Thermomechanical properties of polybenzoxazine modified with dianhydrides

Abstract

To study the mixture between benzoxazine resin (BA-a) and dianhydrides, i.e. 3, 3’, 4, 4’ benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA) or 3, 3’, 4, 4’ biphenyltetracarboxylic dianhydride (s-BPDA) at various mole ratios of BA-a: dianhydrides on thermal and mechanical characteristics. The glass transition temperature (Tg) and the storage modulus (E’) values of BA-a: BTDA, BA-a: PMDA, and BA-a: s-BPDA films were observed to be significantly higher than that of the neat polybenzoxazine (PBA-a) owing to the enhanced crosslink density. This greater crosslink density resulted from esterification reaction between the hydroxyl group of polybenzoxazine and the carboxylic group of dianhydride, which formed by thermal curing. The maximum Tg values of BA-a: PMDA > BA-a: s-BPDA > BA-a: BTDA were observed at an alloy composition of 1.5: 1 mole ratio. Moreover, the degradation temperature (Td) reported at 10 percent weight loss under nitrogen atmosphere and char yield at 800 degresss celsius of the polymer alloys were found to be much greater than those of the neat polybenzoxazine (PBA-a) while the calculated LOI of all BA-a: dianhydride alloys were above the self-extinguishable limit i.e. > 26. In addition, tensile strength, tensile elongation at break, tensile modulus, and toughness of PBA-a increased by alloying with BTDA or PMDA or s-BPDA. These results suggested the alloys to be casted to yield tougher and stronger films. The ultimate mechanical and thermal properties for BA-a: dianhydrides were also obtained at 1.5:1 mole ratio. The obtained alloy sample is appropriate for an application as polymeric film for high temperature resistance material such as electronic packaging, thermal resistance coating and matrix for composite materials.