Process for preparing resorcinol copolymers

A process for preparing a resorcinol copolymer, comprising reacting at least one phenol having the general formula, ##STR2## in which R.sub.1 is --CH.sub.3 or --OCH.sub.3, and R.sub.2 is hydrogen or --CH.sub.3, with formaldehyde in an amount of 0.6 to 2.4 moles per mole of said phenol, in the presence of an alkaline catalyst, to obtain a resol-type precondensate containing 1 to 30%, based on the initial amount, of residual unreacted formaldehyde, and, then, adding said resol-type precondensate to a mixture of an acid, equivalent to said alkaline catalyst or 10 mol % excess with reference to said phenol, and at least one member selected from the group consisting of resorcinol and lower alkyl-substituted resorcinols, in an amount of 0.4 to 2.5 moles per mole of said phenol, to effect co-condensation.