Initiator persulfate

In a series of experiments at 60 C, the rate of polymerization of styrene agitated in water containing persulfate initiator was measuredt for different concentrations of sodium dodecyl sulfate emulsifier. The following results were obtained ... 

Various initiation strategies and surfactant/cosurfactant systems have been used. Early work involved in situ alkoxyamine formation with either oil soluble (BPO) or water soluble initiators (persulfate) and traditional surfactant and hydrophobic cosurfactants. Later work established that preformed polymer could perform the role of the cosurfactant and surfactant-free systems with persulfate initiation were also developed, l90 222,2i3 Oil soluble (PS capped with TEMPO,221 111,224 PBA capped with 89) and water soluble alkoxyamines (110, sodium salt""4) have also been used as initiators. Addition of ascorbic acid, which reduces the nitroxide which exits the particles to the corresponding hydroxylamine, gave enhanced rates and improved conversions in miniemulsion polymerization with TEMPO.225 Ascorbic acid is localized in the aqueous phase by solubility. 

As an even more explicit example of this effect Figure 6 shows that EPM is able to reproduce fairly well the experimentally observed dependence of the particle number on surfactant concentration for a different monomer, namely methyl methacrylate (MMA). The polymerization was carried at 80°C at a fixed concentration of ammonium persulfate initiator (0.00635 mol dm 3). Because methyl methacrylate is much more water soluble than styrene, the drop off in particle number is not as steep around the critical micelle concentration (22.) In this instance the experimental data do show a leveling off of the particle number at high and low surfactant concentrations as expected from the theory of particle formation by coagulative nucleation of precursor particles formed by homogeneous nucleation, which has been incorporated into EPM. 

Rasmussen and co-workers. Chapter 10, have shown that many free-radical polymerizations can be conducted in two-phase systems using potassium persulfate and either crown ethers or quaternary ammonium salts as initiators. When transferred to the organic phase persulfate performs far more efficiently as an initiator than conventional materials such as azobisisobutyronitrile or benzoyl peroxide. In vinyl polymerizations using PTC-persulfate initiation one can exercise precise control over reaction rates, even at low temperatures. Mechanistic aspects of these complicated systems have been worked out for this highly useful and economical method of initiation of free-radical polymerizations. 

Emulsifier is not a necessary component for emulsion polymerization if ihe following conditions are satisfied The particles are formed by homogeneous nucleation mechanism, and the particles are stabilized by factor(s) olher than emulsifier. As to the latter, the sulfate end group that is the residue of persulfate initiator serves for stabilization of dispersion via interparticle electrorepulsive force (20). When the stabilization mechanism works well, a small number of particles grow during polymerization without aggregation, keeping the size distribution narrow. Finally stable, monodisperse, anionic particles are obtained. 

Ammonium persulfate initiates radical formation to begin gel polymerization. Riboflavin in the presence of light also produces radicals. 

The sample used to study the relationship between the volume phase transition and the frictional property is poly( /V-isopropylacrylamide) gel which shows a small discontinuous volume phase transition at 33.6 °C. The sample gel is prepared by free radical polymerization 7.8 g of re-crystallized N-iso-propylacrylamide (main constituent, Kodak), 0.133 g lV,iV -methylenebis-acrylamide (cross-linker, Bio-Rad), 240 ml tetramethylenediamine (accelerator, Bio-Rad), and 40 mg ammonium persulfate (initiator, Mallinckrodt) are dissolved in distilled water (100 ml) at 0°C. The gel mold is immersed in the pre-gel solution and then degassed for 40 min at 0°C. The temperature is raised to 20.0 °C after this treatment to initiate the gelation reaction. The sample gel thus obtained is homogeneous and transparent, at least by visual inspection. 

The individual side reactions (Table 3) result in the overall rate equation of persulfate initiation [10] ... 

Polystyrene latexes have been prepared using persulfate initiator for many years, but only recently have methods been developed to determine the number and loci of the sulfate surface groups. To determine these surface groups, the latex is cleaned to remove the adsorbed emulsifier and solute electrolyte, then the surface sulfate groups in the H+ form are titrated conductometrically with base. The latexes can be cleaned effectively by ion exchange (2-5) or serum replacement (6) dialysis is not effective in removing the adsorbed emulsifier and solute electrolyte (3,5,6). +... 

The extent of the side reaction of sulfate ion-radicals with water to produce hydroxyl radicals was postulated to increase with decreasing pH. Therefore, polymerizations were carried out using persulfate initiator but with the pH of the polymerization adjusted to values in the range of pH range 2-8 (9). Table III (9) shows that, at the lowest pH, the endgroups were about 90% hydroxyls and 10% sulfates at pH 7-8, they were all sulfates. 

