Solid copolymers are produced by copolymerizing a mixture of: (A) at least 30% by weight of a monomer having the formula: ##EQU1## wherein R.sub.1 is H or CH.sub.3 and R.sub.2 is an alkyl radical containing from 1 to 14 carbon atoms; (B) from 3 to 20% by weight of an ethylenic .alpha., .beta. unsaturated carboxylic acid or anhydride thereof, or from 3 to 40% by weight of glycidyl acrylate or glycidyl methacrylate; and (C) from 0 to 67% by weight of a monomer copolymerizable with said monomers (A) and (B). Preferably, the mixture is first bulk-polymerized until conversion to the copolymer is from 10% to 80% by weight and the polymerization is completed by suspension-polymerization. Thermosetting solid coating compositions are produced by mixing and melting 60 to 95 parts by weight of the solid copolymer and 40 to 5 parts by weight of a cross-linking compound or of an epoxy resin containing at least 2 epoxy radicals in the molecule in presence of a tertiary amine curing accelerator.