Abstract
Filler with enhanced thermal conductivity, including hexagonal boron nitride and its modified analogues with surface hydroxyl groups, and titanium and zirconium diborides having Lewis acid properties were introduced into polyurethane/epoxy compositions. The curing kinetics of these compositions (with filler loading level 0.5–15 wt%) were studied using dynamic and isothermal DSC and kinetic parameters (rate constants and activation energies) were determined. It was shown that the curing process has complex character and includes several of concurrent reactions, i.e. polyaddition reactions and the cationic polymerization of oxirane rings. The increase of loading level leads to depression of the cationic polymerization of oxirane rings and the formation of less ordered PU/epoxy networks. As a result, the mechanical properties of high-filled compositions were also suppressed (the decrease up to 70% of the initial tensile strength). The thermal conductivity of PU/epoxy compositions increased proportionally to the loading levels with maximal values found for composition filled with surface modified hexagonal boron nitride (1.5-fold increase).
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