PROPERTY ENHANCEMENT OF POLYBENZOXAZINE MODIFIED WITH MONOANHYDRIDES AND DIANHYDRIDES

Abstract

Recent development of polybenzoxazine (PBA-a) focuses primarily on broadening their thermal and mechanical properties such as their glass transition temperature (Tg), degradation temperature (Td) as well as their flexibility and toughness. In this research, It is revealed that the incorporation of mono and dianhydrides can improve both properties of PBA-a but different manner. PBA-a property enhancement by monoanhydrides (i.e. phthalic anhydride, PA and napthalic anhydride, NA) and dianhydrides (i.e. pyromellitic dianhydride, PMDA and naphthalene tetracarboxyllic dianhydride, NTDA) are systematically investigated and compared. The Tg of the alloys was found to be in order of PBA-a:NTDA(304oC)>PBA-a:PMDA(296oC)>>PBA-a:NA (247oC)>PBA-a:PA(223oC). Furthermore, The Tg of the alloys was observed to be significantly higher than that of the neat PBA-a owing to the enhanced crosslink density by the anhydride addition. This greater crosslink density results from additional ester linkage formation which is a covalent interaction between phenolic hydroxyl groups of PBA-a and anhydride groups in anhydride as confirmed by Fourier transform infrared spectroscopic technique. From thermogravimetric studies, the alloys display relatively high Td reported at 10% weight loss up to 430 oC under nitrogen atmosphere and substantial enhancement in char yield at 800 oC with a value of up to 63% by weight. On the other hand, it was found that tensile strength and elongation at break of monoanhydrides modified PBA-a are significantly greater than that those of dianhydrides modified system comparing at the same mole fraction of modifiers. The above results suggest effective methods to improve thermal properties of the PBA-a with an incorporation of the dianhydrides while better mechanical properties require monoanhydrides as a PBA-a modifiers.