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°C with a maximum at 247°C. The incorporation of ATBN lowered the onset and the maximum of the exotherm to 180°C and 216°C respectively. The incorporation of HPMI initiated the ring opening of Ba at a temperature as low as 160°C with a maximum at 200°C. 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.