Thiol end-functionalized polycaprolactone(HS-PCL) and amphiphilic -poly (ethylene glycol)-b- polycaprolactone (PEG-b-PCL) were synthesized via ring-opening polymerization of ε-caprolactone (ε-CL) using Novozym 435 (immobilized form of lipase B from Candida antarctica) as biocatalyst

and 2-mercaptoethanol and methoxy poly(ethylene glycol) (MPEG) as initiators

respectively.The structure of the obtained polymers was characterized by means of IR

1H-NMR and GPC.The effects of the feed ratio of initiator to CL

polymerization temperature and time on the monomer conversions and molecular weights of polymers were investigated.Oxidation of the thiol end groups of HSPCL to form disulfide bonds was studied in a series of solvents including DMSO

THF and acetone.The structure and sizes of the copolymer PEG-b-PCL micelles were analyzed by means of DLS and 1H-NMR.The results showed that the obtained polymers had the expected structure; Novozym 435 had high catalytic activity

for the bulk polymerizaion with 10 wt% Novozym 435

the monomer conversion achieved ca. 80% within 2 h at 70℃; 2-mercaptoethanol and MPEG could effectively initiate the ringopening polymerization of CL; HS-PCL samples were placed in DMSO (or THF or acetone) under ambient atmosphere at a certain temperature

such as 37℃ or 70℃

the molecular weights of the oxidized products increased

but less than 2 times that of HS-PCL

indicating that some HS-PCL molecules were oxidized to form PCL-S-S-PCL.The PEG-b-PCL copolymers could self-assemble into nanosized micelles composed of hydrophobic PCL core and hydrophilic PEG shell in aqueous solution.The hydrodynamic diameters of micelles varied from 64 nm to 122 nm as the increase of ［CL］/［EO］ of copolymer from 0.23 to 1.70.