Anthony J. Paine

Dispersion polymerization of styrene in polar solvents: I. Grafting mechanism of stabilization by hydroxypropyl cellulose

Abstract The true steric stabilizer in hydroxypropyl cellulose (HPC)-stabilized dispersion polymerization of styrene in polar solvents is grafted HPC-polystyrene, formed in situ , which ends up on the particle surface. The pyrene-labeled HPC experienced a molecular weight increase similar in magnitude to the molecular weight of polystyrene formed by dispersion polymerization. The pyrene-containing polymer also had solubility properties consistent with graft. Kinetic analysis for grafting via chain transfer in solution polymerization predicts a grafting probability of about 1 in 200 polystyrene chains, so the particles must be large (on the order of 0.1 μm) before being sterically stabilized. Precipitation experiments were designed to separate nucleation and stabilization from concurrent polymerization. Precipitation of dispersion-polymerized particles from dioxane with methanol produced new particles with the same morphology as the original particles. The size of these precipitated particles was inversely proportional to the addition rate of nonsolvent to the 0.4 power, but the size distributions were very wide. In contrast, precipitation of commercially available polystyrene from dioxane in the presence of HPC did not produce stable particles. These experiments also suggest that nuclei coalesce extensively until they are sterically stabilized by graft.

Dispersion polymerization of styrene in polar solvents: II. Visualization of surface layers of steric stabilizer on dispersion-polymerized and precipitated polystyrene latex particles by transmission electron microscopy

Abstract Steric stabilizers employed in the dispersion polymerization of styrene in polar solvents include hydroxypropyl cellulose, poly(N-vinylpyrrolidone) and poly(acrylic acid). These steric stabilizers were found, for the first time, in 10–20-nm layers on the polystyrene particle surfaces by direct observation of stained thin sections of the particles using transmission electron microscopy. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results support the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents and suggest that the growing or precipitating particles are able to rearrange to maintain the grafted steric stabilizer on the particle surface at all times.

Surfactant analysis by matrix-assisted laser desorption time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to characterize nonionic, anionic and cationic surfactants. Rapid mass analyses can be achieved with proper choice of matrix material. The technique is suitable for development as a routine analytical tool.

Mechanisms and intermediates for squaric acid synthesis from hexachlorobutadiene and morpholine

Abstract The mechanistic course of the 3-stage synthesis of squaric acid from hexachlorobutadiene and morpholine has been elucidated, and 5 novel intermediates isolated and characterized.