Characterization of pH-dependent micellization of polystyrene-based cationic block copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization |
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Authors: | Yoshiro Mitsukami Akihito Hashidzume Yotaro Morishima Andrew B. Lowe |
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Affiliation: | a Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan b Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2201, Japan c Faculty of Engineering, Fukui University of Technology, 6-3-1 Gakuen, Fukui, Fukui 910-8505, Japan d Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043, USA e Department of Polymer Science, University of Southern Mississippi, Hattiesburg, MS 39406-0076, USA |
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Abstract: | A series of block copolymers composed of a fixed length of an (ar-vinylbenzyl)trimethylammonium chloride (Q) block (the number average degree of polymerization of the Q block, DPn,Q=57) and varying lengths of an N,N-dimethylvinylbenzylamine (A) block (the number average degrees of polymerization of the A blocks, DPn,A, ranging 11-50) were prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization, and their pH-dependent micellization was characterized by potentiometric titration, 1H NMR spectroscopy, dynamic and static light scattering, and fluorescence techniques as a function of the A block length. At pH<5.5, the A block is fully protonated, and hence the block copolymers act as a simple polyelectrolyte, dissolving molecularly in acidic water. At pH>7, the A block becomes deprotonated, and thereby the block copolymers aggregate into a micelle composed of hydrophobic microdomains formed from the deprotonated A blocks. Results of light scattering and fluorescence measurements indicated that the micellization behavior depended strongly on the length of the A block. The number of polymer chains comprising one micelle (i.e. mean aggregation number, Nagg) increased from 3 to 12 as DPn,A increased from 11 to 50 at pH 10.0. In the case of a random copolymer of Q and A with an A/Q molar ratio similar to that of a block copolymer with DPn,A=50, Nagg∼1 (i.e. unimolecular micelle) was confirmed by static light scattering at pH 10.0. |
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Keywords: | pH-Dependent micellization Polystyrene-based cationic block copolymers Reversible addition-fragmentation chain transfer (RAFT) radical polymerization |
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