Lecture 1 – Free Radical Polymerization Mechanisms and Kinetics
F. Joseph Schork
A review of the principles of free radical-initiated polymerization, including the four basic reactions of initiation, propagation, termination and transfer, inhibition, molecular weight and molecular weight distribution, effect of temperature and pressure, autoacceleration and diffusion control of termination and propagation, and copolymerization including copolymerization reactivity ratios and copolymer sequence distribution.
Lecture 2 – Emulsion Polymerization Mechanisms and Kinetics
Gary W. Poehlein
Reaction mechanisms and kinetics of free radical polymerization will be reviewed. The unique features of emulsion polymerization will be outlined and the influence of the colloidal size of the reaction sites discussed. Kinetic theories due to Smith & Ewart, Stockmayer, O’Toole, Roe, Fitch, Ugelstad, and Gilbert will be discussed.
Lecture 3 – Branching and Grafting in Emulsion Polymerizations
Peter A. Lovell
Branching in polymers produced by free-radical polymerization arises from chain transfer to polymer and has important effects on polymer properties. In emulsion polymerization, intermolecular chain transfer to polymer can lead to grafting of water-soluble polymers to latex particles, facilitating control of colloidal stability and latex rheology. Such branching and grafting is used to good effect in the emulsion polymer industry to control the end-use performance of latexes and emulsion polymers. This lecture will begin with an overview of the chemistry of branching and grafting. Case studies of branching in acrylate and vinyl acetate homopolymerizations and synergistic effects in copolymerization will then be presented, together with strategies for controlling the level of branching. This will provide the basis for considering grafting of water-soluble polymers used as colloid stabilizers in emulsion polymerizations. The chemical processes which the most commonly-used water-soluble polymers may undergo during emulsion polymerization will be illustrated through case studies that highlight the key principles for their control.
Lecture 4 – The Role of Surfactants in Emulsion Polymerization Processes and Kinetics
Mohamed S. El-Aasser
Surfactants play major roles in emulsion polymerization during the particle nucleation and growth stages, with direct impact on latex particle size, size distribution, polymerization rate, polymer molecular weight, and particle morphology. Surfactants are also essential during post-polymerization processes: stripping, storage, shipping, and formulation for several applications. The general characteristics of surfactants and their adsorption profiles on latex particles will be reviewed. The specific role of surfactants (single and mixtures of surfactants) on the kinetics of emulsion polymerization (rate of polymerization and evolution particle number as a function of polymerization time according to the various nucleation mechanisms) will be described. The influence of water-solubility of monomers, partition of the surfactant between the monomer and aqueous phases, and the use of single vs. mixtures of anionic and non-ionic surfactants on the kinetics results of emulsion polymerization will also presented and discussed. Three alternatives to conventional surfactants, including ionic monomers, block copolymers, and the recent work on reactive surfactants in emulsion polymerization and characterization results of their loci in the final copolymer latex particles as well as properties of films cast from these latexes be discussed.
Lecture 5 (a) – Latexes for Industrial Applications
Lecture 5 (b) – Methods of Reducing Residual Monomers in Latexes Systems
James W. Taylor
Industrial Uses of Latexes: About 10 million metric tons (~20 billion pounds) of dry latex polymers are being consumed annually in a very large number of industrial applications, including paints and coatings (~26% of the total annual latex consumption), paper and paperboard applications (~24%), adhesives (~23%), carpet backsizing (~10%), etc. This part of the talk will review the major industrial applications and types of latexes, and then the important latex variables affecting the properties of latexes for various applications will be discussed. Furthermore, industrial latexes will be grouped in terms of their Tg ranges for various applications which are in turn grouped in terms of filler levels. Finally, some specific applications will be highlighted and their latex requirements and future needs will be discussed.
