Amorphous poly[(R,S)-beta-hydroxybutyrate], containing both phosphonoacetate and carboxylate functional end groups, was synthesized via anionic polymerization of racemic beta-butyrolactone initiated by supramolecular complexes of potassium P,P-dimethylphosphonoacetate. The living homopolymers, with alkali metal counter ions complexed with a crown ether, were utilized for the synthesis of block copolymers via condensation reaction with alkylene dihalides. As a result of this approach, coupled block copolymers containing phosphonoacetate functional end groups were obtained.