In this research, the incorporation of either monoanhydrides or dianhydrides with polybenzoxazine (PBA-a) can improve both thermal and mechanical properties with different manner. The property enhancements of PBA-a by monoanhydrides and dianhydrides were systematically investigated and compared. The glass transition temperatures (T g ) of the alloys were in order of PBA-a:NTDA>PBA-a:PMDA>>PBA-a:NA>PBA-a:PA. Furthermore, the T g of the alloys was observed to be higher than that of neat PBA-a owing to the crosslink density enhanced by the addition of anhydride. This greater crosslink density also results from additional ester linkage formation. The alloys display high decomposition temperature (T d ) reported at 10 % weight loss up to 430°C under nitrogen atmosphere and substantial enhancement in char yield at 800°C with a value of up to 63 % by weight. Additionally, toughness of the alloy films has been significantly improved with an addition of both types of the anhydrides. The results of this work suggest effective methods to enhance thermal properties of the PBA-a with an incorporation of the dianhydrides, while monoanhydrides were required as a PBA-a modifiers for better mechanical properties.

Recent development of polybenzoxazines focuses primarily on broadening their thermal and mechanical properties such as their glass transition temperature, thermal degradation temperature as well as their flexibility and toughness. In this work, we have demonstrated that the incorporation of mono-or dianhydrides can improve both properties of polybenzoxazines but with different manner. Polybenzoxazine property enhancement by phthalic anhydride, PA, (monofunction) and pyromellitic dianhydride, PMDA, (bifunction) are systematically investigated and compared. It was observed that both mono-and dianhydrides can form covalent bonds through ester linkages with benzoxazine resin as confirmed by Fourier transform infrared spectroscopic technique. From thermogravimetric studies, degradation temperature of both anhydrides modified polybenzoxazines shows substantial improvement with increasing the amount of the anhydrides. Furthermore, char formation of the polybenzoxazine copolymers exhibits synergistic behavior with an addition of the dianhydride whereas that of monoanhydride-modified system shows a linear increase. On the other hand, it was found that tensile strength and elongation at break of monoanhydride modified polybenzoxazine are significantly greater than those of dianhydride-modified system comparing at the same mole fraction of the modifiers. However, tensile moduli of PA-and PMDA-modified polybenzoxazines are about the same and reveal an increasing trend with an addition of both types of anhydrides. The above results suggest effective methods to improve thermal properties of the polybenzoxazine with an incorporation of the dianhydride while better mechanical properties require monoanhydride as a polybenzoxazine modifier. The resulting copolymers can be used as high temperature matrix for carbon or glass fiber reinforced composite products.