José C. de la Cal

Modeling particle size distribution (PSD) in emulsion copolymerization reactions in a continuous loop reactor

A detailed dynamic mathematical model that describes the evolution of particle size distributions (PSD) during emulsion copolymerization reactions in a continous loop reactor is developed and compared with experimental data. The model is based on the assumption that two distinct particle populations exist: precusor particles and stable latex particles. Precursor particles are colloidally unstable and therefore may undergo coagulation with other precursors and be absorbed by stable latex particles. It is shown that the kinetic model is able to reproduce the rather complex dynamic behavior of the vinyl acetate/Veova 10 emulsion copolymerization in a continuous loop reactor.

Kinetics of the styrene emulsion polymerization using n‐dodecyl mercaptan as chain‐transfer agent

The kinetics of the styrene emulsion polymerization using n-dodecyl mercaptan as chain-transfer agent was studied. It was found that the chain-transfer agent (CTA) had no effect on polymerization rate but substantially affected the molecular weight distribution (MWD). The efficiency of the CTA in reducing the MWD was lowered by the mass-transfer limitations. The process variables affecting CTA mass transfer were investigated. A mathematical model for the process was developed. The outputs of the model include monomer conversion, particle diameter, number of polymer particles, and number-average and weight-average molecular weights. The model was validated by fitting the experimental data.

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.

Emulsion Polymerization in a Loop Reactor: Effect of the Operation Conditions

ABSTRACTThe effect of several operation conditions (temperature, residence time, recycle ratio, initiator concentration and emulsifier concentration) on the performance of a continuous loop reactor during the redox initiated emulsion copolymerization of vinyl acetate and Veova 10 was investigated. The study was carried out under industrial-like conditions, namely, high solids content latexes (55wt%) and high conversions (~90%). Both polymerization mechanisms and practical issues such as production rate and product quality are discussed.

Surfactant Kinetics and Their Importance in Nucleation Events in (Mini)emulsion Polymerization Revealed by Quartz Crystal Microbalance with Dissipation Monitoring

Surfactants are vital components of almost all heterogeneous polymerizations for maintaining colloidal stability, but they also play an important role in the kinetics and mechanism of particle nucleation. Despite many decades of research, the knowledge of adsorption-desorption surfactant kinetics and their application in (mini)emulsion polymerization is largely based on qualitative arguments. In this paper we show that the use of a quartz crystal microbalance with dissipation monitoring can provide quantitative information on both the adsorption equilibrium of ionic and nonionic surfactants, and also the kinetics of adsorption/desorption, that can be applied to the understanding of nucleation processes in (mini)emulsion polymerization. We show that surfactant dynamics and nucleation phenomena in (mini)emulsion polymerization are not dominated by diffusion phenomena linked to molecular size of surfactant as previously thought but rather are driven by the large differences in the rate of surfactant adsorption and desorption at the polymer-water interface. Finally, we show the application of this knowledge to explain the differences between nucleation processes for ionic and nonionic surfactants in emulsion polymerization.

Kinetics of the photoinitiated inverse microemulsion polymerization of 2-methacryloyl oxyethyl trimethyl ammonium chloride

The polymerization of inverse microemulsions of 2-methacryloyl oxyethyl trimethyl ammonium chloride stabilized by a blend of nonionic emulsifiers (a sorbitan sesquioleate and a sorbitan monooleate) and initiated by UV light in the presence of Azobis(isobutyronitrile) (AIBN) was investigated. The effect of initiator concentration, light intensity, emulsifier concentration, and dispersed phase weight fraction on the polymerization rate (Rp), number of polymer particles (Np), and polymer molecular weight (Mw) was studied. The application of this process to tubular reactors is discussed.

Modeling emulsion polymerization stabilized by polymerizable surfactants

A mathematical model for seeded emulsion polymerization stabilized with polymerizable surfactants (surfmers) was developed. The model accounts for the main features of the process and provides information about surfmer conversion as well as surfmer burying inside the polymer particles. The model was validated by comparing its predictions with the experimental results for the effect of particle size, surface properties of the surfmer, and type of initiator on surfmer conversion. The effect of surfmer reactivity on surfmer incorporation to the polymer backbone is also discussed.

Determining the effect of side reactions on product distributions in RAFT polymerization by MALDI-TOF MS

Reversible Addition–Fragmentation chain Transfer (RAFT) polymerization has emerged as one of the most versatile reversible deactivation radical polymerization techniques and is capable of polymerizing a wide range of monomers under various conditions. One of the most important factors governing the success of a RAFT polymerization is the fraction of living chains at the end of the reaction, which can be maximized by using a low amount of initiator. From the point of view of the process, it is tempting to perform the polymerization in solution, which allows a better mixing. However, in this work it is shown that this choice may be negative for the quality of the polymer. Detailed analysis using Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) of poly(n-butyl acrylate) (pBA) obtained at high conversion in the RAFT solution polymerization revealed that in addition to the polymer chains, formed by the RAFT mechanism, there were two distinct populations resulting from chain transfer to solvent and transfer to polymer followed by β-scission. Complementary results from Size Exclusion Chromatography coupled with Multi Angle Light Scattering detector (SEC/MALS), quantum chemical calculations, and a mathematical model that predicts product distributions, were also used to further confirm the assigned structures. The results highlight the scope and limitation on the living fraction of chains due to chain transfer events using RAFT polymerization and reversible deactivation radical polymerizations in general, and furthermore, yielded information about the fate of midchain radicals formed by intramolecular transfer to polymer.

Highly Hydrophobic Coatings from Waterborne Latexes

This work reports on the formation of highly hydrophobic coatings from waterborne latexes able to form films at ambient temperature. The contact angle of film forming copolymers of 2-ethylhexyl acrylate and perfluorodecyl acrylate (PFDA) was limited to 114° because flat surfaces were obtained. Attempts to increase the roughness of the film using blends of film-forming latexes with the latex of PFDA homopolymer (which is not film forming) were not successful under regular casting conditions because the PFDA particles accumulated at the film-substrate interface. Film formation engineering allowed modifying the morphology of the film obtaining a contact angle of 137°.

Synthesis of cationic polyelectrolytes by inverse microemulsion polymerization.

The inverse microemulsion copolymerization of acrylamide and [2-(acryloyloxy)ethyl]- trimethylammonium chloride (Adamquat) was investigated using different reactors (batch, semicontinuous, and CSTR). It was found that formation of long branches through extensive intermolecular chain transfer occurred at low temperature (35 °C). Molecular weights and long branching levels were correlated and decreased as batch > semicontinuous > CSTR. These differences affected the performance of the copolymers as flocculants. Results indicated that successful flocculant should contain a good balance between short and long chains.