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
Abstract
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.
本文以通用雙酚A環(huán)氧樹脂（E-51）為基體、4,4’-二氨基二苯甲烷（DDM）為固化劑，以4,4’-二羥基聯(lián)苯（BP）和1,6’-二溴己烯一步縮合反應合成的含柔性基團的聯(lián)苯型液晶單體（BLCM）為共固化劑，經(jīng)澆注固化制備本征高導熱液晶環(huán)氧樹脂（LCER）。核磁共振和傅里葉變換紅外光譜證明具有預期結(jié)構(gòu)的BLCM已成功合成。廣角X射線衍射和偏光顯微鏡證明聯(lián)苯液晶基元間的相互堆疊促使局部有序結(jié)構(gòu)的形成，且LCER的結(jié)構(gòu)有序度隨BLCM質(zhì)量分數(shù)的增加而增強。當BLCM的質(zhì)量分數(shù)為E-51的60%時，LCER3的導熱系數(shù)（λ）為0.42 W/(m·K)，是僅用DDM固化的環(huán)氧樹脂（LCER0）λ（0.20 W/(m·K)）的2.1倍。此外，LCER3兼具良好的熱穩(wěn)定性和力學性能，其耐熱指數(shù)（THRI）、彈性模量和硬度分別為176.8oC、4.8 GPa和0.32 GPa，也均優(yōu)于相應的LCER0（THRI=172.2oC，彈性模量和硬度分別為3.7 GPa和0.27 GPa）。
本文亮點
1. 核磁共振和傅里葉變換紅外光譜證明具有預期結(jié)構(gòu)的BLCM已成功合成。廣角X射線衍射和偏光顯微鏡證明聯(lián)苯液晶基元間的相互堆疊促使局部有序結(jié)構(gòu)的形成，且LCER的結(jié)構(gòu)有序度隨BLCM質(zhì)量分數(shù)的增加而增強。
2. 當BLCM的質(zhì)量分數(shù)為E-51的60%時，LCER3的導熱系數(shù)（λ）為0.42 W/(m·K)，是僅用DDM固化的環(huán)氧樹脂（LCER0）λ（0.20 W/(m·K)）的2.1倍。
3. LCER3兼具良好的熱穩(wěn)定性和力學性能，其耐熱指數(shù)（THRI）、彈性模量和硬度分別為176.8oC、4.8 GPa和0.32 GPa，也均優(yōu)于相應的LCER0（THRI=172.2oC，彈性模量和硬度分別為3.7 GPa和0.27 GPa）。
第一作者：黨金金
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