Curing Reaction Of Benzoxazine Research Articles

The chemical effect of furfuryl amide on the enhanced performance of the diphenolic acid derived bio‐polybenzoxazine resin

AbstractAs a renewable chemical, diphenolic acid (DPA) has attracted immense interest in bio‐based polymer science. However, its application for polybenzoxazines is limited due to decarboxylation, that is, the release of CO2 during the curing reaction of benzoxazine. In this study, the amidation strategy of converting DPA to diphenolic amides (DPAM) was demonstrated to solve this problem while simultaneously improving the thermal properties of polybenzoxazine. DPA was amidated by separately using four amines (hexamine, cyclohexylamine, furfurylamine, and aniline), then reacted with furfurylamine and paraformaldehyde to synthesize their benzoxazine monomers. By using TGA and DMA, all amide‐containing polybenzoxazines were found to exhibit excellent thermal stabilities. Among all of the benzoxazine resins, poly(DFA‐fa), which was obtained from amidation with furfurylamine, exhibited the highest glass transition temperature (Tg) of 310°C and a decomposition temperature (Td10) of 406°C. Furthermore, a possible post‐curing reaction mechanism was proposed to explain the outstanding thermal performance of poly(DFA‐fa) resin. This study proposes an innovative strategy to solve the decarboxylation of DPA‐based polymers, which is of significance for high‐performance bio‐based polymers.

Preparation and characterization of a novel benzoxazines/bismaleimide/2,2′-diallylbisphenol A blend with multiphase structures

Novel benzoxazine (BOZ)/bismaleimide (BMI)/2,2′-diallylbisphenol A (BA), with a multiphase structure, was successfully prepared under the catalysis of methyl p-toluenesulfonate (PTSM) through reaction-induced phase separation. The curing reaction of BOZ with BMI and ring-opening polymerization of BOZ under the catalysis of PTSM were studied by Fourier transform-infrared spectroscopy and differential scanning calorimetry analyses, respectively. Mechanical measurements, thermogravimetric analysis, and microanalyses were conducted to assess the toughness and morphology of the composite. The reaction between BOZ and 4,4′-bismaleimidodiphenyl methane (BDM) occurs at a relatively high temperature. The ring-opening reaction of BOZ starts at a low temperature of 100°C because of the catalysis of PTSM. The BOZ/BDM/BA system with an appropriate amount of BOZ significantly improves the impact strength and flexural strength compared with those of the BA/BDM resin. The BOZ/BDM/BA system with PTSM also features high impact strength and flexural strength. Scanning electron microscopy images and energy-dispersive spectroscopy results show that BOZ-rich phase is dispersed in BDM-rich phase in the BOZ/BDM/BA system with PTSM. Thermogravimetric data show that the BOZ/BDM/BA blend with a multiphase structure exhibits superior thermal resistance to those of the BOZ/BDM/BA and BA/BDM resins. The formation mechanism of the ternary system under the catalysis of PTSM is elucidated with Gibbs free energy theory.

Synthesis and characterization of novel bisphthalonitrile resins linked by different molecular weight main-chain polybenzoxazines

ABSTRACTA series of novel type bisphthalonitriles with different molecular weight main-chain polybenzoxazines as linkages have been successfully synthesized using 4, 4′-diaminodiphenyl methane, paraformaldehyde, bisphenol A and 4-nitrophthalonitrile as initial materials. The structures were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H-NMR). The formation of benzoxazine and the existence of nitrile groups were confirmed by the absorbance at 950cm−1 of benzene attached with oxazine ring and 2231 cm−1 of nitrile groups. The characteristic resonance peaks observed at about 4.52 (C-CH2-N) and 5.28 ppm (N-CH2-O) also determined the structure of benzoxazine ring. The curing behaviors were monitored by differential scanning calorimetry (DSC) and FT-IR. Two-stage polymerization mechanisms were observed according to the ring-opening of benzoxazine and the polymerization of nitrile groups catalyzed by phenolic hydroxyl groups, which generated during the curing reaction of benzoxazine. The polymerization of these bisphthalonitriles exhibited self-promoted curing behaviors. The completion of polymerization was proved by the disappearance of the band located at 950 cm−1 in FT-IR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results showed that the cured polymers achieved extremely high char yield from 61.1% up to 74.2% at 800°C under nitrogen and exhibited increasing decomposition temperature as the contents of phthalonitrile groups increased, which indicated that the polymerization of phthalonitriles could improve the thermal stability.

The curing reaction of benzoxazine with bismaleimide/cyanate ester resin and the properties of the terpolymer

Thermosetting terpolymer composed of benzoxazine (BOZ), cyanate ester (BADCy) and maleimide resin (BMI) was prepared via co-curing reactions. The curing reaction of benzoxazine with bismaleimide/cyanate ester resin and the properties of the terpolymer were studied by differential scanning calorimetry (DSC) and Fourier transform-infrared spectroscopy (FT-IR), and the thermal, mechanical and dielectric properties of the terpolymer were also characterized. The FT-IR was applied to monitor the curing reactions of the reactive blends. Three reactions were observed in the curing reactions: the first is the polymerization of cyanate ester after oxazine ring opening, producing the triazine structure; the second is the coreaction between the triazine structure and benzoxazine, forming alkyl isocyanurate and diphenyl ether linkages, followed by the further reaction of the isocyanurate linkage; and the third is the self-polymerization of maleimide resin and benzoxazine, and coreaction with each other. Compared to the polybenzoxazine, the higher crosslinking density of the terpolymer led to the higher glass transition temperature (Tg), as well as the 5% weight loss temperatures (Td5), indicating the better thermal stability of the terpolymer at service temperature. And the data for the mechanical and dielectric properties also showed that the terpolymer performs better than polybenzoxazine and the copolymer.

New Thermosetting Resin from Benzoxazine and Cyanate Ester Resin

AbstractA curing reaction of benzoxazine with cyanate ester resin and the properties of the cured new thermosetting resin were investigated. In particular, the effect of the content of cyanate ester resin on the cure behavior and the properties of the cured new thermosetting resins were investigated. As a result, it was found that the ring‐opening reaction of a benzoxazine ring and thermal self‐cyclotrimerization of a cyanate ester group occurred, then the phenolic hydroxyl group generated by the ring‐opening reaction of the benzoxazine ring might coreact with the cyanate ester group. As the content of cyanate ester resin increased, the gelation reaction proceeded more quickly. The cured new thermosetting resin from benzoxazine and cyanate ester resin showed good thermal stability, high electrical resistivity, and high water resistance. As the content of cyanate ester resin increased, the glass transition temperature and electrical resistivity became especially higher. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E651–E659, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21308

High Performance Composites of Polybenzoxazine and Polyarylene Ether Nitriles (PEN)

Polybenzoxazine (PBa) was modified by polyarylene ether nitriles (PEN) via in situ curing reaction of benzoxazine in the presence of PEN to improve toughness and thermal properties. DSC measurements of the cured blends containing PBa and PEN showed single glass-transition temperatures (Tg's) when the amount of PEN in the blends less than 20%, and the blends have significantly higher glass transition temperatures than those of each homopolymer. Tensile measurements of the films revealed that the strength and elongation was dramatically enhanced by the addition of PEN, the toughness of the PBa/PEN films was greatly enhanced. The thermal stability also increased with the increase of PEN content as evidenced by TGA. All of the mechanical and thermal characteristics show that the blends can be good candidates for the matrix resin of advanced composite materials.