Oxazine Resins With High Heat-Resistant And Flame-Retardant Properties

Polybenzoxazine as a novel phenolic type thermoset has been developed to overcome the short-comings associated with traditional phenolics resins such as releasing condensation by-products and using strong acids as catalysts, while retaining good thermal properties and flame retardance of phenolic resins. Polybenzoxazines have not only the advantageous properties of conventional phenolic resins but also other interesting advantages such as heat resistance, superior electronic properties, low water absorption, low surface energy, and excellent dimensional stability.Polybenzoxazine can be prepared from benzoxazines via thermally induced ring opening polymerization. Benzoxazines are readily synthesized either in solution or by a solventless reaction using a combination of a phenolic derivative, formaldehyde, and a primary amine derivative.Recently, the demand for high performance polybenzoxazines has increased tremendously due to the rapid development of microelectronics and aerospace industries. Among the studies on polybenzoxazines, the issue of enhancing the glass transition temperatures (Tg) and flame-retardant performance of polybenzoxazines are highly expected.In this dissertation, we described the synthesis and characterization of a series of polybenzoxazines with high Tg and high flame retardance obtained from the incorporation of polymerizable nitrile group or rigid units into benzoxazines, respectively. The main contents of the dissertation were showed as follows:1. Mono-functional and bi-functional benzoxazines (NBZ-m and NBZ-b) containing nitrile groups were synthesized from4-cyanophenol, formaldehyde, and phenylamine or4,4-diaminodiphenyl methane. The monomers were characterized by nuclear magnetic resonance (NMR), fourier transform infrared spectroscopy (FTIR), and elemental analysis. FeCl3and Dibutyltin dilaurate (DBTL) were used as catalysts to promote the conversation of cyano-group and to reduce the ring-opening polymerization temperature. The results showed that FeCl3significantly increases the conversation rate of cyano groups from21%to43%and reduce the ring-opening polymerization temperature by15℃; DBTL improve Tg of P(NBZ-m) by55℃.2. A new synthetic route was designed to significantly increase the content of triazine structure in benzoxazine resin.2,4,6-Tri(4-hydroxylphenyl)-13,5-s-triazine (TP) was synthesized by cyclotrimerization of4-cyanolphenol and then benzoxazine monomer containing triazine [2,4,6-tri(3-phenyl-3,4-dihydro-2H-1,3-benzoxazin-6-y1)-1,3,5-s-triazine (BZ-ta)] was synthesized via Mannich reaction from TP. Finally, the cross-linked polymer P(BZ-ta) was produced by thermal polymerization of BZ-ta. BZ-ta was characteized by NMR, FTIR, mass spectrum (MS), elemental analysis, and viscosity measurement. Curing behavior of BZ-ta was studied by differential scanning calorimetry (DSC), FTIR, and gel permeation chromatography (GPC). The structure and properties of P(BZ-ta) were investigated by powder X-ray diffraction (XRD), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The results showed that the P(BZ-ta) had high Tg (322℃), excellent thermal oxidation stability (5and10%weight loss temperatures in air up to403and453℃, respectively), high char yield (64%,800℃in nitrogen), and high flame-retardance (limiting oxygen index,39.7).3. In order to obtain high performance polybenzoxazine with high content of phthalocyanine structure, novel benzoxazine monomer containing phthalocyanine structure BZ-Pc was synthesized and polymerized using4-nitrophthalonitrile and4-aminophenoxy as starting materials. BZ-Pc was characterized by NMR, FTIR, ultraviolet spectrum (UV), MS, and elemental analysis. Thermal cross-linking reaction of the monomer was investigated by DSC and FTIR. The structure of P(Bz-Pc) was characterized by XRD. Thermal properties of (P(Bz-Pc)) were evaluated by DMA and TGA. The results showed that P(BZ-Pc) had high Tg (297℃), excellent thermal stability (5%,10%weight loss temperatures up to438and515℃, respectively), and high char yield (69.5%at800℃).4. Pyrido[2,3-d:2',3'-d']di[1,3]oxazine (PyDOx) monomer was synthesized at the first time from2,6-diaminopyridine, formaldehyde, and4-methylphenol at a molar ratio of1:6:2via Mannich reaction and the subsequent ring-condensation. The PyDOx was fully characterized by FTIR, NMR, MS, and element analysis. The synthesis mechanism of PyDOx has been investigated by analyzing the intermediates of the reaction. Also we proposed the polymerization mechanism of PyDOx. Thermal properties of P(PyDOx) were evaluated by DMA and TGA. The results showed that the P(PyDOx) had high Tg (245.5℃) and high char yield (48.7%at800℃).