][11][12] stilbene, [13][14][15][16][17][18][19][20][21] azomethine, [22][23][24][25][26][27] ester, [28][29]…”

Curing behavior of Azo‐containing twin liquid crystalline epoxy resins with anhydride

“…Although a few models were employed to study the curing kinetics and phase changes, none of them is on the curing reaction of twin LC epoxy resins, which are prone to form a smectic mesophase [16–18]. Twin LC epoxy resins containing azomethine [19, 20] and aromatic ester [21] were synthesized respectively by Ribera and Ober.…”