Peroxodisulfate, initiator

In a comprehensive study about the more hydrophilic potassium peroxodisulfate initiator influence during PTP of styrene in (KPS) or the much more hydrophobic miniemulsions it turned out that medium 22 -azobis(2-methyl-butyronitrile) (V59)J ... 

Here R is the charged primary radical derived from peroxodisulfate initiator (1), M monomer in the water phase, RM and RM growing radicals, RMz the surface active radical with a high degree of hydrophobicity and RMj the primary particle. The surface active radical enters the polymer particle or monomer swollen micelles, and start the polymerization. 

Reactions involving the peroxodisulfate ion are usually slow at ca 20°C. The peroxodisulfate ion decomposes into free radicals, which are initiators for numerous chain reactions. These radicals act either thermally or by electron transfer with transition-metal ions or reducing agents (79). 

The principal use of the peroxodisulfate salts is as initiators (qv) for olefin polymerisation in aqueous systems, particularly for the manufacture of polyacrylonitrile and its copolymers (see Acrylonitrile polymers). These salts are used in the emulsion polymerisation of vinyl chloride, styrene—butadiene, vinyl acetate, neoprene, and acryhc esters (see Acrylic ester polymers Styrene Vinyl polymers). 

An expanding development is the use of peroxodisulfates as oxidants in organic chemistry (80,81). These reactions are initiated by heat, light, gamma rays, or transition-metal ions. The primary oxidising species is usually the sulfate ion radical, P hskip -3pt peroxodisulfate anion... 

Beaded acrylamide resins (28) are generally produced by w/o inverse-suspension polymerization. This involves the dispersion of an aqueous solution of the monomer and an initiator (e.g., ammonium peroxodisulfates) with a droplet stabilizer such as carboxymethylcellulose or cellulose acetate butyrate in an immiscible liquid (the oil phase), such as 1,2-dichloroethane, toluene, or a liquid paraffin. A polymerization catalyst, usually tetramethylethylenediamine, may also be added to the monomer mixture. The polymerization of beaded acrylamide resin is carried out at relatively low temperatures (20-50°C), and the polymerization is complete within a relatively short period (1-5 hr). The polymerization of most acrylamides proceeds at a substantially faster rate than that of styrene in o/w suspension polymerization. The problem with droplet coagulation during the synthesis of beaded polyacrylamide by w/o suspension polymerization is usually less critical than that with a styrene-based resin. 

When aqueous solutions of the polymerisation initiators 2,2/-azobis(2-amidinio-propane) chloride and sodium peroxodisulfate are mixed, the title compound separates as a water insoluble shock-sensitive salt. The shock-sensitivity increases as the moisture level decreases, and is comparable with that of lead azide. Stringent measures should be used to prevent contact of the solutions outside the polymerisation environment. (The instability derives from the high nitrogen (21.4%) and oxygen (31.6%) contents, and substantial oxygen balance, as well as the structural factors present in the salt.)... 

CEC capillary columns filled with hydrophilic polymer gels mimic those used for capillary gel electrophoresis [91]. Typically, the capillary is filled with an aqueous polymerization mixture that contains monovinyl and divinyl (crosslinking) acrylamide-based monomers as well as a redox free radical initiating system, such as ammonium peroxodisulfate and tetramethylethylenediamine (TEMED). Since initiation of the polymerization process begins immediately upon mixing all of the components at room temperature, the reaction mixture must be used immediately. It should be noted, that these gels are very loose, highly swollen materials that usually contain no more than 5% solid polymer. 

Temperature and pressure effects on rate constants for [Fe(phen)3] +/[Fe(phen)3] + electron transfer in water and in acetonitrile have yielded activation parameters AF was discussed in relation to possible nonadiabaticity and solvation contributions. Solvation effects on AF° for [Fe(diimine)3] " " " " half-cells, related diimine/cyanide ternary systems (diimine = phen, bipy), and also [Fe(CN)6] and Fe aq/Fe aq, have been assessed. Initial state-transition state analyses for base hydrolysis and for peroxodisulfate oxidation for [Fe(diimine)3] +, [Fe(tsb)2] ", [Fe(cage)] " " in DMSO-water mixtures suggest that base hydrolysis is generally controlled by hydroxide (de)hydration, but that in peroxodisulfate oxidation solvation changes for both reactants are significant in determining the overall reactivity pattern. ... 

Reaction kinetics and mechanisms for oxidation of [Fe(diimine)2(CN)2], [Fe(diimine)(CN)4] (diimine = bipy or phen) (and indeed [Fe(CN)6] ) by peroxoanions such as (S20g, HSOs", P20g ) have been reviewed. Reactivity trends have been established, and initial state— transition state analyses carried out, for peroxodisulfate oxidation of [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4] , and [Fe(Me2bsb)(CN)4] in DMSO—water mixtures. Whereas in base hydrolysis of iron(II)-diimine complexes reactivity trends in binary aqueous solvent mixtures are generally determined by hydroxide solvation, in these peroxodisulfate oxidations solvation changes for both partners affect the observed pattern. ... 

Kinetics of peroxodisulfate oxidation of [Fe(terpy)(CN)3] in water and in binary aqueous solvent mixtures have been analyzed, with the aid of measured solubilities of [Ph4As][Fe(terpy)(CN)3], to separate the initial state and transition state contributions to the observed reactivity trend. ... 

Water-soluble initiators (potassium peroxodisulfate redox systems) are used except for a few special cases. 

