Synthesis of a benzoxazine with precisely two phenolic OH linkages and the properties of its high‐performance copolymers

Abstract

A phenolic OH‐containing benzoxazine (F‐ap), which cannot be directly synthesized from the condensation of bisphenol F, aminophenol, and formaldehyde by traditional procedures, has been successfully prepared in our alternative synthetic approach. F‐ap was prepared by three steps including (a) condensation of 4‐aminophenol and 5,5'‐methylenebis(2‐hydroxybenzaldehyde) (1), (b) reduction of the resulting imine linkage by sodium borohydride, and (c) ring closure condensation by formaldehyde. The key starting material, (1), was prepared from 2‐hydroxybenzaldehyde and s‐trioxane in the presence of sulfuric acid. F‐ap is structurally similar to bis(3,4‐dihydro‐2H‐3‐phenyl‐1,3‐benzoxazinyl)methane (F‐a, a commercial benzoxazine based on bisphenol F/aniline/formaldehyde) except for two phenolic OHs. The phenolic OHs can provide reaction sites with epoxy and 1,1'‐(methylenedi‐p‐phenylene)bismaleimide (BMI). The structure–property relationships between the thermosets of F‐ap/epoxy, F‐a/epoxy, F‐ap/BMI, and F‐a/BMI were discussed. Experimental data showed that thermosets based on F‐ap/epoxy and F‐ap/BMI provided much better thermal properties than those based on F‐a/epoxy and F‐a/BMI. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2686–2694

Smart and sustainable design of latent catalyst-containing benzoxazine-bio-resins and application studies

“…4 However, multi-step reactions, use of protecting groups, and utilization of catalytic systems are indispensable to produce such compounds, as in the case of the synthesis of phenolic hydroxyl group-containing benzoxazines. 20,21 These steps are necessary because the hydroxyl group must be unreactive during the synthesis of the resins, but reactive once the benzoxazine has been already synthesized. Moreover, reaction temperatures must also be carefully controlled since the phenolic -OH is an effective catalyst promoting the ring-opening of benzoxazines.…”

“…However, most of these studied initiators and/or catalysts show poor solubility or mis-cibility with the benzoxazine systems, and in those cases the good shelf life of the benzoxazine resins is understandably greatly reduced. Alternatively, some catalytically active functionalities, such as hydroxyethyl 19 and phenolic hydroxyl 20,21 have been incorporated into the chemical structure of the benzoxazine itself. Although the active groups enhance the polymerization rate, shortening of the shelf life must be overcome since the catalytically active group disrupts the natural stability of benzoxazine resins.…”

Chrysin-Based Bio-Benzoxazine: A Copolymerizable Green Additive for Lowering Curing Temperatures and Improving Thermal Properties of Various Thermosetting Resins

“…In general, synthesizing phenolic hydroxyl-containing benzoxazines requires a multistep reaction . In order to scale up the resin synthesis, such a synthesis approach with complex reaction steps is not acceptable due to the high cost and environmental issues.…”

Solvent-free synthesis of a formaldehyde-free benzoxazine monomer: study of its curing acceleration effect for commercial benzoxazine

“…The curing acceleration ability of phenol-containing benzoxazines has been reported several times in the literature. 53,56,57 The basic principle is to blend a given monomer with a lower curing one (an accelerator) to decrease the global polymerisation temperatures. For instance, Zhu et al studied blends of pyrogallol-based benzoxazines and p -phenylenediamine-phenol ( p -ddm) benzoxazine.…”

“…165 °C. 53 The direct polymerisation after melting has been observed for nearly all the phenol-containing benzoxazine monomers. 54–59 Among these very reactive benzoxazine monomers, some present the lowest polymerisation temperatures for all benzoxazine structures.…”