Emulsion polymerization of VAc

Oscillations in the number of polymer particles, the monomer conversion, and the molecular weight of the polymers produced, which are mainly observed in a CSTR, have attracted considerable interest. Therefore, many experimental and theoretical studies dealing with these oscillations have been published [328]. Recently,Nomura et al. [340] conducted an extensive experimental study on the oscillatory behavior of the continuous emulsion polymerization of VAc in a single CSTR. Several researchers have proposed mathematical models that quantitatively describe complete kinetics, including oscillatory behavior [341-343]. Tauer and Muller [344] proposed a simple mathematical model for the continuous emulsion polymerization of VCl to explain the sustained oscillations observed. Their numerical analysis showed that the oscillations depend on the rates of particle growth and coalescence. However, it still seems to be difficult to quantitatively describe the kinetic behavior (including oscillations) of the continuous emulsion polymerization of monomers, especially those with relatively high solubility in water. This is mainly because the kinetics and mech-... 

This can be explained by the fact that the flow in the CCTVFR became closer to plug flow as the Taylor number was dropped closer to. Therefore, the steady-state particle number and the steady-state monomer conversion could be arbitrarily varied by simply varying the rotational speed of the inner cylinder. Moreover, no oscillations were observed, and the rotational speed of the inner cylinder could be kept low, so that the possibility of shear-induced coagulation could be decreased. Therefore, a CCTVFR with these characteristics is considered to be highly suitable as a pre-reactor for a continuous emulsion polymerization process. In the case of the continuous emulsion polymerization of VAc carried out with the same CCTVFR, however, the situation was quite different [365]. Oscillations in monomer conversion were observed, and almost no appreciable increase in steady-state monomer conversion occurred even when the rotational speed of the inner cylinder was decreased to a value close to. Why the kinetic behavior with VAc is so different to that with St cannot be explained at present. 

While the various intervals in emulsion polymerization of VAc have a profound affect on the development of molar mass, other components added during the polymerization can also affect molar mass. Lee and Mallinson [21] determined that simple components such as surfactants can profoundly influence molar mass. They studied Aerosol OT [sodium bis-(2-ethylhexyl) sulfosuccinate] (AOT) and determined it can change the molar mass of a product by broadening the molar mass distribution. They reported an increase in polydispersity from 4.2-14 when AOT was substituted for sodium dodecyl sulfate in a VAc system. They attributed these results to significant chain transfer effects of AOT. 

The molar mass obtained during the emulsion polymerization of VAc changes through each of the two intervals as discussed above. These changes are influenced by chain transfer to polymer (CTTP) and terminal double bond polymmza-tion, as discussed by Tobita [19] and others [20]. The transfer reactions to polymer increase during Interval III since the concentration of polymer is much higher. 

Calorimetry Semibatch emulsion polymerization of VAc/BA [66, 67] Epoxy-amine curing polymerization [86] Non-invasive, robust and almost continuous/ Requires state estimators and the values of the reactivity ratios for multimonomer systems All polymerization techniques... 

Figure 6.16 shows the evolution of the risk parameters as a function of the polymer/monomer ratio for the emulsion polymerization of VAc/BA/AA (78.5 18.5 3) as obtained in a VSP2 reactor (Fauske Associates). The particle size of the seed and the initiator/monomer ratio were the same in all the experiments. 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

This short discussion of problems associated with stabilizing dispersions of PVAc and its copolymers leads to the conclusion that the hydrophilic nature of VAc make placement of stabilizing species (surfactant, charge, hydrated layer, etc.) difficult without incurring additional problems (decrease in rate of polymerization, increase in the concentration of water-soluble oligomers, increase in viscosity, etc.). As a result, a combination of approaches is often used in commercial latex production. The need for better surfactants, especially reactive surfactants, for the emulsion polymerization of vinyl monomers is still evident... 

Badran et al. [4] explored the effects of otho- bisulfite adducts with potassium persulfate through the addition of sodium bisulfite to the carbonyl functionality on boizaldehyde, acetaldehyde, octyl aldehyde, methyl propyl keteme and acetone. The rate of polymerization, Rp, in the presence of these bisulfite adducts was a function of initiahn ctHicentration, [I], to the 0.54,0.66,0.95,1.0, and 1.1 powers reqrectivefy for surfactant-free emulsion polymerization at 40 °C where ... 

Gas chromatography Solution and emulsion polymerization systems (VAc/BA, all acrylics, BA/St, St/AN,.,.) [87-90] Ring-opening polymerization [91] and polyolefin gas-phase polymerization [92] Direct measurement of concentrations/Invasive, non-robust in industrial environment, requires sampling and dilutions loops or head-space (equilibrium parameters required) All polymerization techniques... 

CHDF (capillary hydrodynamic fractionation) Semibatch emulsion polymerization of styrene, and VAc/BA [49, 123] PSD directly measured/Invasive, dilution or sampling loop required, non-robust for industrial environment, time delay Emulsion polymerization... 

The emulsion copolymerization of VAc/BuA monomer system can be performed by other emulsion pol3mrierization methods, mini-emulsion and micro-emulsion polymerizations. When the mini-emulsion copol5nnerization carries out with the 50/50 molar ratio of VAc/BuA in the presence of sodium hexadecyl sulfate emulsifier, hexadecane co-surfactant and ammonium persulfate initiator, the results of this polymerization conducted in a batch process are different from that of conventional batch polymerization of this monomer couple [94]. For the mini-emulsion polymerization the polymerization rate is slowed done. 

Fig. 6.16. Evolution of the risk parameters as a function of the polymer/monomer ratio for a VAc/BA/AA emulsion polymerization of high solids content.

Typical S-shaped conversion time curves of the emulsion polymerization of MMA, MMA/St or St in the presence of PVC-VAc seed latex (with weight ratio monomer/polymer (M/P) = 2) were obtained. The rate of polymerization of MMA (in interval 2) (Rp = 13.8 g polymer/min) was much higher than that of St (Rp = 2.1 g polymer/min). The comonomer system (MMA/St, 20/30, wt. ratio) revealed an intermediate feature between the two systems (Rp = 5.5 g polymer/min). The same initial rate (Rp = 0.03 g polymer/min) was observed in St and MMA/St runs. In the MMA system, the interval 1 (the low conversion range) was very short (- 5 min). In contrast, the interval 1 is very long in polymerizations of St ( 350 min) and MMA/St ( 250 min). The secondary nucleation of particles was proportional to the SDS concentration. The secondary nucleation was suppressed when the small seed particles with a smaller monomer/polymer ratio were used. In addition, the choice of a less water-soluble monomer is a key factor in performing complete seed polymerization without nucleation of secondary particles. 

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