Ammonium peroxodisulfate is more soluble in water than the potassium salt furthermore, it dissolves in more polar organic solvents (e.g., DMF), so that it is sometimes also used for initiating polymerizations in organic media. In polymerizations initiated by peroxodisulfates the reaction medium is liable to become acidic, so that buffering is generally necessary (see Example 3-2). 

Hydrophobic monolithic methacrylate capillary columns have been introduced by copolymerization of butyl methacrylate and EDMA as cross-linking agent. The polymerization, however, was not thermally or photochemically but chemically initiated ammonium peroxodisulfate [154]. The resulting monolithic columns were applied to RP separation of small analytes like uracil, phenol, or alkylbenzenes. Reasonable results have been obtained under isocratic conditions, delivering typical values for theoretical plate height ranging between 40 and 50 pm. 

The most commonly used water-soluble initiator is the potassium, ammonium, or sodium salt of peroxodisulfates. Redox initiators (Fe2+salt/peroxodisul-fate, etc.) are used for polymerization at low temperatures. Oil-soluble initiators, such as azo compounds, benzoyl peroxides, etc., are also used in emulsion polymerization. They are, however, less efficient than water-soluble peroxodisulfates. This results from the immobilization of oil-soluble initiator in polymer matrix, the cage effect, the induced decomposition of initiator in the particle interior, and the deactivation of radicals during des orption/re-entry events [14, 15]. 

Starting from those two dispersion situations, the locus of initiation is expected to have a great influence on the reaction products and the quality of the obtained copolymers. Therefore three different initiators were used, an oil-soluble initiator (e.g., 2,2 azobis(2,4-dimethylvaleronitrile (ADVN)), an interfacial active initiator (e.g., PEGA200), and a water-soluble initiator (e.g., potassium peroxodisulfate (KPS)) in order to initiate the polymerization selectively in one of the phases or at the interface. 

Vaskova V, Hlouskova Z, Barton J, Juranicova V (1992) Polymerization in inverse microemulsions, 4 locus of initiation by ammonium peroxodisulfate and 2,2-azoisobutyronitrile. Macromol Chem 193(3) 627-637... 

Many oxidations (e.g., of oxalate) by the peroxodisulfate ion are catalyzed by Ag+ ion, and the kinetics are best interpreted by assuming initial oxidation to Ag2+, which is then reduced by the substrate. Decarboxylation of carboxylic acids are also promoted by Ag11 complexes, such as (18-I-IX) and others. 

A polymerization vessel was charged with water (300 g), 33% polymer styrene latex (62 g, dso of 30 nm), 10% of the initiator solution, and sodium peroxodisulfate and then heated to 95°C. Using two separate feeds, the monomer emulsion present in... 

Barton et al. [232] conducted the emulsion polymerization of the sparingly water-soluble monomer St and of the fairly water-soluble monomer MMA in the presence and absence of the water-soluble inhibitor, potassium nitrosodi-sulfonate (Fremy s salt). By using oil-soluble dibenzoyl peroxide (DBP) and water-soluble ammonium peroxodisulfate (APS) as the free-radical initiators, they examined the effect of the location of the initiator on the kinetics of these emulsion polymerizations with SDS as the emulsifier. Figure 7 shows an example of the experimental results. 

Regarding the initiation process of polymerization, it can be started by y-radiation. It is a method that has been used for the synthesis of hydrogels of PEO as well as hydrogels based on vinyl monomers " in this latter case, azo-compounds such as 2,2-azo-isobutyroni-trile (AIBN)f or 2,2 -azobis (2-amidine-propane) dihydrochloride or V-SO, and aqueous salt solutions such as aqueous ammonium peroxodisulfate are also used. Among the monomers most used in the preparation of hydrogels through free-radical polymerization are 2-hydroxyethyl methacrylate (HEMA) and A-vinyl-2-pyrrolidone (VP). ... 

Most of the peroxodisulfate produced (>65%) is used as a polymerization initiator in the production of poly(acrylonitrile), emulsion-polymerized PVC etc. The rest is utilized in numerous applications (etching of printed circuit boards, bleaching processes etc.). 

Copper-based ATRP in emulsion has been achieved successfully under reverse ATRP conditions, where one starts with a conventional free radical initiator and CuBr2/dNbpy as a catalyst [226]. Typical commercial water-soluble free radical initiators such as potassium peroxodisulfate (in a phosphate buffer, pH = 7), 2,2 -azo-... 

Organic peroxides and peroxodisulfates as well as some azo compounds and carbon-carbon compounds are mainly used as initiators in radical polymerization. The production volume of these initiators exceeds 250,000 metric tons. More than 50% of all polymers are made industrially by radical polymerization. Considering that the annual worldwide production of polymers is in the range of 200 Mio metric tons, it indicates that initiators have fundamental importance. The quantity of initiator used varies in a range from 0.01- 5% depending on the process and polymer applied (Fig. 1). Their decomposition products become incorporated or remain as a residue in this large volume of polymers (Fig. 2). 

Table 1 Organic peroxides consist mainly of eight different basic substance classes. Peroxodi-sulfates are also important radical generators on a smaller scale azo-initiators and carbon-carbon initiators are used Dialkylperoxides Hydroperoxides Perester Perketales Ketonperoxides Diacylperoxides Peroxidicarbonates Peracids Peroxodisulfates Azo-initiators CC-initiators...

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