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

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), H-1 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-Abased benzoxazine (BA-a), especially the char yields at 800 degrees 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.