Switchable colloidal L-proline and ruthenium nanoparticle catalysts based on responsive microgels

Kleinschmidt, Denise; Pich, Andrij (Thesis advisor); Herres-Pawlis, Sonja (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

Exploring and controlling chemical reactions by the use of responsive polymers is a challenge often addressed to modern polymer chemistry by immobilization of catalytically active substances on suitable substrates. Due to phase boundaries conventional immobilization can lead to substantial reduction of efficiency of the catalysts. Recently, microgels have been used as substrates for catalytically active materials. In general, microgels are crosslinked, porous and mostly spherical polymer particles, which can form stable dispersions in continuous medium (e. g. water or organic solvents) as these materials are permeated by the solvent. Methods of synthesizing microgels are often straight forward and allow easy variation of the amount and distribution of incorporated functional groups, such as catalysts. Additionally, by variation of their swelling degree, polarity of the interior or their surface charge, stimuli-responsive microgels respond to changes of their surrounding, what makes them ideal candidates as active support materials for application in catalysis. In this Thesis different types of catalysts are immobilized into responsive microgels. The aim of this Thesis is to generate an understanding of how the porous polymer network of microgels can control the performance of incorporated catalysts in batch and in continuous reactions, considering the amount and distribution of the catalysts, as well as the responsive behavior of the microgels. This Thesis is divided into four Parts: In the first Part of this Thesis, a series of poly(N-isopropylacrylamide) (PNIPAM) microgels with a covalently bound L-proline moiety as organocatalyst will be synthesized, characterized by several analytical methods and tested for their catalytic performance in the aldol reaction of 4-nitrobenzaldehyde with cyclohexanone. In the second Part, the catalytic reaction is further examined. The aim of this Part is to systematically explore the influence of the microgel network on the catalytic performance of the PNIPAM-L-proline microgels. More precisely, this Part will focus on the impact originating from the localization of the catalytic groups within the microgel network (core and shell) in homogeneous and heterogeneous reaction media, as well as the responsivity of the microgels triggered by temperature and the principle of cononsolvency. In the third Part of this Thesis, the PNIPAM-L-proline microgel will be immobilized in different approaches in order to allow processing of the catalytic reaction in continuous reaction mode. In the last Part of this Thesis poly(N-isopropylacrylamide-co-acetoacetoxy ethyl methacrylate) (PNIPAM-AAEM) microgels with incorporated Ruthenium nanoparticles are synthesized, characterized and applied as catalytic active materials in various reactions.