Synthesis of ferrocene containing polymer, characterization and fabrication of nanofiber

Among a variety of metallopolymers, metallocene bearing polymers have attracted significant attention in materials science due to their interesting properties that arise from their unique sandwich-like structures. After the discovery of ferrocene, macromolecules, including oligomers, polymers, and dendrimers, functionalized with metallocene moieties have quickly found uses in applications such as redox sensors, catalysts, nanolithography, nanoceramic materials, and biomedical applications. These metallocene bearing macromolecules can be seen as bridging together several subfields of chemistry including inorganic, organic, polymer, or dendrimer chemistry as well as materials science. Generally, there are two classes of metallocene polymers: side-chain metallocene-containing polymers with the metallocene unit as a pendant group and main-chain metallocene bearing polymers with the metallocene as an integral part of polymer backbone. Earlier studies of ferrocene-functionalized polymers were focused on side-chain polymers such as poly(vinylferrocene) because of facile electrophilic substitution of ferrocene. A few acrylate and methacrylatemonomers have been polymerized by conventional techniques such as free radical, cationic, and anionic polymerization. However, most of these organometallic polymers developed in the 1970s and 1980s lacked control on molecular weight and molecular weight distribution and were incapable of producing advanced topology such as block copolymers. Since then, side-chain ferrocene bearing polymers have been much less explored. Meanwhile, a seminal work on strained, ring-tilted metallocenophanes opened a new era in the field of ferrocene bearing polymers, that is, to develop well-defined high-molecular-weight main-chain ferrocene-containing polymers by anionic ring-opening polymerization. This field has been flourishing over the last two decades. A variety of main-chain ferrocenecontaining polymers have been developed. These ferrocene bearing polymers have found applications in magnetic ceramics, variable refractive index sensors, nonlinear optical materials, plasma etch-resistant materials, and so forth. ATRP is one of the poylmerization techniques. ATRP was used to polymerize the six different ferrocene monomers. The polymerization conditions were kept the same for all monomers to compare the kinetics and monomer activities. Copper(I) chloride, bpy, and ethyl 2-bromoisobutyrate (EBIB) were used as the catalyst, ligand, and initiator, respectively. Electrospinning process was used in this study to manufacture nanofibers. Electrospinning is a fiber production method which uses electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of some hundred nanometers. Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practiced; this method ensures that no solvent can be carried over into the final product. When a sufficiently high voltage is applied to a liquid droplet, the body of the liquid becomes charged, and electrostatic repulsion counteracts the surface tension and the droplet is stretched; at a critical point a stream of liquid erupts from the surface. This point of eruption is known as the Taylor cone. If the molecular cohesion of the liquid is sufficiently high, stream breakup does not occur (if it does, droplets are electrosprayed) and a charged liquid jet is formed. As the jet dries in flight, the mode of current flow changes from ohmic to convective as the charge migrates to the surface of the fiber. The jet is then elongated by a whipping process caused by electrostatic repulsion initiated at small bends in the fiber, until it is finally deposited on the grounded collector. The elongation and thinning of the fiber resulting from this bending instability leads to the formation of uniform fibers with nanometer-scale diameters. In the first part of this study, monomer compound was synthesized like that: Ferrocenecarboxylic acid (2.01 g, 8.74 mmol), 2-hydroxyethyl acrylate (1,3 mL, 11.33 mmol), and DMAP (0.13 g, 1.06 mmol) were dissolved in 100-mL dry dichloromethane, purged with N2 gas, and cooled to 0 C. DCC (2.15 g, 10.44 mmol) was dissolved in dry DCM (20 mL) and added dropwise to the solution over 1 h and then stirred at room temperature for 24 h. The solution was filtered, concentrated, and the mixture was separated by column chromatography (silica gel, eluent: 12:1 hexane/ethyl acetate). The product was collected, concentrated, and vacuum dried, yielding a yellow/orange solid (2.0 g, 70%). After that a new ferrocene bearing polymer was synthesized like that; for a typical polymerization, the ferrocene-containing (meth)- acrylate (100 M equiv), Cu(I)Cl (2 M equiv), and bpy (4 M equiv) were added to a 10-mL Schlenk flask and degassed by purging with nitrogen. Distilled toluene (1 mL) was added to a 5-mL round-bottom flask and degassed by bubbling the solution with nitrogen gas for 10 min. EBIB (1 M equiv) was added directly to the Schlenk flask followed by addition of the degassed toluene. The mixture was further degassed by nitrogen bubbling for 5 min. The reaction was stirred at room temperature for 15 min before the flask was placed in an oil bath preheated to 90 C. An initial sample was taken to accurately determine the reaction conversion by 1H NMR. Samples were periodically taken over the course of the polymerization for 1H NMR and GPC analysis. The polymerization was quenched by placing the Schlenk flask in an ice bath. The mixtures were then passed through a short neutral alumina plug, concentrated, and precipitated into hexane at least two times and vacuum dried. In the secon part, %10 PAN solution was prepared for using in electrospinning process. Nanofiber was fabricated from this solution. Several solutions with increasing amount of ferrocene containing polymer (0,025g, 0,05g, 0,1g, 0,2g) also were prepared and nanofibers were also manufactured from these solutions. Characteristic properties of fabricated nanofibers were investigated with SEM, EIS and contact angle measurements. According to SEM images fiber diameters are increasing with increasing amount of ferrocene containing polymer in fibers and it indicates that ferrocene containing polymer is in the blend. EIS measurements show that with increasing amount of ferrocene containing polymer in fibers, conductivity increases. Hydrophobicity of nanofibers are increase with increasing amount of ferrocene containing polymer in fibers.