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Main Title: Thermoresponsive self-assembly of twofold fluorescently labeled block copolymers in aqueous solution and microemulsions
Author(s): Hechenbichler, Michelle
Prause, Albert
Gradzielski, Michael
Laschewsky, André
Type: Article
Abstract: 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(N,N-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(N-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.
Subject(s): watersoluble polymer
associative polymer
fluorescence label
Issue Date: 4-Nov-2021
Date Available: 29-Jun-2022
Language Code: en
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Journal Title: Langmuir
Publisher: American Chemical Society
Volume: 38
Issue: 17
Publisher DOI: 10.1021/acs.langmuir.1c02318
Page Start: 5166
Page End: 5182
EISSN: 1520-5827
ISSN: 0743-7463
TU Affiliation(s): Fak. 2 Mathematik und Naturwissenschaften » Inst. Chemie » FG Physikalische Chemie / Molekulare Materialwissenschaften
Appears in Collections:Technische Universität Berlin » Publications

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