Benzoxazines resins

Recently, the transfer of benzoxazine chemistry to the field of water-based emulsions was demonstrated for the synthesis of benzoxazine resin miniemulsions stabilized with polymerizable, non-ionic benzoxazine surfactants. In contrast to... 

Benzoxazi ne Resi ns. Benzoxazine resins are prepared by the reaction of phenol, formaldehyde, and an amine. In one particular example a benzoxazine is prepared from bisphenol A, formaldehyde, and anihne to give 2,2 -bis(3-phenyl-4-dihydro-l,3,2-benzoxazine) propane. When heated to about 200°C the methylene bond to oxygen breaks and reforms onto the available ortho positions of adjacent moieties to give dibenzylamine structures. Resin formulations have been developed and formulated, in some cases with epoxy and phenolic resins to give ternary systems with Tg as high as 170°C (Fig. 4) (43-46). 

J. Hacaloglu, T. Uyar, and H. Ishidci, Thermal Degradation Mechanisms of Polyhenzoxazines, in H. Ishida and T. Agag, Handbook of Benzoxazine Resins, Elsevier, pp. 287-305,2011. 

Novolaks. Novolak resins are typically cured with 5—15% hexa as the cross-linking agent. The reaction mechanism and reactive intermediates have been studied by classical chemical techniques (3,4) and the results showed that as much as 75% of nitrogen is chemically bound. More recent studies of resin cure (42—45) have made use of tga, dta, gc, k, and nmr (15). They confirm that the cure begins with the formation of benzoxazine (12), progresses through a benzyl amine intermediate, and finally forms (hydroxy)diphenyknethanes (DPM). 

The polybenzoxazines (PBZs) provide a new class of phenolic resins that were first described by Ishida in 1998 (Ref. 15). Synthesis of the resins involves three components a phenol, a primary amine and formaldehyde. The first stage involves the formation of a multifunctional benzoxazine monomer Figure 23.30 a)). The monomer can then be ring-opened at elevated temperatures (160-220 C) to yield a polymeric stmcture (Figure 23.30(b)). 

As previously described, die main intermediates generated from die initial reaction between ortho reactive sites on novolac resins and HMTA are hydroxy-benzylamines and benzoxazines.44 Triazines, diamines, and, in die presence of trace amounts of water, benzyl alcohols and ethers also form (Fig. 7.16). Similar intermediates, with the exception of benzoxazines, are also observed when para sites react with HMTA. 

Examples of the preparation of oxazines and thiazines on insoluble supports are listed in Table 15.34. 3,l-Benzoxazin-4-ones can be prepared by intramolecular O-acy-lation of /V-aminocarbonyl anthranilic acids (Entry 1, Table 15.34). The resulting ben-zoxazinones are sufficiently stable towards acids to enable TFA-mediated cleavage from a Wang linker [410]. 1,3-Oxazines have also been obtained by acidolytic cleavage of functionalized 3-amino-l-propanols from Wang resin (Entry 4, Table 3.30). 

To 2.0 ml of Amberlite XAD 7 was added 2.0 ml of a 0.05 M phosphoric acid buffer (pH 7.0) having dissolved therein 20 mg of lipoprotein lipase, and the system was allowed to stand at room temperature for 18 hours to thereby adsorb the enzyme onto the resin. The resin was filtered. A solution of 250 mg of 3,5-dinitrobenzoyl derivative of ()-3-acetoxymethyl-7,8-difluoro-2,3-dihydro-4H-[l,4]benzoxazine as a substrate in 25 ml of a mixed solvent of benzene and n-hexane (4 1 by volume) was added to the resin, followed by... 

A method for preparing thermosets by modifying o,p-phenol-formaldehyde resins using paraformaldehyde and aniline to provide A-phenyl benzoxazine having a melt viscosity between 2 and 4 poise at 125°C is described. 

Schreiber, for the preparation of phenolic resins with improved thermal, mechanical, and dielectric characteristics. However, no systematic study was reported in Schreiber s patents. Thus, it was of interest to examine in more detail several points such as 1) the synthesis of an homologeous series of benzoxazines, 2) their reaction with phenols, which may be considered as the initiation step of the polymerization by a ring opening mechanism, 3) the pol3nnerization kinetics of benzoxazines, initiated either thermally or with phenols, and 4) the application possibilities of these monomers and polymers. 

As a family of resins originally developed in the early twentieth century, the nature and potential of phenolic resins have been explored thoroughly to produce an extensive body of technical literature (1-9). A symposium sponsored by the American Chemical Society commemorated 75 years of phenolic resin chemistry in 1983 (10), and in 1987 the Phenolic Molding Division of the Society of the Plastics Industry (SPI) sponsored a conference on phenolics in the twenty-first century (1). Exciting new developments continue as new systems are developed for carbon-carbon composites, aramid honeycombs, and new derivative chemistries such as cyanate esters and benzoxazines. New U.S. patents with phenolic resins in the claims are growing at about 150 patents per year. 

The resin rich in 2,2 -methylene exhibited the lowest activation energy, gel temperature, and DSC exotherm. The high concentration of the slightly acidic 2,2 -diphenylmethane end groups may accoimt for the higher reactivity. These end groups should react with hexa to form benzoxazine intermediates first, which then decompose to react with vacant positions throughout the novolak molecule. 

Cardanol has also been used in benzoxazine-type resins prepared from cardanol-based monobenzoxazine monomer, which in turn was produced by the reaction of cardanol with ammonia and formaldehyde (Calo et al., 2007), or from a monofunctional benzoxazine monomer synthesized by the condensation of aniline and formaldehyde with cardanol (Rao and Palanisamy, 2011). 

Grishchuk S, Mbhele Z, Schmitt S and Karger-Kocsis J (2011), Structure, thermal and fracture mechanical properties of benzoxazine-modified amine-cured DGEiBA epoxy resins . Express Polym Lett, 5, 213—2W., and references therein. 

Yang P and Gu Y (2012), Synthesis of a novel benzoxazine-containing benzoxazole structure and its high performance thermoset , J Appl Polym Sci, 124, 2415-2422. Yoonessi M, Toghiani H, Wheeler R, Porcar L, Kline S and Pittman Jr C U (2008), Neutron scattering, electron microscopy and dynamic mechanical studies of carbon nanofiber/phenolic resin composites . Carbon, 46, 577-588, and references therein. Yosomiya R (1990), Adhesion and Bonding in Composites, New York, Marcel Dekker, l-A. 

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