Radicals In Aqueous Phase Research Articles

Effect of the presence of polymer in miniemulsion droplets on the kinetics of polymerization

AbstractSolution of polystyrene in styrene were dispersed in an aqueous gel phase comprising sodium lauryl sulfate, cetyl alcohol, and water using an emulsification process known to produce monomer droplet sizes inthe submicron size range (referred to as miniemulsion droplets). The shelf‐life stabilities of these miniemulsions were studied to determine their relative droplet sizes, and the emulsions were concommitantly polymerized in an isothermal batch reaction calorimeter. The polymerization kinetics and final particle sizes produced were compared with miniemulsion and conventional emulsion polymerizations prepared using equivalent recipes without the addition of polystyrene. The results indicate that polymerization of miniemulsions prepared from polymer solutions produce significantly different kinetics than both miniemulsion and conventional emulsion polymerizations. In general, a small amount of polymer greatly increases the rate of polymerization and the final number of particles produced in the polymerization to the extent where even conventional polymerizations carried out above the critical micelle concentration of the surfactant polymerize more slowly. The results are explained by considering the system to be comprised of small, stable pre‐formed monomer‐swollen polymer particles which are able to efficiently capture aqueous phase radicals. This enables the system to produce a large final number of particles, similar to the initial number of pre‐formed polymer particles, as opposed to miniemulsions and micelles in which only a relatively small fraction of the initial number of species (droplets or micelles) become polymer particles. © 1994 John Wiley & Sons, Inc.

Determining the location of hydrophobic spin traps within liposomes

We have recently reported on an initial study of free radical penetration into liposomal membrane using two new hydrophobic spin traps, namely 2,2-dimethyl-4-phenyl-2H-imidazole 1-oxide (DMPIO) and its 2-methyl-2-nonyl analogue (MNPIO). The radical trapping data was most readily resolved by positing that only MNPIO is lodged completely within the lipid bilayer; the N-oxide group of DMPIO, on the other hand, is actually located at or near the lipid/water interface, available for interaction with aqueous phase radicals. We have been able to confirm these results by using the 13C chemical shifts of these spin traps as a gauge with which to measure the polarity of the microenvironment experienced by the carbons. As expected, the spin traps experience a gradient of solvent polarities, increasing as one goes from deep within the lipid bilayer out toward the aqueous phase.

Preparation and characterization of cationic copolymer latex. 1. Emulsion copolymerization of styrene with 4-vinylpyridine in the presence of non-ionic emulsifier

A study was made of the effect of 4-vinylpyridine (VP) on the kinetics of the emulsion polymerization of styrene (St) and on the distribution of polymeric VP in the cationic latex. Bimodal distribution of particle diameter was obtained in the polymerization under the conditions of low emulsifier concentration and high VP fraction in monomer feed. This would be caused by insufficient stabilization of resulting particles and by some changes in the character of growing radicals in aqueous phase with conversion. Polymerization under acidic conditions was affected by the amphiphilicity of VP-rich radicals which depended on VP fraction in monomer feed. On the surface of the latex particles prepared at pH 2 polymeric VP located preferentially whereas the latex particles prepared at pH 11 had a nearly statistical distribution of VP on their surface.