pH- and Ionic-Strength-Induced Contraction of Polybasic Micelles in Buffered Aqueous Solutions
pH- and Ionic-Strength-Induced Contraction of Polybasic Micelles in Buffered Aqueous Solutions
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DOI：
10.1021/acs.macromol.5b00360
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发表时间：
2015-04-28
期刊：
影响因子：
5.5
通讯作者：
Lodge, Timothy P.
中科院分区：
文献类型：
--
作者：
Laaser, Jennifer E.;Jiang, Yaming;Lodge, Timothy P.
采用RAFT聚合法合成了聚甲基丙烯酸二甲氨基乙酯-聚苯乙烯（PDMAEMA-b-PS）嵌段共聚物。这些聚合物形成均匀的球形胶束与分散小于0.05时，加入水性缓冲液的聚合物溶液中的DMF。在恒定离子强度条件下的电位滴定产生了PDMAEMA均聚物和胶束的第一个严格的离子强度有效pK（a）对应关系。我们证明，有效的聚合物pK（a）单调增加的单体pK（a）随着离子强度的增加，但略有下降后，缔合聚合物链成胶束。我们进一步表征的pH值和离子强度引起的收缩的胶束冠在缓冲水溶液中。在单质子缓冲液中，胶束冠表现为盐的渗透刷，如在非缓冲溶液中观察到的其他嵌段胶束系统。然而，在多质子缓冲液中，我们观察到异常高程度的电晕收缩。我们证明，通过一个简单的两域平衡模型，这种收缩可能会产生从浓度的带电缓冲液中的胶束电晕，这将缓冲液的解离平衡进一步向多价物种比在散装。
We report the synthesis and characterization of poly(dimethylaminoethyl methacrylate)-block-poly(styrene) (PDMAEMA-b-PS) diblock copolymers by RAFT polymerization. These polymers form uniform spherical micelles with dispersities less than 0.05 upon addition of aqueous buffer to polymer solutions in DMF. Potentiometric titrations under constant ionic strength conditions yield the first rigorous ionic-strength-effective pK(a) correspondence for PDMAEMA homopolymers and micelles. We demonstrate that the effective polymer pK(a) increases monotonically toward the monomer pK(a) with increasing ionic strength, but decreases slightly upon association of polymer chains into micelles. We further characterize the pH- and ionic-strength-induced contraction of the micelle coronas in buffered aqueous solutions. In monoprotic buffers, the micelle corona behaves as a salted osmotic brush, as has been observed for other block polyelectrolyte micelle systems in unbuffered solutions. In polyprotic buffers, however, we observe an anomalously high degree of corona contraction. We demonstrate through a simple two-domain equilibrium model that this contraction likely arises from concentration of the charged buffer species in the micelle corona, which shifts the buffer dissociation equilibrium farther toward multivalent species than in the bulk.