Research Projects

Professor

Tel: (613) 533-3097
Fax: (613) 533-6637
Email: robin.hutchinson@queensu.ca
Office: Dupuis Hall 426

Publications

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Professor

Our process development/modeling efforts are only possible with knowledge of the underlying polymerization mechanisms and accurate values of kinetic rate coefficients. Thus, many of our projects include the study of polymerization kinetics using the PLP/MMD technique, in which pulsed-laser polymerization (PLP) is combined with analysis of the resulting polymer molar mass distribution (MMD) to directly estimate kp, the chain growth rate coefficient for radical polymerization.

Dr. Hutchinson is a pioneer in the development and application of PLP, leading a program to utilize the new technique to measure kp values for many monomers of industrial interest while at DuPont (1991-2000). He is currently co-chair of the IUPAC (Polymer Division) subcommittee on Polymerization Mechanisms and Kinetics. The laser setup at Queen's is the only one of its kind in North America. Our laser for PLP/MMD studies was purchased in 2013 thanks to an NSERC "Research Tools and Instrumentation" grant, and sees continuous use supporting a range of recent and ongoing projects:

  • Copolymerization kinetics of hydroxyl-functional monomers for coatings applications (Loretta Idowu, sponsored by Axalta  Coating Systems)
  • Radical copolymerization kinetics in aqueous vs organic solution (Maryam Agboluaje, sponsored by NSERC)

Findings from the PLP/MMD technique are often combined with NMR measurements of copolymer composition or branching levels to develop new mechanistic insights regarding hydrogen-bonding effects on polymerization kinetics, copolymerization penultimate effects, and acrylate side-reactions. In addition, we continue to study new monomer systems to support development of new materials for biomedical applications.

Recent Publications

Rooney, T. R., A. Chovancová, I. Lacík, R. A. Hutchinson, "Pulsed Laser Studies of Cationic Reactive Surfactant Propagation Kinetics", Polymer 130, 39-49, 2017 [More information]

Schier, J. E. S., D. Cohen-Sacal, R. A. Hutchinson, "Hydrogen Bonding in Radical Solution Copolymerization Kinetics of Acrylates and Methacrylates: A Comparison of Hydroxy- and Methoxy- Functionality", Polym. Chem. 8, 1943-1952, 2017 [More information].

Rooney, T. R., D. Moscatelli, R. A. Hutchinson, “Polylactic Acid Macromonomer Radical Propagation Kinetics and Degradation Behaviour”, React. Chem. Eng. 2, 487-497, 2017 [More information]

Barner-Kowollik, C., S. Beuermann, M. Buback, R. A. Hutchinson, T. Junkers, H. Kattner, B. Manders,  A. N. Nikitin, G. T. Russell, A. M. van Herk, "Critically Evaluated Rate Coefficients in Radical Polymerization – 8. Propagation Rate Coefficients for Vinyl Acetate in Bulk", Macromol. Chem. Phys. 218, 1600357, 2017 [More information].

Nikitin, A. N., I. Lacík, R. A. Hutchinson, “A 3D Simulation Investigation of the Influence of Temperature Increases on the Accuracy of Propagation Rate Coefficients Determined by Pulsed-Laser Polymerization”, Macromolecules 49, 9320-9335, 2016 [More information].

Monyatsi, O., R. A. Hutchinson, "Vinyl Pivalate Propagation Kinetics in Radical Polymerization", Macromol. Chem. Phys. 217, 51-58, 2016 [More information].

Past Graduate Students who have used the PLP/MMD technique in their research

Sharmaine Luk (MSc, 2015-2017) "Radical Polymerization Kinetics of Bio-renewable Butyrolactone Monomers in Aqueous Solution"

Jan Schier (PhD, 2013-2017) "Hydrogen Bonding in Radical Copolymerization: A Kinetic Investigation under Industrially Relevant Conditions"

Thomas Rooney (PhD, 2012-2017) "Synthesis, Polymerization Kinetics and Applications of Novel Macromonomer-Based Degradable Materials"

Otlaatla Monyatsi (MSc, 2013-2015) "Radical Polymerization Studies of Vinyl Ester Monomers using Pulsed‐Lased Polymerization with Size Exclusion Chromatography (PLP‐SEC)"

