Persulfate-bisulfite-iron system

The polymerizations were carried out in a pressurized continuous polymerization reactor of 8 1 capacity (Autoclave Engineers). While most of the polymerization runs actually would not have required pressure, all runs were carried out at 2.5 x 10 Pa (Nj), which was convenient for the AN/VBr runs. The dispersion polymerization, at a water/monomer ratio of 3.5 (by weight), was catalyzed by a persulfate — bisulfite iron system... 

Fe+2 + HSdg SCHEME 22.6 The persulfate-bisulfite-iron system. 

Fitch and Tsai describe the preparation of monodisperse, emulsifier-free latexes made from methyl methacrylate and stabilized solely by end-groups [1]. The initiator system was persulfate-bisulfite-iron ((R-3) and (R-4)) and the temperature was always 30 °C. At a constant rate of initiation they found that the number of particles, N, was independent of the initial monomer concentration over the range 0.00380 to 0.0951 molar, while the particle diameter increased from 35.4 to 105.4 nm. In another experiment at a lower R , they obtained a final particle diameter of 172 nm and JV=1.1 X 10 1 , compared to Z)=68.7 nm and JV = 1.8x 10 1 at the same monomer concentration (0.035 M) but higher R,-. They estimated in the former case that each ionic group occupied 24.7 nm at the point when self-stabilization by... 

Persulfate/Bisulfite/Iron (PBI) Initiation, The particle size distributions, when not monodisperse, (an example of which is shown in Figure 3) were usually polymodal as exemplified in Figures 4 and 5, The results for the PBI system are shown in Table I and the corresponding calculated values of N are given in Table II, A log-log plot of the latter data is given in Figure 6, Several observations can be made ... 

M. Initiator system persulfate-bisulfite iron (PBI), with rate of initiation, R = 7.74 x 10 radicals /l/sec. Cross-hatched region indicates monodisperse particle size distributions.. 

Redox systems Persulfate/ bisulfite/iron McCarvill and Fitch (1978)... 

This redox system works at pH levels in the range 2-4, where the bisulfite iron predominates. Two main reactions account for radical production. These are the oxidation of ferrous iron by persulfate, and the reduction of ferric iron by SO2 in the bisulfite form. 

The oxyacids of sulfur such as sulphite, bisulfite, bisulfate, thiosulfate, metabisulfite, and dithionate proved to be efficient reducing agents in the redox-initiated polymerization of vinyl monomers. Numerous articles in these areas have been reported in the literature. Palit et al. [161-164] and Roskin et al. [165-167] have reported the polymerization of vinyl monomers using the persulfate-dithionate redox system. Chaddha et al, [168] also reported the persulfate-sulfide redox system to initiate polymerization. The use of sulfide [169,170] and dithionate [171] as reducing agents in conjunction with organic hydroperoxide, like cumene hydroperoxide and iron salt in emulsion... 

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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