The chemoenzymatic synthesis of a novel CBABC-type pentablock copolymer and its self-assembled crew-cut aggregation

A symmetric linear CBABC pentablock copolymer consisting of poly(ethylene oxide) (PEO), polycaprolactone (PCL), and polystyrene (PSt) was synthesized by the combination of enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Dihydroxyl-capped PEO first initiated eROP of c-CL in the presence of biocatalyst Novozyme 435. Subsequently, the resulting dihydroxyl-terminated copolymer PCL-b-PEO-b-PCL was converted to bromine-ended triblock macroinitiator by the esterification with alpha-bromopropionyl bromide. Pentablock copolymer PSt-b-PCL-b-PEO-b-PCL-b-PSt was obtained via a subsequent ATRP of styrene(St), and its kinetics analysis indicated a living/controlled radical polymerization. The self-assembly behavior of pentablock copolymer was investigated in aqueous media. The crew-cut aggregates of various morphologies were observed, such as normal spherical micelles, rodlike micelles, vesicles, lamellae, and large compound micelles (LCMs). In addition, it was found that both the copolymer composition and the copolymer concentration in THF had a great influence on the morphologies of the aggregates.