Enhancing intrinsic thermal conductivities of epoxy resins by introducing biphenyl mesogen-containing liquid crystalline co-curing agents

Epoxy resins were prepared with an enhanced intrinsic thermal conductivity of 0.42 W (m K)−1 using a biphenyl mesogen-containing co-curing agent.

Discotic Liquid Crystal Epoxy Resins Integrating Intrinsic High Thermal Conductivity and Intrinsic Flame Retardancy

The integration of intrinsic thermal conductivity and intrinsic flame retardancy of epoxy resins shows wider application prospects in electricals and electronics. Discotic liquid crystal epoxy (D-LCE) is synthesized from pyrocatechol, 2-allyloxyethanol, and 3-chloroperoxybenzoic acid. P/Si synergistic flame-retardant co-curing agent (DOPO-POSS, DP) is synthesized from p-hydroxybenzaldehyde, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), and amino terminated polysilsesquioxane (POSS). Finally, D-LCE is cured within liquid crystal range with 4, 4'-diaminodiphenyl methane (DDM) and DP, to obtain intrinsic highly thermal conductive/flame-retardant epoxy resins (D-LCER_DP ). D-LCER_DP-10.0 (10.0 wt% DP) synchronously possesses excellent intrinsic thermal conductivity and intrinsic flame retardancy, with thermal conductivity coefficient in vertical and parallel direction (λ_⊥ and λ_∥ ) of 0.34 and 1.30 W m^-1 K^-1 , much higher than that of general bisphenol A epoxy resin (E-51, λ_⊥ of 0.19 W m^-1 K^-1 , λ_∥ of 0.65 W m^-1 K^-1 ). The limiting oxygen index (LOI) value of D-LCER_DP-10.0 reaches 31.1, also better than those of E-51 (19.8) and D-LCER (21.3).

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

In order to enhance the thermomechanical behaviors of epoxy molding compounds, the hexagonal boron nitride (h-BN) fillers were incorporated in a ketone mesogenic liquid crystalline epoxy (K–LCE) matrix to prepare a high-performance epoxy composites. The h-BN was modified by surface coupling agent 3-aminopropyltriethoxysilane (APTES). The grafting of silane molecules onto the surface of BN fillers improved the compatibility and homogeneous dispersion state of BN fillers in the K–LCE matrix with a strong interface interaction. The surface-modified BN fillers were characterized using Fourier transform infrared spectroscopy. The thermomechanical properties and morphologies of K–LCE/BN composites loading with different contents of modified BN fillers, ranging from 0.50 to 5.00 wt%, were investigated. These results show that modified BN fillers uniformly dispersed in K–LCE matrix, contributing to the enhancement in storage modulus, glass transition temperatures, impact strength and reduction in the coefficient of thermal expansion (CTE). The thermal stability and char yield of the K–LCE/BN composites were increased by increasing the amount of modified BN fillers and the thermal decomposition temperatures of composites were over 370 °C. The thermal conductivity of the K–LCE/BN composites was up to 0.6 W/m·K, for LC epoxy filled with 5.00-wt%-modified BN fillers. Furthermore, the K–LCE/BN composites have excellent thermal and mechanical properties compared to those of the DGEBA/BN composites.

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

A novel tetrafunctional mesogenic epoxy monomer with a cyclic-siloxane chain as a central part was successfully synthesized and characterized by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, and polarized optical microscopy. The transition temperature and liquid crystallinity of cyclic-siloxane type mesogenic epoxy were compared with those of linear-siloxane type mesogenic epoxy. Moreover, epoxy thermosets were prepared based on the cyclic- and linear-siloxane type mesogenic epoxy monomers and 4,4′-diaminodiphenylethane. The effects of epoxy backbone moiety on thermal and mechanical properties were investigated in detail. As a result, the cyclic-siloxane type mesogenic epoxy thermoset shows glass transition temperature-less behavior and low coefficient of linear thermal expansion without a decrease in toughness.