Architecturally Diverse Polymer Brushes Prepared via Surface-Initiated Atom Transfer Radical Polymerization

Polymer brushes, which are polymers anchored to a solid substrate by one chainend, have the ability to modify the properties of an underlying substrate, offeringintriguing features such as enhanced lubrication, reduced friction, colloidal stability, and antifouling characteristics. These properties can be further modulatedby varying the polymer brush architecture. Examples from literature include crosslinking polymer brushes to influence the swelling characteristics, makingloops to reduce friction, or introduce branching to enhance the antifouling properties. Theoretical work has also suggested that introducing branching near the site tethering the polymer chain to the surface could alter the tension at the polymer – substrate interface, which could impact the mechanical stability of these polymer brush layers. To prepare these attractive architectures, surface-initiated controlled radical polymerization (SI-CRP) techniques, such as atom-transfer radical polymerization (ATRP), have been utilized as they offer control over the polymer molecular weight, or film thickness, via the reaction time and tolerate a wide monomer scope. The aim of this thesis is to study the stability of different polymer brushes and prepare different polymer brush architectures by SI-ATRP which can bridge the gap between polymer brush architecture and mechanical stability. Results could pave the way to a new class of mechanically responsive surfaces.In Chapter 1 the basic background on polymer brushes, how they can be prepared and methods to determine the grafting density will be discussed. Further, literature will be presented, where the effect of polymer brush architecture on different properties has been examined. And finally, the mechanical stability andthe influence of architecture is discussed.Chapter 2 investigates the stability of the poly(ethylene glycol) (PEG)-coated mesoporous silica nanoparticles. Particles are prepared with different PEG molecular weights and at different grafting densities. The stability is probed by sonicating the particles and analyzing the supernatant for possible degrafted PEG chains.Chapter 3 aims to investigate the effect of aqueous LiCl and NaCl solutions at different ionic strengths on the swelling of poly(3-sulfopropyl methacrylate) (PSPMA) brushes. Additionally, the mechanical stability is investigated in the same salt solutions by the means of degrafting studies.Chapter 4 presents the preparation of linear, Y-, and ι-shaped poly(methyl methacrylate) (PMMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes from a homologous series of ATRP initiators. The growth profiles of the two polymers are established for all initiators. The swelling characteristics of the different brush architectures are studied. The grafting density of the different brush grafts is determined by cleaving brushes from the surface and through swelling experiments. The mechanical stability of PDMAEMA brushes is additionally probed.In Chapter 5 a strategy towards tethered bottlebrushes is proposed based on 2-aminoethyl methacrylate (AEMA). The backbone is first prepared by SI-ATRP, then in a post-polymerization reaction new ATRP initiators are introduced from which the polymeric side chains are prepared. By polymerizing AEMA again in the side chains, this strategy holds the potential to prepare highly branched polymer brushes.