Low dielectric constant and high thermal stability of liquid crystal epoxy polymers based on functionalized poly(phenylene oxide)

Abstract

Epoxy resins exhibit poor thermal and dielectric properties because of the disordered entanglement of the chain segments and a large number of hydroxyl groups generated after curing by diamine curing agents. Herein, to prepare high-Tg and low-dielectric epoxy thermosets, two functionalized poly(phenylene oxide) (PPOs) were synthesized by redistribution and esterification reactions and used as curing agents to cure liquid crystal epoxy (t-BPDGE). The modified PPOs (TMPA and TMBPA) contain six active ester functional groups, which not only improved the compatibility and the degree of cross-linking of the PPOs with the epoxy monomers but also avoided the generation of hydroxyl groups after curing. The curing mechanism was investigated using TBB cured glycidyl phenyl ether as a model reaction, and the effects of TMPA and TMBPA on the curing behavior and performances were also studied. Due to the ordered arrangement of the liquid crystal epoxy resins and the presence of PPOs, the overall performances of PPOs-based/t-BPDGE are significantly improved. Specifically, the results showed that TMPA/t-BPDGE possessed a high glass transition temperature (Tg) of 199.47 °C and a char rate of 21.84%, which was 77.09 °C and 3.63 times higher than that of the DDM/t-BPDGE, respectively. Moreover, TMPA/t-BPDGE exhibited a lower moisture absorption (0.23%), dielectric constant and loss (2.94 and 0.00815 at 1 GHz) compared to the DDM/t-BPDGE (0.48%, 3.95 and 0.01898, respectively). The findings provide a new design strategy for preparing high-Tg and low-dielectric epoxy thermosets.