SURFACE POLYMERIZATION OF INORGANIC MATERIALS FOR RENEWABLE ENERGY, INTELLIGENT MATERIALS, AND BIO-MATERIALS APPLICATIONS
AdvisorFuchs, Alan W.
Chemical and Materials Engineering
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Controlled radical polymerization techniques, such as atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) are discussed and used for surface grafting polymers onto inorganic substrates. The surface grafted polymer/inorganic materials can be used for various applications and fields, including renewable energy, intelligent materials, and bio-materials. In general, surface polymerization based on controlled radical polymerization (CRP) offers various benefits, including uniform coating thickness due to controlled molecular weight and polydispersity index of polymer, the polymer coating is covalently bonded to the surface, and various monomers can be polymerized directly on the surface.Novel composite proton exchange membranes have been prepared from non-fluorinated polymers and non- and surface coated heteropoly acids (HPA) using atom transfer radical polymerization (ATRP). Polyether sulfone (PES) and poly(ether ether ketone) (PEEK) were used as a polymer matrix. Phosphotungstic acid (PWA), phosphomolybdic acid (PMoA) and silicotungstic acid (SiWA) were used as HPA. It was found that the SiWA has a higher conductivity compared with PWA, at the same concentration. In addition, zirconium sulfate (ZrSO4) was also investigated as an inorganic proton conductor. Composite membrane ZrSO4/SPEEK was synthesized. PES and PEEK were sulfonated using chlorosulfonic acid. The highest conductivity for sulfonated PES with 60 wt.% PWA was 1.7 x 10-2 S/cm. In order to increase the compatibility between SiWA and PES, the SiWA was surface coated. Surface coated SiWA particles can be added to the polymer matrix up to 50 wt.% to form a homogeneous membrane. This route also has the potential to increase the conductivity by sulfonation of grafted polymer backbone, and to avoid "washing out" of HPA in a fuel cell device. In addition, novel composite proton exchange membranes have also been prepared from surface coated poly(sodium 4-vinyl benzene sulfonate) (poly(S4VBS))/ silicotungstic acid and sulfonated PEEK. A surface grafting technique for poly(2-fluorostyrene) onto iron particles via atom transfer radical polymerization (ATRP) is described. The grafted polymer-iron particles showed a higher thermal transition temperature compared to bulk polymer because the covalent bond between the polymer backbone and the surface of the iron particles restricts the molecular mobility. The molecular weight of synthesized poly(2-fluorostyrene) has been measured and it has a narrow molecular weight distribution (Mw/Mn < 1.1). From thermogravimetric analysis, the thermal stability of poly(2-fluorostyrene) was better than polystyrene. Also, the high viscosity magnetorheological fluid (HVMRF) prepared from surface coated iron particles has excellent thermo-oxidative stability, having nearly constant viscosity. These materials exhibit high change in shear yield stress for off- and on-state as compared to a benchmark HVMRF and non-surface coated iron particles HVMRF. In addition, this type of fluid eliminates iron particle settling which is a common problem found in traditional magnetorheological fluid (MRF). The preparation and characterization of surface grafted poly(N-isopropylacrylamide) and poly(carboxylic acid)-micron-size iron particles via atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) is discussed. The surface grafted polymers-iron particles result in multifunctional materials which can be used in biomedical applications. The functionalities consist of cell targeting, imaging, drug delivery, and immunological response. The multifunctional materials are synthesized in two steps. First, surface grafting is used to place polymer molecules on the iron particles surface. Second, is conjugation of the bio-molecules onto the polymer backbone. The thickness of the grafted polymers and glass transition temperature of the surface grafted polymers were determined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The covalent bond between grafted polymers and iron particles caused higher glass transition temperature as compared with non-grafted polymers. The ability to target the bio-molecule and provide fluorescent imaging was simulated by conjugation of rat immunoglobulin and fluorescein isothiocyanate (FITC) labeled anti-rat. The fluorescence intensity was determined using flow cytometry and conjugated IgG-FITC anti-rat on iron particles which was imaged using fluorescence microscopy. A surface grafting technique of poly(pentafluorostyrene) via reversible addition fragmentation chain transfer onto iron particles is reported. 4-methoxydithiobenzoate is used for RAFT chain transfer agent. The grafted poly(pentafluorostyrene)-iron particles showed a higher thermal transition temperature compared to non-grafted polymer because the covalent bond between the polymer backbone and the surface of the iron particles restricts the molecular mobility. The monomer conversion is found to be increased by the amount of CTA concentration at early polymerization time. The grafted poly(pentafluorostyrene) shows a "hairy" like polymer architecture with thickness in the range of 80-100nm. Thin coating is expected to maintain the magnetic saturation properties of iron particles. The combination of reversible addition fragmentation chain transfer (RAFT) and click chemistry is successfully demonstrated for surface grafting poly(tetrafluoropropyl methacrylate) on the iron particles. 3-benzylsulfanylthiocarbonylsufanyl propionic acid is synthesized and used as a chain transfer agent. CTA and iron particles are functionalized with alkyne and azide groups, respectively. The CTA molecular weight, surface morphology and thermal properties of grafted polymer are reported. From the electron microscope, the grafted poly(tetrafluoropropyl methacrylate) results in uniform thin coating. The grafted polymer-iron particles show a higher thermal transition temperature compared to non-grafted. The covalent bond between the polymer and the surface of the iron particles restricts the molecular mobility. The surface coated iron particles via click chemistry-RAFT are expected to provide better interface between iron particles and polymer matrix for magnetorheological elastomer (MRE). Various types and shapes of MRE are fabricated and characterized. The MR effect of MRE achieves up to 90%.
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