Browsing by Subject "Cross-linked"
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Item Open Access Cross-linked main-chain polybenzoxazine nanofibers by photo and thermal curing; stable at high temperatures and harsh acidic conditions(Elsevier, 2016-02) Ertaş, Yelda; Uyar, TamerIn 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).Item Open Access Polybenzoxazine-based nanofibers by electrospinning(Elsevier Inc., 2017) Ertaş, Yelda; Uyar, Tamer; Ishida, H.; Froimowicz, P.In this chapter recent progress in the production of polybenzoxazine-based nanofibrous mats by electrospinning is highlighted. The benzoxazine monomers could easily form thermosetting polybenzoxazines by in situ thermally initiated ring-opening polymerization, hence, they are promising materials for both the surface modification of polymeric nanofibrous mats and the production of polybenzoxazine-based composite nanofibers. After curing, polybenzoxazines provide hydrophobic characteristic for the modified polymeric nanofiber surfaces by in situ polymerization of the benzoxazines because of their highly cross-linked structure. Also, they allow for the further functionalization of the surfaces as superhydrophobic and superleophilic by the incorporation of SiO2 nanoparticles into the benzoxazine solution. In addtion, benzoxazine monomers could be directly added into electrospinning solutions and the thermal curing of the obtained nanofibrous mat could yield hydrophobic composite nanofibers. Moreover, because of outstanding properties, such as near-zero volumetric change upon curing, low water absorption, high glass transition temperature, high char yield, and no by-products without any catalysts during curing, polybenzoxazines are good a candidate as a precursor for the production of carbon nanofibers. In addition, the molecular structure of polybenzoxazines facilitates immense design flexibility, which enables the tailoring of the properties of the cured material. Therefore, suitable polybenzoxazines can be synthesized, and cross-linked polybenzoxazine nanofibers, with enhanced thermal and mechanical properties, can be obtained by electrospinning without the blending of other polymers. By combining the unique properties of nanofibers and the facinating properties of polybenzoxazines, highly cross-linked polybenzoxazine-based nanofibrous mats can be obtained and these materials are quite useful, especially in filtration applications. © 2017 Elsevier Inc. All rights reserved.