Synthesis and characterization of well-defined cyclodextrin-centered seven-arm star poly(ε-caprolactone)s and amphiphilic star poly(ε-caprolactone-b-ethylene glycol)s

Per-2,3-acetyl-beta-cyclodextrin with seven primary hydroxyl groups was synthesized by selective modification and used as multifunctional initiator for the ring-opening polymerization of F-caprolactone (CL). Well-defined beta-cyclodextrin-centered seven-arm star poly(epsilon-caprolactone)s (CDSPCLs) with narrow molecular weight distributions (<= 1.15) have been successfully prepared in the presence of Sn(Oct)(2) at 120 degrees C. The molecular weight of CDSPCLs was characterized by end group H-1 NMR analyses and size-exclusion chromatography (SEC), which could be well controlled by the molar ratio of the monomer to the initiator. Furthermore, amphiphilic seven-arm star poly(epsilon-caprolactone-b-ethylene glycol)s (CDSPCL-b-PEGs) were synthesized by the coupling reaction of CDSPCLs with carboxyl-terminated mPEGs. 1H NMR and SEC analyses confirmed the expected star block structures. Differential scanning calorimetry analyses suggested that the melting temperature (T-c), the crystallization temperature (T-m), and the crystallinity degree (X-c) of CDSPCLs all increased with the increasing of the molecular weight, and were lower than that of the linear poly(epsilon-caprolactone). As for CDSPCL-b-PEGs, the T-c and T-m of the PCL blocks were significantly influenced by the PEG segments in the copolymers. Moreover, these amphiphilic star block copolymers could self-assemble into spherical micelles with the particle size ranging from 10 to 40 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. (C) 2008 Wiley Periodicals, Inc.