Persulfate redox initiation

Personal exposure limit (PEL), for nickel compounds, 17 120. See also Permissible exposure limits (PEL) Personal hazard protection, 21 838 Personnel. See also People commitment of, 15 474 health and safety of, 21 826-827 selection and training of, 21 857 training requirements for, 24 345-347 Persulfate redox initiation, in aqueous dispersion polymerization, 11 197-198,199 Persulfates, 18 408 26 189-190 Persulfate salts, 18 409 Persulfuric acid, 18 407—408 Perturbation... 

Water-soluble peroxide salts, such as ammonium or sodium persulfate, are the usual initiators. The initiating species is the sulfate radical anion generated from either the thermal or redox cleavage of the persulfate anion. The thermal dissociation of the persulfate anion, which is a first-order process at constant temperature (106), can be greatly accelerated by the addition of certain reducing agents or small amounts of polyvalent metal salts, or both (87). By using redox initiator systems, rapid polymerizations are possible at much lower temperatures (25—60°C) than are practical with a thermally initiated system (75—90°C). 

Polymerization in aqueous solution of acrylamide can also be fulfilled in thin layers (up to 20 mm) applied on a steel plate or a traveling steel band. Polymerization is initiated by persulfates, redox system, UV or y radiation. Polymerization proceeds in isothermal conditions as the heat of polymerization is dissipated in the environment and, additionally, absorbed by the steel carrier. Nonadhesion of the polymer to the carrier is ensured by the addition of glycerol to isopropyl alcohol or by precoating the steel band with a film based on fluor-containing polymers. This makes polymerization possible at a high concentration of the monomer (20-45%) and in a wider process temperature range. This film of polyacrylamide is removed from the band, crushed, dried, and packed. 

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

Several articles [7,8] have reported that a persulfate-amine system, particularly persulfate-triethanol amine and persulfate-tetramethylethylenediamine (TMEDA) can be used as redox initiators in aqueous solution polymerization of vinyl monomers. Recently, we studied the effect of various amines on the AAM aqueous solution polymerization and found that not only tertiary amine but also secondary and even primary aliphatic amine and their polyamines can promote the vinyl polymerization as shown in Table 6 [40-42]. 

Recently, Si et al. [59,60] have investigated the synthesis of polymerizable amines, such as N-(3-dimethyl-aminopropyl) acrylamide(DMAPAA) and N-(3-dimeth-ylaminopropyl) methacrylamide (DMAPMA), and their copolymerization reaction. DMAPAA or DMAPMA in conjunction with ammonium persulfate was used as a redox initiator for vinyl polymerization. Copolymers having amino pendant groups, such as copolymer of... 

Recently Uniqema has introduced commercially a Surfmer under the trade name of Maxemul 5011. Maxemul is produced by esterification of an unsaturated fatty anhydride with a methoxy PEG such that the reactive group is close to the hydrophilic moiety [ 34 ]. Stable latexes with a solid content of 52% were produced in the seeded emulsion polymerization of film-forming methyl methacrylate/butyl acrylate/acrylic acid (3% Surfmer on monomers, constant monomer feeding rate over 4 h, potassium persulfate/sodium metabisulfate redox initiator). The latexes were stable to electrolytes but not to freeze-thaw. 

Redox initiators. Free radicals are produced in redox initiators by one-electron transfer reactions. This t T)e of initiator is particularly useful in initiation of low-temperature polymerization and emulsion polymerization. Some typical examples are persulfate + reducing agents hydroperoxides -i- ferrous ion. 

Redox reactions can be used to initiate free radicals as well. Typical examples include persulfate/bisulfite systems. Redox initiation can be used at lower temperatures than thermal initiation reactions. This is useful for polymerization systems that are unstable or show undesirable side reactions at higher temperatures. 

Polymerization in aqueous suspension is by far the most convenient and widely used technique. The monomer is moderately soluble in water, and the pol3uner usually separates as a fine white floe which can be filtered easily and washed. A particular advantage of aqueous polymerization is that one can employ redox initiators such as persulfate-bisulfite r chlorate-sulflte. These catalysts permit rapid polymerization to high conversion at relatively low temperatures, usually 20-40 C. Emulsifying agents may be present, and it is possible to prepare polymer in the form of a stable latex. ... 

Polymer Synthesis. Copolymers of alkylacrylamide (R) and acrylamide (AM), which we called RAM, were prepared with a micellar polymerization technique (4). A micellar surfactant solution was used to disperse the hydrophobic alkylacrylamide monomer into an aqueous phase that contained acrylamide. The monomers were polymerized with a standard free-radical initiator (e.g., potassium persulfate) or a redox initiator to yield the desired random copolymer. Varied temperature and initiator concentrations were used to provide polymers of different molecular weights. Polymerizations were taken to essentially complete conversion. Compositions, in terms of hydrophobe level reported in this chapter, were based on amounts charged to the reactor. Further details on the synthesis and structure of these RAM polymers... 

Acrylamide was polymerized in aqueous solution using ammonium persulfate and sodium metabisulfite for redox initiation [13]. Typical batch data are in Table 1.11. 

Wolfram [90] has shown that polymer add-on increases with pH of the reducing solution, up to pH 7, where it appears to level, and THPC dissociation and sulfur-sulfur bond cleavage also increase with pH. The fact that polymer add-on is not higher at pH 9.2 than at pH 7.0 suggests interference of alkahnity in a subsequent reaction step. The most probable complications are in the chain initiation or propagation steps, given that Wolfram indicates that the cysteine-persulfate redox system is optimum in the pH region of 1.5 to 3.5. 

Redox initiators such as potassium persulfete-sodium metabisulfite or ammonium persulfate-sodium sulfite have been patented for use in poly(vinyl fluoride) emulsion polymerizations [52]. 

In free-radical polymerization carried out in aqueous medium, the decomposition of peroxide or persulfate is greatly accelerated by the presence of a reducing system. This method of free-radical initiation is referred to as redox initiation. The initiation resulting from the thermal decomposition of oiganic compounds discussed above is appropriate only for polymerizations carried out at room temperature or higher. The enhanced rate of free-radical formation in redox reactions permits polymerization at relatively lower temperatures. Typical redox reactions for emulsion polymerization are shown in Equations 1.5-11. 

Persulfate ion initiator (e.g., fromKjSjOg) reacts with a reducing agent such as a bisulfite ion (e.g., from NaHSOj) to produce radicals for redox initiation (Equations 2.5 and 2.6). Ferric ion may also be used as a source of radicals (Equation 2.7). Other redox reactions involve the use of alkyl hydroxides and a reducing agent such as ferrous ion (Equation 2.8). 

Polyacrylonitrile, like PVC, is insoluble in its own monomer. Consequently, the polymer precipitates from the system during bulk polymerization. Aerylonitrile ean be polymerized in solution in water or dimethyl formamide (DMF) with ammonium persulfate as the initiator (redox initiation). The polyacrylonitrile homopolymer ean be dry spun from DMF direetly from the polymerization reactor or wet spun... 

PNIPAAm has been synthesized from N-isopropylacrylamide (NIPAAm) by a variety of techniques, the most widely used being free-radical initiation of organic solutions [147] and redox initiation in aqueous media [148]. Redox polymerization of NIPAAm in aqueous media typically uses ammonium persulfate or potassium persulfate as the initiator and either sodium metabisulfite or N,N,N N -tetramethylethylenediamine (TEMED) as the accelerator. In addition, the solutions are usually buffered to constant pH since in the absence of buffer much greater polydispersity is obtained. Whether one polymerizes NIPAAm in organic or aqueous solution also affects polymer properties [149]. 

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. 

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