Emulsifier and initiator concentration

Continuous Polymerizations As previously mentioned, fifteen continuous polymerizations in the tubular reactor were performed at different flow rates (i.e. (Nj g) ) with twelve runs using identical formulations and three runs having different emulsifier and initiator concentrations. A summary of the experimental runs is presented in Table IV and the styrene conversion vs reaction time data are presented graphically in Figures 7 to 9. It is important to note that the measurements of pressure and temperature profiles, flow rate and the latex properties indicated that steady state operation was reached after a period corresponding to twice the residence time in the tubular reactor. This agrees with Ghosh s results ). 

In continuous emulsion polymerization of styrene in a series of CSTR s, it was clarified that almost all the particles formed in the first reactor (.2/2) Since the rate of polymerization is, under normal reaction conditions, proportional to the number of polymer particles present, the number of succeeding reactors after the first can be decreased if the number of polymer particles produced in the first stage reactor is increased. This can be realized by increasing emulsifier and initiator concentrations in the feed stream and by lowering the temperature of the first reactor where particle formation is taking place (2) The former choice is not desirable because production cost and impurities which may be involved in the polymers will increase. The latter practice could be employed in parallel with the technique given in this paper. 

Dependence of latex particle number on emulsifier and initiator concentrations... 

Neelson et al. [138] investigated the emulsion polymerization of vinyl chloride in the presence of inhibitors. The used p-benzoquinone and a stable radical 2,2, 6,6 -tetramethylpyperidine-JV-oxide at concentrations 1 x 10 mol dm After the consumption of inhibitor, the conversion vs. time curve was the same shape as that without inhibitor. In some experiments the inhibition period varies with the emulsifier and initiator concentration. The inhibitor efficiency decreased with increasing concentration of emulsifier. The solubilization of inhibitor is expected to decrease the amount of inhibitor available for reactions with radicals. For this reason, the inhibitor acts more efficiently at the low emulsifier concentration as it was reported in Ref. [139]. 

In technical conditions at 1% concentration of emulsifier and initiator concentration of about 0.1% in 1 cm the number of molecules (grains) in pol Tner is of the order of 10 ". ... 

For some apphcations, eg, foam mbber, high soHds (>60%) latices are requited. In the direct process, the polymerization conditions are adjusted to favor the production of relatively large average particle-size latices by lowering the initial emulsifier and electrolyte concentration and the water level ia the recipe, and by controlling the initiation step to produce fewer particles. Emulsifier and electrolyte are added ia increments as the polymerization progresses to control latex stabiUty. A latex of wt% soHds is obtained and concentrated by evaporation to 60—65 wt % soHds. 

The homogeneous nucleation theory may suggest that the dependence of particle number on the concentrations of emulsifier and initiator changes from monomer to monomer. In fact, z in Eq. (4) is 0.6 for a water-insoluble monomer such as styrene (as predicted by Smith-Ewert) but decreases with increasing solubility of monomer in water or increasing transfer of radicals out of particles (12) ... 

It is well known that in the emulsion polymerization of styrene, particle size and size distribution can be varied bv changing the amount of emulsifier, the initiator concentration, the ratio of monomer... 

Figs.7 and 8 respectively show the effect of Initial initiator concentration on the number of polymer particles and the progress of polymerization at fixed Initial emulsifier and monomer concentrations. It can be concluded that the number of polymer particles Is Independent of Initial Initiator concentration, as shown In Fig.7. Fig.9 shows log-log plots of polymerization raterp(g/ cc-HaO sec)versus Initiator concentration, rp Is calculated from the slope of the linear portion of the monomer conversion versus time plot shown In Fig.8. The order of reaction with respect to the Initiator concentration Is found to be approximately 0.5 from... 

Effect of initiator, emulsifier and monomer concentrations on molecular weight development ... 

Equations 10.1 and 10.4 show that the number of polymer particles is crucial in determining both the rate and degree of polymerization. The mechanism of polymer particle formation indicates clearly that the number of polymer particles will depend on the emulsifier, its initial concentration (which determines the number of micelles), and the rate of generation of primary radicals. Smith and Ewart have shown that... 

