Graduate Research Projects
Prof. Robin A. Hutchinson
Free-Radical Polymerization Kinetics of
Solvent-Borne Acrylic Coatings
Background:
The long-term objective of this research is to improve industrial polymerization processes and to contribute to the design of new polymeric materials by developing a deeper understanding of free-radical polymerization kinetics and capturing that knowledge in modelling-based tools. The production of solvent-borne acrylic resins for the coatings industry has been chosen as a focal point for the effort. Composition and properties of polymeric coatings have changed greatly over the past decade, largely as a response to environmental concerns. Acrylic resins, the base polymer for many coatings, are now produced with lower solvent levels and at higher temperatures than before; the low viscosity material must have sufficient chemical functionality to further react on the surface to form a tough durable coating. Our knowledge of the basic free-radical mechanisms and kinetics has greatly increased over the past several years due to the advent of new experimental pulsed-laser techniques. However, little is known about the high-temperature secondary reactions that play an important role in controlling rate and molecular structure, which in turn determines the end-use properties and product value of the polymers produced.
Project #1 (MSc project completed, Adam Peck: potential followup project available) : A thorough examination of acrylate homopolymerization kinetics, using both mathematical modelling and experimental data to refine the mechanistic pathway and quantify the kinetics of hydrogen abstraction, chain scission, long-chain branching, and double-bond polymerization. The task will be to hypothesize a consistent set of mechanisms and kinetic rate coefficients, implement these in Predici , and verify them against data collected under a range of operating conditions. Important variables to be examined include polymer and initiator concentration, batch time, and temperature. The study will start with a detailed analysis of poly(butyl acrylate) samples provided by DuPont, followed by the design and execution of experiments in the new setup at Queen's. In addition to the measurement of typical properties such as polymer conversion and MW distribution, more detailed structural information (terminal double bonds, end groups, branch points) will be measured using NMR (Queen's Chemistry Department) and electrospray ionization mass spectroscopy techniques available at DuPont.
Project #2 (PhD project in progress, Deheng Li): Construction of a detailed model applicable for high temperature synthesis of free-radical copolymers, including side-reactions such as depropagation, chain-scission, and long-chain branching. The model, to be implemented in Predici , will not be treated as an end result, but rather a tool that, when combined with experimental data, helps to focus attention on what is not known about the process and identifies new development opportunities. In addition to incorporating the findings from the homopolymerization study described above, challenges include a generalized treatment of copolymerization termination kinetics. The model will be tested against labscale experiments for a typical terpolymer styrene/acrylate/methacrylate coating system; additional specialized kinetic studies will be performed if needed.
Project #3 (MSc project nearing completion, Ning Li): We are using Pulsed-Laser Polymerization as an experimental tool to study the complex propagation kinetics of styrene/butyl methacrylate under high-temperature conditions. Specific issues include penultimate effects on observed propagation behaviour, and the extent of depropagation under high-temperature conditions.
Project #4 (PhD project in progress, Siziwe Bebe): A typical coating is a complex copolymer containing 2-5 different monomeric repeat units, selected from over 30 choices. Thus the number of kinetic coefficients required for a generalized database is very large. With improved measurement techniques, some consistent trends relating monomer and radical structure to reactivity are emerging. This project explores the possibility of developing correlative techniques for the prediction of unknown rate coefficients, based upon thermochemical arguments and calculations (collaboration with Prof. Linda Broadbelt, NWU).
Project #5 (MSc project in progress, Luis Fernando Perea): With improved knowledge of the polymerization kinetics under starved-feed high-temperature conditions comes the opportunity to optimize the reactor operation strategy, thereby reducing cycle time and material (initiator) cost. These changes must be implemented without changing the inherent robustness of the current process. We are exploring the application of some of the control tools developed in the group of Dr. Martin Guay to our particular system.
These graduate research projects, while distinct, will use common tools for polymer synthesis, polymer analysis, and mathematical modelling of the system. The research direction in the later years of the projects depend upon the initial findings. Possible extensions include the formulation and testing of new operating strategies to reduce batch time while producing polymer of more uniform MW and composition, and/or the testing of on-line instrumentation for the robust control of these semibatch systems, a task made difficult by the multicomponent nature of coatings.
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