The ring-opening polymerization of two caprolactone monomers catalyzed by zinc undecylenate (ZU) is reported. Polymerizations were performed in bulk with benzyl alcohol (BnOH) as an initiator at 90 and 110 degrees C, respectively. A slower polymerization rate was observed for ?-octyloxy-?-caprolactone as compared to ?-caprolactone. Diblock copolymers were synthesized by the sequential monomer addition at 90 and 110 degrees C. The kinetic studies performed for the ring-opening polymerization of ?-caprolactone and ?-octyloxy-?-caprolactone and the successful synthesis of diblock copolymers by the sequential monomer addition confirmed the controlled/living nature of zinc undecylenate catalyzed reactions.