Methods of Reducing Residual Monomer: Historically, butadiene-containing copolymer latexes, such as gel-free SBR (styrene butadiene rubber) and crosslinked S/B latexes, have been steam stripped to remove their residual monomers, whereas the residual monomers of non-gel forming polymer latexes, such as acrylic latexes, have been burned out (i.e., cooked down) in their post-polymerization steps by using organic peroxides and reducing agents known as “chaser catalysts” in the industry. However, public demands and government regulations for ever lower amounts of residual monomers and VOC’s contained in latexes and latex-containing coating formulations may require the industry to consider many different approaches to meet the challenges. For example, in some cases where the post-polymerization burnout alone may not be sufficient to meet the demands, the burnout approach must be either combined with or entirely switched to steam stripping or other approaches. This part of talk will discuss the mechanisms for both batch and continuous steam stripping processes, the post-polymerization burnout mechanisms, various initiator systems for the burnout, and other considerations.
Lecture 6 – Colloidal Stabilization and Destabilization Mechanisms of Latex Systems
Mohamed S. El-Aasser
Colloidal stability are essential both during the entire course of an emulsion polymerization process in order to eliminate coagulum formation and to avoid reactor fouling. Latex stability is also essential for many of the post-polymerization processes such as storage, transportation, steam stripping of residual monomer, as well as formulation involving additives (such as pigments, fillers or coalescing aids,) and latex applications methods which my involve subjecting the latex system to mechanical sheer.
In this lecture we will introduce the electrostatic and steric colloidal stabilization mechanisms of latex systems. We will discuss in details the key parameters responsible for repulsion and attraction between latex particles in light of the Derjaiguin – Landau – Verwey – Overbeek (DLVO) theory, for latex particles that carry negative or positive surface charges due to adsorption of surfactants and/or chemically bound ionized functional groups. We will also discuss the entropy and enthalpy contributions to steric stabilization of latex systems in light of the 2nd law of thermodynamic, due to the presence of non-ionic species at the particle surface such as non-ionic surfactants and/or anchored polymer chain molecules with affinity to the surrounding aqueous phase. The reverse of colloidal stabilization, namely destabilization or aggregation (coagulation and flocculation) of latex systems will be discussed. In this regards, the influence of chemical additives (such as electrolytes, acids, solvents on non-solvents) on stabilization/destabilization will be presented. Also the influence of physical effects (such as agitation and mechanical sheer as well as temperature changes including freeze/thaw cycles) on stabilization/destabilization will be presented. Ways to assess the critical concentrations of additives, and levels of temperature changes as well as mechanical sheer that cause destabilization of a colloidally-stable latex particles will be discussed. Experimental results will be used to illustrate some of the basic concept and the influence of chemical additives and physical effects on stabilization/destabilization mechanisms of latex systems.
Lecture 7 – Experimental Methods for the Characterization of Latex Particle Size and Particle Size Distribution
Cesar A. Silebi
The application of fractionation and non-fractionation methods for the determination of particle size distribution, the range of applicability, and advantages and disadvantages and their on-line measurement capability will be discussed. Among the methods examined are: classical and dynamic light scattering, sedimentation, disc centrifugation, electrozone sensing, sedimentation field flow fractionation, capillary hydrodynamic fractionation, and recent advances in hybrid methods of analysis. Comparisons of several of these methods will be used to illustrate problems often encountered in the particle size distribution determination of latexes.
Lecture 8 – Semi-Continuous Emulsion Polymerization and Structured Latexes
Michael F. Cunningham
Semi-continuous (or semi-batch) polymerizations in which the monomer is added incrementally during the course of reaction are commonly used in industrial processes because they allow control of the polymerization rate, and because they can be used to control the particle morphology. “Structured latexes” are emulsion polymer particles in which the internal morphology and/or composition vary through the particle. Examples include core-shell particles, and particles with radial composition gradients between the particle core and surface. The discussion will describe how semi-continuous processes are run, the unique features of operating an emulsion polymerization in semi-continuous mode, and how structured latexes can be synthesized.
