A series of copolymers containing epsilon-caprolactone (CL) and 4-methyl-epsilon-caprolactone (MeCL) were synthesized by ring-opening polymerization (ROP) using Tin(II) bis(2-ethylhexanoate)(Sn(Oct)(2)) or Novozym 435 as catalyst. The molecular structure and weight of copolymers were determined by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Our kinetic study showed that the monomer reactivity ratios for CL (r(1)) and MeCL (r(2)) using Sn(Oct) 2 as catalyst were estimated to be near unity and r(1) x r(2) = 1, indicating the random distribution of the monomers in the final copolymer. The results of DSC and XRD consistently indicated that the copolymers were inclined to be amorphous with the increasing of MeCL fraction. Microspheres were prepared from copolymers and characterized by SEM. The preliminary degradability and biocompatibility studies on these copolymers were also assessed. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 5293-5300, 2011