Kinetic modeling of miniemulsion nitroxide mediated polymerization of styrene: Effect of particle diameter and nitroxide partitioning up to high conversion

The miniemulsion polymerization of styrene mediated by N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (SG1) at 396 K is modeled up to high conversion as a function of the targeted chain length (TCL) and particle diameter. Thermal self-initiation and diffusional limitations are explicitly accounted for. The importance of the compartmentalization of nitroxide, initiator and macroradicals and of nitroxide partitioning is assessed using 3-dimensional Smith-Ewart equations. Diffusional limitations on termination are important for higher particle diameters only (>similar to 70 nm). The influence of diffusional limitations on deactivation, however, can be significant even for intermediate particles diameters (similar to 40 nm). For a TCL of 300, low particle diameters (<similar to 20 nm) provide theoretically both a better livingness and control over chain length compared to the bulk case at the expense of a significant reduction of the polymerization rate. For a sufficiently high particle diameter (similar to 30 nm), a rate acceleration can be obtained accompanied by an improved livingness but with a somewhat reduced control over chain length. For TCLs higher than 300, better overall average polymer properties can be achieved up to particle diameters of similar to 50 nm. Nitroxide partitioning is shown to lead on average to a limited increase of the polymerization rate without significantly affecting the average polymer properties. (C) 2011 Elsevier Ltd. All rights reserved.