Reactive Polymer Platforms Based on Atom Transfer Radical Polymerization of Pentafluorophenyl Methacrylate and Their Applications

Abstract

During the past decades, functional polymers have been emerging as a promising candidate for advanced materials in a wide range of application fields such as biotechnology, photonics, and optoelectronics with advanced properties such as fluorescence, stimuli-responsiveness, and biocompatibility. Depending on particular application, the properties and nanostructures of functional polymer should be tailed to achieve those of interested. As requirements on functional polymers become more complicated, tedious synthesis and polymerization were often required to realize polymers with desired functionalities and structures. Furthermore, modification of pre-formed structure is difficult and extensive. Thus, modular platforms that allow facile synthesis and modification are highly desired. Activated ester containing monomers have been extensively studied to demonstrate modular synthesis of versatile functional polymers by simple modification with various amine. More specifically, pentafluorophenyl methacrylate (PFPMA) has been actively studied since it has high reactivity with various amines, better controllability, and stability than N-hydroxysuccinimide (NHS) and their acrylate counterpart. While reversible addition-fragmentation chain-transfer (RAFT) of PFPMA has been intensively reported, reports on the atom transfer radical polymerization (ATRP) of PFPMA are rare due to poisoning of catalyst and initiator by reacting monomer with them. ATRP is one of valuable tool to design and synthesis of polymer with various composition and topology. Furthermore, various components for ATRP allow fine control of growing radical, resulting pre-determined molecular weight and narrow polydispersity index. All components for ATRP are also free from difficult synthesis step since most of chemicals are commercially available. The cumbersome optimization of ATRP condition for new functional monomers is one of challenges for wide application of ATRP. By combining merits of PFPMA with ATRP, this challenge enable to be solve. Optimized condition with proper components is obtained after series of ATRP of PFPMA under various condition. Details about kinetics studies on ATRP of PFPMA will be discussed in chapter 2. With optimized conditions for controlled ATRP of PFPMA in hand, we demonstrate reactive polymer nanoparticle (PNP) platforms, which enable to convert their functionalities, by nanoprecipitation that allows fast and simple preparation of nanoparticles without surfactant (chapter 3). Fluorescent polymer nanoparticles are realized by simple modification of reactive polymer with commercially available dansylcadaverine as a model study. Control of size, size distribution and photophysical properties are studied. Well-defined fluorescent nanoparticles are prepared and those show 4.5 fold enhanced relative quantum yields compared with dansylcadaverine in water. Our strategy allows facile and modular synthesis of functional polymer nanoparticles with desired properties. Furthermore, imparting other functions on nanoparticles are enabled by further modification of remaining activated ester group. Structural stability, however, should be ensured during further modification to prevent dissolution of polymer in various organic solvent. By employing coumarin that enable to undergo photo-reversible dimerization into reactive polymer, robust, reactive PNP platforms have been realized. Using light as an external trigger for cross-link, structural stability enable to be obtained without destruction of structure and inter-particle cross-link. Reactive PNP platforms are treated with not only small molecules including isopropylamine, N-(2-aminoehtyl)-3-(3,3-dimethyl-6-nitrospiro[chromene-2,2-indolin]-1yl) propanamide (spiro-pyran-amine), or dansylcadaverine, but also amine terminated polymer (poly(N-isopropylacrylamide) (poly(NIPAAm)) to prove the possibility of further modification. Through DLS and photo physical studies, we confirm that resulting functional PNPs show thermo-, and photo-responsiveness, respectively. In chapter 4, reactive polymer brushes platform is demonstrated by surface-initiated (SI)-ATRP of PFPMA from ITO surface for electrical application. Polymerization of PFPMA is conducted with ITO modified by immersing into different concentration of initiator solution in toluene. AFM measurement confirms that height of optimized poly(PFPMA) on ITO (ITO-g-p(PFPMA)) is 8 nm and grafting density of that is 0.2 chains/mn2. The reactive polymer brush platform is treated with 4-amino-2,2,6,6,-tetramethylpiperidine 1-oxyl (4-amino-TEMPO) which has bistable state (or called as redox properties) to impart electrochemical properties on surface. Surface characterization conducted with FT-IR and x-ray photoelectron spectroscopy (XPS) confirm that the PFP group was successfully replaced to TEMPO molecules (yields =100 %, calculated by XPS). In conclusion, modular platforms that allow facile and modular synthesis of functional material are demonstrated from monomer to polymer and polymer to nanostructures. We believe that our system and the strategy used for its achievement constitutes a novel approach that provides a facile process towards functional polymer, polymer nanoparticles, and polymer brushes and widening the application of polymer by eliminating difficult multistep of synthesis.