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

Abstract

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 (150e225 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 C), in good solvents (chloroform, DMF, 1,4-dioxane, DMAc, THF) and highly concentrated strong acids (HCl, HNO 3 , H 2 SO 4).

Significant Improvement on Polybenzoxazine Toughness Achieved by Amine/Benzoxazine Copolymerization‐Induced Phase Separation

“…Polybenzoxazines belong to phenolic resins but contain tertiary amine moieties in the crosslinking networks. They have significant advantages in terms of mechanical performance, [1][2][3] thermal stability, [4][5][6][7][8] near-zero shrinkage upon curing, [9] and molecular design flexibility. [10][11][12][13][14][15] Especially, the last merit has attracted wide attention in the field of high-performance polymers, and numerous desired benzoxazines were synthesized to improve material properties of polybenzoxazine resin.…”

Synthesis and properties of main‐chain polybenzoxazines based on bisphenol‐S

“…The aromatic protons of bisphenol‐S appear between 6.5 and 8.0 ppm for all the three PBz precursors. The aliphatic chain protons of ethylenediamine, dibutylamine, and tetraethylene pentamine appear between 1 and 3 ppm, in which the amine protons appear between 2.4 and 2.8 ppm, whereas the alkyl protons appear between 1.56 and 1.51 ppm . The peak at 2.5 for all the three PBz precursors is due to the solvent peak (DMSO).…”

“…The concept of preparing main‐chain PBz (MCPBz) precursors has been developed recently . The reaction involves the use of a di‐functional phenolic derivative and diamine, producing a linear polymer that contains oxazine rings in its main‐chain . These types of polymeric precursors are preferred over monomeric or dimeric benzoxazines for further polymerization.…”

Fabrication of Thermally Crosslinked Hydrolyzed Polymers of Intrinsic Microporosity (HPIM)/Polybenzoxazine Electrospun Nanofibrous Membranes

“…These properties enable the production of high‐performance composite materials . Thus, immense research has been conducted on different forms of polybenzoxazines including bulk, film, aerogel, membrane, and nanofibers . However, far too little attention has been paid to the incorporation of polybenzoxazine into polymeric nanofibers …”