Effect of Buffer Anions on Pearl-Necklace Morphology of Tertiary Amine-Containing Binary Heterografted Linear Molecular Bottlebrushes in Acidic Aqueous Buffers
Effect of Buffer Anions on Pearl-Necklace Morphology of Tertiary Amine-Containing Binary Heterografted Linear Molecular Bottlebrushes in Acidic Aqueous Buffers
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缓冲液阴离子对酸性水缓冲液中含叔胺二元异质接枝线性分子瓶刷珍珠项链形貌的影响
DOI：
10.1021/acs.langmuir.0c02435
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发表时间：
2020
期刊：
影响因子：
3.9
通讯作者：
Zhao, Bin
中科院分区：
文献类型：
--
作者：
Kent, Ethan W.;Lewoczko, Evan M.;Zhao, Bin
分子瓶刷可以在不同条件下表现出多种不同的构象，并且对其形态的精确控制可以促进此类材料在潜在应用中的更好使用。本文报道了缓冲阴离子对线性二元异质接枝分子刷珍珠项链形态的影响，该分子刷由pKa为7.40的pH响应性聚（2-N，N-二乙基氨基）乙基甲基丙烯酸酯（PDEAEMA）和低临界溶解温度为9 °C的温度响应性聚（乙氧基二（乙二醇）丙烯酸酯）（PDEGEA）组成。利用铜催化的叠氮-炔环加成反应，通过接枝的方法制备了分子刷BMB。动态光散射研究表明，在1 °C下，在pH为6.50的水性缓冲液中，BMB的表观流体动力学尺寸随着缓冲阴离子的化合价的增加而减小，从具有1-电荷的乙酸根阴离子到携带2-和1-电荷的磷酸根阴离子以及在pH = 6.50下携带3-和2-电荷的柠檬酸根阴离子。原子力显微镜显示，当在0 °C下旋转浇铸时，BMB在pH为6.50的所有三种水性缓冲液中表现出珍珠项链形态。AFM图像分析表明，BMB的平均长度和每个刷分子的珠的数量随着缓冲阴离子的化合价的增加而减少，而珠的大小和高度增加。BMB的珍珠项链形态被认为是中性PDEGEA和带电PDEAEMA侧链沿刷状骨架沿着微相分离的结果。多价亲液缓冲阴离子形成质子化叔胺部分之间的桥接键，从而“交联”的带电PDEAEMA侧链，导致BMB的收缩和增强的微相分离的两个侧链聚合物。
Molecular bottlebrushes can exhibit a multitude of distinct conformations under different conditions, and precise control of their morphology can facilitate better use of such materials in potential applications. Herein, we report a study on the effect of buffer anions on the pearl-necklace morphology of linear binary heterografted molecular brushes consisting of pH-responsive poly(2-N,N-diethylamino)ethyl methacrylate) (PDEAEMA) with a pKaof 7.40 and thermoresponsive poly(ethoxydi(ethylene glycol) acrylate) (PDEGEA) with a lower critical solution temperature of 9 °C as side chains in various acidic aqueous buffers at 0 °C. The molecular brushes, denotated as BMB, were prepared by a grafting-to approach using copper(I)-catalyzed azide–alkyne cycloaddition reaction. Dynamic light scattering studies showed that the apparent hydrodynamic size of BMB in aqueous buffers with a pH of 6.50 at 1 °C decreased with increasing valency of buffer anions, from acetate anions with a charge of 1–, to phosphate anions carrying charges of 2– and 1– and citrate anions bearing charges of 3– and 2– at pH = 6.50. Atomic force microscopy revealed that BMB exhibited a pearl-necklace morphology from all three aqueous buffers with a pH of 6.50 when spin-cast at 0 °C. Analysis of AFM images showed that the average length of BMB and the number of beads per brush molecule decreased with increasing valency of buffer anions while the size and height of the beads increased. The pearl-necklace morphology of BMB was believed to be the result of microphase separation of the neutral PDEGEA and the charged PDEAEMA side chains along the brush backbone. Multivalent kosmotropic buffer anions formed bridging linkages between protonated tertiary amine moieties and thus “crosslinked” the charged PDEAEMA side chains, resulting in the shrinkage of BMB and enhanced microphase separation of two side chain polymers.