J. M. Asua

Surfactants in heterophase polymerization: A study of film formation using atomic force microscopy

Film formation of three different latices was studied using atomic force microscopy. The latices were made from a mixture of butyl acrylate, styrene, and acrylic acid using either a polymerizable or an unreactive anionic surfactant as an emulsifier. Sodium 11-crotonoyloxyundecan-1-ylsulfate and sodium 3-(sulfopropyl)tetradecylmaleate were used as a reactive surfactant and the unreactive surfactant was sodium dodecylsulfate (SDS). The conventional surfactant was found to migrate to the surface of the latex film to a much greater extent than did the reactive surfactants; however, also, the latter were incompletely anchored to the particle. The maleate surfactant was bound to a higher degree than was the crotonate, a finding which is in line with the relative reactivities of the two surfactants.

Estimation of conversion and copolymer composition in semicontinuous emulsion polymerization using calorimetric data

Abstract A new approach to estimate conversion and copolymer composition in semicontinuous emulsion copolymerization systems based on calorimetric measurements was developed. The proposed approach was checked for two different monomer systems: butyl acrylate-styrene and vinyl acetate—butyl acrylate. The estimated values of conversion and copolymer composition obtained from calorimetric data were compared with measurements of conversion and cumulative copolymer composition by gravimetry, gas chromatography and 1 H n.m.r. A good agreement was achieved.

Reactive surfactants in heterophase polymerization. XXIV. Emulsion polymerization of styrene with maleate- and succinate-containing cationic surfactants

A series of alkyl pyridinium bromide maleate and succinate diester surfactants has been used as stabilizers in the free radical emulsion polymerization of styrene. High conversions of styrene were achieved readily with the maleate surfactants, but the succinates gave rise to varying levels of retardation. In two of the latter cases, use of the surfactant at a concentration below its crucial micelle concentration appears to be a key factor, but the other retardations are difficult to account for. Little difference in reactivity and latex properties was found with the maleate surfactants despite the position of the maleate group being very different in the series of molecules examined. Chemical incorporation of the maleate surfmers into the polymer particles appears to occur early on in the polymerizations, but a sufficiently high proportion of groups is on the surface to yield stable latex emulsions. The surface tensions of the final latices produced with both the maleate and succinate surfactants are high, suggesting a large proportion of succinate species are also surface adsorbed. However, the surface tensions of these latices are a little lower than those of latices produced with the maleates, suggesting the proportion of solubilized succinate surfactant is a little higher. This seems to be important in terms of the robustness of the stability of the latices to the addition of electrolytes, the succinate-stabilized species being consistently more tolerant. This suggests that while chemically bound surfactants can improve some of the properties of latices, e.g. the hydrophobicity of films, this might be at the expense of latex stability.

Maximizing production and polymer quality (MWD and composition) in emulsion polymerization reactors with limited capacity of heat removal

In this work, an on-line control strategy based on reaction calorimetry was used to maximize the production of styrene/n-butyl acrylate latex with desired copolymer composition and molecular weight distribution in reactors with limited capacity of heat removal. For this purpose, nonlinear model-based controllers were used to maximize the production maintaining simultaneously the ratios of each comonomer concentration and of the overall unreacted monomer concentration to chain transfer agent at the required values.

Factors affecting kinetics and coagulum formation during the emulsion copolymerization of styrene/butyl acrylate

The effect of the agitation rate, feeding time, initiation rate and latex viscosity on coagulum formation in the emulsion copolymerization of styrene and butyl acrylate under industrial-like conditions was investigated. The results were analyzed using computational fluid dynamics to simulate the flow pattern in the reactor.

Molecular-weight distributions in the miniemulsion polymerization of styrene initiated by oil-soluble initiators

Abstract The evolution of the molecular-weight distributions in the batch miniemulsion polymerization of styrene initiated by different oil-soluble initiators (lauroyl peroxide, benzoyl peroxide and azobisisobutyronitrile) was investigated. Two series of polymerizations were carried out. In the first, miniemulsions contained only oil-soluble initiators to minimize monomer droplet degradation by molecular diffusion. In the second, the stability of the monomer droplets was reinforced with hexadecane. Also, a series of conventional emulsion polymerizations were carried out. The effect of both the type of initiator and the extent of the compartmentalization of initiator radicals between the polymer particles on the molecular-weight distributions were analysed by means of a mathematical model. A good agreement between experimental results and model predictions was achieved.

VOC formation during monomer removal by post-polymerization

The formation of volatile organic compounds through secondary reactions during the post-polymerization of vinyl acetate containing latexes using organic hydroperoxides with ascorbic acid as redox initiator was investigated. It was found that such initiator systems are highly effective in reducing free vinyl acetate but organic by-products are produced. A reaction scheme consistent with the kinetic data is presented.

Kinetics of the emulsion copolymerization of styrene and butyl acrylate

The kinetics of the chemically initiated seeded emulsion copolymerization of styrene and butyl acrylate was investigated in experiments in which the diameter of the seed, the number of seed particles, and the concentration of initiator were widely varied. The experimental data were fitted with a model in which the rate coefficients for radical entry and exit were the adjustable parameters.

High-solids-content batch miniemulsion polymerization

Abstract The feasibility of obtaining high-solids-content latexes through miniemulsion polymerization was investigated. It was found that, for the batch terpolymerization of styrene, 2-ethylhexyl acrylate and methacrylic acid, coagulum-free 60 wt% solids-content latexes can be obtained through the miniemulsion process, whereas the maximum coagulum-free solids-content latex attainable by means of conventional emulsion polymerization was 50 wt%. The effect of the type and amount of surfactant, amount of cosurfactant and sonication time on both the amount of coagulum and particle size was studied. In addition, the chemical, freeze-thaw and mechanical stabilities of the latexes were determined.

Effect of the preparation on the activity and selectivity of supported nickel catalysts

Abstract The influence of the method of preparation and type of support on the activity and selectivity of supported nickel catalysts was investigated. Silica and silica alumina were used as supports. Catalysts were prepared over these supports by incipient wetness impregnation and by precipitation-deposition. In each instance two different temperatures of reduction (300 and 500°C) were used. Physico-chemical characterization included total nickel content, total surface area, metallic surface area, degree of reduction, mean particle size and temperature-programmed reduction. The reactions of n-pentane in the presence of hydrogen and the hydrogenation of benzene were studied. The former was found to be structure sensitive with a well defined maximum of activity as the particle size increased. On the other hand, owing to the scatter of the data, the results obtained for the hydrogenation of benzene are open to discussion. The selectivity of the reaction of n-pentane in the presence of hydrogen was not affected by the type of support but it was significantly influenced by the method of preparation.