A thermodynamic covalent cross-linking system utilizing alkoxyamine units as thermally reversible covalent bonds was demonstrated. By heating the poly(methacrylic ester)s containing alkoxyamine units on the side chain, the cross-linking reaction was achieved as a result of a radical exchange reaction of alkoxyamine moieties. Kinetic studies have revealed that the cross-linking behavior depends remarkably on concentration and reaches equilibrium at a given reaction time, and characteristic reaction behaviors for thermodynamic reactions have been observed. The de-cross-linking reaction wits carried Out by heating the cross-linked polymer in the presence of an excess amount of alkoxyamine. It was found that the cross-linked points thermally dissociate and that the reaction system is reversible under stoichiometric control.