The robustness of a thermoset of a main-chain type polybenzoxazine precursor prepared through a strategy of A–A and B–B polycondensation

Abstract

A polybenzoxazine precursor, P(BF-bapp)-1, was prepared through a strategy of A–A and B–B polycondensation. The A–A monomer is 5,5′-methylenebis(2-hydroxybenzaldehyde), and the B–B monomer is 2,2-bis[4-(4-aminophenoxy)phenyl] propane (BAPP). The inherent viscosity (at 0.5 g dL⁻¹ in NMP) of P(BF-bapp)-1 is as high as 0.34 dL g⁻¹, which is higher than that (0.23 dL g⁻¹) of a structurally similar polybenzoxazine precursor, P(BF-bapp)-2, that was prepared through traditional Mannich condensation of BAPP/bisphenol F/paraformaldehyde. A third structurally similar polybenzoxazine precursor, P(BF-bapp)-3, with an inherent viscosity of 0.09 dL g⁻¹, and a phenol and BAPP-based benzoxazine monomer, P-bapp, were prepared for properties comparison. After thermal curing of the benzoxazines, we found that a benzoxazine thermoset based on a high molecular weight precursor has advantages in higher T_g, higher char yield, lower refractive index (low dielectric constant according to Maxwell's equation), and better mechanical properties. The results demonstrate the robustness of a polybenzoxazine precursor prepared through a strategy of A–A and B–B polycondensation, which has never been reported in the benzoxazine field.