Synthesis, characterization, and thermomechanical properties of liquid crystalline epoxy resin containing ketone mesogen

Abstract

This study focuses on the synthesis of a novel liquid crystalline epoxy resin (LCER) based on ketone mesogenic group. The chemical structure, melting range, and liquid-crystalline phase transition behavior of the LCER were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, mass spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Two endothermal peaks and one exothermal peak appeared in the DSC curves. A birefringent liquid crystalline texture was observed with POM during heating. The curing reaction of the LCER was monitored by DSC using diaminodipheylmethane (DDM) and diaminodiphenylsulfone (DDS) as curing agents, respectively. The results showed that the curing reaction of LCER/DDM proceeded faster than that of LCER/DDS in the initial stage. Birefringence was observed with POM during the curing processes. The results of thermomechanical properties showed that the glass transition temperatures of the cured LCERs were higher than 2308C, and that the LCER crosslinked networks were thermally stable up to 3608C. The LCER crosslinked networks showed much higher glass transition temperature, storage modulus, and thermal conductivity, and a lower coefficient of thermal expansion both in the glassy region and the rubbery region compared to those of a common epoxy resin (diglycidyl ether of bisphenol A).

Preparation and Thermomechanical Properties of Ketone Mesogenic Liquid Crystalline Epoxy Resin Composites with Functionalized Boron Nitride

“…The K–LCE was synthesized following the method described in our previous work [ 9 ]. The synthetic route of K–LCE is shown in Scheme 1 .…”

“…However, common epoxy resins have poor thermal properties such as high CTE and low thermal conductivity (0.17–0.20 W/m·K), but these properties of epoxides can be improved by the rigid rod structures with liquid crystalline characteristics introduced [ 5 , 6 , 7 , 8 ]. We have reported that the liquid crystalline (LC) epoxy resin exhibited much lower CTE and a higher thermal conductivity (0.34 W/m·K) compared to those of a traditional epoxy resin (DGEBA) [ 9 ]. In general, the ICs are encapsulated by silica-filled epoxy composites, but the thermal conductivity of the composites is less than 1.0 W/m·K, which is far below the demand of ICs heat dissipation [ 10 ].…”

Fracture toughness of highly ordered liquid crystalline epoxy thermosets achieved by optimized composition of curing agents

“…This is attributed to the induced molecular orientation in the networked epoxy polymer chains. Frequently used mesogenic backbone structures include biphenyl, [4][5][6][7] terphenyl, 8 stilbene, [9][10][11][12][13][14][15][16][17][18][19][20] azomethine, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] ester, [37][38][39][40][41][42][43][44][45][46][47][48][49] ketone, 50 and azo. 51,52 In an earlier study, we reported a remarkable improvement in both the thermal and mechanical properties.…”

Synthesis of multifunctional liquid crystalline epoxy resin embedded cyclic-siloxane chain with Tg-less behavior and enhanced toughness

“…Liquid crystalline (LC) epoxy resins are known to give both excellent mechanical and thermal properties due to the rigid mesogenic structure existing in the backbone moiety of networked polymer chains, such as biphenyl, 3 –7 stilbene, 8 –17 azomethine, 18 –27 ester, 28 –39 ketone, 40 and azo. 41,42 We have reported a remarkable improvement in fracture toughness and suggested the toughening mechanism of LC epoxy thermosets based on an analysis of the fracture process.…”