Lecture 9 – Film Formation
Peter A. Lovell
Understanding film formation is important for all applications where latexes are dried, which includes obvious applications such as water-borne paints, inks and adhesives, but also those which are less obvious, such as binding of non-woven fabrics, sealants and foamed products. This lecture will describe the fundamental principles underlying the process of film formation from latexes, including the key stages and the molecular processes that are necessary for the formation of coherent films. Factors that influence film
Lecture 10 (a) – A Mechanistic Study of Water Evaporation from Wet Acrylic Latex Films
James W. Taylor
This talk discusses factors that control the evaporation rate of water from acrylic latexes during the film formation process. For stage 1 of the film formation process a mechanistic model is developed that shows that the instantaneous drying rate of either latex decreases linearly as the fractional-surface area of water decreases during the drying process. This mechanistic model postulates acrylic particles at the liquid-air interface that inhibit the evaporation of water. At 42 to 45% solids the initial instantaneous drying rate for the two latexes is ~26% less than that of pure water. At 75% solids a change in slope of the instantaneous drying rate as a function of time identifies stage 2 of the drying process.
Lecture 10 (b) – Glass Transition Evolution of Plasticized Latex Films: An Important Process in the Application of Everyday Latex Paints
James W. Taylor
The commercialization of latexes in 1946 created a need for understanding film formation from discrete polymeric particles. Aided by technological advances and pushed by environmental considerations, there has since been a steady shift from solvent-borne to water-borne polymers. Early film formation theories focused on solvent-free waterborne latexes. However, significant levels of filming aids or solvents are used to optimize the performance of industrial and maintenance coatings. Better understanding of the role filming aids play in the film formation process will aid in the selection of the most efficient filming aid combination for optimizing coating performance.
This lecture focuses on important parameters such as the glass transition temperature of filming aids and polymers, the volatility of filming aids in the presence of water and polymeric particles, the distribution coefficients of filming aids, and the Fox-Flory equation are used to predict the MFT of latex particles at deformation. A new experimental method that obtains the activity coefficients of filming aids during the drying process of latex films is demonstrated. These activity coefficients are used to predict the total solvent loss during the wet evaporation stage of the film formation process. Additionally, the clear film composition is modeled for the ensuing “volatility-controlled” stage that defines the time line where solvent evaporation is not diffusion controlled. The ability of the model to predict or follow the Tg of a “drying system” is demonstrated. The model presented can assist in the selection of filming aids for water-borne latex-based formulations and can provide important criteria for optimizing particle composition and morphology.
Lecture 11 – Miniemulsions and Their Latex Systems via Polymerization in Monomer Droplets and Direct Emulsification of Polymer Solutions
Mohamed S. El-Aasser
In this lecture the early development of the miniemulsion concept will be reviewed, and current state-of-the-art including theory and practice of miniemulsions will be discussed.
The concept of miniemulsions was invented at Lehigh University in 1972. Despite the fact that the first miniemulsion polymerization was also carried out at the same time, the term “miniemulsion” was coined only in 1981. Since that time the number of publications and patents on miniemulsions has been increasing exponentially.
Miniemulsions are relatively stable oil-in-water emulsions with average droplet diameters ranging from 50 to 500 nm. These are typically prepared using a mixture of a surfactant and a low molecular weight, highly water-insoluble costabilizer (sometimes referred to as cosurfactant). In miniemulsion polymerization for the preparation of polymer colloids (latexes), since the surfactant concentration in the aqueous phase is below the CMC, the submicron monomer droplets are the main sites for particle nucleation (and growth) via free radical initiation using oil-soluble or water-soluble initiators. An alternative approach for making latexes based on miniemulsions is the direct emulsification of polymer solutions. The formation and shelf-life stability of miniemulsions are explained based Ostwald ripening and the 2nd law thermodynamics. Miniemulsions have been exploited in making new types of polymer colloids (latexes) that were difficult and sometimes impossible to make using conventional emulsification and/or emulsion polymerization processes. These include preparation of artificial latexes and hybrid latexes, high solids latexes, polymerization of highly water-insoluble monomers and macromonomers, controlled polymer microstructure and morphology, controlled polymer molecular weight distribution via living free radical polymerization, and encapsulation of liquids, inorganic particles, inorganic and organic pigments and dyes.
Lecture 12 – Formation of Nanocapsules and Their Biomedical Applications
Polymeric nanocapsules offer the versatility to cover a wide range of mesoscopic properties for sophisticated applications. By means of the miniemulsion process, custom-made nanocapule systems for different purposes can be designed. The encapsulation and release of a great variety of payloads, ranging from hydrophobic to hydrophilic substances, have been successfully achieved in a highly controlled manner and with an unmatched high encapsulation efficiency.
