Synthesis of Star-Shaped Poly(ε-caprolactone)-<i>b</i>-poly(<scp>dl</scp>-lactic acid-<i>alt</i>-glycolic acid) with Multifunctional Initiator and Stannous Octoate Catalyst

Abstract

Two types of three-arm or four-arm star-shaped hydroxy-terminated poly(ε-caprolactone) (PCL) were successfully synthesized via the ring-opening polymerization of ε-caprolactone (CL) with multifunctional initiator, such as trimethylolpropane (TMP) or pentaerythritol (PTOL), and stannous octoate (SnOct2) catalyst in bulk at 110 °C. The number-average molecular weight of PCL is proportional to the molar ratio of monomer to initiator. 1H NMR spectroscopy of the resulting PCL indicates that it contains a primary hydroxy end group in each arm. The star-shaped PCL with hydroxy end groups can be used as a macroinitiator for block copolymerization with dl-3-methylglycolide (MG) using SnOct2 catalyst in bulk at 115 °C. 1H NMR spectra of the resulting block copolymers show that the molecular weights and the unit compositions of the block copolymers were controlled by the molar ratios of MG monomer to hydroxy groups of PCL and MG to CL in feed, respectively. Moreover, the molecular weights of the resulting block copolymers linearly increased with the increase of the molar ratios of MG to CL in feed. The molecular weight distributions of the block copolymers were rather narrow (Mw/Mn = 1.09−1.26). 13C NMR spectra of the resulting block copolymers clearly show their diblock structures, that is, PCL as the first block and poly(dl-lactic acid-alt-glycolic acid) (dl-PLGA50) with alternating structures of lactyl and glycolyl units as the second block. Therefore, two types of three-arm or four-arm star-shaped diblock copolyesters comprising the first block PCL and the second block dl-PLGA50 were successfully synthesized via the sequential ring-opening polymerization of CL with multifunctional initiator and SnOct2 catalyst and then followed by copolymerization with MG.