Interfacial Mass Transfer in Nitroxide-Mediated Miniemulsion Polymerization

Abstract

A mathematical model has been developed to describe the interfacial mass transfer of TEMPO in a nitroxide‐mediated miniemulsion polymerization (NMMP) system in the absence of chemical reactions. The model is used to examine how the diffusivity of TEMPO in the aqueous and organic droplet phases, the average droplet diameter and the nitroxide partition coefficient influences the time required for the nitroxide to reach phase equilibrium under non‐steady state conditions. Our model predicts that phase equilibrium is achieved quickly (< 1 × 10−4 s) in NMMP systems under typical polymerization conditions and even at high monomer conversions when there is significant resistance to molecular diffusion. The characteristic time for reversible radical deactivation by TEMPO was found to be more than ten times greater than the predicted equilibration times, indicating that phase equilibrium will be achieved before TEMPO has an opportunity to react with active polymer radicals. However, significantly longer equilibration times are predicted, when average droplet diameters are as large as those typically found in emulsion and suspension polymerization systems, indicating that the aqueous and organic phase concentrations of nitroxide may not always be at phase equilibrium during polymerization in these systems.

Optimizing nitroxide-mediated miniemulsion polymerization processes

“…[15][16][17][18] For example, Figure 1 shows monomer conversion versus time of the miniemulsion polymerization of styrene (at 135°C) initiated by the alkoxyamine BST (Scheme 3) at different BST concentrations. A summary of the experimental conditions used in these experiments is given in Table 1.…”

Model for a solid–liquid stirred tank two-phase partitioning bioscrubber for the treatment of BTEX

“…Concentration gradients develop within the polymer particles during dynamic operation, in response to dynamic changes in BTEX concentrations in the aqueous phase. Instead of predicting these gradients and the associated diffusion rates explicitly using partial differential equations, mass transfer from the particles can be adequately described using inside-the-particle mass transfer coefficients that have been developed and used for other types of reactors that contain polymer particles [22,23]. 8.…”

“…However, both approaches account for the same macroscopic observation and are related by Eq. (22), which was used to determine the parameter value of k d…”

Nitroxide‐Mediated Radical Polymerization in Microemulsion

“…Figure 1(b) shows the conversion-time data, revealing that the polymerizations were indeed much faster than when using TEMPO; >75% conversion was reached in 2 h. These R p values are in fact comparable with bulk data for S/SG1. [58] The most likely explanation for the apparent lack of retardation in microemulsion in the case of SG1 is that the confined space effect on deactivation is counteracted by exit of SG1 (the water solubility of SG1 is expected to be significantly higher than that of TEMPO [60] ). The particle sizes were in the range of 21-37 nm, much smaller than for the TEMPO-based systems, resulting in translucent microemulsions [inset in Figure 1(b)].…”