High intrinsic thermal conductivity and low dielectric constant of liquid crystalline epoxy resins with fluorine-containing semi-IPN structures

High integration, high frequency, high power, and miniaturization of electrical and electronic devices have raised higher demands for epoxy resins with both high intrinsic thermal conductivity and low dielectric properties. Herein, a series of linear fluorinated epoxy copolymers (poly(PFS-co-GMA)) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Poly(PFS-co-GMA) was introduced into the cross-linked network of a biphenyl-based liquid crystalline epoxy (LCE) by forming a semi-interpenetrating polymer network (semi-IPN). The prepared liquid crystalline epoxy resins (LCERs) simultaneously exhibited high intrinsic thermal conductivity and low dielectric properties. The molar mass and mass fraction of poly(PFS-co-GMA) were found to have a profound effect on the thermal conductivity and dielectric performance of LCERs. For instance, poly(PFS-co-GMA) with the number average molar mass (M_n) of 4300 and 7800 g/mol showed a decreasing effect on the thermal conductivity (λ) of LCERs whereas the polymer with M_n of 10500 g/mol enhanced the λ. The intrinsic λ of LCERs increased to a remarkable highest value of 0.40 W/(m K), which was twice that of conventional epoxy resin (0.20 W/(m·K)). In addition, introducing poly(PFS-co-GMA) would significantly decrease the dielectric constant (ε) and dielectric loss tangent (tanδ) of LCERs from 3.44 and 0.035 to 2.49 and 0.001 at 1 MHz, respectively. Notably, the ε and tanδ could remain relatively stable over a wide range of frequencies and temperatures up to 120 °C. Additionally, the semi-IPN structure enhanced the hardness, electrical insulation, and hydrophobicity of LCERs.