Ether crosslinks

Several authors (1-6) have proposed that the crosslinking reactions of epoxy resins with anhydrides is a two or three step process formation of the monoester, formation of the diester and formation of ether crosslinks. It is hoped that this work may assist in a better understanding of this process. 

The functionality may vary with reaction conditions. For example, in base-catalyzed copolymerization of phenol and formaldehyde, both monomers are bifunctional at ambient temperature, but phenol becomes trifunctional if the temperature is raised sufficiently. Copolymerization at ambient temperature can produce essentially linear, liquid, resole-type "prepolymers" of low molecular weight. Upon acidification and heat-curing, methylene and ether crosslinks formed by the now trifunctional phenol units transform the polymer into an insoluble resin [7] (see next page). The original Bakelite was such a "thermosetting" product. 

In view of the demonstration of the attachment of the roono-hydroxy analog of bis-phenol AF to the VF2/BFP pol ner upon addition of its potassium salt in the presence of DBU and because of nucleophilic attack by hydroxide ion on the unsaturated polymer, it is concluded that in practical vulcanization a bis-phenol-derived phenolate probably also attacks the intermediate diene and leads to the dienic phenyl ether crosslinks shown in Figure 6. Attack on the dioie phenoxide, unlike attack by hydroxide, is not expected to proceed beyond vinylic nucleophilic substitution and, therefore, the expected paroduct is the pheiyl ether that corresponds to the dienol proposed as an intermediate in attack by hydroxide. 

Hazardous Decomp. Prods. CO, CO2, heated to decomp., emits acrid smoke and fumes NFPA Health 4, Flammability 3, Reactivity 1 Uses Intermediate for pharmaceuticals and other org. chemicals mfg. of glycerol, acrolein, herbicides, resins, plasticizers, allyl diglycol carbonate, allyl glycidyl ether, crosslinking agents solvent Regulatory SARA reportable Manuf./Distrib. ABCR UK http //www.abcr.de, Aldrich http //www.sigma-aidrich.com, Alfa Aesar http //www.aifa.com. Avocado Research... 

Definition Polymer of maleic anhydride and methyl vinyl ether crosslinked with 1,9-decadiene Uses Binder, film-former, emollient, thickener, stabilizer in detergents, cosmetics Manuf./Distrib. United-Guardian http //www.u-g.com... 

Model studies have shown that the ageing of ENR sulphur vulcanizates occurs by acid-catalysed ring-opening of epoxide groups with the formation of ether crosslinks. The acids are produced by the thermal decomposition of oxidized sulphides. 

Figure 5. Dependence of current density on hydrogen peroxide concentration for cathodes based on different peroxidases, (open circles) NaI04 treated horseradish peroxidase (closed circles) native horseradish peroxidase (open squares) lactoperoxidase (closed squares) Aithromyces ramosus. Each electrode contains approximately 10/ g osmium redox polymer, polyethylene glycol diglycidyl ether crosslinker and 1 to 4/

In principle, termination of two alkoxy radicals would give a peroxide cross-link, whilst termination of an alkoxy radical with an alkyl radical would give an ether crosslink. It is very difficult to get direct experimental evidence for either of these reactions, since both dialkyl peroxides and ethers are difficult to detect, however, there is no doubt that chain scission is dominant in saturated hydrocarbon polymers. 

In the first step (the dehydrofluorination) Viton copolymer is attacked by the intermediate described below, creating diene. Then, the bisphenol-derived phenolate ("OArOH) attacks the intermediate diene and finally leads to the dienic phenyl ether crosslinks [32,33]. This reaction is a substitution. The resulting product surprisingly shows good properties, particularly with regard to oxidative and hydrophilic stabihty. 

Noppakundilograt, S. Miyagawa, N. Takahara, S. Yamaoka, T. Visible light-sensitive positive-working photopolymer based on poly( -hydroxystyrene) and vinyl ether crosslinker. J. Photopolym. Sci. Technol. 2000, 13, 719-721. 

These arylene ethers crosslink a fluorinated polyimide at 300 to... 

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