Polymer alloys with high thermal properties consisting of polyfunctional benzoxazine derived from an oligonuclear phenolic compound and bismaleimide

Polymer alloy films were prepared by blending a polyfunctional benzoxazine monomer (OP-p), which was derived from an oligonuclear phenolic compound with a 4,4ʹ-dimethylenebiphenyl group as the phenol linker, and 4,4′-bismaleimidodiphenylmethane (BMI; 10–90 wt.%), followed by thermal curing up to 240 °C. The polymerization behavior was investigated via differential scanning calorimetry and Fourier transform infrared analyses; the results indicated that the obtained polymer alloys consisted of an AB crosslinked network structure formed through the ether linkage between the hydroxyl group of polybenzoxazine and the double bond of BMI. The obtained polymer alloy films were self-standing, homogeneous, and transparent. Based on the dynamic mechanical analysis of the films, the glass transition temperature (T_g) increased to 228 °C and 329 °C for the polymer alloy films with BMI contents of 60 wt.% and 75 wt.%, respectively, which were higher than those of the POP-p or PBMI homopolymer. Despite the improvement in the T_g, the alloy films exhibited sufficient toughness as evidenced via the tensile test. Moreover, thermogravimetric analysis of the polymer alloys revealed that the thermal stability increased with increasing BMI content.