Polymerization conditions hydrogen peroxide concentration

The synthetic reactions are also carried out in water-immiscible solvents such as benzene, toluene, chloroform, and tetrahydrofuran in the presence of a buffer. The pH of the buffer has been varied from 5.5 to 7.5 to study the kinetics of the polymerization in the biphasic system. The enzyme and the monomer are solubilized in aqueous and solvent phases, respectively. The polymerization reaction is initiated by the addition of hydrogen peroxide in small increments to the aqueous phase. The polymer is formed at the biphasic interphase and falls out of the reaction mixture as polymerization progresses. Precipitate formed is isolated by centrifugation, washed, and purified to determine the nonlinear optical properties. The schematics of the reaction are given in Fig. 4. Other reaction conditions such as the enzyme, monomer and hydrogen peroxide concentration, and reaction time are given above and were published earlier [11]. 

In aqueous solution, all the sodium peroxoborates dissociate for the most part into boric acid, or its anion, and hydrogen peroxide. Peroxoborate species are also present in these solutions, depending on the pH and the concentration for the species type. The nature of these species has been extensively examined by classical physicochemical methods (13), by nmr, and by Raman spectroscopy (14—17). Both monomeric and polymeric species are usually present. There is some evidence (18) suggesting that these peroxoborates are more reactive than hydrogen peroxide alone under similar conditions. 

From such considerations, the technique that has emerged is to expose the cellulose first to a solution of ferrous salt. The ferrous ions are absorbed by the cellulose, and in subsequent contact with hydrogen peroxide and monomer the initiation will take place in close proximity to the cellulose molecules and under conditions where the concentration of the latter is high. An advantage of this technique already recognized by Lipson and Speakman (31) is that polymerization mostly occurs inside the fibers and only small amounts of homopolymer are formed. 

Today s most stable Me-N-C catalysts are the Me-PANI-C catalysts of Zelenay s group [11]. In order to obtain the nitrogen precursor, aniline is impregnated on a carbon support and then an oxidative polymerization is initiated in the presence of iron chlorine and/or cobalt nitride (both in various concentrations). As oxidant, either hydrogen peroxide or ammonium peroxydisulfate can be used [38]. In order to obtain the final catalysts, two heat treatment steps are performed, both at the same temperature and both followed by an acid leaching. Best results were obtained for catalysts prepared at 900 °C [29]. These catalysts were stable for 4 weeks of FC run under potentiostatic conditions (0.4 V) and even showed increasing currents... 

Enzymatic polymerization of aniline by using another enzyn , bilirubin oxidase (BOD) has been reported [116]. BOD is a copper-containii oxido-reductase which oxidizes bilirubin to biliverdin and hydrogen peroxide with consumption of dissolved oxygen. The enzymatic polymerization took place on the glass surface of a BOD-adsorbed solid matrix, which was in contact with a buffer solution containing aniline. The enzymatic reaction markedly depended upon the concentration of BOD and aniline imder appropriate conditions, a hlm-like precipitate formed on the glass surface. The enzymatically synthesized polyaniline is considered to contain 1,4- and 1,2-substitution structures, which are partially different form those of chemically or electrochemically prepared polyaniline. 

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