Synthesis of novel allylamine-fluorene based benzoxazine and its copolymerization with typical benzoxazine: Curing behavior and thermal properties
In this paper, 2,7-dihydroxy-9,9-bis(4-aminophenyl)-fluorene monomer (BADHF) was synthesized by direct condensation reaction catalyzed by methylsulfonic acid. A novel allylamine-based benzoxazine monomer containing fluorene group and polymerizable group (t-BF-sa-a) was obtained via o-hydroxy-benzyl amine method combining with one stage Mannich condensation reaction. The result showed that the introduction of fluorene rings and polymerizable groups and the increase of oxazine rings in the polymer network structure can result in an obvious increase in the crosslinking density of polymers. Therefore, the t-BF-sa-a polybenzoxazine (poly(t-BF-sa-a)) exhibited a higher glass transition temperature (Tg) and better thermal stability. The synthesized t-BF-sa-a monomer was used to modify traditional phenol-aniline-based mono-functional phenol-aniline (P-a) and bisphenol A-aniline-based bifunctional (BA-a) benzoxazines. Due to the introduction of heat-resistant fluorene rings and the increase of crosslinking degree of copolymers, the copolymers (poly(P-a/t-BF-sa-a) and poly(BA-a/t-BF-sa-a)) showed excellent thermal properties. Among them, the Tg, T5, T10, and Yc of poly(P-a/t-BF-sa-a) were increased by 34 oC, 58 oC, 35 oC, and 8%, respectively, even higher than that of bisphenol fluorene aniline-based polybenzoxazine. Furthermore, due to the long alkyl chain in the t-BF-sa-a monomer, the E'of the copolymers was decreased significantly, which greatly improved the shortcomings of traditional polybenzoxazines, such as high brittleness and poor toughness.