Polymerization aqueous-phase

Aqueous-Phase Polymerization of Butadiene Initated by Cobalt (in) Acetylacetonate... 

Molybdenum provides an example of a fission product which would appear in the dissolver solution in oxidation state (VI). However, the half lives of the molybdenum isotopes produced are sufficiently short for decay processes largely to eliminate this element before fuel reprocessing is undertaken. The extraction of Mo by TBP from aqueous nitrate solutions of pH ().5-3.0 has been investigated. It was found that at Mg concentrations above 10 M, slow aqueous phase polymerization reactions gave rise to time dependent extraction behaviour. Thus Dmo between TBP and a solution containing 1.0 M KNOj and 1.5xlO M Mg at pH 3 rose to 0.1 over a period of 12 hours. At Mg concentrations below 10 M, equilibrium was rapidly attained and in this case was at a maximum of 0.08 between pH 0.5 and pH 1.0, falling off steeply at... 

Water as a co-catalyst was early reported in the ROMP of (strained) cycloolefins, with the catalysts being the hydrates of RuClj, OsClj, and CrClj in refluxing ethanol [Eq. (1)] [8], Redox equilibria to generate Ru(II) active catalysts seem to be engaged but the mode of metal carbene formation finally remains unclear. These catalysts, however, initiate the aqueous-phase polymerization of substituted norbomenes in the presence of anionic emulsifiers and suitable reducing agents [9], even though the overall yield of polymers is still low. 

Harkins calculated from the solubility of styrene in water (0.00368 mol dm at 50 °C [50]) that there are 4 x 10 molecules dm . In a 3% solution of potassium dodecanoate there are about 1 x 10 micelles dm , but with 61 molecules per micelle with an unswollen radius of 2.1 nm the cross-sectional area of the monomer-swollen micelles exceeds that of the styrene molecules by a factor of at least 12. Hence the micelles are more likely to capture initiator radicals produced in the aqueous phase. Polymerization within the micelles must be much faster than in the water because the concentration of styrene will be much the same as in bulk (8.5 mol dm ). The molar mass of the polystyrene produced is much larger than the molar mass of all the styrene molecules solubilized in a micelle thus, the monomer must be able to diffuse through the aqueous phase from other micelles and monomer droplets to allow the polymer radical to continue to grow until it is finally terminated by the entry of another initiator radical from the aqueous phase. Under the standard conditions of the mutual recipe (Table 4.1) there is 180 g water to 100 g styrene taking the emulsion droplets to have a radius of 1 pm, the ratio of the total cross-sectional areas of droplets to micelles to monomer molecules is about 1 30 2.5. The ratio of total surface areas would be even more heavily biased in favour of micelles. Hence it is probable that many more radicals will be captured from the aqueous phase by the micelles than by the emulsion droplets or than react with the monomer molecules in aqueous solution. 

From a synthetic point of view, emuision poiymerization is not suitabie for all monomers. For monomers that are highly water-soluble or, on the other hand, almost insoluble in water, the standard emulsion polymerization technique is not suitable. For water-soluble monomers, besides emulsion polymerization, aqueous phase polymerization can also occur, in which case one could resort to inverse emulsion polymerization, whereby water droplets containing the monomer are polymerized in an oil phase. 

At high conversion, as in the case of commercial continuous polymerizations, the monomer concentration is low and many polymer particles are present. Aqueous phase polymerization is slow and the aqueous radicals are likely to be captured on the particle surface by a sorption mechanism. The particle surface may be richer in monomer than the aqueous phase. Therefore, the polymerization continues in this monomer-rich layer and the sorption becomes irreversible as the chain end grows into the particle. 

Lee, B., and G.A. Sotzing. 2002. Aqueous phase polymerization of thieno[3,4-b]thiophene. Polym Prepr (Am Chem Soc Div Polym Chem) 43 568. 

Keywords aqueous-phase polymerization free-radical polymerization methacrylic acid PLP-SEC propagation rate coefficients pulsed-laser initiation water-soluble monomers... 

