GB942057A - Process for the production of cross-linked synthetic resins of high molecular weight - Google Patents

Abstract

Aldehydes are condensed with aromatic ethers or polynuclear aromatic hydrocarbons in an organic solvent inert with respect to aldehydes containing at least 3% by weight of the ether or hydrocarbon of a strong organic acid, the concentration of the acid being maintained throughout the reaction. The aromatic compounds are water-insoluble and polyfunctional with respect to aldehydes and may be substituted but should not contain any groups capable of ion-exchange nor any groups which are water-solubilizing. Suitable ethers are aromaticaliphatic, e.g. anisole; phenetole; phenyl butyl, phenyl isopropyl, naphthyl methyl and naphthyl ethyl ethers; the methyl ether of m-hydroxydiphenyl or of 1,3,5-xylenol; and ethylene or butylene glycol diphenyl ethers. Completely aromatic ethers such as diphenyl oxide or phenyl naphthyl ether including cyclic aromatic ethers, e.g. diphenylene dioxide also are usable. Suitable hydrocarbons are naphthalene, anthracene, phenanthrone, acenaphthene, and methyl naphthalene. The ethers and hydrocarbons may be substituted by halogen, halogenoalkyl, nitro or cyano groups. Lower aliphatic aldehydes, e.g. acetaldehyde or butyraldehyde may be used, but formaldehyde and substances yielding it, e.g. paraformaldehyde and trioxymethylene are preferred. The reaction may be starting using an aliphatic aldehyde such as acetaldehyde and completed using formaldehyde. The strong organic acids have pKa not more than 2.87, e.g. monodi-, and tri-chloroacetic and their bromine analogues; toluene, benzene, chlorobenzene, dichlorobenzene, isopropylbenzene and nitrobenzene sulphonic acids, and 2,6-dichlorophenyl-4 sulphonic acid; methyl, ethyl and propyl sulphonic acids are also suitable. The solvent may be halogenated hydrocarbon, e.g. ethylenedichloride, 1,2-dichloroethane, trichlorethylene, tetrachlorethane, 1,4-dichlorobutane, chlorobenzene, di- and tri-chlorobenzene, and their bromine analogues; phenols substituted by alkyl or halo groups in the 2,4,6 positions, e.g. 2,4,6,-trichloro or 2-chloro-4-nitro-6- methyl phenol; aliphatic hydrocarbons in combination with halogenated hydrocarbons, e.g. n-hexane, n-heptane, neopentane, or isooctane, the hydrocarbon preferably not exceeding 70% of the solvent by volume; or cyclic ethers, e.g. dioxan. The condensation is preferably effected at 70-130 DEG C., the reaction time being 4-24 hours, 1-3 mols. of formaldehyde are preferably used per mol. of aromatic reactant. The preferred reaction conditions are the use of halogenated hydrocarbons and 3-50% of acid based on the aromatic reactant. Water formed during the reaction tends to form a separate layer in which the catalyst dissolves and should therefore be removed, e.g. by distillation, by combination with anhydrous salts, e.g. Na2SO4, or by reaction with acid chlorides or anhydrides, e.g. acetyl chloride or acetic anhydride. The use of solvents such as dioxan or haloacetic acids which dissolve the water and swell the product makes removal of water unnecessary when phenoxyethyl chloride is condensed. The ratio of aromatic reactant to solvent is advantageously 1:0.5 to 1:2. The use of poor solvents such as alcohols, carboxylic acids or aliphatic hydrocarbons, in admixture with good solvents leads to spongy structures for the products. The products may be homogeneous gels, opaque, cloudy gels, permeated by fine pores, or of a sponge-like structure. They may be produced as diaphragms or foils by carrying out the reaction in a suitable cavity, e.g. between glass plates or if acid-resisting fabric e.g. of PVC., polyacrylonitrile, or polyvinylidene chloride is impregnated with the reaction solution and condensation carried out, plasticizers, e.g. dioctyl or dibutyl phthalate, dioctyl sebacate, or tricresyl phosphate improve the elasticity of the diaphragms. The products may be formed as beads by disposal of the organic solvent solution of reactants and acids in an aqueous phase; addition of a strong inorganic acid to the water causes most of the organic acid to remain in the organic phase. Suitable solvents for this procedure are tetrachlorethane, 1,4 dichlorobutane, mono-, di- or trichlorobenzenes, and mono or di bromobenzenes. Alternatively, the reactants may be condensed in organic medium with 3-20% of the organic acid present, then a 20-50% solution of strong inorganic acid in water added, or the reactants condensed in aqueous suspension without an organic solvent but with an organic acid, and an organic solvent added later to break up the organic phase into beads. The presence of the organic solvent causes the molecules of the product to have a loose, open structure although considerably cross-linked, and this allows ready substitution of the resins to form ion-exchangers. Chloromethyl, sulphonic acid and phosphoric acid groups may be readily introduced and further modification, e.g. of halo to amino and then further modification of the amino groups with chloroacetic acid is then possible.