Nitroxide-Mediated Living Free Radical Miniemulsion Polymerization of Styrene

Abstract

The miniemulsion technique was applied to the controlled/living free radical polymerization of styrene utilizing TEMPO-terminated oligomers of polystyrene (TTOPS) as a macroinitiator species to initiate the polymerization at 125 °C. Miniemulsion polymerizations of styrene using different amounts of TTOPS were studied. It was found that the polymerization rate of a miniemulsion containing no TTOPS was significantly faster than those containing TTOPS. In the latter reactions, the molecular weight of the polymer increased almost linearly with conversion up to 75% conversion. The slope of the molecular weight vs conversion curve increased with decreasing TTOPS concentration as expected. Particle size distributions were measured by both TEM and CHDF and were found to be broad. Using the kinetics and particle size data, the average number of active free radicals per particle (n̄ in classical emulsion polymerization systems) was estimated and found to be low (≤0.005).

Effect of stirring rate on particle formation in emulsifier-free, organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of styrene

“…11,12 Because the control agents used for CLRP thus far have typically been hydrophobic, most of the research efforts in this area have studied miniemulsion polymerization, which ideally proceeds in hydrophobic monomer droplets. [13][14][15][16][17] There has been great interest in the possibility of applying CLRP to emulsion polymerization, but it has been difficult to realize because of problems with the transfer of the control agent. Specifically, the main problem is that the hydrophobic control agent in a monomer droplet does not transfer smoothly into micelles (particles) as polymerization loci via an aqueous medium.…”

Interfacial Mass Transfer in Nitroxide-Mediated Miniemulsion Polymerization

“…There is interest in performing NMP in heterogeneous systems, in particular miniemulsion, [1,2,[6][7][8][9][10][11][12][13] because of the benefits gained by operating in a water-based medium (e.g., lower operating viscosities, improved heat transfer, and reduced need for solvents). The mechanisms involved in miniemulsion polymerization are similar to conventional emulsion polymerization, with the primary difference being that submicron monomer droplets (50-300 nm in diameter) act as the primary nucleation and polymerization locus, instead of monomer-swollen micelles.…”

Controlled/Living Radical Polymerization in Aqueous Miniemulsion

“…nitroxide-terminated oligomers). In the latter case, the macroalkoxyamine is generally a short PS-TEMPO, either synthesized and isolated prior to its use in miniemulsion [70,76,77,79,81,82,95], or synthesized after a first step in bulk stopped at low monomer conversion followed by emulsification of the medium without further purification [74,80].…”

“…Pan et al used a PS-TEMPO macroinitiator (M n = 7050 g.mol· 1 ) at 125°C with hexadecane as a costabilizer and Dowfax 8390 as a surfactant [76,77,95]. However, thermal autoinitiation of styrene was noticed leading to molecular weights lower than expected ones together with PDI increasing up to -1.8 with monomer conversion (~70% in 12 h).…”