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COLLOIDAL DISPERSIONS AND PROCESSING

Polymer Stabilized Liposomes in Biomedicine

Professor Yuzhuo Li and his group are doing research that involves liposomes. The study of liposomes is very important due their similarity to biological membranes and their therapeutic value as delivery agents for enzymes, drugs, genetic manipulation, and diagnostic imaging. The behavior of a liposome as a biological agent is dependent upon the size, as well as other physical characteristics, including composition, surface properties, lamellarity, and diffusion rates for small molecules. For example, polymers attached to the surface of a liposome (Stealth Liposome) can significantly alter its lifetime in a biological system. Working with Dr. Greg Slack at DuPont Pharmaceuticals, Professor Li and his graduate student Nicole Heldt and undergraduate student Michele Gauger have investigated a range of issues related to the characterization and preparation of polymer stabilized lipsome systems. They have examined the effect on the size of the vesicles by quantitative addition of a hydrotrope and a polymer to a vesicle-forming system. They have also investigated the usefulness of a range of analytical techniques in the characterization and comparison of conventional and stealth liposome systems including NMR, TEM, Fluorescence, and dynamic light scattering. The goal of this research is to develop an optimized liposome system for drug delivery and medical diagnostic applications.

Amphiphilic Block Copolymers and Biocompatible/Biodegradable Copolymers

Professor Gary Ga-Er Yu has been working on the preparation and solution properties of amphiphilic block copolymers, including AB type diblock copolymers: PEO-b-PPO, PEO-b-PBO, PAA-b-PS, PAA-PMMA, ABA type triblock copolymers: PEO-PPO-PEO, PEO-PBO-PEO, etc.. Recently, he and his group have experimentally proved that uniform amphiphilic diblock and triblock copolymers with the same composition and the same hydrophilic block length or A_mB_n and A_mB_2nA_m form micelles in aqueous solutions with the same hydrodynamic radii. Now he is developing ABC type amphiphilic block copolymer systems for better solubilization properties, e.g., for drug delivery purposes or solubilization of organic compounds in the micelles. Biodegradable and biocompatible polymers and copolymers are the topics he has been actively involved in.. Professor Yu has developed methods for obtaining low molecular weight poly(3-hydroxyalkanoate)s (PHA) from bacterial PHA and the preparation of amphiphilic block copolymers with PEO (collaborating with Professor R.H. Marchessault at McGill University).

Block Copolymer Production

Professor Devon Shipp's research, conducted in association with workers at Carnegie Mellon University, led to several breakthroughs in polymer synthesis, especially the production of block copolymers via living radical polymerization. This research has resulted in the first report of using atom transfer radical polymerization (ATRP) to synthesize water-borne block copolymers. These block copolymers had well-defined molecular weights and molecular weight distributions. Other work has also produced all-acrylic thermoplastic elastomers, based on methyl methacrylate and n-butyl acrylate. This was achieved using a one-pot ATRP procedure that allows for easy synthesis and used readily available starting materials. Physical characterization of the all-acrylic polymers showed they exhibit typical thermoplastic elastomer behavior, and thus could become an alternative to styrene-diene analogues. They may also offer several advantages like superior processability and better resistance to solvent and thermal degradation. Kinetic modeling has been successful in showing the importance of the persistent radical effect in ATRP, as well as the significance of chain length dependent termination rate coefficients. The model developed for ATRP allows one to predict various outcomes of the polymerization, including molecular weight, reaction rates and polymer chain functionality. Professor Shipp's current work is focused on further ATRP studies, and on developing another living radical polymerization method - nitroxide-mediated polymerization (NMP). He plans to use NMP for the production of polymer-silicate (clay) nanocomposites, and to expand NMP so as to allow polymerization to be photo-initiated.

NANOPARTICLE / POLYMER COMPOSITES

Professor Raymond Mackay and graduate student Florentina Pavel have used w/o microemulsions stabilized by a polymerizable surfactant to produce polymethacrylate nanolatexes on the order of 5-10 nanometers in diameter. Recently, these studies have been extended to systems in which the oil itself is a polymerizable monomer. Nanoparticles have been synthesized in-situ in the liquid microemulsions, which are subsequently polymerized to form transparent polymer-nanoparticle composites. Studies are underway to explore the range of composition to which this process can be applied. Some of these results were recently reported at the International Conference on surface and Interface Science at the University of Bristo