Stepwise Conformational Transitions of Stimuli-Responsive Linear Ternary Heterografted Bottlebrush Polymers in Aqueous Solution
Stepwise Conformational Transitions of Stimuli-Responsive Linear Ternary Heterografted Bottlebrush Polymers in Aqueous Solution
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DOI：
10.1021/acs.macromol.1c02662
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发表时间：
2022-03-08
期刊：
影响因子：
5.5
通讯作者：
Zhao, Bin
中科院分区：
文献类型：
--
作者：
Kelly, Michael T.;Kent, Ethan W.;Zhao, Bin
利用两种不同的刺激响应性聚合物和聚氧化乙烯（PEO）作为侧链，实现了分子瓶刷（MBBs）在水溶液中从伸展蠕虫状到部分塌陷和稳定球形的逐步构象转变，其中PEO在响应性侧链变得不溶时充当稳定剂.通过点击接枝法合成了三种双重响应刷聚合物，它们由两种不同的pH响应性聚合物或两种不同的温度响应性聚合物或一种pH响应性聚合物和一种温度响应性聚合物组成，并沿着在骨架聚合物上随机接枝PEO。动态光散射研究表明，所有三个刷状聚合物显示两个连续的阶梯状的大小转变，在水溶液中响应于外部刺激的应用，与整体尺寸减小27- 29%。1H-1 NMR光谱分析证实，MBBs的尺寸转变源于pH诱导的可溶性到不溶性和/或温度触发的低临界溶液温度转变的响应侧链聚合物在刷。原子力显微镜显示逐步从扩展蠕虫状（有和没有珍珠项链形态）的构象变化，部分塌陷（收缩蠕虫状或波浪状或C-/S-形）和球状纳米物体稳定的PEO侧链。作为潜在应用的证明，尼罗红作为疏水模型药物包封在双重pH响应的球形MBB中，并且其逐步释放在逐渐降低pH时实现。
Stepwise conformational transitions of molecular bottlebrushes (MBBs) from extended wormlike to partially collapsed and stable globular in aqueous solution were realized with the use of two distinct stimuli-responsive polymers and poly(ethylene oxide) (PEO) as the side chains, where PEO served as a stabilizer when the responsive side chains became insoluble. Three dually responsive brush polymers, composed of either two distinct pH-responsive or two different thermoresponsive or one pH-responsive and one thermoresponsive polymers along with PEO randomly grafted on the backbone polymer, were synthesized by a click grafting-to method. Dynamic light scattering studies showed that all three brush polymers displayed two successive steplike size transitions in aqueous solutions in response to application of external stimuli, with overall size decreases of 27-29%. H-1 NMR spectroscopy analysis confirmed that the size transitions of MBBs originated from the pH-induced soluble-to-insoluble and/or the temperature-triggered lower critical solution temperature transitions of responsive side-chain polymers in the brushes. Atomic force microscopy revealed stepwise conformational changes from extended wormlike (with and without a pearl-necklace morphology) to partially collapsed (shrunken wormlike or wavelike or C-/S-shaped) and globular nano-objects stabilized by PEO side chains. As a demonstration of potential applications, Nile Red was encapsulated in the dually pH-responsive globular MBBs as a hydrophobic model drug, and its stepwise release was achieved upon gradually decreasing the pH.