Thermal Conductivity and Orientation Structure of Liquid Crystalline Epoxy Thermosets Prepared by Latent Curing Catalyst

Abstract

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a diglycidyl ether of 1-methyl-3-(4-phenylcyclohex-1-enyl)benzene was successfully synthesized as an LC epoxy and the LC temperature range was evaluated via differential scanning calorimeter (DSC). The synthesized LC epoxy was cured with m-phenylenediamine (m-PDA) as an amine-type curing agent and 1-(2-cyanoethyl)-2-undecylimidazole (CEUI) as a latent curing catalyst, respectively. The LC phase structure and domain size of the resultant epoxy thermosets were analyzed through X-ray diffraction (XRD) and polarized optical microscopy (POM). High thermal conductivity was observed in the m-PDA system (0.31 W/(m·K)) compared to the CEUI system (0.27 W/(m·K)). On the other hand, in composites loaded with 55 vol% Al2O3 particles as a thermal conductive filler, the CEUI composites showed a higher thermal conductivity value of 2.47 W/(m·K) than the m-PDA composites (1.70 W/(m·K)). This difference was attributed to the LC orientation of the epoxy matrix, induced by the hydroxyl groups on the alumina surface and the latent curing reaction.

Advancements in The Cross-Linking and Morphology of Liquid Crystals

“…The use of m-phenylenediamine (m-PDA) as a hardener causes changes in the process when the conversion of the epoxy group increases significantly in the early stage of hardening and then gradually decreases [33]. Studies indicate that m-PDA, in comparison to other compounds, leads to a superior alignment of liquid crystal mesogens [34]. The kinetics of the hardening reaction also depend on the stereochemical components of the hardener.…”

“…hardening and then gradually decreases [33]. Studies indicate that m-PDA, in comparison to other compounds, leads to a superior alignment of liquid crystal mesogens [34]. The kinetics of the hardening reaction also depend on the stereochemical components of the hardener.…”