The preparation of nanocontainers with a hydrophilic core from water in-oil emulsions and their subsequent transfer to aqueous medium is of special importance since it enables the efficient encapsulation of hydrophilic payloads in large quantities. However, major challenges are associated with their synthesis include low colloidal stability, leakage of encapsulated payloads due to osmotic pressure, and a demanding transfer of the nanocontainers from non-polar to aqueous media. Synthesizing nanocarriers for biomedical applications requires that the nanocarriers are first invisible for most of the cells, that means that they show stealth properties. In a second step, targeting can be achieved in order to deliver ‘payloads’ to a particular tissue for any in vivo application. Critical issues here are the efficient encapsulation and protection of therapeutic agents, colloidal stability of nanocarriers against aggregation in blood induced by the adsorption of blood proteins and the composition of protein corona to achieve a long circulation time, and bioimaging.
Lecture 13 – Living Radical Polymerization and Advances in Future Directions for Emulsion Polymers/Polymer Colloids
Michael F. Cunningham
While significant advances have occurred in emulsion polymerization in recent decades, in both our fundamental understanding and in practice, the basic chemistry of the process has seen little change until recently. Significant for the development of future commercial products are advances being made in polymer chemistry and catalysis that allow synthesis of polymer colloids with control of the polymer microstructure, polymer colloids made using monomers not previously polymerizable in water-based systems, and in the development of polymer colloids from renewable resources including natural polymers. As this chemistry matures, new classes of polymer colloids will emerge, possibly ushering in entirely new fields of application and considerable opportunities for product innovation. For example, “living” (or “controlled”) radical polymerizations (LRP/ CRP) provide a novel and potentially inexpensive route to designing polymers with controlled microstucture (e.g. block copolymers) and narrow molecular weight distributions. Earlier studies focused on homogeneous bulk and solution living radical polymerizations, but our ability to conduct LRP in aqueous dispersed phase systems has now progressed to a point where commercial applications are feasible. This presentation introduces the three major living radical polymerization chemistries (nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP) and reversible-addition-fragmentation-transfer polymerization (RAFT)), and summarizes recent progress of these systems in bulk and emulsion-based systems. The emphasis will be on those aspects of operating in a heterogeneous environment that influence the polymerization rate, the molecular weight distribution and the livingness of the system. The presentation will also highlight recent advances in the use of other non-radical chemistries to make polymer colloids, and in progress to make “green” polymer colloids from renewable feedstocks and natural polymers.
Lecture 14 – Latex Rheology
Cesar A. Silebi
Review of experimental studies illustrating the various factors that influence the rheological properties of latexes. Topics to be covered include the effects of solids concentration, particle size and distribution, electrolyte content, particle aggregation, adsorbed surfactants, non-spherical particle morphology, particle swelling, and the use of water-soluble associative and non-associative polymeric thickeners. Consideration will also be given to thickened latexes and variables affecting their rheological flow curves.
Lecture 15 – Waterborne Pressure Sensitive Adhesives
Pressure sensitive adhesives (PSAs) are permanently tacky and adhere to substrates without the need of more than finger or hand pressure. Water borne PSAs are widely used in permanent and removable tapes and label stocks. The lecture will cover basics of PSAs and testing, waterborne PSA compositions and sizes on adhesive performance, as well as challenges of emulsion PSAs.
Lecture 16 – Fundamentals and Advancement of Waterborne Epoxy and Polyurethanes
This talk will be given in two parts.
Part I. Epoxy resins were first commercialized more than 60 years ago. Two component (2K) solventborne (SB) epoxy coatings based on epoxy/polyamide chemistry were developed and heavily used for direct-to-metal coatings and concrete coatings. These 2K SB epoxy coatings deliver excellent adhesion, chemical resistance and corrosion protection, but these coating systems have the negative attribute of high solvent content (VOC). In the last three decades, increasing health and safety awareness and regulatory compliance directives have challenged the coatings industry to develop lower Volatile Organic Component (VOC) coating solutions. In the early 1980’s, waterborne epoxy coatings emerged to primarily fulfill the need for lower paint odor and fast return to service requirements in institutional and maintenance coatings. Waterborne epoxy systems have been improved over several technology generations to provide additional benefits such as shorter induction time, fast dry time, extended re-coatability while maintaining traditional epoxy coating attributes such as chemical and corrosion resistance, toughness, and adhesion.
