Synthesis of Well-Defined Binary Mixed Brushes on 20 nm Silica Nanoparticles and Asymmetrically End- Functionalized Semicrystalline Poly(ε-caprolactone)s

Well-defined polymers and polymer brushes play an important role in the understanding of their behavior under various conditions and in the fabrication of nanostructured functional materials. This Master’s thesis work focuses the synthesis of two well-defined systems: binary mixed homopolymer brushes grafted on 20 nm silica nanoparticles (NPs) for understanding their microphase separation behavior and asymmetrically end-functionalized semicrystalline poly(- caprolactone) polymers for use in the fabrication of multicomponent polymer brushes on flat substrates with various architectures. While theoretical and simulation studies have revealed intriguing morphologies of mixed homopolymer brushes grafted on nanospheres with a size similar to those of grafted polymer chains, no experimental investigation has been performed, mainly because of the difficulty in the preparation of such NP brushes with well-defined molecular weights and grafting densities. To overcome this synthetic challenge, a surface-immobilizable, monochlorosilane-functionalized asymmetric difunctional initiator, containing initiating moieties for atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP), was synthesized via a new method and immobilized on the surface of 20 nm silica NPs. A series of well-defined mixed poly(t-butyl acylate) (PtBA)/polystyrene (PS) brush-grafted NP samples with the same PtBA molecular weight but varying PS chain lengths were prepared by sequential surface-initiated ATRP and NMRP with the addition of a corresponding free initiator in each step. The grafting densities of the two polymers in these NP brush samples were similar, with a total grafting density in the range of 0.64 – 0.86 chains/nm2. Preliminary studies of selected NP brush samples using transmission electron microscopy revealed intriguing microphase separated patterns. In the second project, well-defined semicrystalline poly(-caprolactone)s (PCLs), with one end functionalized iv with a mono- or difunctional polymerization initiator and the other end capped with a surfaceimmobilizable triethoxysilane group were synthesized by ring-opening polymerization and subsequent end-group functionalization. Size exclusion chromatography and 1H NMR spectroscopy analysis indicated that the polymerizations were well-controlled, and the end group installation was quantitative. These PCLs will be used in the fabrication of well-defined multicomponent polymer brushes with various architectures on flat substrates by combining polymer-single-crystal-assisted “grafting to” and surface-initiated reversible deactivation radical polymerization.