Styrene emulsion polymerization

In case of styrene emulsion polymerization, X 2 is 0.43. If Mq is further decreased below Mc, the number of polymer particles formed increases with decreasing MQ, as shown in Figure 6. The solid lines in the figures represent theoretical values predicted by Eq.(40) using the following numerical constants ... 

Figure 2. Styrene emulsion polymerization—instantaneous rate data for mono-dispersed latices showing the effect of particle size (—LHp = 16.4 kcal/gmol)...

Figure 3. Styrene emulsion polymerization—variation of the propagation constant with temperature during adiabatic polymerization of 395-A latex particles (kp in...

Figure 6. Styrene emulsion polymerization—critical conversion for diffusion-controlled propagation as a function of temperature (---) X cr2 0. 740 + 1.846 X...

Figure 7. Styrene emulsion polymerization—variation of the termination constant with free volume according to Equation 3 with molecular weight changes neglected during adiabatic polymerization of 1650-A latex particles over the conversion range, 0.7-0.911 ((A = 0.44 = 0.0708)...

Catalysis of Thermal Initiation of Styrene Emulsion Polymerization by Emulsifiers... 

We hav shown that with the use of a mixed surfactant system in styrene emulsion polymerization, the composition of the mixed surfactant has an effect on the rate of polymerization, the number of particles formed and the particle size distribution. We have also shown that a change in the ratio, r of the two surfactants in the mixture results in a considerable change in the micellar weight of the resultant mixed micelles. We have thus proposed and proven that the efficiency of nucleation of particles (even when the same number of micelles is used in the experiment) is dependent on the size of the mixed micelle, and that there is an optimum size at which the polymerization rate is the fastest and the particle size distribution is the narrowest. 

A aubstantial amount of recent experimental data demonstrate that the model of styrene emulsion polymerization (1.2) on which the quantitative theory is based (, is not capable of adeqiiate interpretation of polymerization in many real systems. An attempt to use the theoretical relationships to describe polymerization of such industrially important monomers as vluyl acetate, vinyl chloride, alkylacrylates, as well as copolymerization of common monomers with functionally substituted ones, leads to a conclusion that the theory disregards some of the essential factors of the process. Therefore, this theory cannot be a foimdatlon for polymerization technology of the above monomers to be modernized and automatized. 

Although theoretical models seem to be quite adequate for styrene emulsion polymerization in either batch reactors or CSTR s, such is not the case with other monomers like vinyl acetate, methyl acrylate, methyl methacrylate, vinyl chloride, etc. One of the early papers to discuss scane of the important mechanisms involved with these other moncaners was written by Priest ( ). He studied the emulsion polymerization of vinyl acetate and identified most of the key mechanisms involved. Priest s paper has been largely overlooked, however, perhaps because of the success of the Smith-Ewart approach to styrene. 

Matsuura and Kato (3 ) predict the possibility of multiple steady states under isothermal conditions because of the gel effect, and Gerrens et al (20) experimentally verified these predictions with styrene emulsion polymerization. 

Fig. 10. Total number of panicles after styrene emulsion polymerizations as a concentration of free SD in the water phase before polymerization, initiators K,S20b (PPS) and dibenzoyl peroxide (BP). Other experimental conditions as in Fig. 9. Theoretical curves A-E calculated from the absorption isotherm, Eq. (107-108). Curves A-B, a = 4 g/dm . curves C-E, a = OA g/dm. (Reprinted by permission of J. Polym. Sci.)...

Analytic solutions for Eq. (5) provide the most direct path of the prediction of PSD evolution. For batch polymerizations in Interval II, however, analytic solutions have only been achieved for the so-called zero-one system (Lichti et al., 1981). These are systems wherein negligibly few particles contain two or more free radicals because of the rapidity of the bimolecular termination reaction (e.g., in styrene emulsion polymerizations with small latex particles). In this case, Eq. (5) may be written as follows ... 

Lin and Chiu (1979) have reported measurements of P as a function of time for an ab initio styrene emulsion polymerization. They also found that P was slightly in excess of 2 for a considerable part of the reaction, but their actual molecular weight averages were much Iown than those of Piirma et al. (1975). This suggests that their surfactant may have been acting as a chain-transfer agent. 

Harkins (1947) and Smith and Ewart 11948) assumed that in emulsion polymerization the polymerization loci were inside the particles because the rate of styrene emulsion polymerization, for example, was proportional to the number of polymer particles present, However, the polymerization loci in the emulsion polymerization of water-soluble monomers such as vinyl acetate and vinyl chloride heve long been discussed because the rate of emulsion polymerization of these monomers was not proportional to tbe number of polymer particles present. 

Equation (29) is an empirical equation presented by Ugelstad and Merk (1970) and may be useful in styrene emulsion polymerization because tbe value of w is about 10 or less than that under normal reaction conditions in this system. On the other hand, Eqs, (30) and (33) are applicable to vinyl acetate and vinyl chloride emulsion polymerizations (Ugelstad et al.. 1969 Harada et al., 1971 Friis and Nyhagen, 1973). Equation (34) explains very well tbc rate of aqueous dispersion polymerization of vinyl acetate in tha absence of emulsifier (Nomura et a ., 1978). 

This corresponds to Smith-Ewart Case II kinetics and is applicable to styrene emulsion polymerization under normal conditions. On the other hand, when radical desorption from the particles is dominant (i.e., o = ) Eq.(IOS) lesdsto... 

Nomura et ol. (1972) solved Eqs. (112) to (118) on a digital computer and analyzed the particle formation in styrene emulsion polymerization where kf = 0 approximately held under normal conditions and found that the value of was 1.3 x 10. This value is about 10 times greater than that predicted by the diffusion theory which assumes that k, = 2jtDd and k2 = 2nDdp, and where D is the diffusion coefficient of a radical in the water phase. 

Figures 2 and 3 show a comparison of Eqs. (ll) and (13) with data for styrene emulsion polymerization over a wide range of experimental conditions. The rate data fit the theory quite well and the particle number data...

The model based on S-E Case 2 kinetics has been quite successful in handling steady-state data for styrene emulsion polymerizations in a CSTR. One or more of the mechanisms described above, however, generally cause other monomer systems to deviate from this simple model. The nature of these deviations varies among the different monomers. If published literature data are fitted to equations of the type listed below one can obtain values for the exponents a, h, and c. 

An understanding of the transient hehavior of continuous reactors is important for start-up and reactor control considerations. Continuous oscillations have been observed by a number of workers. Figures 10 and 11 show data for styrene and methyl methacrylate. Gerrens and Ley (1974) reported continuous, undamped oscillations in surf e tension during a styrene emulsion polymerization run which lasted for more than 50 mean residence times. Nearly five complete cycles were observed during this run. Berens (1974) conducted experiments with vinyl chloride in whidi the measured panicle size changed with time. No steady state was achieved with the data shown in Fig. 12. 

The gel eflPect at high conversions in styrene emulsion polymerization (17)... 

Kato S, Sato K, Maeda D, Nomura M. A kinetic investigation of styrene emulsion polymerization with surface active polyelectrolytes as the emulsifier. II Effects of molecular weight and composition. Colloids Surf 1999 A153 127-131. 

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