Microphase separation of carbohydrate-based star-block copolymers with sub-10 nm periodicity. Issue 9 (25th January 2019)

• Record Type: Journal Article
• Authors: Isono, Takuya; Kawakami, Nao; Watanabe, Kodai; Yoshida, Kohei; Otsuka, Issei; Mamiya, Hiroaki; Ito, Hajime; Yamamoto, Takuya; Tajima, Kenji; Borsali, Redouane; Satoh, Toshifumi
• Is Part Of: Polymer chemistry. Volume 10:Issue 9(2019)
• Page Start: 1119
• Page End: 1129
• Publication Date: 2019-01-25
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/c8py01745j
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : Star-block copolymers consisting of polycaprolactone and maltotriose segments with three, four, and six arms were synthesized to achieve sub-10 nm microphase-separated structures. Abstract : Block copolymers (BCPs) with a high Flory–Huggins interaction parameter ( χ ) and a low degree of polymerization ( N ) are being investigated to create microphase-separated structures with sub-10 nm periodicity ( d ). However, the lowered N value also leads to undesirable properties. In this paper, we demonstrate that the use of a star-block architecture is an effective way to achieve microphase separation with sub-10 nm d without reducing the molecular weight. Thus, three-, four-, and six-armed star-block copolymers consisting of poly(ε-caprolactone) (PCL) and maltotriose (MT), i.e., (PCL- b -MT) x ( x = 3, 4, and 6, respectively), with comparable arm lengths and MT volume fractions were synthesized in three steps involving the ring-opening polymerization of ε-caprolactone, chain end modification, and click reaction. Small angle X-ray scattering experiments revealed that the (PCL- b -MT) x microphase separated into hexagonally close-packed cylindrical structures with a d of 6–8 nm. The d value and morphology of (PCL- b -MT) x are essentially the same as those of the corresponding arm unit, i.e., linear diblock copolymers (PCL- b -MTs). In other words, the d value can be fixed at less than 10 nm even though the total molecular weight of the BCP is increased by increasing the arm number. In addition, (PCL- b -MT) x had the advantages of an increased order–disorder transition temperature as well as better quality of the nanostructure formed in the thin film state compared to PCL- b -MT. Overall, well-ordered microphase-separated structures with a d value less than 10 nm were obtained, while the total molecular weight of the BCPs is higher than 10 000 g mol −1 .