Key Laboratory for Advanced Materials and Department of Chemistry, East China University of Science and Technology, Shanghai 200237, China.
Soft Matter. 2015 Jun 28;11(24):4830-9. doi: 10.1039/c5sm00859j. Epub 2015 May 19.
This work reports on the aqueous stimuli-responsive behaviors of an ABA triblock copolymer, a BAB triblock copolymer, an AB diblock copolymer and citrate-based gold nanoparticles decorated with AB diblock copolymers (where A is the pH- and thermo-responsive poly[N,N-(dimethylamino)ethyl methacrylate] (PDMAEMA) and B is the thermo-responsive poly[2-(2-methoxyethoxy)ethyl methacrylate] (PMEO2MA)). The symmetric triblock polymers were synthesized via sequential atom transfer radical polymerization (ATRP) using a disulfide-functionalized initiator. Subsequently, the thiol-ended diblock copolymers were facilely obtained by reducing these triblock copolymers and were grafted onto gold nanoparticle (AuNP) surfaces via ligand exchange to yield stimuli-sensitive gold nanoparticles (Au@AB and Au@BA). The ABA and BAB triblock copolymers exhibited two-step thermo-induced aggregation behavior in water at a pH near the isoelectric point (IEP), which resulted in the formation of micelles after the first lower critical solution temperature (LCST) and large aggregates consisting of clustered micelles above the second LCST transition. The significant difference between the micelle sizes of the ABA and BAB copolymers, such that the micelle size of the BAB copolymer was smaller than that of the ABA copolymer although both had a similar unit composition, suggests a distinction between the micelle structures. The "branch" and "flower-like" micelles that are formed in the ABA and BAB aqueous solutions, respectively, ultimately governed the phase transition behaviors. The AB diblock copolymer exhibited similar micellization behavior and a micelle size roughly similar to that of the ABA triblock copolymer, although the chain length of the AB copolymer is only half that of the ABA copolymer. Both Au@PDMAEMA-PMEO2MA and Au@PMEO2MA-PDMAEMA showed similar dual LCST behaviors and pH-responsive behaviors in aqueous solutions without the addition of salt. A significant difference was observed between the two types of hybrid AuNPs in salty solutions, in which only the Au@PDMAEMA-PMEO2MA system exhibited thermo-induced aggregation behavior. These hybrid nanoparticles can be used as phase transfer reagents. Additionally, AuNPs capped with PDMAEMA-PMEO2MA diblock copolymer can spontaneously transfer across a water-toluene interface.
本文报道了 ABA 三嵌段共聚物、BAB 三嵌段共聚物、AB 二嵌段共聚物以及柠檬酸基金纳米粒子上接枝 AB 二嵌段共聚物（其中 A 为 pH 和温度响应性聚[N,N-（二甲氨基）乙基甲基丙烯酸酯]（PDMAEMA），B 为温度响应性聚[2-（2-甲氧基乙氧基）乙基甲基丙烯酸酯]（PMEO2MA））的水相刺激响应行为。对称的三嵌段聚合物是通过使用二硫键官能化引发剂的顺序原子转移自由基聚合（ATRP）合成的。随后，通过还原这些三嵌段聚合物，很容易得到巯基封端的二嵌段共聚物，并通过配体交换接枝到金纳米粒子（AuNP）表面，得到刺激敏感的金纳米粒子（Au@AB 和 Au@BA）。ABA 和 BAB 三嵌段共聚物在接近等电点（IEP）的 pH 下表现出两步热诱导聚集行为，这导致在第一次低临界溶液温度（LCST）后形成胶束，并且在第二次 LCST 转变之上形成由聚集胶束组成的大聚集体。ABA 和 BAB 共聚物的胶束尺寸有显著差异，尽管它们具有相似的单元组成，但 BAB 共聚物的胶束尺寸小于 ABA 共聚物，这表明胶束结构之间存在区别。分别在 ABA 和 BAB 水溶液中形成的“支化”和“花状”胶束最终控制了相转变行为。AB 二嵌段共聚物表现出相似的胶束化行为和大致与 ABA 三嵌段共聚物相似的胶束尺寸，尽管 AB 共聚物的链长仅为 ABA 共聚物的一半。在没有添加盐的情况下，Au@PDMAEMA-PMEO2MA 和 Au@PMEO2MA-PDMAEMA 在水溶液中均表现出类似的双重 LCST 行为和 pH 响应行为。在含盐溶液中，两种类型的混合 AuNP 之间存在显著差异，只有 Au@PDMAEMA-PMEO2MA 体系表现出热诱导聚集行为。这些混合纳米粒子可用作相转移试剂。此外，用 PDMAEMA-PMEO2MA 二嵌段共聚物封端的 AuNPs 可以自发跨水-甲苯界面转移。
