Measuring monomer partition

A high-pressure unit with on-line sampling of the aqueous phase has been developed to measure monomer partition coefficients [19]. Eig. 14.4 shows a schematic set-up of the equipment and a description of the relevant components and features. With this equipment, the partition coefficient m2 given by Eq. (7) can be measured as a function of pressure and temperature. 

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. 

Tognacci et al. [ 183] discussed various methods for measuring the monomer concentration in the polymer particles. The method proposed by the authors is a direct estimation of the solvent activity by the GC (gas chromatography) measurement of its partial pressure in the gas phase at equilibrium with the polymer particle, monomer droplet (if any) and aqueous phase in the latex. They proposed an original measuring technique and carried out measurements for different monomers (St, MMA, and VAc) and polymeric matrices (PSt and MMA-VAc copolymer), both above and below saturation conditions (corresponding to Intervals II and III). They compared the experimental data with that predicted by the monomer partitioning relationships derived by Maxwell et al. [166,170] and Noel et al. [172]. 

The semi-empirical proach to monomer partitioning developed by German, Maxwell and co-workers has the major benefit of facilitating prediction of copolymerization behaviour from a few readily measured quantities and has given predictions which are in good agreement with experimental measurements for the systems studied to date [20-28]. However, the assumptions inherent in the development of the approach are likely to result in deficiencies for systems where... 

In order to develop efficient post-polymerization and devolatilization operations, it is critical to know where the residual monomer and VOCs are located, that is, if they are mainly in the polymer particles or in the aqueous phase. Table 18.1 (in Section 18.4.2.1) summarizes the partition coefficients (defined as the ratio between the concentrations of monomer/VOC in the polymer particles and in the aqueous phase) measured for several monomers and VOCs in latexes. It can be seen that the monomers are mainly located in the polymer particles. On the other hand, water-soluble VOCs such as acetaldehyde and tert-butanol are mainly in the aqueous phase. It is worth pointing out that the partition coefficient decreases (that is, the monomer partitioning shifts toward the aqueous phase) as the average monomer concentration in the system decreases [56, 57]. 

Figure 8. Simulated and measured values of the apparent HCB-soil distribution coefficient (K ) as a function of Tween 80 concentration and the HCB-monomer partition coefficient (K. Input parameters CMC = 35 mg/L b = 8.0 L/g = 5.99 g/kg Kj, = 403.4 L/kg = 0.0 Ldcg = 0.09 L/kg.

For very active transfer agents, the transfer agent-derived radical (T ) may partition between adding to monomer and reacting with the polymeric transfer agent (Pn 1) even at low conversions. The transfer constant measured according to the Mayo or related methods will appear to be dependent on the transfer agent concentration (and on the monomer conversion).40 2 A reverse transfer constant can be defined as follows (eq. 20) ... 

Barrett and Thomas (10)proposed that these effects of differential monomer adsorption could be modeled by correcting homogeneous solution copolymerization reactivity ratios with the monomer s partition coefficient between the particles and the diluent. The partition coefficient is measured by static equilibrium experiments. Barrett s suggested equations are ... 

Complete description of the thermodynamics of partitioning of monomers between the aqueous phase, monomer droplets and latex particles obviously is more complex and requires knowledge of many quantities that are difficult to measure, such as interaction paramet and interfacial tensions [6,7]. As a consequence, there have been essentially two types of approach used to account for... 

The principal distinction between the use of Equations (7.29) and (7.21) for Intervals II and IB is that for Interval IB, [MIab and [M]Ba are related dirough Equation (7.26), but cannot be separately defined in terms of easily measurable quantities (unlike the situation for Interval B, where Equations (7.16) and (7.17) also are applicable). Haice, iterative solution of Equations (7.29) and (7.21) is necessary in order to predict /Ap when monomer droplets are absent. Nevertheless, good predictions of partitioning have been obtained in this way [23-28]. 

The extent to which the dimer is favored over that of the monomer is determined by the magnitude of This added seeondary equihbrium, this time appearing in the organic phase, is shown in Figure 3.5. The fundamental basis for the partitioning of HOAc between ether and water as introduced by the Nernst law is not violated and still is given by Kj). The measurable concentrations [HOAcjether and [HOAcjaq will definitely differ with this added dimerization reaction. Let us define D for this distribution equilibrium involving weak acid dissociation of HOAc in the aqueous phase and, at the same time, dimerization of HOAc in the ether phase as follows ... 

The reduction of methyl methacrylate in a PMMA latex was studied. Pulsed electron beam experiments were performed to study the effect of supercritical carbon dioxide on the monomer concentration inside the polymer particles during the polymerization reaction. The partitioning behaviour of methyl methacrylate between water and carbon dioxide was measured as a function of pressure and temperature. 28 refs. 

---