Kun Liang (PhD, 2009-2013) "Free-Radical Copolymerization of Hydroxy-functional Monomers: Kinetic and Semibatch Studies"

Robert Cockburn (MSc, 2009-2011) "Kinetics, Synthesis and Characterization of Copolymers Containing the Bio-Renewable Monomer g-Methyl-a-Methylene-g-Butyrolactone"

Wei Wang (PhD, 2006-2010) "A Comprehensive Kinetic Model for High Temperature Free Radical Production of Styrene/Methacrylate/Acrylate Resins"

Siziwe Bebe (PhD, 2002-2008) "Estimation of Free Radical Polymerization Rate Coefficients using Computational Chemistry"

Ning Li (MSc, 2003-2005) "Investigation of Free Radical Polymerization Propagation Kinetics by Pulsed-Laser Polymerization"

Deheng Li (MSc, PhD, 2001-2006) "Modeling of Kinetic Complexities in High Temperature Free Radical Terpolymerization for Production of Acrylic Coatings Resins"

In addition, the equipment has been used for a number of undergraduate thesis projects supporting research efforts in the Hutchinson group.

Water-soluble polymers are used for a wide range of applications in the cosmetics, pharmaceutical, water treatment, and coatings industries. Funded by BASF (Germany), we work closely with the research groups of Professor Michael Buback (University of Göttingen, Germany) and Professor Igor Lacík (Polymer Institute of the Slovak Academy of Sciences, Bratislava, Slovakia), who are applying pulsed-laser techniques to the study of polymerization kinetics in water. They have shown that the propagation kinetics of these monomers vary with concentration and conversion when polymerized in the aqueous phase, a behavior not seen for polymerization in organic solvents. In addition, the formation and consumption of midchain radicals affects aqueous phase (co)polymerization rates of acrylic acid and acrylamide.

Based on this new understanding, the Hutchinson group has developed computer models for the batch and semibatch aqueous-phase homo and copolymerization of a range of systems, verified against experiments conducted in the laboratory. The studies not only supply information useful for industrial process and product development of these environmentally-friendly polymerization systems, they also provide unique insight to the effect of solvent on radical polymerization kinetics.

Current PhD candidate Ikenna Ezenwajiaku is developing models to represent the copolymerization of cationic monomers with acrylic acid. The behavior of this system is complex, and follows up the previous efforts of Calista Preusser who studied the copolymerization of acrylic acid and acrylamide as a function of monomer concentration and system pH. Key to the studies is experimental determination of comonomer composition drift using an in-situ NMR technique.

Recent Publications

Preusser, C., A. Chornocová, I. Lacík, R. A. Hutchinson, "Modeling The Radical Batch Polymerization of Acrylamide in Aqueous Solution", Macromol. React. Eng. 10, 490-501, 2016 [More information].

Preusser, C., R. A. Hutchinson, "Measuring and Modeling The Peculiarities of Aqueous-Phase Radical Polymerization", Can. J. Chem. Eng. 94, 2045-2051, 2016 [More information].

Preusser, C., I.R. A. Hutchinson, "The Combined Influence of Monomer Concentration and Ionization on Acrylamide/Acrylic Acid Composition in Aqueous Solution Radical Batch Copolymerization", Macromolecules 49, 4746-4756, 2016 [More information].

Wittenberg, N. F. G., C. Preusser, H. Kattner, M. Stach, I. Lacík, R. A. Hutchinson, M. Buback, "Modeling Acrylic Acid Radical Polymerization in Aqueous Solution," Macromol. React. Eng. 10, 95-107, 2016 [More information].

Preusser, C., R. A. Hutchinson, "An in-situ NMR study of Radical Copolymerization Kinetics of Acrylamide and Non-Ionized Acrylic Acid in Aqueous Solution," Macromol. Symp. 333, 122-137, 2013 [More information].

Santanakrishnan, S., R. A. Hutchinson, "Free-Radical Polymerization of N-Vinylimidazole and Quaternized Vinylimidazole in Aqueous Solution," Macromol. Chem. Phys. 214, 1140-1146, 2013 [More information].

Santanakrishnan, S., M. Stach, I. Lacik, R. A. Hutchinson, "Aqueous-Phase Copolymerization of N-vinylpyrrolidone and N-vinylformamide," Macromol. Chem. Phys. 213, 1330-1338, 2012 [More information].