These results showed that monodisperse polystyrene particles prepared using persulfate initiator and bicarbonate buffer contain both sulfate and hydroxyl surface groups. Some sulfate groups are on the particle surface, while others are buried inside the particle. All of the hydroxyl groups are on the particle surface. These results also showed that careful control of the pH during polymerization can produce latex particles stabilized with only surface sulfate groups. 

Seven polystyrene latexes prepared with persulfate initiator and bicarbonate buffer were characterized to demonstrate the efficacy of this method (6). Three were monodisperse latexes prepared using conventional emulsifiers four were prepared using sodium styrene sulfonate or sodium vinyltoluene sulfonate as canan-omeric emulsifiers. Each latex was subjected to serum replacement with... 

The foregoing latexes prepared using persulfate initiator and bicarbonate buffer contained surface sulfate groups and, in some cases, surface hydroxyl groups. None of these latexes contained carboxyl groups. These latexes had final pH values of 7-8. If the bicarbonate buffer was omitted, the final pH of the latex was 2-3 because of the bisulfate ion generated by the persulfate decomposition. 

These results are in disagreement with the foregoing findings that only sulfate and hydroxyl groups are produced by persulfate initiator, particularly with bicarbonate buffer. There are several possible sources of the carboxyl groups found by others (i) hydrolysis of sulfate groups followed by oxidation ... 

Vinyl acetate-butyl acrylate copolymers (0-100% butyl acrylate) were prepared by both batch and starved semi-continuous polymerization using sodium lauryl sulfate emulsifier, potassium persulfate initiator, and sodium bicarbonate buffer. This copolymer system was selected, not only because of its industrial importance, but also because of its copolymerization reactivity ratios, which predict a critical dependence of copolymer compositional distribution on the technique of polymerization. The butyl acrylate is so much more reactive than the vinyl acetate that batch polymerization of any monomer ratio would be expected to give a butyl acrylate-rich copolymer until the butyl acrylate is exhausted and polyvinyl acetate thereafter. 

The stability of latexes during and after polymerization may be assessed at least qualitatively by the theoretical relationships describing the stability of lyophobic colloids. The Verwey-Overbeek theory (2) combines the electrostatic forces of repulsion between colloidal particles with the London-van der Waals forces of attraction. The electrostatic forces of repulsion arise from the surface charge, e.g., from adsorbed emulsifier ions, surface sulfate endgroups introduced by persulfate initiator, or ionic groups introduced by using functional monomers. These electro-... 

Materials. Methyl methacrylate (MMA) and methacrylic acid (MAA) monomers (Rohm and Haas), and n-dodecyl mercapten (Eastman Kodak Co.) were purified by vacuum distillation under nitrogen atmosphere to remove the inhibitor. Distilled-deionized and deoxygenated water was used in all polymerizations. Sodium lauryl sulfate (99% Onyx Maprofix 563) and Triton X-100 nonionic surfactant (Rohm and Haas), and potassium persulfate initiator (Fisher Scientific Co.) were used as received without further purification. 

Bartholme t al. (22) found for styrene with persulfate initiation and a sodium alkyl benzene sulfonate emulsifier that there was a discrepancy between their measured value of E (21.7 kJ mol- ) and that calculated (on the assumption that Att = 0) from the expression EN = /5(E - E ). However their value of E (which was derived from measuremlnts of the rate of seeded emulsion polymerization experiments in which N was the same at all temperatures) now seems to be too high probably because the average number of radicals per particle, n < 0.5 at the lower temperatures taking E =32.5 kJ mol-1 as the best estimate, AHg can be calculated rom AHg = /2(E (exp) - E (calc))... 

The currently available commercial grades Teflon AF 1600 and Teflon AF 2400 produced by du Pont are copolymers of PDD and tetrafluoroethylene with respective glass transition temperatures of 160 and 240°C (320 and 464°F).2 They are produced by aqueous copolymerization of PDD and TEE using fluorosurfactant and ammonium persulfate or other metal persulfate initiators.3... 

Figure 4. Styrene-butadiene latex (carboxylated-persulfate initiated)...

The first pilot plant grafting that was run with the commercial 2000 A latex from B. F. Goodrich coagulated. We switched Run 17B formulation with the pentamine/peroxide initiator system to the persulfate initiator system, Run 26 (Table VII). Based on tensile impact data, No. 26 had almost the same impact resistance as No. 17B. 

In Run 17B we increased the mercaptan level by 25% and doubled the pentamine/peroxide initiator levels. This produced a tough polymer. Run 17B had a slightly higher impact resistance than the polymer made in Run 26 which was made with the persulfate initiator system. Run 17B was scaled-up in the pilot plant. 

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