Redox systems potassium persulfate

Polymers were obtained by radical copolymerization in aqueous media of acrylamide and the corresponding ionic acrylic comonomers (AMPS or MSA). By using a redox system (potassium persulfate, N,iV,iV, j V, tetramethylene diamine) the polymerization can be performed at a temperature lower than 35° [17-18] which avoids branching the latter may occur at a reaction temperature higher than 60°. Polymers are recovered from the reaction medium by precipitation in ethanol. 

The most common water-soluble initiators are ammonium persulfate, potassium persulfate, and hydrogen peroxide. These can be made to decompose by high temperature or through redox reactions. The latter method offers versatility in choosing the temperature of polymerization with —50 to 70°C possible. A typical redox system combines a persulfate with ferrous ion ... 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

The initiators used in emulsion polymerization are water-soluble initiators such as potassium or ammonium persulfate, hydrogen peroxide, and 2,2 -azobis(2-amidinopropane) dihydrochloride. Partially water-soluble peroxides such a succinic acid peroxide and f-butyl hydroperoxide and azo compounds such as 4,4 -azobis(4-cyanopentanoic acid) have also been used. Redox systems such as persulfate with ferrous ion (Eq. 3-38a) are commonly used. Redox systems are advantageous in yielding desirable initiation rates at temperatures below 50°C. Other useful redox systems include cumyl hydroperoxide or hydrogen peroxide with ferrous, sulfite, or bisulfite ion. 

The potassium persulfate-sodium bisulfite redox system was used as the initiator for Experiments A, B, C, D, whereas potassium persulfate only was used in Experiment E. Quantities of initiator were chosen accurately so that the reaction rate was always about the same. 

Redox systems which have been the subject of recent examlnC atlon include potassiian permanganate - tartaric acid ( ), and potassium persulfate — ascorbic acid.( ) Whilst experiments were with the water soluble acrylamid they should be adaptable to emulsion conditions. The ascorbic acid reductant is of inters est as it is not interfered with by air or monomer stabilisers. 

In cold polymerization, the most widely used initiator system is the redox reaction between chelated iron and organic peroxide using sodium formaldehyde sulfoxide (SFS) as a reducing agent [see Eqs. (1) and 2]. In hot polymerization, potassium persulfate is used as an initiator. 

Acrylamide grouts at ambient temperatures are catalyzed with a two-component redox system. One part, the initiator or catalyst, can be a peroxide or a persalt. Ammonium persulfate (AP), a powder, is most commonly used. The second part, the accelerator or activator, is an organic such as triethanolamine, (TEA), nitrilotrispropionamide (NTP), or dimethylaminiopropionitrile (DMAPN). All three have disadvantages. DMAPN, a liquid, is best from a control point of view but is considered a health hazard. NTP, a powder, has limited solubility in water, particularly at low temperatures. TEA, a liquid, is somewhat metal-sensitive. At the present time virtually all U.S. applications use TEA. There are also materials which act as inhibitors and can be used reliably to control gel time. Potassium ferricyanide, KFe, is most often used. 

The above initiators are thermal initiators that require heat to produce radicals. Redox systems offer further degrees of freedom in that they allow free-radical polymerizations without the use of significant quantities of heat Tertiary-butyl hydroperoxide/sodium formaldehyde sulfoxylate or potassium persulfate/sodhim... 

The kinetics of aqueous dispersion polymerization differ very little from acrylonitrile bulk or emulsion polymerization. Redox initiation is normally used in commercial production of polymers for acrylic fibers. This type of initiator can generate free radicals in an aqueous medium efficiently at relatively low temperatures. The most common redox system consists of ammonium or potassium persulfate (oxidizer), sodium bisulfite (reducing agent), and ferric or ferrous iron (catalyst). This system gives the added benefit of supplying dye sites for the fiber. 

The systems discussed up to now produce free radicals singly, so the free radical yield is equal to unity. However, certain redox systems produce free radicals in pairs, so that cage effects and reduced free radical yield are produced. The potassium persulfate and mercaptan systems, for example, belong to this category... 

