Jinjin Dang, Junliang Zhang*, Mukun Li, Lin Dang and Junwei Gu*. Enhancing intrinsic thermal conductivities of epoxy resins by introducing biphenyl mesogen-containing liquid crystalline co-curing agents. Polymer Chemistry, 2022, 13(42): 6046-6053. 2021IF=5.364.

https://doi.org/10.1039/D2PY01157C

In this work, a biphenyl liquid crystalline small molecule (BLCM) containing flexible units was synthesized via a one-step condensation reaction of 4,4′-dihydroxybiphenyl (BP) and 1,6′-dibromohexene. Then, the commercially available bisphenol A epoxy (E-51) was used as a matrix, 4,4′-diaminodiphenylmethane (DDM) as a curing agent, and the BLCM as a co-curing agent to prepare highly intrinsic thermally conductive liquid crystalline epoxy resins (LCER) by a casting method. Nuclear magnetic resonance spectroscopy, high-resolution mass spectroscopy, and Fourier transform infrared spectroscopy demonstrated that the BLCM with a designed structure was synthesized successfully. Wide-angle X-ray diffraction, small-angle X-ray scattering, and polarized light microscopy proved that the inter-stacking of biphenyl mesogens promoted the formation of locally ordered regions in the LCER. Meanwhile, the ordered structure of the LCER was enhanced with an increase of the BLCM mass fraction, resulting in the higher intrinsic thermal conductivity. When the mass fraction of the BLCM was 60% of E-51 (LCER3), the thermal conductivity (λ) of LCER3 was 0.42 W/(m·K), which was 2.1 times that of an epoxy resin cured with DDM only (LCER0, λwas 0.20 W/(m·K)). Besides, LCER3 presented a high heat resistance index (THRI) of 176.8°C, elastic modulus of 4.8 GPa, and hardness of 0.32 GPa, which was also higher than LCER0 with a THRI of 172.2°C, elastic modulus of 3.7 GPa, and hardness of 0.27 GPa.

本文以通用双酚A环氧树脂（E-51）为基体、4,4’-二氨基二苯甲烷（DDM）为固化剂，以4,4’-二羟基联苯（BP）和1,6’-二溴己烯一步缩合反应合成的含柔性基团的联苯型液晶单体（BLCM）为共固化剂，经浇注固化制备本征高导热液晶环氧树脂（LCER）。核磁共振和傅里叶变换红外光谱证明具有预期结构的BLCM已成功合成。广角X射线衍射和偏光显微镜证明联苯液晶基元间的相互堆叠促使局部有序结构的形成，且LCER的结构有序度随BLCM质量分数的增加而增强。当BLCM的质量分数为E-51的60%时，LCER3的导热系数（λ）为0.42 W/(m·K)，是仅用DDM固化的环氧树脂（LCER0）λ（0.20 W/(m·K)）的2.1倍。此外，LCER3兼具良好的热稳定性和力学性能，其耐热指数（THRI）、弹性模量和硬度分别为176.8^oC、4.8 GPa和0.32 GPa，也均优于相应的LCER0（THRI=172.2^oC，弹性模量和硬度分别为3.7 GPa和0.27 GPa）。