LECTURE ABSTRACTS
Living Radical Polymerization in Bulk, Miniemulsion and Emulsion
Michael F. Cunningham (Queen's University)
Living (or controlled) radical polymerizations provide a novel and potentially inexpensive
route to designing polymers with controlled microstucture (e.g. block copolymers, star polymers)
and narrow molecular weight distributions. While extensive research has been conducted into
homogeneous bulk and solution living radical polymerizations, investigations into aqueous
dispersed phase systems (emulsion and miniemulsion polymerization) have only recently appeared.
Although little progress has been realized with emulsion polymerization, considerable success has
been achieved using miniemulsion polymerization with living radical systems. 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, miniemulsion and emulsion. The emphasis will be on heterogeneous systems, and more specifically on those aspects of
operating in a heterogeneous environment that influence the polymerization rate, the molecular
weight distribution and the livingness of the system.
Semi-Continuous Emulsion Polymerization and Structured Latexes
Michael Cunningham (Queen's University)
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 an/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.
The Future of Polymer Colloids
Michael Cunningham (Queen's University)
While significant advances have occurred in emulsion polymerization in recent decades, in both our fundamental understanding
and in practice, two features have not changed much. First, the monomers used to make emulsion polymers have been primarily
those readily polymerized by a free radical mechanism. Second, the range of applications has remained largely confined to
traditional areas such as coatings and adhesives. However in recent years two major trends have become apparent, one
related to the types of applications found for polymer colloids, and the other for the types of monomers that may be used.
Polymer colloids are increasingly being used for a variety of applications outside traditional areas, including fields such as health
sciences, microelectronics and information technology. This presentation will give an overview of applications in these areas.
Even more significant for the future however, are the rapid advances currently being made in macromolecular chemistry and
catalysis that allow synthesis of polymer colloids using monomers not previously polymerizable in water-based systems.
These polymers are often not based on a free radical mechanism. 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.
An overview of these emerging techniques will be presented, along with specific examples.
The Role of Surfactants in Emulsion Polymerization Processes
Mohamed S. El-Aasser (Lehigh University)
Surfactants play major roles during the particle nucleation and growth stages, with direct impact on latex particle size, size distribution, polymerization rate, 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 in determining the particle number according to the various nucleation mechanisms will be described. Three alternatives to conventional surfactants will be reviewed.
Stabilization Mechanisms in Aqueous and Non-Aqueous Latexes
Mohamed S. El-Aasser (Lehigh University)
The basic concepts and terminology of colloid science will be introduced. The principles of electrostatic and steric stabilization mechanisms will then be reviewed. The inverse problem of coagulating and flocculating latexes will also be discussed.
Advances in Miniemulsion Polymerization
Mohamed S. El-Aasser (Lehigh University)
Despite the fact that the first miniemulsion polymerization was carried out at Lehigh University
in 1972, the word miniemulsion was coined only in 1981. The number of publications on miniemulsions
has been increasing exponentially over the past decade, including a few patents.
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 (referred to as cosurfactant).
In miniemulsion polymerization, the submicron size monomer droplets are the main sites for particle
nucleation and growth via free radical initiation using oil-soluble or water-soluble initiators.
The Theory of Miniemulsions has been developed based on the well known concepts of Ostwald ripening
and thermodynamics. Miniemulsions have been exploited in making new types of polymer colloids (latexes)
that were difficult and sometimes impossible to make by using conventional emulsification 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, encapsulation of pigments and dyes,
and controlled molecular weight via living free radical polymerization. In this lecture
both the theory and practice of Miniemulsions will be discussed.
Film Formation and Cohesive Strength Development from Latex Systems
Andrew Klein (Lehigh University)
The cohesive properties of polymer films from latexes are dependent on the film formation mechanism.
