Synthesis, characterization, effect of architecture on crystallization of biodegradable poly(ε-caprolactone)b-poly(ethylene oxide) copolymers with different arms and nanoparticles thereof

Well-defined biodegradable Poly(epsilon-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) copolymers with different aims were synthesized via controlled ring-opening polymerization of E-caprolactone, followed by coupling reaction with carboxyl-terminated PEO, where these copolymers included both star-shaped copolymers having four and six arms and linear analogues having one and two arms. When the weight percent of both PCL and PEO blocks within copolymer was similar to each other, the maximal melting temperature, the crystallization temperature, degree of crystallinity, and the spherulitic growth rate of these copolymers decreased with the increasing arm number of polymer. Moreover, the diameter of nanoparficles fabricated from these copolymers had a decreased tendency over the arm number of polymer, while it slightly increased with increasing weight percent of PCL within copolymer. These results indicate that both the arm number of polymer (macromolecular architecture) and the arm length ratio of PCL to PEO not only controlled the crystallization behavior and spherulitic growth, but also adjusted the size of nanoparticles. Significantly, this will provide a starting point not only to improve the physical properties and drug release profiles of PCL-based biomaterials, but also to design new PCL/PEO-based biomaterials from both the arm number of polymer and the balance between hydrophobic PCL and hydrophilic PEO. (C) 2007 Wiley Periodicals, Inc.