Further improvements have been underway to make waterborne epoxy coatings even more viable alternatives to solventborne coatings, especially in challenging metal coating applications. Combining the fundamentals of colloidal, interfacial, and material science in the design of epoxy and curing agent chemistries has led to further improvements in waterborne epoxy coatings. For example, novel high performance waterborne zinc rich primers that provide easier dispersibility and stability for zinc powders (up to 80-85 wt%) have been developed to replace solventborne 3K epoxy zinc rich primers. These low VOC waterborne zinc rich coating systems provide easier application, good flexibility, good adhesion, and outstanding corrosion protection. Additionally, an ultra-low VOC WB epoxy coating (<50 g/L) for concrete (floors, walls and interior building structures) have also been developed. A novel polymer composition incorporating a custom designed specialty surfactant within the polymer architecture provides a ZVOC curing agent is capable of emulsifying epoxy resins. This waterborne epoxy system provides low viscosity, ease of application and improved adhesion in challenging concrete coatings. These advancements in waterborne technologies have also led to development of high performance ZVOC epoxy dispersions and curing agents for low (< 50 g/L) and zero VOC coating formulations. This presentation will focus on the development of advanced waterborne epoxy coating systems and summarize the performance attributes obtained from these coating systems.
Part II. Polyurethanes are unique materials with a wide range of physical, chemical and mechanical properties. Aqueous polyurethane dispersions (PUDs) have recently emerged to replace their solvent-based counterparts in various applications due to increasing health and environmental issues. This paper will provide an overview of the fundamentals for the preparation of solvent-free and high solids content (~60 wt%) aqueous PUDs from aromatic isocyanate/polyether and aliphatic isocyanate/polyester prepolymers using a high shear continuous mechanical dispersion process. It was shown that the chemical composition of the PU prepolymer (nonionic or anionic) and type and amount of surface active agents(s) play critical role in the formation and stabilization of submicron size colloidally stable particles in this process. The kinetics of polyurethane and polyurea polymerization PUD formation and process was also investigated. Understanding of reaction kinetics and fundamentals of colloidal and interfacial science allowed the preparation of solvent-free polyurethane dispersions for a myriad of applications from a well-designed combination of a variety of commercially available raw materials. Effect of the time and temperature on the film formation and coalescence of soft and hard PUDs, crosslinking of polyurethanes with organofunctional silanes and incorporation of inorganic fillers were also investigated for various applications.
Lecture 17 – Nanocomposite and Nanostructured Polymer Coatings: Recent Advances
Today nanotechnology is used to formulate paints and coatings with various functionalities including anti-microbial, anti-scratch, self-healing and super-hydrophobicity. In this lecture, the unique properties of particles at the nanoscale to realize functional coatings will be discussed. We will also cover the fundamentals of interaction between nanoparticles and polymers in aqueous systems ranging from the early use of nanoclays in nanocomposite latexes and nanostructured polymer colloids. The challenges of using nanoparticles in coatings, including nano-scale dispersion, nano-scale characterization and the health and safety of using new nanoparticles will also be reviewed.
Lecture 18 – Recent Patent Activity Involving Emulsion Polymers
The patent literature can provide valuable insights into unmet market needs and technology gaps as well as activity of industrial competitors. Patent search strategies and tools will be described as background. Recent patent activity around emulsion polymers and processes will be reviewed to identify trends.
Lecture 19 – Monodisperse Latex Particles – Preparation, Surface Modification, Characterization and Applications
Mohamed S. El-Aasser
The preparation of monodisperse latex particles were developed at Dow Chemical Co. in the early 1950’s, using emulsion and seeded emulsion polymerization. Monodisperse particles found a wide variety of applications in small-volume high-value applications such as calibration of instruments, medical diagnostic tests, determinations of pore size membranes, sensors, etc. Over the past few decades a noticeable expansion is seen in the use of monodisperse latex particles in biomedical applications. Common characteristics of latex particles for these applications include: colloidal stability, uniform particle size (in the range of 50 nm – 100 µm), and type and density of functional groups/unit surface area. Surface functionality such as carboxyl, amines, or hydroxyl groups are particularly useful for surface modification of latex particles for coupling reactions of proteins using reagents such as Woodward’s, carbodiimide, and cyanogen bromide.