Past Graduate Students

Calista Preusser (PhD, 2010-2015) "Kinetics and Modeling of Free Radical Aqueous‐Phase Polymerization of Acrylamide with Acrylic Acid at Varying Degrees of Ionization"

Sandhya Santanakrishnan (PhD, 2007-2011) "Kinetic Modeling of Homo- and Co- Polymerization of Water-Soluble N-Vinyl Monomers"

Inga Utz (MSc, 2007-2008) "Modeling of Aqueous-Phase Free-Radical Polymerization Kinetics"

Lina Tang (2004-2007) "Free Radical Polymerization Kinetics of N-Vinyl Pyrrolidone in Aqueous Solution"

The manufacture of synthetic polymers produced via radical polymerization is energy intensive and often utilizes solvents to control system viscosity or for heat removal. This strong impetus to reduce the environmental footprint has led to a shift in the process technology used to produce the polymer component of most automotive clearcoats. Currently, low molar mass polymer chains are produced with low solvent content; these chains form a polymer network on the surface to be coated via reaction of the functional groups with an added cross-linking agent. Sufficient functional monomer (e.g., hydroxyethyl acrylate, glycidyl methacrylate) must be included in the resin recipe to ensure that close to 100% of the chains participate in the cross-linking reactions.

Secondary reactions have a marked effect on rate and polymer structure under the polymerization conditions used industrially. The Hutchinson group has studied the mechanisms and constructed models to represent how methacrylate depropagation, acrylate branching and scission, and penultimate chain-growth copolymerization kinetics control reaction rate and polymer molecular weight during high-temperature acrylate/methacrylate, styrene/methacrylate, and styrene/acrylate copolymerization. The improved understanding is captured in models used by industry to improve manufacturing practices and reduce the effort required to develop new coatings resins. Current efforts have extended the studies to include hydroxyfunctional monomers. This research has been funded continuously by Axalta Coating Systems (formerly DuPont Performance Coatings) since 2001, with matching funds obtained at times through NSERC.

Current and recent projects in this area include:

  • Solution copolymerization kinetics and semibatch production of polymers with hydroxyl-functional monomers (Loretta Idowu, sponsored by Axalta Coating Systems)
  • Acrylic dispersant design for non-aqueous dispersions for automotive coatings (Mingmin Zhang, sponsored by Axalta Coating Systems)
  • Accelerated Monte-Carlo techniques for modeling of polymer architecture (Amin Nasrefsahani, sponsored by Coating Systems)

1L automated

The 1 L automated reactor system used to investigate
semibatch production of acrylic coatings resins.

Recent publications

Zhang, M., R. A. Hutchinson, “Synthesis and Utilization of Low Dispersity Acrylic Macromonomer as Dispersant for Nonaqueous Dispersion Polymerization”, Macromolecules 51, 6267-6275, 2018 [More information].

Nasresfahani, A., R. A. Hutchinson, “Modeling the Distribution of Functional Groups in Semibatch Radical Copolymerization: An Accelerated Stochastic Approach”, Ind. Eng. Chem. Res. 57, 9407-9419, 2018 [More information].

Zhang, M., R. A. Hutchinson, “Design of Acrylic Dispersants for Nonaqueous Dispersion Polymerization: The Importance of Thermodynamics”, Macromol. React. Eng. 12, 1800025, 2018 [More information].

Schier, J. E. S., M. Zhang, M. C. Grady, R. A. Hutchinson, “Modeling of Semi-batch Solution Radical Copolymerization of Butyl Methacrylate and 2-Hydroxyethyl Acrylate”, Macromol. React. Eng. 12, 1800008, 2018 [More information].

Yang, W., R. A. Hutchinson, “The Influence of Adding Functionality to Dispersant and Particle Core Compositions in Non-Aqueous Dispersion Polymerization”, React. Funct. Polym. 114, 31-37, 2017 [More information].

