Synthesis and characterization of poly(ε-caprolactone)s with controlled architecture

Abstract

Star-shaped poly(ε-caprolactone)s were synthesized via $Sn(Oct)_2$ catalyzed ring-opening polymerization. Even though the polymers have controlled molecular weight and narrow polydispersity, side products (less than 10 mol%) are detected as a result of the cleavage of phenylic-ester bond. These side products can be completely removed by reprecipitation into methanol, when the polymers have the degree of polymerization (DP) more than 20. The linear and star-shaped poly(ε-caprolactone)s with the controlled number of hydroxyl end-groups and well defined structures were synthesized. These polymers were designed to have 2, 4 or 8 hydroxyl end-groups and number-average molecular weights of 9000-10000 g/mol. The viscosity of star shaped PCLs is lower than that of linear analog, and star-shaped PCLs exhibited lower melting points and melting enthalpies than linear PCLs. The effect of hydroxyl end-groups in periphery of the polymers is not significant, but the polymers with multi-hydroxyl end-groups derived from the bis-MPA have higher thermal stability than the unprotected PCLs.