Copolymers having improved machining and water resistant properties are produced using a monomer containing an adduct protecting group, particularly an alkyl boronic acid adduct, of glyceryl acrylate or glyceryl methacrylate, in combination with an alkyl acrylate or methacrylate, and optionally a glycidyl acrylate or methacrylate. After machining and shaping, the adduct is removed to provide a hydrogel useful as a contact lens material.