Abstract: There is described a novel copolymer comprising approximately equimolar proportions of N-vinylcarbazole and a copolymerisable ethylenically unsaturated carboxylic acid such as acrylic acid or methacrylic acid, which can be prepared by mixing the monomers in a wide range of relative proportions, alone or diluted in a solvent, and initiating copolymerisation by methods known to the art, and which can be cross-linked, e.g. by means of polyvalent metal cations; this cross-linking is reversible on treatment with strong acid. The copolymer has good thermal and mechanical properties and adhesive properties, e.g. for metals, and can be used to form protective coatings on metals and to form metal and metal/plastics laminates.