F. J. Schork

Emulsion and miniemulsion copolymerization of acrylic monomers in the presence of alkyd resin

Emulsion and miniemulsion copolymerizations were carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of an alkyd resin. Poly(methyl methacrylate) was used as a hydrophobe or cosurfactant in the miniemulsion reactions. The results demonstrate that miniemulsion polymerization is the preferred process, probably because of mass transport limitations of the alkyd in the conventional emulsion polymerization reactions. The monomer emulsions prepared for the miniemulsion reactions were much more stable and the polymerizations were free of coagulum. Reaction rates, particle size characteristics, grafting efficiencies, and some film properties were measured.

Waterborne oil-modified polyurethane coatings via hybrid miniemulsion polymerization

As part of a wider effort to develop a new class of waterborne coatings, hybrid miniemulsion polymerization was carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of oil-modified polyurethane resin. Latexes with different ratios of resin to acrylic monomers were synthesized. The monomer emulsions prepared for hybrid miniemulsion polymerization showed excellent shelf-life stability (>5 months) and the polymerization was run free of coagulation. Solvent extraction indicated that the grafting efficiency of polyacrylics was greater than 29% for all the samples produced. A 13C solution NMR spectrum showed that a substantial fraction of the original carbon double bonds (>61%) in oil-modified polyurethane remained after polymerization for film curing. Films obtained from the latexes presented good adhesion properties and fair hardness properties.

Robust nucleation in polymer‐stabilized miniemulsion polymerization

The addition of a monomer soluble polymer to an emulsion was found to slow the effects of Ostwald ripening and impart diffusional stability to the droplets. Droplet nucleation was found to be the dominant nucleation mechanism in the polymerization of these polymer-stabilized miniemulsions (as distinguished from true miniemulsions). As a result these nucleations were more robust, and the polymerizations were less sensitive to variations in the recipe or contaminants levels. This was evident in the rates of polymerization and in the particle numbers. The miniemulsion polymerizations were subjected to changes in initiator concentration, a water-phase retarder, an oil-phase inhibitor, and agitation. Particle number was found to vary with each of these factors to the powers of 0.002, 0.02, 0.0031, and −0.026, respectively. The corresponding exponents for conventional emulsion were one to two orders of magnitude greater. These results demonstrate the potential of miniemulsion polymerization to greatly reduce the variability in particle number found in conventional emulsion polymerizations.

Predominant droplet nucleation in emulsion polymerization

Emulsions stabilized against diffusional degradation by incorporating a polymeric cosurfactant have been produced and polymerized. The presence of large numbers of small droplets shifts the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. When an efficient cosurfactant is used, this process is referred to as miniemulsion polymerization. Polymer, however, is known to be a poor cosurfactant. Its advantage is that, unlike most cosurfactants, it is innocuous in the recipe. Results indicate that even a poor cosurfactant (polymer) is adequate to stabilize small droplets against diffusional degradation long enough to nucleate them into polymer particles. The dependence of the concentration and molecular weight of the cosurfactant on the droplet size and distribution is investigated. Droplet diameters range from 19.5 to 141.2 nm with polydispersities of about 1.023. The polymeric cosurfactant is found to affect the mechanism of nucleation. On-line conductance measurements are used to successfully differentiate between nucleation mechanisms. The observed reaction rates are dependent on the amount of polymeric cosurfactant present. In addition, the latexes prepared with the polymeric cosurfactant have lower polydispersities (1.006) than either latexes prepared from classical emulsions (1.049) or from alkane-stabilized miniemulsions (1.037).