Jose R. Leiza

Seeded semibatch emulsion polymerization of butyl acrylate : Effect of the chain-transfer agent on the kinetics and structural properties

The effect of dodecane-1-thiol on the kinetics, gel fraction, level of branches, and sol molecular weight distribution of the seeded semibatch emulsion polymerization of n-butyl acrylate carried out at 75 °C was investigated. The gel fraction was strongly affected by the content of the chain-transfer agent (CTA). The sol weight-average molecular weights decreased with increasing CTA concentration, whereas no effect on the kinetics and the level of branches was observed. The experimental data were analyzed with a mathematical model of the process that was able to catch fairly well the effect of the process variable. In addition, adhesive tests were carried out to check the effect of the gel fraction on the adhesive properties.

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.

Particle Size Distribution Measurements of PolymericDispersions: A Comparative Study

Average particle sizes and particle size distributions (PSD) were measured using four different commercial techniques for standard polystyrene latexes in the submicron range, dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), disk centrifuge photosedimentometry (DCP) and transmission electron microscope (TEM). Both monodisperse latexes and broad particle size distribution latexes (obtained by mixing two or three monodisperse standards) were used in each equipment. It was found that for monodisperse latexes, DLS, CHDF and DCP gave similar measurements of particle size, which were also comparable to the particle sizes measured by TEM and reported by the supplier of the standard latexes. However, with the lowest particle size standard (39 nm), both DLS and CHDF gave larger particle size values, whereas with DCP, reasonable agreement with the measured size was obtained only when extremely long centrifugation times (at least 6 h) were used. For latexes having bimodal and trimodal distributions, both CHDF and DCP were able to reproduce the entire distribution, providing relatively accurate values for the average size of each mode and also the relative masses of each population of particles. However, the analysis time required by CHDF was shorter than by DCP, but the broadness of the peak was better captured by DCP than CHDF, which always provided broader peaks. DLS failed in most cases when measuring the broad size populations when the size ratio was greater than 2 : 1.

UV screening clear coats based on encapsulated CeO2 hybrid latexes

CeO2 nanoparticles have been successfully incorporated into acrylic latex particles with an excellent homogeneous distribution (mostly one inorganic particle per polymer particle) and limited aggregation (inorganic nanoparticles predominantly in the 17–26 nm range, when the original cerium oxide dispersion had a volume average diameter of 8 nm). The hydrophobicity and wettability of the inorganic nanoparticles with the monomer mixture and the process used, semibatch emulsion polymerization on a seed produced by miniemulsion polymerization containing the whole load of the metal oxide, were the key aspects to achieve this morphology for the first time at industrially relevant solids content (40 wt%). Furthermore, the transparency and the substantially enhanced UV-Vis absorbance capacity make those hybrid acrylic/CeO2 dispersions excellent candidates for a large number of applications including clear coatings and cosmetics.

On-line calorimetric control of emulsion polymerization reactors

Abstract Reaction calorimetry was used to monitor and control unseeded semi-batch emulsion copolymerization of VAc and BuA. An external PC, using the information derived from a commercial reaction calorimeter, calculated on-line the thermal and material balances of the calorimetric reactor, and thus the monomer conversions. For a desired copolymer composition profile, previously calculated conversion-dependent monomer feed profiles were used to determine the rates of monomer addition every 20 seconds. Gas chromatography and gravimetry confirmed that copolymers having the desired variable composition profiles were successfully obtained. The control strategy devised lends itself to polymer quality control and safe operation, since variable monomer inhibitor levels or sudden inhibition during the reaction do not lead either to the formation of off-composition polymer nor to monomer accumulation in the reactor. Furthermore, the rate of polymerization can be reduced by fixing upper limits for monomer concentrations in the polymer particles, useful in cases where the minimum-time optimal feed profile, which corresponds to maximum swelling, might lead to thermal runaway.

