Cross-linked main-chain polybenzoxazine nanofibers by photo and thermal curing; stable at high temperatures and harsh acidic conditions

In this study, for the first time cross-linking of linear aliphatic diamine-based main-chain polybenzoxazine (MCPBz) electrospun nanofibers were accomplished by two-step approach consisting of photo and thermal curing. Initially, two novel MCPBz resins which comprise of a benzophenone unit in the polymer main-chain were synthesized and uniform MCPBz nanofibers were produced by electrospinning. At first step, photo curing was performed by free radical polymerization initiated by UV-light and thermal stability of nanofibers was enhanced. At second step, thermal curing was carried out at different temperatures (150-225 degrees C) and ring opening and cross-linking of benzoxazine groups in the fiber structure were achieved. After two-step curing, cross-linked MCPBz nanofibers were obtained as free-standing material with good mechanical properties. Moreover, it was shown that these two crosslinked MCPBz nanofibers were structurally stable and maintained their fibrous morphology at high temperatures (400 degrees C), in good solvents (chloroform, DMF, 1,4-dioxane, DMAc, THF) and highly concentrated strong acids (HCl, HNO3, H2SO4). (C) 2015 Elsevier Ltd. All rights reserved.