Thermal conductivity and mechanical properties of thermally conductive composites based on multifunctional epoxyorganosiloxanes and hexagonal boron nitride

As electronics become portable and compact with concomitant thermal issues, the demand for high-performance thermal interface materials has increased. However, the low thermal conductivity of polymers and the poor dispersion of fillers impede the realization of high filler loading composites, and this in turn limits the increase in thermal conductivity. To overcome this, multifunctional epoxyorganosiloxanes (MEOSs) were synthesized and used to fabricate thermally conductive composites in this study. In the first part of this study, the effect of the molecular weights of MEOSs on the curing behaviors of the MEOSs/trimethylolpropane tris(3mercaptopropioante)/1-methyl imidazole systems was investigated by a DSC analysis. Both the nonisothermal and isothermal curing of the epoxy compositions (ECs) verified that the reaction rate of EC-1 containing MEOS-1 with lower molecular weight was faster than that of EC-2. In addition, mechanical properties of the cured EC-1 were superior to those of its counterpart because of a higher density in crosslinking. In the second part, EC-1 was admixed with h-BN to fabricate thermally conductive (TC) composites. Owing to the low viscosity (1.6 Pa s at 0.1 Hz) of EC-1, a TC-3 composite containing 45 wt% h-BN fillers was obtained, and the in-plane and throughplane thermal conductivity of the cured TC-3 composite reached 3.55 +/- 0.29 Wm- 1K-1 and 1.08 +/- 0.08 Wm- 1K-1, respectively. Furthermore, the tensile modulus of the cured TC-3 was measured as 76.3 +/- 6.1 MPa, which was 9.1 times higher than that of the cured EC-1. Both the high thermal conductivity and good mechanical properties of the cured TC-3 composite were ascribed to the percolation of h-BN networks stemming from the high filler loading.

Automated summary

This study synthesized multifunctional epoxyorganosiloxanes (MEOSs) to fabricate thermally conductive composites, demonstrating that lower molecular weight MEOSs can improve reaction rates and enhance the mechanical properties of cured composites. Furthermore, by mixing EC-1 with h-BN to fabricate composites, high filler loading was achieved, leading to high thermal conductivity and good mechanical properties in the cured composite.