The studies into kp of non-ionized MAA suggest that the strong dependence of kp values on monomer concentration that has been observed for other water-soluble monomers in aqueous-phase polymerization [1 43,17,i8] likely also a genuine... 

Our preceding kinetic studies into the aqueous-phase polymerization of AA with propionic add being present and also into the polymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) up to high degrees of monomer conversion provided some indication that kp depends on the total concentration of carboxylic groups, which may be part of the monomer, the polymer, or a carboxylic acid cosolvent, rather than only on monomer concentration. The PLP-SEC-derived kp values for AA were lowered upon increasing the concentration of propionic acid and kp for AMPS, as obtained from a combination of the single pulse (SP)-PLP technique with chemically initiated polymerization, appeared to be independent of monomer conversion. ... 

Figure 1. Although the MWD is relatively broad (M = 55000 g mol Mw = 370000 g mor, polydispersity index = 6.7), inflection points of PLP-produced samples may be clearly identified, if they occur at molecular weights below 30000 g moP. According to ref. the molecular weights for the primary inflection points. Mi, in aqueous-phase polymerizations at MAA contents of 20 wt.-% should be located at 20000 g mol for a pulse repetition rate of 40 Hz. Under such conditions even secondary points of inflection, M, may be observed. Also on the basis of the experience from ref., the initial DMPA concentration was chosen to be cdmpa = 2 mmol L . Within the MAA polymerizations in the presence of IBA, a laser pulse repetition rate of 20 Hz was used.

Some interest continues to be shown in the matter of the aqueous-phase polymerization of butadiene catalysed by metal compounds. Two papers by Georgiev et are concerned with this topic. In the first of these, kinetic... 

Figo 6o Dependence of the particle number N on sodium dodecyl sulfate concentration [SDS] in aqueous phase polymerization of MMA at various monomer concentrations. N denotes the number of particles per liter of reaction mixture. Initial monomer concentrations, [M]o, are O 0.0038, 0.019, O 0.035, 0.0571, 0o0761,... 

Deviations in the emulsion polymerization of VC from the expected behavior were discussed by Chedron [104] in terms of the aqueous polymerization and its competition with the micellar polymerization. The monomer-saturated aqueous phase and precipitation of growing radicals should support the importance of the aqueous-phase polymerization. The molecular weights of poly(vinyl chloride) slightly decreased with emulsifier concentration and increase with conversion. The trend of the molecular weights vs conversion dependence was similar to that in Ref. [102]. 

Hydrophilic S04 radicals derived from peroxodisulfate do not enter the hydrophobic monomer-swollen micelles or polymer particles (Fig. 3). The aqueous phase polymerization generates the surface active ohgomeric radicals (RMz) which can enter the hydrophobic polymer particles. The charged ohgomeric radical enters the polymer parhcle in such a way that the charged group projects to the aqueous phase while the hydrophobic radical end penetrates into the particle surface layer. 

Sajjadi [47] developed two mechanistic models for the particle nucleation process involved in the semibatch emulsion polymerization of styrene under the monomer-starved condition. In the first model, Smith-Ewart theory was extended to take into account the particle nucleation under the monomer-starved condition. The number of latex particles per unit volume of water is proportional to the surfactant concentration, the rate of initiator decomposition, and the rate of monomer addition, respectively, to the 1.0,2/3, and -2/3 powers. The second model considers the aqueous phase polymerization kinetics and its effect on the efficiency of free radical capture by the monomer-swollen micelles. This model is capable of predicting some features of the particle nucleation process. 

FIGURE 4.6 Increase in polymerization rate by addition of reducing agent, NajSjO, to reaction initiated by K2S2OJ. Slope of log-log plot is 0.5 in either case. (Data from Riggs, J. R., The Aqueous Phase Polymerization of Acrylamide A Kinetics and Mechanism Study, PhD thesis, Cornell University Press, Ithaca, NY, 1964.)... 

Riggs, J. R. The Aqueous Phase Polymerization of Acrylamide A Kinetics and Mechanism Study, PhD thesis, Cornell University Press, Ithaca, NY, 1964. 

---