Study On Synthesis And Properties Of Ferrocene-based Polymers

Ferrocene-based polymer as a new class of functional polymer with special electronic, electrochemical, optical, and magnetic properties has extensive application prospects and important values in academic research.In this paper, five series of polyferrocenylsilanes (PFS), polyferrocenyldimethylsilane (PFDMS) , polyferrocenylmethylphenylsilane (PFMPS) , polyferrocenylmethyl (3-diethyl-amino-) phenoxysilane (PFMDEAS), polyferrocenylmethy (4-butoxycarbonyl-) phenoxysilane (PFMBOCS) , polyferrocenylmethyl (4-dimethylamino-) phenylsilane (PFMDMAS) , are synthesized, and PFMDEAS, PFMBOCS, PFMDMAS are new polymers which have not been reported in literatures. The structures of the resultant polymers are characterized by 'H-NMR, FT-IR, UV-Vis spectra. The molecular weights and polydispersities of the polymers are measured by GPC. The UV-Vis spectra of PFS indicate that the substitution groups on the Si bridge of PFS have some influence on charge distribution and electronic transition of the molecule, therefore affect their electronic spectra. The electronic effect of the substituents can pass through the Si bridge in some extent. The thermal properties of the resultant polymers are investigated by the DSC and TGA techniques. The results indicate that the molecular structure of polymer has significant effect on the crystallization of PFS. The PFDMS with small and symmetric substitution groups on the Si bridge exhibits the thermal properties of partial crystallization and its glass transition temperature (T_g) is low (lower than 40℃). The substituents on the Si bridge of PFMPS and PFMDMAS are large and unsymmetrical. The phenyl groups link directly with main chains by means of C-Si bond. The steric hindrance makes the polymers exhibit the thermal properties of non-crystalline and their glass-transition temperatures are high (higher than 90℃). The substitution groups on Si bridges of PFMBOCS and PFMDEAS are large and unsymmetrical, but the phenyl rings link with main chains through C-O-Si bond which has more flexibility than C-Si bond, so that the PFMBOCS and PFMDEAS exhibit the thermal properties of partial crystallization, but their degrees of crystallinity and melting enthalpies A H_m are lower than those of PFDMS, and their glass-transition temperatures T_g are higher than that of PFDMS (higher than 50 ℃). However, PFS has high thermal stability in nitrogen atmosphere. PFS suffers weight loss at ca. 400-600 ℃. Our studies have also shown that the substituents on silicon greatly affect stability of the polymers. The thermal stabilities of PFS withsymmetric substituents and C-Si bonds are higher than those with unsymmetrical substituents and C-O-Si bonds. The single-molecular force spectroscopy (SMFS) of PFDMS and PFMPS before and after oxidation is obtained by using AFM-based single-molecular force spectroscopy. The two polymers show similar elasticity in normal form, and their single-chain enthalpic elasticity is 22 nN, though bearing different side groups. However, in the oxidized form the difference between o-PFDMS and o-PFMPS in their enthalpic elasticity due to steric effect of side groups on single-chain elasticity are found, the single-chain enthalpic elasticity of o-PFDMS is 53 nN, and that of o-PFMPS is 200 nN.The electrochemical behaviors of PFS have been studied by means of cyclic voltammetry (CV) and electrochemical quartz crystals microbalance (EQCM). The CV behaviors of PFDMS film and PFMPS film in eight kinds of aqueous electrolyte solutions, and the effects of various factors, such as potential scan rate, electrolyte concentration, temperature, and film thickness on the CV behaviors of PFDMS film and PFMPS film in LiC104 aqueous solutions have been investigated. The CV behaviors of PFDMS film, PFMPS film, PFMDEAS film, and PFMBOCS film in eight kinds of organic solutions, and the CV behaviors of PFDMS film in NaBPh4, BU4NCIO4, BU4NBF4 solutions have also been investigated. Some results have been found. The PFS film on electrode surface will be oxidized to cationic polyferrocenium during oxidation process, and the electrolyte anions will penetrate into the film for charge neutrality. So that, the solvent, electrolyte, concentration of electrolyte, temperature and thickness of film will affect the electrochemical behavior of PFS film. It is found that the electrochemical redox processes of PFS films in aqueous and organic solutions all are diffusion controlled ones. The experimental results indicate that PFS films are poor-solvent-swollen in aqueous electrolyte solutions, and this result in a high resistance of mass transfer, slow rate of electrode