Functional and Responsive Polymers via Controlled Radical Polymerization

This Thesis is built around 4 topics, which share in common that they all take advantage of the assets of controlled radical polymerization to either (i) prepare well-defined model systems to address fundamental research questions with regard to the sensitivity of chemical bonds towards mechanical forces or (ii) to synthesize ultrathin, surface-grafted polymer brush films that can serve as light-activatable bioadhesives or which possess non-centrosymmetric materials properties. Chapter 2 demonstrates the use of SI-ATRP to prepare PtBMA brush films that are used as a model system to better understand the effect of weak mechanical forces on the hydrolysis of ester/amide and siloxane bond. The motivation originates from previous reports that describe the degrafting of hydrophilic polymer brushes in aqueous media. The fundamental question is that decoupling the effect of swelling and the water contribution to the rate of the hydrolysis is not possible. Using the hydrophobic brushes here, it has been possible for the first time to unambiguously decouple swelling and bond hydrolysis. Comparison of reaction rate constants measured in solvents of different quality suggested that degrafting correlates with brush swelling, demonstrating the mechanochemical nature of this process In Chapter 3, the sensitivity of ester bond hydrolysis towards external mechanical forces is investigated, focusing on ester bond hydrolysis. ATRP is used to construct a series of polystyrene polymers that contain two central ester bonds. Solution ultrasonication experiments, which were performed in THF and THF water mixture with different molecular weights and under different power densities provided evidences for an increase in the apparent rate constants for ester hydrolysis with increasing mechanical force generated via mild ultrasonication. Chapter 4 and Chapter 5 present the use of SI-ATRP to produce thin, functional polymer films. Chapter 4 focuses on the development of thin polymer films that allow to control adhesion between synthetic materials and tissue. PHEMA brushes have been prepared that can be transformed, on-demand using UV light from a non-fouling surface coating into a bioadhesive interface. Two synthetic approaches towards such films are discussed. A first strategy involves direct irradiation of a PHEMA brush film with UV-light. The second strategy uses PHEMA brushes that have been post-modified to introduce photo-reactive diazirine moieties. Chapter 5 attempts to understand the pyroelectric behavior of thin PE brushes prepared via SI-ATRP. This chapter builds upon the serendipitous discovery that was made when a substrate modified with a PE brush was connected to an open circuit and subjected to an alternating sequence of temperature changes. Surprisingly, a clear current change was detected in the circuit upon the temperature change. We hypothesize that the pyroelectric current which is generated upon applying an alternating sequence of temperature changes because of a permanent dipole moment in the materials. This permanent dipole moment is believed to be the consequence of a non-neutral net charge within the polymer brush film.