Diacetylene-Containing Dual-Functional Liquid Crystal Epoxy Resin: Strategic Phase Control for Topochemical Polymerization of Diacetylenes and Thermal Conductivity Enhancement

Abstract

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 pi-conjugation networks synergistically suppressing the phonon scattering. As a key design functional group, the diphenyl-diacetylene (DPDA) mesogen was employed to assemble a highly ordered lamellar microstructure and create interchain pi-conjugation networks via topochemical polymerization of well-organized diacetylenes. The thermal conductivity of cured DPDA epoxy resin with a highly ordered lamellar structure (similar to 0.43 W m(-1) K-1) was 194% compared to a commercial epoxy resin (similar to 0.22 W m(-1) K-1). Thermal conductivity was further increased up to 227% (similar to 0.50 W m(-1) K-1) via post-topochemical polymerization of diacetylenes, leading to pi-conjugation and interchain pi-pi 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-thermal-conductivity composites.