Irja Piirma

Adsorption of ionic surfactants on latex particles

Abstract The adsorption of two ionic surfactants, sodium alkyl sulfate and potassium oleate, was investigated using polystyrene, poly(methyl methacrylate), and their copolymer latices. The molecular areas at saturation adsorption of these surfactants on latex particles were calculated from surface tension titration curves and also from electron microscopy data. The adsorption data were determined as a function of temperature, the electrolyte concentration of the medium, the alkyl chain length of the surfactant, the particle size of the latex, and the composition and nature of the polymers. The saturation molecular area of the surfactants was also measured on the organic solvent swollen latex particles. All the results indicated that the effectiveness of adsorption, i.e., the amount of surfactant adsorbed on polymer surface at saturation adsorption, depends on the above-named variables. These observed effects are discussed and explained in terms of the adsorption equilibrium, the orientation of the surfactant molecules on the surface, the affinity of the surfactant molecule with the surface, and the “penetration effect” of the surfactant.

The stabilization effect of mixed-surfactants in the emulsion polymerization of styrene

SummaryThe emulsion polymerization of styrene was performed at 50°C with a mixture of anionic and nonionic surfactants using different surfactant concentrations. In the single-surfactant systems, a proportional relationship was observed between the total particle surface area per cm3 of aqueous solution at 90% conversion (TS) and the amount of surfactant used for each polymerization. For mixed-surfactant systems an additivity was established between the TS value and surfactant composition. The study of the particle size data from low to high conversion showed that the particle number changed with conversion.

Synthesis of poly(vinyl alcohol-co-vinyl gallate) by the chemical modification of poly(vinyl alcohol)

SummaryPoly(vinyl alcohol-co-vinyl gallate) was successfully synthesized utilizing an esterification reaction in which poly(vinyl alcohol) was transesterified with methyl gallate under alkaline conditions. Aqueous solutions of this copolymer exhibited a sharp critical micelle concentration value, indicating that surface activity is exhibited by the copolymer. Most aqueous solutions of this copolymer possess a black coloring, which indicates that the gallate group is complexing with metal ions present in solution.

The use of sequence distributions to determine monomer feed compositions in the emulsion copolymerization of chlorotrifluoroethylene with vinyl acetate and vinyl propionate

Abstract Emulsion copolymerizations of chlorotrifluoroethylene (CTFE) vinyl acetate (VAc) and vinyl propionate (VPr) under redox initiation conditions were investigated. Reactivity ratios (r) determined for VAc and CTFE in the VAc/CTFE system were 0.68 ± 0.11 and 0.04 ± 0.02, respectively. The reactivity ratios for VPr and CTFE in the VPr/CTFE system were 0.63 ± 0.04 and 0.08 ± 0.01, respectively. Vinyl ester-centred triad distributions of the copolymers were measured by 1H nuclear magnetic resonance spectroscopy and were used to calculate conditional probabilities for monomer placements. These values were compared to conditional probabilities calculated from reactivity ratios, conversions and monomer feed compositions. Significant differences between the experimental and calculated conditional probabilities were observed. The variations in the conditional probabilities could be attributed to the dissimilar comonomer solubilities, which results in a different monomer concentration at the site of polymerization than is expected based on the amounts added to the reactor. This work cites the danger of using emulsion polymerization to obtain r values for monomer pairs. By using sequence distribution information, the concentration of monomers at the site of polymerization can be calculated, which is useful for investigating the location of polymerization.

Emulsion Polymerization: Some Nonionic Emulsifier Effects

SummaryThe colloidal properties of aqueous solutions of surface active materials have been found to have profound effects on the properties of latexes produced via emulsion polymerization. It has been observed that depending on the polymerization temperature and the concentration of the ingredients it is possible to create either an oil-in-water or a water-in-oil emulsion at the beginning of the reaction. This may, as the polymerization proceeds, undergo phase inversion and lead to two constant rate regions and a bimodally distributed particle size latex.

Preparation of a water soluble polyester surfactant and its use in the emulsion polymerization of styrene

SummaryThe synthesis procedure of Chen and Liu (1) was used to prepare a polyester surfactant from dimethyl 5-sulfoisophthalate, sodium salt, polyoxyethylene (MW 200) and phthalic anhydride by a two step esterification process. The surfactant has the unique structural features of multiple ionic groups and polyoxyethylene chains for hydrophilicity and aromatic ester linkages for hydrophobicity. The polyester surfactant exhibited a CMC of 0.25% (w/v) and a surface tension lowering of 23 dynes/cm. The use of the surfactant as stabilizer for the emulsion polymerization of styrene produced some unusual results. While the rate of polymerization was independent of surfactant concentration, the number of particles increased as N ∝ [S]0.91. The molecular weight of polystyrene produced was low and found not to be a function of surfactant concentration. The structural features of the surfactant suggest that a depletion stabilization mechanism might be operative in this system.

Synthesis and characterization of amphipathic poly(methyl methacrylate)-b-poly(ethylene oxide) diblock copolymers

SummaryThis paper describes the synthesis and characterization of amphipathic diblock copolymers of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO). The synthesis involved the coupling of acyl chloride-terminated PMMA block with methoxy poly(ethylene oxide) (MPEO). Carboxylic acid chloride-terminated PMMA was generated by treating with thionyl chloride the parent carboxylic PMMA, which was prepared by free radical polymerization of methyl methacrylate (MMA) using benzoyl peroxide (BPO) as the initiator and β-mercaptopropionic acid (MPA) as the chain transfer agent. The proposed mechanism of MMA polymerization is in good agreement with the experimental results which indicate that as a side reaction nonfunctional (aromatic) counterpart is produced in a small quantity. The coupling of the acyl chloride-terminated PMMA with MPEO was quantitative.

Synthesis of poly(vinyl alcohol-g-4-vinylpyridine hydrochloride) for application as a surfactant in emulsion polymerization of methyl methacrylate

SummaryA redox initiation system composed of ceric ion and poly(vinyl alcohol) was used to successfully synthesize poly(vinyl alcohol-g-4-vinylpyridine hydrochloride). The aqueous solutions of this polycationic surfactant exhibited no sharp CMC value and tended to become turbid upon standing. This turbidity was related to the formation of crystalline-like aggregates in solution, and was thermally reversible. PMMA latices were unstable when formulated with turbid surfactant solutions, but when surfactant solutions were thermally equilibrated, the final PMMA latices were stable.