Sub-10 nm Nano-Organization in AB2- and AB3-Type Miktoarm Star Copolymers Consisting of Maltoheptaose and Polycaprolactone

The AB(2)- and AB(3)-type miktoarm star copolymers consisting of maltoheptaose (MH, as A block) and poly(epsilon-caprolactone) (PCL, as B block), namely MH-b-(PCL)(2) and MH-b-(PCL)(3), were synthesized, and their nano-organization was characterized. The syntheses of MHb-(PCL)(2) and MH-b-(PCL)(3) were carried out through two reaction steps: (1) preparation of linear and three-branched PCLs bearing an azido group on the chain center (N-3-(PCL)(2) and N-3-(PCL)(3)) by the diphenyl phosphate-catalyzed ring-opening polymerization of epsilon-caprolactone (epsilon-CL) using azido-functionalized di- and triols (N-3-(OH)(2) and N-3-(OH)(3)) as the initiators and (2) the copper-catalyzed azide-alkyne cycloaddition of N-3-(PCL)(2) and N-3-(PCL)(3) with the ethynyl-functionalized MH. The miktoarm star copolymers having M-n for the PCL block of ca. 5000 (MH-b-(PCL2.5k)(2) and MH-b-(PCL1.7k)(3)) and 10 000 (MH-b-(PCL5k)(2) and MH-b-(PCL3.3k)(3)) were obtained with a very narrow polydispersity index of less than 1.05. Bulk samples of the four types of miktoarm star copolymers exhibited body centered cubic phases, as determined by small angle X-ray diffraction experiments. The domain spacing were determined to be 9.8 nm for MH-b-(PCL2.5k)(2), 8.8 nm for MH-b-(PCL1.7k)(3), 10.5 nm for MH-b-(PCL5k)(2), and 9.8 nm for MH-b-(PCL3.3k)(3), which were smaller than those of the corresponding linear diblock copolymers.