Hydrogen peroxide, initiator

Aqueous Phase. In contrast to photolysis of ozone in moist air, photolysis in the aqueous phase can produce hydrogen peroxide initially because the hydroxyl radicals do not escape the solvent cage in which they are formed (36). 

Polystyrene can be prepared as follows A mixture of styrene, detergent (Na-dodecanoate), and water is agitated ultrasonically to produce a fine emulsion. On the addition of hydrogen peroxide (initiator), PS is obtained as a polymer, which can be extracted after filtration. The polymer molecular weight is determined by various methods (such as light scattering and osmotic pressure). 

The first application of the ferrous ion-hydrogen peroxide initiation for polymerizing vinyl monomers on and into cellulose fibers has been reported by Landeias and Whewell (41) in three successive papers. They are apparently the first who applied the "anchored catalyst technique, which other people have termed "in situ polymerization to cellulose grafting. The authors internally deposited methyl methacrylate, acrylonitrile, styrene, methyl vinyl ketone and methacrylamide in amounts between 10 and 80%. No attempt had been made to determine if actual grafting had occurred. In 1961 Richards (42) studied this question in great detail. Products obtained by polymerization of acrylonitrile and of styrene in viscose rayon were acetylated. Fractionation of... 

Company (80). Rayon pretreated with hydrogen peroxide initiated grafting of styrene from an emulsion as reported by Toyo Spinning Company (81). 

P17. Popov, I., Volker, H., and Lewin, G., Photochemiluminescent detection of antiradical activity. V., Application in combination with the hydrogen peroxide-initiated chemiluminescence of blood plasma proteins to evaluate antioxidant homeostasis in humans. Redox Rep. 6,43—48 (2001). 

Peroxides are often added to free-radical reactions as initiators because the oxygen-oxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of the O —O bond in hydrogen peroxide (H —O —O —H) is only 213 kJ/mol (51 kcal/mol). Give a mechanism for the hydrogen peroxide-initiated reaction of cyclopentane with chlorine. The BDE for HO — Cl is 210 kJ/mol (50 kcal/mol). 

The partial oxidation of diselenides with appropriate oxidants such as hydrogen peroxide initially generates the corresponding selenenic acids (29) or anhydrides (28). Further oxidation leads to the corresponding seleninic acids (31) or... 

Scheme 18.20 Decomposition of hydrogen peroxide initiated byTi—O species.

Hydrogen peroxide initially reacts with catalase in the plasma and the white blood cells. Later, it penetrates the cell membrane of erythrocytes (red blood cells), where it reacts with catalase within the cell, and additional oxygen is then released. 

With the present series of monomers, described in Table I, the polymerization methods studied were the same as those described in previous work (2). Again, polymerization of concentrated aqueous solutions of the amine hydrochlorides using the titaneous chloride/ hydrogen peroxide initiation system provided the best polymerization method. Where this technique did not yield polymers, other free-radical initiation systems were equally unsuccessful. Table II gives some examples of the results of these polymerization experiments. 

Continued depletion of L-ascorbic acid in stored fruit-juices may be partly due to interaction with the hydrogen peroxide initially produced by aerobic mechanisms. Indeed, introduction of hydrogen peroxide, in amounts equivalent to the L-ascorbic acid content, into three-month old, blackcurrant-juice samples, caused a 50% loss of L-ascorbic acid in one hour, probably ascribable to formation of dehydro-L-ascorbic acid. 

Essentially electron-donor substituents retarded polymerization, whereas electron-acceptor substituents accelerated the process. In fact, these workers obtained a good correlation between the Hammett a values of the substituents and the polymerization rate. Remaining with benzophenone, the photopolymerization of 1,3,5-trithiane has been found to be inhibited by amines and also the absence of oxygen,whereas in the hydrogen peroxide-initiated photopolymerization of methyl methacrylate-benzophenone has been found to be a powerful accelerator. In the latter study different solvents were found to have different effects on initiation. In solvents giving low conversions, degradative initiator transfer was found to be a dominant process. 