reaction, and weak interaction of active centers, therefore, low-reversible or irreversible CV processes are obtained. There are obvious difference in the CV potential and CV current of PFS films in various aqueous solutions. The reduction potentials of PFDMS range 0.32 V to 0.48 V, and the oxidation potentials of PFDMS range 0.48 V to 0.58 V. The reduction potentials of PFMPS range 0.43 V to 0.59 V, and the oxidation potentials of PFMPS range 0.58 V to 0.73 V. The potential scan rate affects the reversibility of film electrode process. The electrode processes of PFS film are complex due to slow rate and low efficiency of charge transfer in the films. The CV reversibility of PFS decreases with increasing scan rate. The influences of supporting electrolyte concentration are investigated. Below 0.05 M, the increasing the concentration of electrolyte will decrease the resistance of solution, which will be favorable for charge transfer and increase the CV currents. When the concentration is larger than 0.05M, the concentration of electrolyte has very small effect on theCV behavior of the film. The thickness of PFS film affects the electrode process. In aqueous solutions, the CV behavior of PFS film exhibits the character of a single layer film and the peak current increases with increasing the thickness when the film is very thin. But the CV current will not increase with increasing the thickness, and the CV behavior of PFS film exhibits the character of diffusion controlled process when the film is thicker than a critical thickness. Because the thickness of film is thicker than the diffusion layer and the reaction layer of the electrode process in such case, and the film swelling, electrolyte penetration and mass transfer in the film play an important role. The kinetic parameters of film electrode processes, such as the surface transfer coefficient ana, the apparent diffusion coefficient Dapp and standard rate constant k° for electron transfer, for PFS films in LiClO4 aqueous solutions are measured, it is found that these kinetic parameters are all small. This result indicates that the rate of diffusion and the efficiency of charge exchange are very small in the PFS films. Elevated temperature increases the rates of diffusion and electrode process, and improves the reversibility of film electrode process. The CV currents of PFS film increase with increasing temperature. The electrochemical behaviors of PFS films in eight kinds of organic solvents are investigated. In "good" solvents, such as in methanol solutions the films are solvent-swollen moderately, the electrolytes are dissociated almost completely, the electrolyte ions penetrate into and out of the film easily, and the CV behavior of the films exhibits reversible features. In acetonitrile, ethyl acetate, and nitromethane solutions, the PFS films are over-swollen, which lead the films to dissolve gradually into the solutions, and the CV currents of the films attenuate gradually during the scanning, although the CV waves exhibit as the distinguishable double peaks. In ethanol, isopropanol, and n-butanol solutions, the swelling of the films, and the dissociation of electrolytes all reduce successively. The resistances of solutions, the resistances of mass transfer and diffusion in the films increase correspondingly. The CV waves of the films show that the double peaks gradually incorporate into overlapping peaks or single broad peaks, and the reversibility of CV process decrease gradually. In polar organic solutions, the diffusion coefficients of CV process of PFS film are large, which indicate that the film have good swelling, the resistance of mass transfer is small in the films. The diffusion coefficients decrease with decreasing the polarities of organic solvents, which indicate that the swelling of films is reduced. The electrolyte ion size effect on the CV behavior of PFS films in organic solvents is investigated. Electrolyte anions, as counter ions, take part in charges neutralizing in the films, so that the size of anion affects the CV behavior of films remarkably. The electrolyte cations do not take part in charges neutralizing in the films, so that the size of cations do not affect the CV behavior of films on the whole. The molecular structure of PFS has notable influence on the electrochemical behavior of PFS film. The PFDMS with small and symmetric substitution groupson Si bridge presents the symmetric, the narrowest, and the largest current CV peaks, which means the PFDMS film has the fastest rates of mass transfer and electrode reaction. The phenyl groups in PFMPS hobble the chain mobility in polymer, and restrict the surface charge transfer, so