Particle from polymerization rates, latex

Determination of Latex Particle Size from Polymerization Rates... 

Emulsion polymerization reactions are sometimes carried out with small seed particles formed in another reaction system. A number of advantages can he derived from using seed particles. In a batch reactor seed latex can he helpful hi controlling particle concentration, polymerization rate, particle morphology, and particle size characteristics. In a CSTR the use of a feed stream containing seed particles can also help to prevent conversion and/or surface tension oscillations, which are caused by particle formation phenomena, This factor will be discussed in more detail later in this chapter. 

The monomer concentration within the forming latex particles does not change for a long period due to the diffusion of monomer from the droplets to the polymerization loci. Therefore, the rate of the propagation reaction does not change and a constant polymerization rate period is observed in a typical emulsion polymerization system. 

The effect changes in concentration and composition of a number of the constituents in the polymerization recipe have on latex particle size was determined from the polymerization rate data. In this recipe, the redox initiator system is added as two separate components. First, the p-menthane hydroperoxide is Injected into the bottle containing monomer, water, soap, salt and regulator. Then, the ferrous hepto sulfate, versene and sodium sulfoxylate dissolved together in aqueous solution is injected. The effect doubling each of these initiator solutions has on particle size is shown in Table III. 

Finally, an Increase in particle size would be expected from a decrease in emulsifier concentration ( 6 ). This effect was evaluated in several polymerizations and the particle sizes of the latex obtained were always found to be larger for the samples with the least soap present using the polymerization rate analysis. Typical results are shown in Table V. 

As can be seen from Fig. 7, variation of the initial emulsifier concentration from 0-5 to 5% in the aqueous phase results in an increase in the BMA polymerization rate (conversion after 30 min) by about 15 times, whereas the MA polymerization rate essentially does not change with changing emulsifier concentration. The data in Table IV show how emulsifier concentration affects particle size and, accordingly, number. Although for both monomers an increase in the emulsifier concentration results in a decrease in the size and an increase in the number of particles, the effect is much weaker in the case of MA polymerization. A comparison of run 2 with runs 3,4, and 5 in Table IV indicates that at the same initial emulsifier concentration the number of particles in 1 dm of the latex is an... 

Summing up the results presented here it may be concluded that in the polymerization rate equation the reaction order with respect to emulsifier is a variable and a function of the area occupied by the emulsifier molecule in the saturated adsorption layer on particles of the resultant latex x=/(i4s,im)- The basic ififierence of this equation from the equations proposed earlier [Eqs. (I) and (2)] is the presence of a parameter that characterizes the properties of the interface (adsorption capacity), which is necessary for a kinetic equation of polymeriza tion occurring in a colloidal... 

In an emulsion polymerization of isoprene with 0.10 M potassium laurate at 50°C the estimated time required for 100% conversion at steady rate is 30 h. The final latex has 40 g of polymer per 100 mL with particles of 450 A diameter. During stage II, the growing swollen polymer particles contain 20 g of monomer per 100 mL of swollen polymer. Assuming that there is no change in total volume on polymerization, estimate the polymerization rate constant from these data. Assume that the polymer has a density of 0.90 g/cm . 

Kinetic results [11-13] The rate of styraiepolymerizaticm initiated by potassium persulfate in a monodisperse polystyrene (PS) seed latex (c. 200 run in diameter) was ctxistant from 0% up to 60% convositxi, while the monomer concentration in the particles decreased significantly. In order for the polymerization rate to remain constant while the total monomer concentration was halved, the monomer concentration at the site of polymerization must be constant. In terms of the Smith-Ewart theory. Case 2, the rate of polymerization per particle, / pp, is expressed as... 

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