Past graduate students (sponsored by Axalta Coating Systems, Dupont and NSERC, unless otherwise noted)

Mingmin Zhang (PhD, 2015-2018) "Design and Synthesis of Acrylic Dispersants for Nonaqueous Dispersion Polymerization"

Jan Schier (PhD, 2013-2017) "Hydrogen Bonding in Radical Copolymerization: A Kinetic Investigation under Industrially Relevant Conditions"

Weiwei Yang (PhD, 2011-2016) "Non‐Aqueous Dispersion Polymerization for Automotive Coating Applications"

M. Ali Parsa (MSc, 2012-2014) "Combined Monte‐Carlo and Deterministic Modeling Techniques applied to Polymerization Systems"

Kun Liang (PhD, 2009-2013) "Free-Radical Copolymerization of Hydroxy-functional Monomers: Kinetic and Semibatch Studies"

Raul Moraes (PhD, 2007-2011) "Pushing the Boundaries of Concentrated Dispersions: High Solids Content Bimodal Latex for Paper Coating Applications" (sponsored by BASF)

Wei Wang (PhD, 2006-2010) "A Comprehensive Kinetic Model for High Temperature Free Radical Production of Styrene/Methacrylate/Acrylate Resins"

Onyinye Okorafo (MSc, 2007-2009) "On-Line Optimization for a Batch-Fed Copolymerization Reactor with Partial State Measurement"

Luis Fernando Perea (MSc, 2005-2007) "Optimization and Control of Semibatch Free Radical Copolymerization"

Deheng Li (MSc, PhD, 2001-2006) "Modeling of Kinetic Complexities in High Temperature Free Radical Terpolymerization for Production of Acrylic Coatings Resins"

Adam Peck (MSc, 2001-2003) "Investigation of Free Radical Polymerization Propagation Kinetics by Pulsed-Laser Polymerization"

An ongoing program explores the industrial application controlled radical polymerization (CRP) to produce polymers with narrow molar mass distribution and controlled structure. In particular, the group has studied the application of Cu-catalyzed systems known collectively as Atom Transfer Radical Polymerization (ATRP). The technique has great promise, but several factors must be overcome (residual Cu catalyst concentration; expensive reagents; lower polymerization rate) before it is industrially viable. The group has constructed tubular and well-mixed reactor systems for continuous production of polymer with controlled chain lengths at ppm levels of Cu catalyst at reaction rates that approach those of conventional free radical polymerization.

Current and recent projects in this area include:

  • Copper-catalyzed Routes to Acrylate Macromonomers (Niloofar Shiraz zadeh, sponsored by Nipsea Technologies)
  • The use of CRP techniques to synthesize dispersants for non-aqueous dispersion polymerization (Mingmin Zhang, sponsored by Axalta Coating Systems)
  • Industrial process development: low-copper ATRP systems and new alkoxyamines for high temperature (Kevin Payne, sponsored by BASF)

Key Publications

Zhang, M., R. A. Hutchinson, “Synthesis and Utilization of Low Dispersity Acrylic Macromonomer as Dispersant for Nonaqueous Dispersion Polymerization”, Macromolecules 51, 6267-6275, 2018 [More information].

Payne, K. A., J. Debling, P. Nesvadba, M. F. Cunningham R. A. Hutchinson, "NMP of styrene in batch and CSTR at elevated temperatures: Modeling experimental trends", Eur. Polym. J. 80, 186-199, 2016 [More information].

Zhang, M., M. F. Cunningham R. A. Hutchinson, "Aqueous Copper(0) Mediated Reversible Deactivation Radical Polymerization of 2-Hydroxyethyl Acrylate," Polym. Chem. 6, 6509-6518, 2015 [More information].

Payne, K. A., P. Nesvadba, J. Debling, M. F. Cunningham R. A. Hutchinson, "Nitroxide-Mediated Polymerization at Elevated Temperatures," ACS Macro Lett. 4, 280-283, 2015 [More information].

Payne, K. A., D. R. D'hooge, P. H. M. Van Steenberge, M.-F. Reyniers, M. F. Cunningham, R. A. Hutchinson, G. B. Marin, "ARGET ATRP of Butyl Methacrylate: Utilizing Kinetic Modeling to Understand Experimental Trends," Macromolecules 46, 3828-3840, 2013 [More information].

Chan, N., M. F. Cunningham, R. A. Hutchinson, "Copper Mediated Controlled Radical Polymerization in Continuous Flow Processes: Synergy between Polymer Reaction Engineering and Innovative Chemistry," J. Polym. Sci., Part A: Polym. Chem. 51, 3081-3096, 2013 [More information]. Invited Highlight.

