Purely salt-responsive micelle formation and inversion based on a novel schizophrenic sulfobetaine block copolymer: structure and kinetics of micellization.
Purely salt-responsive micelle formation and inversion based on a novel schizophrenic sulfobetaine block copolymer: structure and kinetics of micellization.
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DOI：
10.1021/la702029a
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发表时间：
2007-10
期刊：
影响因子：
--
通讯作者：
Di Wang;Tao Wu;Xuejuan Wan;Xiaofeng Wang;Shiyong Liu
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文献类型：
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作者：
Di Wang;Tao Wu;Xuejuan Wan;Xiaofeng Wang;Shiyong Liu
采用可逆加成-断裂链转移聚合法合成了一种新型的磺基甜菜碱嵌段共聚物聚甲基丙烯酸N-（吗啉代）乙酯-b-聚（4-（2-磺乙基）-1-（4-乙烯基苄基）吡啶甜菜碱）（PMEMA-b-PSVBP）。在水溶液中，PMEMA均聚物在Na 2SO 4（>0.6 M）的存在下变得不溶，而PSVBP均聚物在NaBr（>0.2 M）的存在下分子溶解。因此，PMEMA-b-PSVBP二嵌段共聚物在水溶液中表现出纯粹的盐响应性“精神分裂症”胶束化行为，形成两种类型的具有可逆结构的胶束，即PMEMA-核心胶束和PSVBP-核心胶束，这取决于所添加的盐的浓度和类型（方案1）。这两种类型的胶束的平衡结构，其特征在于通过结合1H NMR和激光光散射（LLS）。我们进一步研究了盐诱导的PMEMA-核心和PSVBP-核心胶束的形成/解离的动力学和它们之间的结构反转采用停流光散射技术。在0.5M NaBr存在下，加入Na 2SO 4（> 0.6M）诱导形成用良好溶剂化的PSVBP冠状物稳定的PMEMA-核心胶束。当最终Na 2SO 4浓度降至0.3 M以下时，在停流装置的死时间内（约2-3 ms），PMEMA-核心胶束发生稀释诱导的解离成单聚体，而PSVBP-核心胶束的盐诱导的分解则相当慢。从PMEMA-核心胶束到PSVBP-核心胶束的结构反转首先进行，PMEMA-核心胶束解离成单聚体，然后形成PSVBP-核心胶束。另一方面，从PSVBP-核心胶束到PMEMA-核心胶束的结构反转表现出不同的动力学序列。在盐跃变之后，PMEMA电晕链立即变得不可溶，并且不稳定的PSVBP核心胶束经历胶束间融合;这伴随着和/或随后是PSVBP核心的溶剂化和结构转化成胶体稳定的PMEMA核心胶束。
A novel sulfobetaine block copolymer, poly(N-(morpholino)ethyl methacrylate)-b-poly(4-(2-sulfoethyl)-1-(4-vinylbenzyl)pyridinium betaine) (PMEMA-b-PSVBP), was synthesized via reversible addition-fragmentation chain transfer polymerization. In aqueous solution, PMEMA homopolymer becomes insoluble in the presence of Na2SO4 (>0.6 M), whereas PSVBP homopolymer molecularly dissolves in the presence of NaBr (>0.2 M). Thus, PMEMA-b-PSVBP diblock copolymer exhibits purely salt-responsive "schizophrenic" micellization behavior in aqueous solution, forming two types of micelles with invertible structures, that is, PMEMA-core and PSVBP-core micelles, depending on the concentrations and types of added salts (Scheme 1). The equilibrium structures of these two types of micelles were characterized via a combination of 1H NMR and laser light scattering (LLS). We further investigated the kinetics of salt-induced formation/dissociation of PMEMA-core and PSVBP-core micelles and the structural inversion between them employing the stopped-flow light scattering technique. In the presence of 0.5 M NaBr, the addition of Na2SO4 (>0.6 M) induces the formation of PMEMA-core micelles stabilized with well-solvated PSVBP coronas. Dilution-induced dissociation of PMEMA-core micelles into unimers occurs within the dead time of the stopped-flow apparatus (approximately 2-3 ms) when the final Na2SO4 concentration drops below 0.3 M, while salt-induced breakup of PSVBP-core micelles is considerably slower. The structural inversion from PMEMA-core to PSVBP-core micelles proceeds first with the dissociation of PMEMA-core micelles into unimers, followed by the formation of PSVBP-core micelles. On the other hand, structural inversion from PSVBP-core to PMEMA-core micelles exhibits different kinetic sequences. Immediately after the salt jump, PMEMA corona chains are rendered insoluble, and unstable PSVBP-core micelles undergo intermicellar fusion; this is accompanied and/or followed by the solvation of PSVBP cores and structural inversion into colloidally stable PMEMA-core micelles.