Cross-linked main-chain polybenzoxazine nanofibers by photo and thermal curing; stable at high temperatures and harsh acidic conditions
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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 °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 cross-linked MCPBz nanofibers were structurally stable and maintained their fibrous morphology at high temperatures (400 °C), in good solvents (chloroform, DMF, 1,4-dioxane, DMAc, THF) and highly concentrated strong acids (HCl, HNO3, H2SO4).