Rod-coil type miktoarm star copolymers consisting of polyfluorene and polylactide: precise synthesis and structure-morphology relationship
Journal
Polymer Chemistry
Journal Volume
6
Journal Issue
39
Pages
6959-6972
Date Issued
2015
Author(s)
Abstract
A series of rod-coil miktoarm star copolymers consisting of poly[2,7-(9,9-dihexylfluorene)] (PF) and polylactide (PLA) arms as the rod and coil segments, respectively, were synthesized by combining the chain-growth Suzuki-Miyaura coupling polymerization and living ring-opening polymerization (ROP). First, PFs having a hydroxyl group at the α-chain end (PF-BnOH) were prepared by the polymerization of 2-(7-bromo-9,9-dihexyl-9H-fluorene-2-yl)4,4,5,5-tetramethyl-1,2,3-dioxaborolane using the initiating system of 4-(tetrahydropyran-2′-yloxymethyl)-iodobenzene/Pd2(dba)3/t-Bu3P. After a couple of chain end modifications, PFs having one, two, and three hydroxyl groups at the α-chain end (PF-OH, PF-(OH)2, and PF-(OH)3, respectively) were obtained with dispersity (D) values of less than 1.29. The obtained PF-OH, PF-(OH)2, and PF-(OH)3 were used as the initiators for the organic base-catalyzed ROP of rac-lactide to produce the AB type linear diblock (PF-b-PLA) and AB2 and AB3 type miktoarm star copolymers (PF-b-(PLA)2 and PF-b-(PLA)3, respectively). The self-assembled nanostructures in the thermally-annealed PF-b-(PLA)xs (x = 1, 2, and 3) were evaluated in the bulk by synchrotron small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The PF-b-PLA, PF-b-(PLA)2, and PF-b-(PLA)3 with the PF weight fractions of 0.52-0.56 were found to form poorly ordered PLA cylindrical structures in the PF matrix due to a strong rod-rod interaction of the PF segment. On the other hand, these BCPs with the PF weight fractions of 0.22-0.23 exhibited the hexagonally close-packed cylinder (Hex) morphologies, in which the cylindrical PF phase was embedded in the PLA matrix. More interestingly, the domain-spacing (d) values for the Hex morphologies decreased with the increasing PLA arm number despite each BCP having a comparable molecular weight and PF weight fraction: d = 26.4 nm for PF-b-PLA, d = 21.7 nm for PF-b-(PLA)2, and d = 18.6 nm for PF-b-(PLA)3.
SDGs
Type
journal article