Xiaoyin Hong

Raman spectroscopic evidence of thickness dependence of the doping level of electrochemically deposited polypyrrole film

In this paper, we present resonance Raman spectroscopic studies on as-grown thin polypyrrole (PPy) films electrochemically deposited on flat platinum electrode surfaces by direct oxidation of pyrrole in acetonitrile. It was found that the overall features of the Raman spectra depend strongly on film thickness, mainly due to that the doping level of PPy increases during film growth process. Electrochemical and X-ray photoelectron spectroscopic (XPS) examinations have confirmed this discovery. The doping level of PPy film with a given thickness also depends on the property of supporting electrolyte.

Template-free electrosynthesis of aligned poly(p-phenylene) microtubules

Poly(p-phenylene) (PPP) microtubules with diameters of 0.2–0.8 μm and lengths of ∼10 μm have been synthesized by direct oxidation of benzene in the mixed electrolyte of boron trifluoride diethyl etherate (BFEE) and trifluoroacetic acid (TFA) (BFEE: TFA=2: 1, by volume), containing a certain amount of sodium dodecylbenzene-sulfonate (SDBS) as surfactant. The microtubules were grown vertically on the working electrode surface. The tubular morphology has been confirmed by scanning and transmission electron microscopies and the chain structure of the skin of the tubules has been characterized by Raman spectroscopy. The electrode property, monomer/surfactant molar ratio and the value of applied potential have strong effects on the morphology of the microtubules.

Low potential electrochemical polymerization of 3-chlorothiophene in mixed electrolytes of boron trifluoride diethyl etherate and trifluoroacetic acid

Abstract Poly(3-chlorothiophene) (PCT) films were synthesized electrochemically by direct oxidation of 3-chlorothiophene (CT) in mixed electrolytes of boron trifluoride diethyl etherate (BFEE) and trifluroacetic acid (TFA). The oxidation potential of 3-chlorothiophene in pure BFEE was measured to be only 1.54 V versus SCE. This value is much lower than that determined in neutral medium (2.18 V vs. SCE). The addition of TFA to BFEE can further decrease the oxidation potential of the monomer. The oxidation potential of CT in the mixed electrolyte of BFEE containing 30% TFA (by volume) was found to be as low as 1.16 V (vs. SCE). PCT films with the highest quality were obtained from the media of BFEE+10–15% TFA and they were characterized to have about 24–32 repeat units. The doping level and conductivity of PCT films also increased significantly by using the mixed electrolytes.

Doping level change of polythiophene film during its electrochemical growth process

Polythiophene (Pth) films have been electrochemically deposited on mirror-like stainless steel (SS) (or gold) electrode surfaces by direct oxidation of thiophene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.3 V (vs. Ag/AgCl). The Raman spectra of Pth films have been investigated by excitation with a 514, 633 or 785 nm laser beam. The 633 nm laser beam was found to be the best among the three excitation lights tried for studying the doping level change of Pth film. The overall features of 633 nm excited resonance Raman spectra of as-grown Pth films depend strongly on film thickness. Raman and X-ray photoelectron energy spectroscopic (XPS) results and electrochemical studies demonstrated that the doping level of the Pth film increased with the increase of film thickness. Furthermore, successive cyclic voltammetric scanning was found to be a more effective approach than applying a constant positive potential for doping a thin compact conducting polymer film.

Synthesis and characterization of a hyperbranched polyol with long flexible chains and its application in cationic UV curing

A hyperbranched polyol with long flexible chains on the molecule surface was synthesized and characterized. The effect of the hyperbranched polyol as flexibilizer and chain-transfer agent on cationic UV curing was investigated. It was found the hyperbranched polyol could markedly improve the mechanical properties of cured film.

Electrochemical polymerization of β-naphthalene sulfonic acid in the mixed electrolyte of boron trifluoride diethyl etherate and trifluoroacetic acid

Abstract β-Naphthalene sulfonic acid (β-NSA) has been electrochemically polymerized in a mixed electrolyte of boron trifluoride diethyl etherate (BFEE) solution and trifluoroacetic acid (TFA). As-grown poly(β-naphthalene sulfonic acid) (PNSA) is partly soluble in methanol and has a conductivity of 0.95 S cm −1 . Its structure has been examined by infrared, H 1 -NMR and UV spectra. Fluorescent spectral studies indicate that the polymer is a blue light emitter with a fluorescence quantum efficiency of 4%.

A novel coating by hybrid polymerization

Abstract Compositions of HMMM (hexamethoxymethyl melamine)–polyol and acrylate can be cured by a hybrid polymerization composed of free radical polymerization and condensation reaction at high temperature in the presence of an acid. Some synergetic effects were observed, such as enhancement of curing rate, energy compensation, improvement of properties of cured film and formation of interpenetrating polymer network (IPN) in situ. To make the formulation more flexible, some crosslinker-initiators were synthesized. It was found that the use of a latent acid catalyst as the source of acid could increase the shelf-time greatly. On the other hand, acrylate can adjust the viscosity of the formulation and reduce the use of organic solvent. By hybrid polymerization of HMMM–polyol–acrylate, it is promising to formulate a high curing rate, low solvent content, energy conservation and high quality coating.

The effect of HMMM in a hybrid polymerization comprising free radical polymerization

Abstract Compositions of hexamethoxymethylmelamine (HMMM)-ether polyol and acrylate can be cured by a hybrid polymerization composed of condensation polymerization and free radical polymerization at higher temperatures in the presence of a latent acid catalyst, but without a free radical initiator. The initiating radicals of the free radical polymerization come from the decomposition of adventitious peroxides. It has been proved that HMMM plays a very important role in this hybrid polymerization. HMMM is not only a crosslinking agent of polyol, bill also acts as a catalyst of formation and decomposition of the peroxides of the active methylene groups of ethyl polyol. The hybrid polymerization system provides a synergetic effect on the curing reaction, partly ascribed to the thermochemistry complementary between endothermic condensation polymerization and exothermic free radical polymerization. This paper presents a review of this research.

Studies on the initiation of a free‐radical condensation hybrid polymerization system

Compositions of hexamethoxymethyl melamine (HMMM)–ether polyol and acrylate can be cured by a hybrid polymerization comprising condensation polymerization and free-radical polymerization, in the presence of a latent acid catalyst at high temperature. It was found that the initiating free radical was derived from the decomposition of hydroperoxides, which was formed by the oxidation of active methylene groups catalyzed by HMMM. It was also found that strong acid could accelerate the free-radical polymerization in the hybrid system. To make the formulations more flexible, the activities of different types of methylene groups were investigated and two compounds with more active methylene groups and hydroxyl were synthesized, characterized, and used as crosslinker–initiators in the hybrid polymerization system.