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(ε-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 MH- b -(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 ε-caprolactone (ε-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 -(PCL 2.5k ) 2 and MH- b -(PCL 1.7k ) 3 ) and 10 000 (MH- b -(PCL 5k ) 2 and MH- b -(PCL 3.3k ) 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 -(PCL 2.5k ) 2, 8.8 nm for MH- b -(PCL 1.7k ) 3, 10.5 nm for MH- b -(PCL 5k ) 2, and 9.8 nm for MH- b -(PCL 3.3k ) 3, which were smaller than those of the corresponding linear diblock copolymers.