Synthesis and curing behavior of a benzoxazine based on phenolphthalein and its high performance polymer

A pure benzoxazine synthesized from phenolphthalein through Mannich reaction, 3,3′-bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazinyl)-1(3H)-isobenzofuranone (Boz-BP), was characterized by FTIR and ¹H NMR. Its curing behavior was different with that of 2,2′-bis(4-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane (Boz-BA) because Boz-BP possesses highly steric and inactivated phenol rings. During curing period, the reactivity of ortho position of phenolic hydroxyl group was retarded and the addition of -CH₂- group generated in ring-opening reaction preferred to taking place on para position of aniline ring, which is beneficial for better thermal properties. Furthermore, additional hydrogen bonding would be formed between carbonyl groups on phthalide structure and hydroxyl groups in Boz-BP based polymer (P(Boz-BP)). Compared with the analogous polymer from Boz-BA (P(Boz-BA)), P(Boz-BP) displayed higher glass transition temperature, better thermal stability, better dimensional stability and flame-retardant properties.