Enzymatic synthesis, structural and thermal properties of poly(ω-pentadecalactone-co-butylene-co-succinate)

Poly(ω-pentadecalactone-co-butylene-co-succinate) copolymers with various compositions were synthesized via copolymerization of dialkyl succinate with 1,4-butandiol and ω-pentadecalactone (PDL) catalyzed by immobilized Candida antarctica lipase B. The monomer unit ratio in the copolymers can be carefully controlled by adjusting monomer feed ratio. NMR spectroscopy shows that the copolymers have nearly random distribution of PDL, butylene, and succinate repeat units, linked by ester groups along the macromolecule. Thermal stability of poly(PDL-co-butylene-co-succinate)s is composition-dependent and increases with increasing PDL unit content. All copolymers are highly crystalline irrespective of their composition and they show iso-dimorphic behavior, with the crystal lattices of poly(ω-pentadecalactone) and of poly(butylene succinate) being capable of hosting foreign comonomer units up to a given extent. The two type crystals are stable in different composition ranges. The Tm/composition dependence shows a minimum at 35 mol% PDL (pseudo-eutectic composition), where PBS-type and PPDL-type crystals co-exist. Co-crystallization with high extent of comonomer inclusion is supported by application of the Wendling-Suter model to the experimental Tm values. Nanoparticles prepared from these copolymers maintain high crystallinity degree associated with iso-dimorphic behavior.