This talk is comprised of two parts.
Part I deals with methods used for “cleaning” and characterization of model monodisperse latex systems with submicron particle dimeters. The cleaning methods involve removal of all adsorbed emulsifies from the particles’ surface and dissolved surfactant molecules and solutes from the aqueous phase. The efficiency of 3 cleaning methods using dialysis, ion exchange and serum replacement are compared. The simple characterization method involving acid/base titration (and in one case electrophoretice mobility measurements) are then used for the characterization and quantitative determination of the number of functional groups/unit area, and surface charge density on the cleaned latex particle surface.
In part II we will review the various methods used in the preparation of monodisperse latex particles in the submicron and micron size range such as emulsion, seeded emulsion, and emulsifier-free emulsion polymerizations, two-step swelling method, and dispersion polymerization. This will be followed by describing methods used for surface modifications and characterization as a result of incorporating functional groups such as carboxyl, hydroxyl, and sulfonate on the particles’ surface to make them suitable for wide range of applications including biomedical applications.
Lecture 20 – Water-Borne Soft-Soft Nanocomposites: Principles and Application Case Studies
Many applications of water-borne polymers prepared by emulsion polymerisation require use of soft polymers with glass transition temperatures below room temperature so that films can be formed. In this lecture an overview of the principles underlying the soft-soft nanocomposite concept for enhancing the performance of soft films produced from water-borne polymers prepared by methods of emulsion polymerisation will be presented and then exemplified through three commercially-relevant application case studies: (i) water-borne pressure-sensitive adhesives; (ii) polybutadiene films as models for nitrile rubber glove applications; and (iii) acrylic latexes for use as binders in surface coatings.
Lecture 21 – Question & Answer Session with Short Course Lecturers and Participants
Lecture 22 – Polyurethane Nanoparticles
In this talk, the large degree of variability in the synthesis of polyurethane dispersions for adhesive properties to a wide variety of different substrates will be shown. Polyurethane particles can be obtained in a secondary or in a primary hetreophase process. A functionalization is achieved in a subsequent step. Additionally, hydrid materials can be synthesized by integrating other polymers or inorganic or organic materials. It will be demonstrated that such an ecofriendly system can be rendered very complex in order to further extend the field of sustainable materials for various demanding applications.
Lecture 23 – Sensors and Controls for Emulsion Polymerization Reactors
F. Joseph Schork
Recent developments in the area of on-line sensors, coupled with the availability of high-performance digital control systems, have opened up new opportunities for the efficient operation and control of latex reactors. Available sensors for on-line analysis will be discussed. The use of such measurements in the application of advanced control techniques to batch and continuous polymerization reactors will be reviewed, with special emphasis on controlling the undesirable process dynamics associated with continuous emulsion polymerization, and optimizing controllers for batch polymerization.
Lecture 24 – Reactor Design and Scale-up in Emulsion Polymerization
Michael F. Cunningham
The principles of designing and safely operating emulsion polymerization reactors will be presented in the context of how the selection of reactor type, mode of operation (batch, semi-batch/semi-continuous, continuous) and specific reaction conditions influence latex product properties and reactor productivity. The first part of the presentation will emphasize the interaction of the chemistry and kinetics of emulsion polymerization with the physical design and operation of the reactor. The second part of the presentation will examine the issues involved in converting a laboratory scale emulsion polymerization process to a production scale process, including consideration of reaction kinetics, heat transfer and mixing. Emulsion polymerizations often pose a difficult scaleup challenge since by their nature the polymerization kinetics are coupled with both heat and mass transfer. Consequently almost any change to the process during scaleup is likely to impact product properties, whereas the primary goal of scaleup is to reproduce the latex properties obtained in bench scale experiments. The principles of scaling up an emulsion polymerization will be introduced, and specific challenges will be discussed.