A powerful strategy to enhance the thermal conductivity of liquid crystalline epoxy resin (LCER) by simply replacing the conventional amine cross-linker with a cationic initiator was developed. The cationic initiator linearly wove the epoxy groups tethered on the microscopically aligned liquid crystal mesogens, resulting in freezing of the ordered LC microstructures even after curing. Owing to the reduced phonon scattering during heat transport through the ordered LC structure, a dramatic improvement in the thermal conductivity of neat cation-cured LCER was achieved to give a value ∼141% (i.e., 0.48 W/mK) higher than that of the amorphous amine-cured LCER. In addition, at the same composite volume fraction in the presence of a 2-D boron nitride filler, an approximately 130% higher thermal conductivity (maximum ∼23 W/mK at 60 vol %) was observed. The nanoarchitecture effect of the ordered LCER on the thermal conductivity was then examined by a systematic investigation using differential scanning calorimetry, polarized optical microscopy, X-ray diffraction, and thermal conductivity measurements. The linear polymerization of LCER can therefore be considered a practical strategy to enable the cost-efficient mass production of heat-dissipating materials, due to its high efficiency and simple process without the requirement for complex equipment.

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Liquid crystal epoxy resins (LCERs) with high thermal conductivity have been drawing significant attention to overcome the thermal conductivity limitation of polymeric composites. Nonetheless, the strategy to enhance the thermal conductivity of LCERs has been primarily focused on improving the well-ordered molecular structure originated from LC phases to reduce phonon scattering. Furthermore, other important factors for the enhancement of thermal conductivity such as intermolecular interaction, fine-tuning of the polymer chain structure, and interchain conjugation have been rarely investigated for LCERs. Here, we introduce a dual-functional LCER enabling the creation of well-ordered microstructures as well as intermolecular π-conjugation networks synergistically suppressing the phonon scattering. As a key design functional group, the diphenyldiacetylene (DPDA) mesogen was employed to assemble a highly ordered lamellar microstructure and create interchain π-conjugation networks via topochemical polymerization of well-organized diacetylenes. The thermal conductivity of cured DPDA epoxy resin with a highly ordered lamellar structure (∼0.43 W m −1 K −1 ) was 194% compared to a commercial epoxy resin (∼0.22 W m −1 K −1 ). Thermal conductivity was further increased up to 227% (∼0.50 W m −1 K −1 ) via post-topochemical polymerization of diacetylenes, leading to π-conjugation and interchain π−π stacking. Furthermore, the thermal conductivity of the composites prepared with hexagonal boron nitride fillers was also increased by 19% after simple heat treatment of the composites, inducing topochemical polymerization of diacetylenes. Finally, a striking thermal conductivity increase from 10.3 W m −1 K −1 to 18.3 W m −1 K −1 was observed by simply replacing the matrix from the commercial one to DPDA epoxy resin (DPDAER), clearly revealing the superiority of our DPDAER in the development of high-thermalconductivity composites.

Boron nitride (BN) nanofiller-based polymer composites have been considered promising candidates for efficient heat-dissipating packaging materials because of their superior thermal conductivity, mechanical strength, and chemical resistance. However, strong aggregation of the BN nanofillers in the composite matrix as well as the difficulty in the modification of the chemically inert surface prevents their effective use in polymer composites. Herein, we report an effective method by using in situ stabilizers to achieve homogeneous dispersion of boron nitride (BN) nanofillers in an epoxy-based polymeric matrix and demonstrate their use as efficient heat-dissipating materials. Poly(4-vinylpyridine) (P4VP) is designed and added into the epoxy resin to produce in situ stabilizers during preparation of hexagonal BNs (h-BNs) and BN nanotubes (BNNTs) dispersion. In-depth experimental and theoretical studies indicated that the homogeneous distribution of BN nanofillers in epoxy composites achieved by using the in situ stabilizer enhanced the thermal conductivity of the composite by ∼27% at the same concentration of the BN nanofillers. In addition, the thermal conductivity of the h-BN/epoxy composite (∼3.3 W/mK) was dramatically improved by ∼48% (4.9 W/mK) when the homogeneously dispersed BNNTs (∼1.8 vol %) were added. The concept of the proposed in situ stabilizer can be further utilized to prepare the epoxy composites with the homogeneous distribution of BN nanofillers, which is critical for reproducible and position-independent composite properties.