Past graduate students (sponsored by NSERC, unless otherwise noted)

Mingmin Zhang (PhD, 2015-2018) "Design and Synthesis of Acrylic Dispersants for Nonaqueous Dispersion Polymerization" (sponsored by Axalta Coating Systems)

Kevin Payne (PhD 2010-2015; co-supervised by M. F. Cunningham) "Controlled Radical Polymerization: Towards an Industrial Process" (sponsored by BASF and NSERC)

Mingmin Zhang (MSc 2013-2015; co-supervised by M. F. Cunningham) "Aqueous Cu(0)‐Mediated Reversible Deactivation Radical Polymerization of 2‐Hydroxyethyl Acrylate"

Nicky Chan (PhD 2006-2012; co-supervised by M. F. Cunningham) "Atom Transfer Radical Polymerization with Low Catalyst Concentration in Continuous Reactors"

Yao Fu (PhD 2002-2007, co-supervised by M. F. Cunningham) "Living Radical Polymerization Techniques applied to Semibatch Solution Polymerization"

The Hutchinson group has used their facilities and expertise in radical polymerization to develop (often collaboratively) novel processes and products.

Current and recent projects in this area are sponsored by NSERC, unless otherwise noted:

  • Hydrolytically Degradable Cationic Flocculants for Improved Water Recovery from Mature Fine Tailings (Derek Russell, Kyle Lister, Georges Younes)
  • Superabsorbent Hydrogels made from Bio-sourced Butyrolactone Monomer in Aqueous Solution (Sharmaine Luk)
  • Acrylic Macromonomers via High Temperature Radical Polymerization (Dr. Nina Heidarzadeh, sponsored by Saint-Gobain Ceramics & Polymers)

Recent publications

Younes, G. R., A. R. Proper, T. R. Rooney, R. A. Hutchinson, S. B. Gumfekar, J. B. P. Soares, “Structure Modifications of Hydrolytically-Degradable Polymer Flocculant for Improved Water Recovery from Mature Fine Tailings”, Ind. Eng. Chem. Res. 57, 10809-10822, 2018. [More information].

Luk, S. B., R. A. Hutchinson, "Radical Copolymerization Kinetics of Bio-Renewable Butyrolactone Monomer in Aqueous Solution", Processes 5, 55, 2017 [More information].

Gumfekar, S. P., T. R. Rooney, R. A. Hutchinson, J. B. P. Soares, "Dewatering Oil Sands Tailings with Degradable Polymer Flocculants", ACS Appl. Mater. Interfaces 9, 36290-36300, 2017 [More information].

Luk, S. B., J. Kollár, A. Chovancová, M. Mrlík, I. Lacík, J. Mosnáček, R. A. Hutchinson, "Superabsorbent Hydrogels made from Bio-sourced Butyrolactone Monomer in Aqueous Solution", Polym. Chem. 8, 1943-1952, 2017 [More information].

Rooney, T. R., D. Moscatelli, R. A. Hutchinson, “Polylactic Acid Macromonomer Radical Propagation Kinetics and Degradation Behaviour”, React. Chem. Eng. 2, 487-497, 2017 [More information].

Past graduate students:

Georges Younes (MSc, 2016-2018) "Hydrolytically Degradable Cationic Flocculants for Improved Water Recovery from Mature Fine Tailings"

Sharmaine Luk (MSc, 2015-2017) "Radical Polymerization Kinetics of Bio-renewable Butyrolactone Monomers in Aqueous Solution"

Thomas Rooney (PhD, 2012-2017) "Synthesis, Polymerization Kinetics, and Applications of Novel Macromonomer-Based Degradable Materials"

Robert Cockburn (MSc, 2009-2011) "Kinetics, Synthesis and Characterization of Copolymers Containing the Bio-Renewable Monomer g-Methyl-a-Methylene-g-Butyrolactone"

Every year finds one or two 4th year CHEE or ENCH students conducting research in the Hutchinson lab. In addition, there is the occasional opportunity to gain summer work experience under the NSERC USRA program. The projects are designed to allow the student to work independently on a topic that is related to an ongoing group research project, under the supervision of a graduate student in the lab. Contact Dr. Hutchinson if you are interested! Some of the students (Adam Peck, Nick Chan, Bob Cockburn, Kevin Payne, Thomas Rooney, Otlaatla Monyatsi, Sharmaine Luk) have stayed with the group as graduate students, and occasionally the undergraduate research leads to a research publication to add to your CV.

