Characterization of pH-dependent micellization of polystyrene-based cationic block copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization
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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DOI：
10.1016/j.polymer.2006.04.026
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发表时间：
2006-05
期刊：
影响因子：
4.6
通讯作者：
Y. Mitsukami;A. Hashidzume;S. Yusa;Y. Morishima;A. Lowe;C. McCormick
中科院分区：
文献类型：
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作者：
Y. Mitsukami;A. Hashidzume;S. Yusa;Y. Morishima;A. Lowe;C. McCormick
由固定长度的嵌段共聚物组成的一系列嵌段共聚物，（芳乙烯基苄基）三甲基氯化铵（Q）嵌段（Q嵌段的数均聚合度，DPn，Q=57）和不同长度的N，N-二甲基乙烯基苄胺（A）嵌段（A嵌段的数均聚合度，DPn，A，通过可逆加成-断裂链转移（RAFT）自由基聚合制备了11-50），并通过电位滴定、1H NMR、动态和静态光散射、和荧光技术作为A嵌段长度的函数。在pH<5.5时，A嵌段完全质子化，因此嵌段共聚物充当简单的聚合物，以分子形式溶解在酸性水中。在pH>7时，A嵌段变得去质子化，从而嵌段共聚物聚集成由去质子化的A嵌段形成的疏水微区组成的胶束。光散射和荧光测量结果表明，胶束化行为强烈依赖于A嵌段的长度。在pH 10.0时，随着DPn，A从11增加到50，包含一个胶束的聚合物链的数目（即平均聚集数，Nagg）从3增加到12。在Q和A的无规共聚物的情况下，A/Q摩尔比类似于具有DPn的嵌段共聚物的A/Q摩尔比，A=50，通过在pH 10.0下的静态光散射确认Nagg λ 1（即单分子胶束）。
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,Aincreased 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.