Mannich reaction of phenolphthalein and synthesis of a novel polybenzoxazine

Abstract

Phenolphthalein (3,3-bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, B-hpi), reacted with paraformaldehyde and allylamine by the Mannich reaction, was investigated as the acid ingredient for the first time, and a novel benzoxazine was synthesized. In order to confirm the structure of benzoxazine, benzyl-terminated B-hpi (3,3-bis(4-benzyloxyphenyl)-1(3H)-isobenzofuranone, B-bpi) was prepared. The chemical structures of B-hpi, B-bpi and benzoxazine were compared by FT-IR, 1H-NMR and 13C-NMR; it was demonstrated that the lactone structure remains in the molecular structure of benzoxazine (3,3-bis(3-allyl-3,4-dihydro-2H-1,3-benzoxazine)-1(3H)- isobenzofuranone, B-adi). B-adi transformed into a quinoid structure in basic medium similar to that of B-hpi. Software of Accelrys' materials studio (DMo13), FT-IR and UV-Vis spectrophotometry were employed to investigate the properties of the quinoid structure of B-adi and B-hpi. In situ FT-IR spectra showed the thermal curing behavior of B-adi. The char yield of polyB-adi was about 40% by weight at 800°C in nitrogen atmosphere, as determined by TGA. Tg values for this polyB-adi were as high as 273°C and 295°C from the maximum of loss modulus and tan δ by DMTA, respectively.