Properties and applications of bottlebrush polymers
Doctor of Philosophy
This work presented in this dissertation aims to understand physical and chemical properties of bottlebrush polymers and determine their potential for applications including for anti-fouling surfaces and for reduction in oil-water interfacial tension. This dissertation focus on the following four parts: the synthesis of well-defined bottlebrush polymers and investigation of stimuli-responsive film properties; analysis of the solution phase behaviors and conformation of bottlebrush polymers with thermally-responsive side chains; the behavior of bottlebrush polymers in blends with linear polymers; and the development of bottlebrush polymers for antifouling surfaces and for reducing the oil-water interfacial tension. In chapter 1, we provide an introduction to bottlebrush polymers. Details on the synthesis, conformation, phase behavior, potential applications, and recent work with bottlebrush polymers are discussed. Chapter 2 describes the preparation of stimuli-responsive bottlebrush thin films with hydrophobic polystyrene (PS) and hydrophilic poly(ethylene oxide) (PEO) amphiphilic side-chains. We find that due to the conformational flexibility of the polymeric side-chains, bottlebrush polymer films exhibit a processing dependent contact angle. This behavior is analogous to that observed for polymer brush films and enables a more scalable approach to responsive, brushy polymer films. In Chapter 3, we explore the solution phase behavior of bottlebrush polymers with thermoresponsive poly(N-isopropylacrylamide) (PNIPAAM) side-chains. PNIPAAM is a water-soluble polymer that exhibits a lower critical solution temperature (LCST). Due to the unique structure of bottlebrush polymers, PNIPAAM bottlebrush polymers exhibit very different solution phase behavior compared with linear PNIPAAM. We show that the LCST depends on the side-chain length and side-chain endgroup, and the bottlebrush polymer side-chains collapse on approaching the LCST. PNIPAAM bottlebrush polymers form lyotropic liquid crystal phases for sufficiently long PNIPAAM side-chains. In Chapter 4 we explore the properties of bottlebrush polymers in blends with linear polymers. This work is aimed at investigating the potential of bottlebrush polymers to be used as additives for modifying polymer thin films. We show that bottlebrush polymers are interfacially active and spontaneously segregate to the film-substrate and film-air interface. The interfacial segregation of bottlebrush polymer additives was systematically studied for varying lengths of linear polymers and bottlebrush polymer side-chains through secondary ion mass spectrometry (SIMS), neutron reflectivity and optical microscopy. These results demonstrate that relatively small amounts of bottlebrush polymer additives can be used to tailor interfaces. Chapter 5 presents preliminary results on the antifouling properties and oil-water interfacial properties of bottlebrush polymers. Stable films were prepared by introducing cross-linker into the bottlebrush side-chains, and we demonstrate that PNIPAAM bottlebrush thin films have comparable cell resistance to that PEO polymer brushes. To study bottlebrush polymers at the oil-water interface, both pure bottlebrush polymers and a mixture of surfactant 4,5-orthoxylene sulfonate (OXS) were used as additives in water-chloroform blends. Experimental measurement of the interfacial tension show that the presence of bottlebrush polymer can reduce the interfacial tension significantly, larger than that for commercial surfactant. Although more work is needed, preliminary results are promising for bottlebrush polymers as interfacial tension reducer and anti-fouling surface materials.
Bottlbrush polymers; Polymer surfactant; Anti-fouling; Chemical engineering