ACM is generally produced by emulsion polymerization in the presence of a free-radical initiator. The polymerization is initiated by organic peroxides or azo compounds. Potassium persulfate or redox systems are also used. 

Besides vinyl acetate monomer, three other components are neeessary to earry out an emulsion polymerization water, an emulsifier and/or a proteetive eolloid, and a water-soluble initiator. Most commonly, anionic long-chain alkyl sulfonates are used as surfactants in amounts up to 6%. Studies have shown that the rate of polymerization is dependent on the amoimt of emulsifier present, with the rates inereasing as the amoimt of emulsifier is increased up to a certain point and then falling olF as free-radieal ehain transfer to the surfaetant beeomes a serious competing side reaetion [240]. In general, surfactants are used in eombination with a protective colloid. Especially useful as protective colloids are poly(vinyl alcohol), hydroxyethyl cellulose, alkyl vinyl ether-maleic anhydride and styrene-allyl alcohol copolymers, and gum arable. Water-soluble initiators, particularly potassium persulfate, alkali peroxydisulfates, hydrogen peroxide, and various redox systems, are most commonly used. 

In a procedure described in Ref. [474], sodium orthosilicate was added to the reaction medium to raise the polymer yield to 95%. The initiator was ammonium persulfate with a special emulsifier that is believed to be perfluorinated carboxylated emulsifier from 3M Corp [458]. Other initiators used are redox systems such as potassium persulfate-sodium metabisulfite or ammonium persulfate-sodium sulfite [475]. Different initiators are also of some interest because they affect the particle diameter of the emulsion. Polymer particles formed with a diameter between 0.36 and 18 pm, depending on the initiator system and the polymerization procedures, are reported [458]. In a patent of Dynamit Nobel [476], iodine-containing compounds such as ammonium iodide or isopropyl iodide are used. These compounds give rise to polymers of improved thermal stability and resistance to color deterioration. The procedure did not require the use of an emulsifier. After 150 min the internal pressure of the autoclave dropped from 2 x 10 to 3 X 10 Pa and a conversion to polymer of 86% was found. More recently Uschold [477] describes also an emulsion polymerization of PVF in high yields and having excellent color. 

Some typical redox systems are potassium persulfate-potassium metabisulfite [160] the monomer-soluble oxidizing agent tert-bwiyX perpivalate and potassium metabisulfite [161] hydrogen peroxide-sodium formaldehyde sulfoxylate [162] hydrogen peroxide-sodium formaldehyde sulfoxylate in the presence of cupric sulfate and EDTA [163] hydrogen peroxide-oxalic acid in the presence of ferrous sulfate [164] and persulfates and sodium formaldehyde sulfoxylate [165]. 

Panels (8.9 x 15.2 x 0.235 cm) were cut consecutively, at all possible locations, from commercial chrome-tanned grain-split blue stock cattlehide. Untreated control panels were included with each treated panel. In the emulsion method, after a separate 30 min conditioning period with the potassium persulfate-sodium bisulfite redox initiator system, the panels to be treated were tumbled at ambient temperature under emulsion conditions with the appropriate monomer for 24 hr. Composite composition was obtained gravimetrically from methanol or air-dried panels. Homopolymer was removed from apparent bound polymer by hot benzene extraction. Standard conditions were water 5 1 based on dry leather ... 

The original wartime GR-S, poly(butadiene-co-styrene), polymerization was carried out at 50 °C using potassium persulfate initiator ( hot rubber). The use of the more efficient redox systems allowed a reduction in polymerization temperature to 5 °C ( cold rubber). The latter has superior properties because the lower polymerization temperature promotes CM-1-4-addition of the butadiene. 

In contrast to UV-initiated graft polymerization, the redox-initiated grafting allows the modification of the polymer membranes in situ, even inside commercial wound membrane elements [71]. Redox system most often used consists of potassium persulfate (K2S2O8) and potassium metabisulfite (K2S2O3) [71,72]. Redox reaction that occurs generates radicals on the membrane surface, upon which monomers can be attached ... 

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