that, the kinetic parameters of PFMPS are smaller than those corresponding to PFDMS. The CV waves of PFMPS film have the broader peak shape, the higher peak potential, and the smaller peak current than those of PFDMS film. The C-O-Si bonds in molecules make the flexibility of PFMDEAS and PFMBOCS be better than PFMPS, which make the rate of mass transfer in PFMDEAS film and PFMBOCS film be faster than in PFMPS film, so that, the CV currents of PFMDEAS film and PFMBOCS film are larger than that of PFMPS film. The ether bonds and amine groups have big electron-donor effect, which make the CV currents of PFMDEAS film and PFMBOCS film be larger than that of PFMPS film. The big substitution groups make PFMDEAS and PFMBOCS have better compatibility with organic solutions, which make PFMDEAS film and PFMBOCS film be solvent swelled and mass losing easily in acetonitrile and acetone solutions. The amount of the redox charge and the response of EQCM in situ during the CV process indicate that there are only partial ferrocene units to take part in redox reaction in the PFS film on the electrode, and the amount of reacted ferrocene decreases with reducing the polarities of the solvents. In aqueous solution, the molar amount of C1O4" penetrating into the PFS film is equal to the molar amount of reacted Fe in the film, and the C1O4" is non-solvated in aqueous, that is, few water molecules accompany with anion into the film. In methanol solution, the C1O4* is solvated, the equal amount of methanol molecules penetrate into the film accompanying with C1O4". In ethanol solution, the CIO4" is solvated too, but the amount of ethanol molecules penetrating into films is smaller than CIO/. In acetone solution, the PFS film and C1O4" are highly solvated, the mass of film decrease gradually during the CV process. The studies on the CV of four PFS CH2C12 solutions indicate that the redox processes of PFS on glassy carbon electrode in CH2CI2 solutions are diffusion controlled reversibility processes. The CV waves of the PFS solutions present double peaks owing to the interaction of the active ferrocene. The oxidated PFS separates from solution and adsorbs on electrode surface during oxidation process. There are anions and solvent molecules penetrating into the adsorption layer. The kinetic analysis points out that the mass transfer process is controlled by solution diffusion, but contains the surface adsorption layer electrode process during the reduction process. The measured diffusion coefficients from PFS CH2C12 solutions are larger than those from PFS film in aqueous solutions, which indicate that the poor swelling film restricts the diffusion of electroactive species. The molecular structure of PFS influences the CV behaviors of PFS solutions. The big substitution groups on Si decrease the rates of mass transfer, so that, the C V current decease, the peak broaden,the potential separation of peak-peak increase in PFMPS solution, and the reversibility of electrode process reduce. The flexibility of PFS elevates the efficiency of mass transfer, and the electron-donor substitution groups on Si enlarge the charge densities of electroactive centers, and increase the charge amount of redox reaction, so that, the CV currents of PFMDEAS and PFMBOCS solutions are larger than that of PFMPS solution.Polycationic polyferrocenylsilanes (PFS+C1") is employed together with commercial poly(sodium styrenesulfonate) (PSS"Na+) in the electrostatic layer-by-layer self-assembly process to form multilayer films on quartz piece and gold electrode. The UV-Vis spectra of the multilayer self-assembly films on quartz are measured. The linear relation between absorbance and the number of bilayers is indicative for the formation of well-defined multilayer. The electrochemistry of PFS+-PSS" multilayer self-assembly films on gold electrodes indicates that the electrochemical properties of multilayer film depend on the number of layers and the properties of outermost layer. At the first few layers, the film electrode processes express as feature of single layer film surface localized. With increasing the number of layers the diffusion of electroactive species gradually become as controlling step. The resistance of mass transport in the film increases and the rate of diffusion in the film decreases with increasing the number of layers. The ratio of reactive ferrocene units in outside layers decreases and the reversibility of CV processes also decrease with increasing the number of layers. When PSS" is outermost layer, anionic film goes against the electrolyte anions penetrating into the multilayer film, and make the CV current smaller than that of below PFS+ layer film.