Synthese von funktionellen Pfropfcopolymeren und Mikrogelen auf Polyvinylalkoholbasis durch eine Cer(IV)-initiierte Pfropfpolymerisation
Palmer, Thorsten; Pich, Andrij (Thesis advisor); Schwaneberg, Ulrich (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2020
In recent years, colloidal, aqueous microgel systems have become increasingly important in research and industry due to their wide range of applications. While the classical polymerization scheme of microgels is based on the precipitation polymerization of monomers with crosslinker and initiator molecules, this work shows an alternative route for the production of thermo-responsive microgels with biomimetic catalytic activity. This route uses as educt polyvinyl alcohol a biocompatible polymer which has a broad application spectrum, triethylene glycol ethyl methacrylate (TEGA) as polymerizable thermo-responsive monomer and ammonium cerium (IV) nitrate as redox initiator. Therefor this method differs fundamentally from the usual synthesis routes. This is due to the fact that the microgels are not exclusively synthesised out of monomers, that they are synthesised without the addition of crosslinker molecules and the simultaneously creation of catalytically active CeO2 nanoparticles inside of the microgel through the use of ammonium cerium (IV) nitrate. In addition to these differences, this reaction control has further advantages. By using a redox initiator, the polymerization reaction can be carried out at low temperatures. Common initiator systems such as azobis(isobutyronitrile) (AIBN) require temperatures around 70° Celsius. At these temperatures, many thermo responsive polymers such as TEGA are already present in the collapsed state. By using redox initiators, temperatures below the lowest critical solution temperature can be selected. This leads to the formation of graft polymers instead of microgels. Therefor the morphology of the products can be controlled with the aid of the reaction temperature and either microgels or graft polymers can be synthesized. The work is divided into four chapters. The first chapter deals with the synthesis of thermo-responsive PVA-g-TEGA microgels/graft polymers. Here, the turnover is determined qualitatively and quantitatively, which is drastically different for microgels and graft polymers. Chapter two describes the behaviour of microgels and graft polymers in water. In particular, the thermo-responsive behaviour with the aid of dynamic light scattering (DLS) is investigated and the differences between microgels and graft polymers are highlighted. In addition, the different morphologies were visualized as evidence by AFM and STEM images. The CeO2 nanoparticles were analysed in chapter three and tested for their catalytic activity. In addition, a direct relationship between TEGA concentration and nanoparticle growth could be demonstrated. The last chapter is dedicated to a possible industrial application of PVA-g-TEGA graft polymers. It was shown that PVA non-wovens can be postmodified with TEGA. This post modification serves as plasticizer and leads to a change in the haptic properties of the PVA non-wovens. This could be interesting for textiles or PVA-based wound dressings.