Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
Division of Applied Chemistry, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
Langmuir. 2021 Jun 15;37(23):6974-6984. doi: 10.1021/acs.langmuir.1c00513. Epub 2021 May 28.
A series of cyclic surfactants were synthesized from a poly(ethylene glycol) (PEG) homopolymer and Pluronic surfactants L35, L64, P123, F68, 10R5, and 17R4, and their interfacial activity depending on the topology, chain ends, and block sequence was investigated. The cyclization was performed in a single step through etherification of the PEG homopolymer and the hydrophilic-hydrophobic-hydrophilic (ABA type) poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG), while the hydrophobic-hydrophilic-hydrophobic (BAB type) PPG-PEG-PPG was cyclized via acetalization. The cyclized surfactants were rigorously characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography. Cyclization of the surfactants induced a significant decrease in the hydrodynamic volume, which was more pronounced than that of the PEG homopolymer. Surface tension (γ) measurements indicated that the interfacial activity of the cyclized surfactants is stronger than their corresponding linear precursors, due to the increase in the surfactant density at the air-water interface as a consequence of the decreased molecular occupational area () upon cyclization. In the case of the PEG homopolymer, considerably decreased from 410 Å for the linear PEG prepolymer to 100 Å for the cyclized PEG product. While the effects of chain-end groups were found to be limited to surfactants of relatively small molecular weights, the influence of cyclization depended strongly on the hydrophilic/hydrophobic ratio; the higher the PEG composition the surfactants had, the larger the decrease in γ and ; in other words, stronger enhancement in the interfacial activity was observed.
一系列环状表面活性剂是由聚乙二醇（PEG）均聚物和 Pluronic 表面活性剂 L35、L64、P123、F68、10R5 和 17R4 合成的，研究了它们的界面活性与拓扑结构、链端和嵌段序列有关。通过 PEG 均聚物和亲水性-疏水性-亲水性（ABA 型）聚乙二醇-聚丙二醇-聚乙二醇（PEG-PPG-PEG）的醚化反应一步即可进行环化，而疏水性-亲水性-疏水性（BAB 型）PPG-PEG-PPG 则通过缩醛化进行环化。环状表面活性剂通过核磁共振波谱和凝胶渗透色谱进行了严格的表征。表面活性剂的环化导致水动力体积显著减小，这比 PEG 均聚物更为明显。表面张力（γ）测量表明，由于环化导致空气-水界面上的表面活性剂密度增加，从而导致分子占据面积（）减小，因此环状表面活性剂的界面活性强于其相应的线性前体。对于 PEG 均聚物，从线性 PEG 预聚物的 410 Å 显著减小到环状 PEG 产物的 100 Å。虽然链端基团的影响仅限于相对较小分子量的表面活性剂，但环化的影响强烈依赖于亲水性/疏水性比；表面活性剂的 PEG 组成越高，γ 和 的降低越大，换句话说，观察到界面活性的增强越大。
