Synthesis and copolymerization of benzoxazines with low-dielectric constants and high thermal stability

Abstract

Two novel bridged benzoxazole-based benzoxazine monomers, HOH-a and FOH-a, were synthesized using a non-solvent method. The structure of HOH-a and FOH-a was confirmed by Fourier transform infrared spectroscopy (FTIR), 1H NMR, and elemental analysis. The curing behaviors of these two monomers were studied by differential scanning calorimetry and FTIR. The corresponding polybenzoxazines, poly(HOH-a) and poly(FOH-a), display higher thermal stability than the polybenzoxazine from common bisphenol-A-based benzoxazine (BA-a), especially the char yields at 800 °C, which are 61% and 62% for poly(HOH-a) and poly(FOH-a), respectively. Moreover, the dielectric constants and dielectric loss of these polybenzoxazines are low and change slightly at room temperature in the frequency range of 0.1 Hz to 1 MHz. The dielectric constant of poly(FOH-a) in 1 MHz is only 2.21. Furthermore, poly(HOH-a/BA-a) and poly(FOH-a/BA-a) copolymers were prepared, and the thermal stability and dielectric and mechanical properties of these copolymers were studied. The flexural modulus and flexural strength of the poly(FOH-a/BA-a) copolymer can be increased to 66% and 41%, respectively, after the addition of 20 wt.% FOH-a.