Effect of hydroxyphenylmaleimide on the curing behaviour and thermomechanical properties of rubber-modified polybenzoxazine

Hydroxyphenylmaleimide (HPMI) and/or amine terminated butadiene acrylonitrile (ATBN)-modified polybenzoxazine were prepared by mixing benzoxazine monomer (Ba), HPMI and ATBN. The onset of the ring opening of the pristine Ba started with differential scanning calorimetry at 223 degreesC with a maximum at 247 degreesC. The incorporation of ATBN lowered the onset and the maximum of the exotherm to 180 degreesC and 216 degreesC respectively. The incorporation of HPMI initiated the ring opening of Ba at a temperature as low as 160 degreesC with a maximum at 200 degreesC. Viscoelastic measurements showed that the incorporation of HPMI increased the T-g and the storage modulus compared to that of the unmodified polybenzoxazine and ATBN-modified polybenzoxazine. Tensile property measurements indicated that the tensile modulus was enhanced with the addition of HPMI to ATBN-modified polybenzoxazine accompanied with little decrease in the elongation at break. Thermogravimetric analysis showed that the addition of HPMI enhanced the thermal stability of polybenzoxazine.