Halogenated epoxide resins

Finally, apart from using halogenated epoxide resins or additives, it is also possible to use halogenated curing agents, examples being... 

Cross-linked epoxy resins are combustible and their burning is self-supporting. They require mainly reactive flame-retardants, such as tetrachloro- or tetrabromobisphenol-A and various halogenated epoxides. Even the cross-linking agent may be flame-retardant, as in the case of chlorendic anhydride, tetrabromo- or tetrachloro-phthalic anhydride, or possibly phosphorus compounds. Halogenated agents can be supplemented with antimony trioxide. 

Early efforts to impart flame retardancy upon epoxide resin formulations involved blending co-reactive halogenated compounds with liquid epoxides. These merely served as diluents and quite often resulted in products with markedly reduced physical properties such as Tg, thermal stability and compressive strengths. In order to avoid these problems, flame retardant epoxide resins have been synthesised containing halogen atoms within their molecular structures and these are now commonly used in epoxide resin based formulations. Their structures... 

Although both brominated and chlorinated epoxide resins have been used, the preferred halogen is bromine. This is because less bromine (by weight) is required to impart flame retardancy than with chlorine. Another important reason for the selection of bromine in preference to chlorine is thermal stability. 

Salts such as ammonium polyphosphate have been successfully utilised as flame retardants in filled epoxide resin systems. It is more usual to employ phosphorus/halogen mixtures in epoxide resins. A combination of 1 5-2% phosphorus with 5-6% of chlorine will impart selfextinguishing properties to epoxides. 

Uracils and related pyrimidines undergo oxidative addition to the 5,6-double bond, and the reaction with a number of oxidants to form 5,6-epoxides and 5,6-diols was discussed in CHEC-II(1996) <1996CHEC-II(6)93>. Oxidative halogenation can also occur <1996SC3583, 1998NN1125>, as shown by the formation of 5-bromo-5,6-dihydro-6-methoxyuracil 100 from uracil 99 by treatment with a mixture of potassium bromate and potassium bromide in the presence of Dowex ion-exchange resin in methanol <1996SC3583>. 

NaBr/H20, LiBr on Amberlyst-15 resin, TiCU-LiCl, " SiCL, I2 with a Sml2 catalyst, and Lil on silica gel. Epoxides can be converted directly to 1,2-dichloro compounds by treatment with SOCI2 and pyridine, or with Ph3P and CCl4. These are two-step reactions a halohydrin is formed first and is then converted by the reagents to the dihalide (10-48). As expected, inversion is found at both carbons. Meso epoxides were cleaved enantioselectively with the chiral B-halodiisopinocampheylboranes (see 15-16), where the halogen was Cl, Br, or I. ° Diatomic iodine gives an iodohydrin with a 2,6-bis[2-(o-aminophenoxy) methyl]-4-bromo-l-methoxybenzene catalyst. ... 

Resin. Polyglycidyl compounds with at least two epoxide groups per molecule, such as polyglycidylether on a base of novolak, bisphenol A, bisphenol F etc., are generally suitable as EP-resin components. Our tests were carried out with epoxidized novolaks (epoxide number between 0.5 and 0.6) and total halogen contents < 0.1 % by weight. 

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

In another procedure, a halogen acid is generated by the reaction of an ionic halide salt, eg, tetraethylammoniiun bromide in acetic acid with perchloric acid with subsequent formation of a halohydrin the epoxy group is determined by back-titration with perchloric acid nsing crystal violet indicator (83). The end point can be determined visually or potentiometrically. A monograph on epoxide determinations was published in 1969 (84). This is the method adopted by ASTM and is currently used by most resin producers. 

Poly(styryldiphenylphosphine)-halogen. complexes are formed by addition of the halogen to a dichloromethane-swollen resin. The complexes react with epoxides to give trans-halohydrins in... 

---