Racemic and optically active 4-carboxy-2-oxetanones have been prepared, starting from racemic, (R)-4-benzyloxycarbonyl-2-oxetanone, by catalytic hydrogenolysis of the lateral benzyl protecting group. This new beta-substituted-beta-lactone (malolactonic acid), which was considered as totally unstable due to the presence of a carboxyl group, has been isolated, characterized and prepared in large quantities. The liberated carboxylic acid function can be used for coupling reactions with different types of molecules in the goal to tailor make functionalized multimeric macromolecules (reactive polymers, supported catalysts, liquid crystals polymers, macromolecular prodrugs). This possibility has been examplified by using 2, 4, 5-trichlorophenol as activating agent and chloramphenicol as bioactive molecule, which have been bound to malolactonic acid and then copolymerized by anionic ring opening polymerization in the presence of 4-benzyloxycarbonyl-2-oxetanone. It has been shown that this new route conducts to activated derivatives of poly (malic acid) and polymeric drug carriers patterns.