Dynamic optimization of non-linear emulsion copolymerization systems: Open-loop control of composition and molecular weight distribution

Time optimal monomer and chain-transfer agent feed profiles were computed and implemented experimentally for the simultaneous control of copolymer composition and molecular weight distribution in non-linear emulsion copolymerization systems. Iterative dynamic programming was used for the off-line calculation of the optimal feed policies. This approach can deal with constrained optimization of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole molecular weight distribution is included. The proposed approach was applied to the semibatch methylmethacrylate (MMA)/n-butylacrylate (n-BA) emulsion copolymerization, using n-dodecanethiol as chain-transfer agent, and allowed the production of copolymers with constant composition and with well-defined molecular weight distributions.

Modeling the equilibrium morphology of nanodroplets in the presence of nanofillers

Waterborne polymer nanocomposites containing carbon nanotubes, clay platelets, laponite disks and other spherical/nonspherical nanofillers have been the focus of many recent investigations. The miniemulsion polymerization has proved to be a powerful technique to create new hybrid waterborne nanocomposites with enhanced properties. It is necessary to understand how the nanofiller shape/size and its compatibility with the phases affects the equilibrium morphology of the polymer nanoparticle to control the morphology and the properties of the resulting polymeric dispersions. With the aid of Monte Carlo simulations, the equilibrium morphology of hybrid monomer nanodroplets in the presence of nanofillers with different characteristics was obtained. A series of morphology maps depending on the nanofiller compatibility with the monomer and water phases and its shape have been obtained. These new maps may help to design and determine the required conditions to synthesize innovative waterborne polymer nanocomposites with specific morphologies through miniemulsion polymerization.

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.

Morphology and properties of waterborne adhesives made from hybrid polyacrylic/montmorillonite clay colloidal dispersions showing improved tack and shear resistance

AbstractThe morphology and adhesive properties of waterborne films from n-butyl acrylate/methyl methacrylate/montmorillonite clay hybrid polymer latexes which were synthesized by miniemulsion polymerization in the presence of a reactive organoclay ((2-methacryloylethyl) hexadecyldimethylammonium modified montmorillonite, CMA16) were investigated. It was found by cryo-TEM analysis that the hybrid dispersions were a mixture of colloidal particles composed of a small fraction of free montmorillonite clay platelets, polymer latex particles, polymer particles to which one or more clay platelets where adhered onto its surface and a fraction of colloidal material consisted of a clay platelet with a polymer lob adhered to either side, in other words hybrid particles with a dumbbell-like morphology. The films made from these waterborne hybrid dispersions presented a homogeneous dispersion of the clay platelets and exfoliated morphology. The shear adhesion failure temperature (SAFT) and shear resistance of the hybrid latex films synthesized with CMA16 were better than those prepared with a commercial clay (Cloisite 30B), but presented a liquid-like probe-tack performance. When allyl methacrylate (AMA) was added in the formulation, SAFT and shear resistance improved, but the film had a very low energy of adhesion due to the excessively crosslinked matrix. In order to reduce crosslink density and thus improve the adhesion energy, small amounts of chain transfer agent, in this case n-dodecyl mercaptan (n-DDM), were used in the miniemulsion polymerization process. Adhesive films made from these waterborne hybrid dispersions showed excellent SAFT and shear resistance, and good energy of adhesion.

On-Line Copolymer Composition Control in the Semicontinuous Emulsion Copolymerization of Ethyl Acrylate and Methyl Methacrylate

ABSTRACTA closed-loop strategy for copolymer composition control in semicontinuous emulsion polymerization systems is presented. This strategy is based on a non-linear adaptive plus proportional-integral controller that calculates the flow rate of the more reactive monomer to be added into the reactor to produce a copolymer of a given composition. The non-linear adaptive part of the controller is based on a simplified mathematical model of the process that includes an on-line adjustable parameter. The controller was checked by computer simulation and also experimentally verified during the semicontinuous emulsion copolymerization of ethyl acrylate and methyl methacrylate carried out in a computer controlled experimental setup using both purified and technical grade monomers.