Synthesis of Well-Defined Block Copolymers of Hyperbranched Polyamide and Polystyrene and Their Micelle-to-Vesicle Transformation in Organic Solvents |
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Authors: | Yoshihiro Ohta Chih-Feng Huang Yi-Huan Lee Chi-An Dai Tsutomu Yokozawa |
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Institution: | 1. Department of Materials and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama, 221-8686 Japan;2. Department of Chemical Engineering, i-Center for Advanced Science and Technology (iCAST), National Chung Hsing University, Taichung, 402-27 Taiwan;3. Department of Molecular Science and Engineering, National Taipei University of Technology, Taipei, 10608 Taiwan;4. Department of Chemical Engineering and Institute of Polymer Science and Engineering, National Taiwan University, Taipei, 10617 Taiwan |
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Abstract: | Well-defined block copolymers consisting of hyperbranched polyamide (HBPA) and polystyrene (PSt) are synthesized, and their self-assembled structures in solutions are investigated. Atom transfer radical polymerization (ATRP) of styrene initiated from an HBPA macroinitiator, prepared by the chain-growth condensation polymerization of an AB2 monomer, followed by introduction of an ATRP initiator unit at the focal point, gives the desired block copolymers, PSt-b-HBPAs, with well-defined molecular weight and narrow molecular weight distribution. The block copolymer (PSt/HBPA = 84/16) undergoes self-assembly in toluene to form spherical micelles (≈10–20 nm), but upon addition of methanol to the toluene solution (toluene/methanol = 0.97/0.03), the morphology changes to vesicles. Further addition of methanol (toluene/methanol = 0.90/0.10) leads to an increase in vesicle size (200–300 nm) and the morphology further transforms from vesicles to large aggregates (>100 nm) at toluene/methanol = 0.80/0.20. In the case of PSt-b-HBPA with shorter PSt segments (PSt/HBPA = 76/24 and 60/40), spherical micelles are formed in toluene, but the micelle morphology remains unchanged when 10 wt% methanol is added, though large aggregates (>100 nm) are still formed in toluene/methanol = 0.80/0.20. Interestingly, the morphological transformations of linear/hyperbranched block copolymers are different from those of their double linear block copolymer counterparts. |
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Keywords: | chain-growth condensation polymerization hyperbranched polymers linear-hyperbranched block copolymers micelles self-assembly vesicles |
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