PS/PU hybrid latex particles were synthesised using water soluble or dispersible PU resins as emulsifiers. Two kinds of PU resins were prepared from isophorone diisocyanate, poly(l,2-propylene glycol)s and 2,2-bis(hydroxymethyl)-propionic acid. Emulsion polymerisation of styrene with the PU resins showed similar kinetic dependence on stabiliser and initiator concentration as with conventional... 

Kinetics styrene emulsion polymerization, varying emulsifier and initiator 428-431 concentration (sodium dodecyl sulfate and potassium peroxodisulfate)... 

Emulsion polymerization of vinyl chloride was also carried out at subsaturation conditions by Butucea et al. [127] who followed the effect of monomer, emulsifier and initiator on the polymerization behavior. Some results from these investigations are summarized in Table 9. This table shows that the rate of polymerization increases with increasing concentration of all these reaction components. From these results the following semiempirical equation for the dependence of the rate on the initiator, monomer (in water) and emulsifier concentrations was suggested. 

The particle size is proportional to the number of particles and decreases exponentially with increasing emulsifier concentration (with constant surfactant type and initiator concentration) until a minimum value is reached. To reduce the particle size beyond this point other techniques have to be used. 

The rate of an ideal emulsion polymerization is given by Eqn (4). In this expression [/] is the initiator concentration, [ ] is the emulsifier concentration, and [M] is the concentration of monomer within the forming latex particles. This value is constant for a long reaction period until all the monomer droplets disappear within the water phase. 

Based on the Smith-Ewart theory, the number of latex particles formed and the rate of polymerization in Interval II is proportional with the 0,6 power of the emulsifier concentration. This relation was also observed experimentally for the emulsion polymerization of styrene by Bartholomeet al. [51], Dunn and Al-Shahib [52] demonstrated that when the concentrations of the different emulsifiers were selected so that the micellar concentrations were equal, the same number of particles having the same size could be obtained by the same polymerization rates in Interval II in the existence of different emulsifiers [52], The number of micelles formed initially in the polymerization medium increases with the increasing emulsifier concentration. This leads to an increase in the total amount of monomer solubilized by micelles. However, the number of emulsifier molecules in one micelle is constant for a certain type of emulsifier and does not change with the emulsifier concentration. The monomer is distributed into more micelles and thus, the... 

After only a small percentage of the monomer has been converted to polymer (in the presence of emulsifier), the initially low surface tension of the aqueous emulsion rises rather abruptly, indicating a decrease in the soap concentration in the aqueous phase of the emulsion. The soap concentration is then too low to maintain micelles, which may therefore be abandoned as a locus for further polymerization beyond this point. As additional evidence of the depletion of soap in the aqueous phase, monomer droplets are no longer stable, and upon discontinuing agitation a supernatant monomer layer is readily formed. 

The rate of polymerization (at constant initiator concentration) depends on the number of micelles and therefore on the emulsifier concentration. The rate and degree of polymerization can be increased simultaneously. 

Smith and Ewart calculated the number of particles having been formed at the end of the first stage of polymerization. The number of particles is affected by the initiator decomposition rate (or radical formation rate) and total surface area of emulsifier to stabilize polymer-monomer particles. Smith and Ewart concluded that the number of particles is proportional to the 0.4 power of the initiator concentration and the 0.6 power of the emulsifier concentration, assuming that the surface area of total polymer-monomer particles is equal to the total surface area of emulsifier molecules when the last micelle disappears. 

Surfactants can act like lipids or emulsifiers in solubilizing flavor materials in surfactant micelles. Headspace analysis techniques were used to follow the release of several common dentifrice flavorants from a solution containing the surfactant sodium lauryl sulfate. Water/micelle partition coefficients were derived to describe the solubilization of the flavorants in tiie surfactant micelle (76). Initially, the flavor is solubilized in the surfactant micelle. As both the micelle and flavor concentration decrease on dilution, flavor compounds, which are highly soluble in the micelle, preferentially increase in the headspace [HGURE11]. 

---