Recent publications with undergrad co-authors in bold

Younes, G. R., A. R. Proper, T. R. Rooney, R. A. Hutchinson, S. B. Gumfekar, J. B. P. Soares, “Structure Modifications of Hydrolytically-Degradable Polymer Flocculant for Improved Water Recovery from Mature Fine Tailings”, Ind. Eng. Chem. Res. 57, 10809-10822, 2018. [More information]

Schier, J. E. S., D. Cohen-Sacal, O. R. Larsen, R. A. Hutchinson, "The Effect of Hydrogen Bonding on Radical Semi-Batch Copolymerization of Butyl Acrylate and 2-Hydroxyethyl Acrylate", Polymers (MDPI), 9, 368-382, 2017 [More information]. Invited contribution

Schier, J. E. S., D. Cohen-Sacal, R. A. Hutchinson, "Hydrogen Bonding in Radical Solution Copolymerization Kinetics of Acrylates and Methacrylates: A Comparison of Hydroxy- and Methoxy- Functionality", Polym. Chem. 8, 1943-1952, 2017 [More information]

Liang, K., T. R. Rooney, R. A. Hutchinson, "Solvent Effects on Kinetics of 2-Hydroxyethyl Methacrylate Semibatch Radical Copolymerization," Ind. Eng. Chem. Res. 53, 7296-7304, 2014 [More information].

List of undergrad research projects (since 2013) with Course Codes

Michelle Gelber (2018-19) CHEM 497
Solvent Effects on the Propagation Kinetics of Water-Soluble Monomers

Morgan Cooze (2018-19) ENCH 417
SET-LRP Production and Chain Extension of Poly(butyl methacrylate) Macroinitiator

Jeremy Hsieh (2018-19) ENCH 417
Synthesis and Characterization of Cationic Copolymers in Aqueous Solution in a Semi-batch Process

Rachel Zigelstein (2018) NSERC USRA Summer Student
Characterization of Acrylic Acid/Cationic Comonomer Monomer and Polymer Aqueous Solutions

Morgan Cooze (2018) Summer Student
SET-LRP Production and Chain Extension of Poly(methyl acrylate) Macroinitiator

Kyle Lister (2017-18) CHEE 421 
Measurement of Polyelectrolyte Properties for Improved Knowledge of Radical Copolymerization of Water-Soluble Monomers

Abbigale Proper (2017) Summer Student
The Influence of Macromonomer Structure on Flocculation of OIl Sands Tailings.

Dustin Boumeester (2016-17) ENCH 417
Solvency Effects upon Nonaqueous Dispersion Polymerization.

Erica Moran (2016-17) ENCH 417
Investigation of Semibatch Copolymerization under Reflux Conditions.

David Cohen-Sacal (2016) NSERC USRA Summer Student
The Influence of Solvent Choice on Acrylate Copolymerization Kinetics.

Arman Al Harari (2015-16) CHEE 421
Testing of Biodegradable Flocculants for theTreatment of Oil Sands Tailings.

Eric Donders (2015-16) ENCH 417
Preparation and Analysis of PVA-Encapsulated Praziquantel Nanosuspensions.

Trevor Hachie (2015-16) ENCH 417 (co-supervised by Lindsay Fitzpatrick)
Production and Investigation of Micro-scale P(MMA-co-MAA) Particles for Tissue Integration in Zebrafish Platform.

Owen Larsen (2015-16) ENCH 417
Semibatch Studies of Butyl Acrylate and 2‐Hydroxyethyl Acrylate Copolymerization.

Eric Donders (2015) NSERC USRA summer student
Application of a New Reactive Dispersant for Non-Aqueous Dispersion Polymerization.

Cameron Giglio (2014-15) ENCH 417
Synthesis and Kinetic Studies of Novel Biodegradable Lactic Acid Based Macromonomers.

Nick Volkmer (2014-15) ENCH 417
Particle Nucleation in Non-Aqueous Dispersion Polymerization.

Sharmaine Luk (2014-15) ENCH 417
Influence of Di(meth)acrylate Impurities in Hydroxy Functional Copolymerization.

Stephanie Wilburn (2013-14) NSERC USRA summer student and ENCH 417
Particle Nucleation in Non-Aqueous Dispersion Polymerization.