Polymer film formation from latex occurs either when: (a) the molecules from the individual polymer
particles interdiffuse and entangle as the particle boundaries gradually disappear, or, when (b) the
molecules partially interpenetrate and cross-link, forming interparticle spot welds, or when (c)
water-soluble molecules react or interact with functional groups on the particle surface.
In the last two cases, the particle boundaries remain distinct. The role of interpenetration
depth and the diffusion rate on cohesive strength development will be discussed, using model latex systems.
Mixing and Scale-Up in Emulsion Polymerization
Andrew Klein (Lehigh University)
The scale-up of the mixing process in emulsion polymerization involves breaking the process down into individual but interrelated steps. The effect of mixing on the microscopic heterogeneity of the continuous phase, fluid shear rates and heat transfer allows each to be considered separately. A few of these effects will be discussed and illustrated with specific examples. The utility of bench scale experimentation with a view toward scale-up with some early experimental results, will also be discussed.
The cohesive properties of polymer films from latexes are dependent on the film formation mechanism. Polymer film formation from latex occurs either when: (a) the molecules from the individual polymer particles interdiffuse and entangle as the particle boundaries gradually disappear, or, when (b) the molecules partially interpenetrate and cross-link, forming interparticle spot welds, or when (c) water-soluble molecules react or interact with functional groups on the particle surface. In the last two cases, the particle boundaries remain distinct. The role of interpenetration depth and the diffusion rate on cohesive strength development will be discussed, using model latex systems.
High-Solids Latex Technology
Do Ik Lee (Western Michigan University)
High-solids latex technology is based on three basic considerations from the viewpoints of dispersion
rheology: (1) The maximization of latex particle packing volume fractions, (2) The minimization of the
effective volumes of latex particles, and (3) The minimization of latex medium viscosity. With these
considerations at hand, the technology is concerned with the maximization of the volume solids of latexes,
while meeting their respective end-use property requirements for a variety of applications. For this reason,
its objective is to increase the volume solids of the existing latexes by 5 to 15% by considering a bimodal
approach only for the packing efficiency, although the technology is capable of achieving 70% or higher
volume solids latexes. This talk will describe the three basic considerations involved in the high-solids
dispersion technology, and then discuss post-polymerization blending (i.e., blending large and small particle
size preformed latexes) and in-situ emulsion polymerization methods (i.e., bimodal emulsion polymerization by
either surfactant or seed addition) for the preparation of high-solids bimodal latexes. Some high-solids latex
examples will be also presented.
Preparation of VOC-Free Latexes
Do Ik Lee (Western Michigan University)
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 forever lower amounts of residual monomers and VOCs 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.
Industrial Uses of Latexes
Do Ik Lee (Western Michigan University)
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 that 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.
Emulsion Polymerization Mechanisms and Kinetics
Gary W. Poehlein (Georgia Institute of Technology)
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 and
Ewart, Stockmayer, O'Toole, Roe, Fitch, Ugelstad, and Gilbert will be discussed.
Engineering of Emulsion Polymerization Reactors
Gary W. Poehlein (Georgia Institute of Technology)
The various types of reactors (batch, semi-batch and continuous), used to produce
synthetic latexes will be reviewed. Pros and cons of various types of processes will be
discussed and theoretical reactor models will be presented where appropriate. Reactor
design and operating factors that influence product properties will also be reviewed.
The Kinetics of Free Radical-Initiated Polymerization
F. Joseph Schork (University of Maryland)
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.
Latex Rheology
F. Joseph Schork (University of Maryland)
This introduction to the rheology of latexes covers the type of rheological measurements that can be
made and the effects of the many variables found in latexes; solids concentration, particle size and
distribution, surface charges, adsorbed surfactants, particle aggregation, non-spherical particle
morphology, swellable particles, and the use of water-soluble polymer thickeners.
Sensors and Control of Emulsion Polymerization Reactors
F. Joseph Schork (University of Maryland)
Recent developments in the area of on-line sensors, coupled with the availability of high-performance digital control systems has 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.