Responsive and functional microgels modified with cyclodextrins

• Responsive und funktionelle Mikrogele modifiziert mit Cyclodextrinen

Schmitz, Dominik; Pich, Andrij (Thesis advisor); Plamper, Felix Alois (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

The present work focuses on the synthesis, characterization and application of poly(N-vinylcaprolactam) (PVCL) microgels functionalized with cyclodextrin (CD) moieties – α- or β-cyclodextrin (αCD, βCD), respectively. Poly(butyl acrylate) (PBuA) microgels functionalized with βCD moieties will also be discussed in one part of the work. Microgels are crosslinked porous polymer particles, which are swollen in water or other suitable solvents; they are not diluted due to their polymeric 3D-network and form stable dispersions. So-called “smart microgels” are responsive to various stimuli, such as temperature (PVCL e.g.), pH, light, etc. and can easily be functionalized in many ways. Due to their porous structure, they have a high surface area and introduced functionalities are well accessible. An example of possible functionalization is the incorporation of cyclodextrins. They can act as hydrophobic pockets, which can take up and release many organic substances by supramolecular host-guest interaction. In the first part of this work, the building blocks for supramolecular crosslinkers based on mono-functional βCD methacrylate host molecules with guest-functionalized poly(ethylene glycol) (PEG) derivatives were synthesized and characterized. Based on these, non-covalent supramolecular crosslinkers were prepared via host-guest complex formation. In the second part of the work, these crosslinkers were used for the synthesis of PVCL-based microgels in aqueous medium by a free-radical precipitation polymerization method. Microgels were obtained, which showed responsivity towards the addition of a molecular trigger substance (1-adamantanecarboxylic acid (AdCOOH)). Microgels degrade by the disintegration of the supramolecular crosslinks via competitive complexation. Furthermore, hybrid microgels were synthesized; therefore, inorganic nanoparticles were incorporated into PVCL-Based microgels containing CD moieties. In collaboration with the group of Y. Lu from the Helmholtz-Zentrum Berlin für Materialien und Energie, gold nanoparticles (Au-NPs) were synthesized in situ inside αCD-functionalized PVCL microgels. In a catalytic reduction reaction, two nitrophenol derivatives were reduced to their corresponding amines. Herein, the CD moieties could influence the reaction of the used nitrophenol derivatives. Additionally, in collaboration with C. Bergs at the DWI – Leibniz-Institut für Interaktive Materialien e. V., zinc peroxide nanoparticles (ZnO2-NPs) were incorporated in βCD-containing PVCL microgels by different methods. Proof-of-principle experiments showed that ZnO2-NPs can generally be stabilized in the microgels and are an interesting basis for further experiments, for example for the catalysis of oxidation reactions. In the last part of this work, which was developed during the research project “Permanente Vektorenschutzausrüstung von Textilien (Vektorenschutz)” (16869 N) in cooperation with R. Meurer, PVCL and PBuA microgels were functionalized with βCD moieties, loaded with the insecticide permethrin and used as functional coatings on textiles for vector protection. The results showed that the hydrophobic PBuA microgels provided a much better uptake of permethrin than the more hydrophilic PVCL microgels. The use of CDs could not improve the uptake properties significantly. The permanency of the functional coating was as well better using PBuA and did not improve when CDs are used; on the contrary, the release of permethrin was accelerated for microgels containing CD moieties. In bioactivity tests, all used samples reached the required specification regarding “knock-down” time.