GB757392A - Preparation of novolak resins - Google Patents

Abstract

A novolak resin is made by condensing a molar excess of phenolic compounds containing phenol, meta-cresol or meta-ethyl phenol with formaldehyde (formalin or paraformaldehyde) in the presence of a salt of a divalent electropositive metal with an organic acid, which salt is at least partially soluble in the reaction mixture and the pH of the reaction mixture being between 4 and 7, until there is no free formaldehyde left in the reaction mixture, raising the temperature of the mixture while allowing volatile materials to distil therefrom to a temperature above 100 DEG C. at which a further condensation takes place, allowing the further condensation reaction to proceed to completion and the water thus formed to distil from the reaction mixture, removing any unwanted unreacted phenolic compounds and cooling the reaction mixture to give a solid product. The preferred ratio of phenolic compound/formaldehyde is from 1.3:1 to 2:1. Other phenols may be mixed with the specified ones. Commercial xylenols containing m-substituted phenols can also be used. Catalysts specified are Ba, Sr, Ca, Mg, Mn, Zn, Cd, Co, Pb, Fe, Cr, Sn and Ni salts of organic acids, e.g. benzoic, formic, acetic and lactic acids, and are used in amount, e.g. of 0.1 to 5.0 per cent by weight of the phenol present. The process is effected by mixing the phenol with the aldehyde, adding the catalyst thereto and gently heating the mixture until reaction occurs. Where formalin is used the initial reaction is controlled by heating under reflux conditions, but where non-aqueous reactants are used control of heat input is necessary to prevent too great a rate of temperature increase. For the further condensation a temperature of 150 DEG to 160 DEG C. is preferred. Many examples are given showing comparative figures of moulding tests on the novel and conventional novolaks.