TABLE IV Emulsion Polymerization of Dithioacids and Biallyl Hydrogen Peroxide Initiated"... 

It is possible to form clear transparent polyacrylonitrile plastic shapes by a special bulk polymerization technique. The reaction is initiated with /7-toluenesulfinic acid-hydrogen peroxide. Initially, heterogeneous polymerizations take place. They are followed by spontaneous transformations, at high conversion, to homogeneous, transparent polyacrylonitrile plastics. A major condition for forming transparent solid polymer is a continuous supply of monomer to fill the gaps formed by volume contraction during the polymerization process. ... 

Poly(dextran-g-acrylamides) from ferrous ion—hydrogen peroxide initiation Graft copolymerization of acrylamide onto dextran with ferrous ion-hydrogen peroxide initiation is being studied in detail. The effect of variation of each reaction parameter on graft copolymerization behavior may be measured by direct gel permeation chromatographic analysis of the final product polymer solution. 

Another point is the presence of carboxyl groups. Ottewill and Shaw (14, 15) found a large proportion of these groups on latex particles prepared with hydrogen peroxide initiator and sodium laurate emulsifier, and cleaned by dialysis. On the other hand, we did not find appreciable concentrations of carboxyl groups in our latexes, whether prepared with sulfonate or carboxylate emulsifier, as evidenced by both conductometric and potentiometric titration curves, infrared spectra of the polymer, and electrophoretic mobility of the particles (however, the infrared spectra gave evidence for hydroxyl groups). 

Table II shows that 45-100% of the sulfur incorporated into the polymer is present on the particle surface. In terms of the surface charge, these amounts cannot be neglected as a factor in latex stability, both during and after polymerization. (This accounts for the fact that polymerizations with hydrogen peroxide initiator and low emulsifier concentrations frequently coagulate at low conversions). For latexes B-1, B-2, and D-4, the charge density due to sulfate endgroups is, respectively, at least 4, 8, and 1.6 times the charge due to adsorbed emulsifier. For the other latexes, it amounts to 20-100% of the emulsifier adsorbed. Thus, this permanent charge is an important factor that has been overlooked in earlier studies of latexes at low emulsifier coverage (16, 17).

Emulsion Polymerization of Vinyl Chloride Hydrogen Peroxide Initiated,... 

Hydrogen peroxide-initiated radical polymerization of myrcene in n-butanol solution at 100°C yields OH-terminated polymyrcenes (besides a considerable fraction of side products and dimerized species) with in the range of 2-4 kg/ mol and fairly low polydispersity index (PDI) = 1.3-1.4. The polymyrcenes coti-sist of predominantly 1,4 structural units (77-85% 1,4 and 15-23% 3,4) (Fig. 2), comparable to polyisoprenes, which is further supported by the low glass transition temperature (Tg) of below —50°C [33]. The polymerization of myrcene with potassium persulfate catalyst in emulsion has also been described, yielding a polymyrcene with predominantly 1,4 structure and relatively low molecular weight (MW inherent viscosity 1.3) [34]. Fractions of cis- and trans-l,A units have not been determined, neither in these nor in the following examples. 

FIG. 5 Monomer conversion data for aqueous vinylpyrrolidone graft polymerization. The initial vinylpyrrolidone monomer, surface vinylsilane, and hydrogen peroxide initiator concentrations are [Mq ] = 2.81 M, = 31 pmol/m, and [Iq ] = 0.043 M, respectively. 

FIG. 11 Percentage contributions of polymer grafting to the overall polymer graft yield of poly(vinylp)m olidone). The three curves correspond to initial vinylpyrrolidone monomer concentrations of 10,30, and 40% by volume. The initial hydrogen peroxide initiator concentration is [Iq ] = 0.043 M. 

Another example is the cathodic reduction of hydrogen peroxide, initiated by oxygen in the presence of hydrogen peroxide the limiting current caused by traces of oxygen shows a ten-fold increase [5, 6]. 

---