Hechenbichler Michelle, Prause Albert, Gradzielski Michael, Laschewsky André
Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, 14476 Potsdam-Golm, Germany.
Stranski-Laboratorium für Physikalische und Theoretische Chemie, FG Physical Chemistry/Molecular Material Science Institute of Chemistry, Technische Universität Berlin, Straße des 17 Juni 124, 10623 Berlin, Germany.
Langmuir. 2022 May 3;38(17):5166-5182. doi: 10.1021/acs.langmuir.1c02318. Epub 2021 Nov 4.
A nonionic double hydrophilic block copolymer with a long permanently hydrophilic and a small thermoresponsive block is synthesized by reversible addition-fragmentation chain-transfer polymerization (RAFT). By employing a specifically designed chain-transfer agent, the polymer is functionalized with complementary end groups which are suited for Förster resonance energy transfer (FRET). The end group attached to the permanently hydrophilic block of poly(,-dimethylacrylamide) pDMAm is designed as a permanently hydrophobic segment ("sticker") comprising a long alkyl chain and the 4-aminonaphthalimide fluorophore. The other end attached to the thermoresponsive block of poly(-isopropylacrylamide) pNiPAm incorporates a coumarin fluorophore. The temperature-dependent self-assembly of the twofold fluorescently labeled copolymer is studied in pure aqueous solution as well as in an o/w microemulsion by several techniques including turbidimetry, dynamic light scattering (DLS), and fluorescence spectroscopy. It is compared to the behaviors of the analogous twofold-labeled pDMAm and pNiPAm homopolymer references. The findings indicate that the block copolymer behaves as a polymeric surfactant at low temperatures, with one relatively small hydrophobic end block and an extended hydrophilic chain forming "hairy micelles". At elevated temperatures above the LCST phase transition of the pNiPAm block, however, the copolymer behaves as an associative telechelic polymer with two nonsymmetrical hydrophobic end blocks, which do not mix. Thus, instead of a network of bridged "flower micelles", large dynamic aggregates are formed. These are connected alternatingly by the original micellar cores as well as by clusters of the collapsed pNiPAm blocks. This type of structure is even more favored in the o/w microemulsion than in pure aqueous solution, as the microemulsion droplets constitute an attractive anchoring point for the hydrophobic dodecyl sticker but not for the collapsed pNiPAm chains.
通过可逆加成-断裂链转移聚合（RAFT）合成了一种具有长永久亲水性嵌段和小热敏性嵌段的非离子型双亲水嵌段共聚物。通过使用专门设计的链转移剂，聚合物被带有互补端基的官能团化，这些端基适用于Förster共振能量转移（FRET）。连接到聚（N，N-二甲基丙烯酰胺）（pDMAm）永久亲水嵌段的端基被设计为包含长烷基链和4-氨基萘二甲酰亚胺荧光团的永久疏水链段（“贴纸”）。连接到聚（N-异丙基丙烯酰胺）（pNiPAm）热敏嵌段的另一端包含香豆素荧光团。通过包括比浊法、动态光散射（DLS）和荧光光谱在内的几种技术，研究了双重荧光标记共聚物在纯水溶液以及o/w微乳液中的温度依赖性自组装。将其与类似的双重标记pDMAm和pNiPAm均聚物参考物的行为进行了比较。研究结果表明，该嵌段共聚物在低温下表现为聚合物表面活性剂，一个相对较小的疏水端嵌段和一条伸展的亲水链形成“毛发状胶束”。然而，在高于pNiPAm嵌段的最低临界溶液温度（LCST）相变的温度下，该共聚物表现为具有两个不对称疏水端嵌段的缔合遥爪聚合物，它们不相容。因此，不是形成桥接“花状胶束”网络，而是形成大的动态聚集体。这些聚集体通过原始胶束核以及塌陷的pNiPAm嵌段簇交替连接。这种结构类型在o/w微乳液中比在纯水溶液中更受青睐，因为微乳液滴对疏水十二烷基贴纸构成有吸引力的锚定点，但对塌陷的pNiPAm链则不然。
