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Polymer science at U of T's Chemistry Department.

Polymer Science at U of T's Chemistry Department

Studies of the chemistry of large molecules at the University of Toronto date back almost a century. Maud Menten, who received her doctoral degree from the U of T in 1911 is famous for her later discovery of the Michaelis-Menten mechanism for the oxidation of biological macromolecules. Sir Frederick Banting won Canada's first Nobel prize in 1923 for his work, in collaboration with Charles Best, on the isolation and purification of insulin, a biopolymer. During the 1930s, H.O.L. Fischer continued his studies on the structure and function of polysaccharides. In the 1950s, Howard Rapson, HFCIC, and Morris Wayman made major advances in the study of cellulose and lignin, the former developing one of the most important industrial processes for bleaching pulp and paper.

In the early 1960s a programme of teaching and research in polymer chemistry was initiated in the U of T chemistry department. Now, 10 faculty members devote some or all of their research efforts to the study of the chemistry of macromolecules, making up the largest academic centre of its kind in Canada (and one of the largest in North America).

The department is equipped to study the synthesis and characterization of both synthetic and natural polymers. In addition to state-of-the-art machines for solid-state and conventional NMR, gel permeation chromatography (GPC), quasi-elastic light scattering (QELS) and x-ray structural studies, the department has recently acquired a scanning tunneling (STM) and atomic force microscope (AFM) capable of atomic resolution. A pico-second laser spectroscopy apparatus is also available. In addition, specialized equipment designed and constructed in the department's own shops, can be used for structural studies using inverse gas chromatography (IGC) and luminescence measurements to study solid state transitions, surface interactions, diffusion and thermodynamics of polymers by methods pioneered by faculty members and their students and associates. Facilities for molding, extrusion and physical property determination of plastics and other polymers are readily available through collaborative programs with members of the large polymer group in U of T's Faculty of Engineering and Applied Sciences.

Many U of T faculty are associated with the Ontario Centre for Materials Research (OCMR), of which James Guillet, FCIC, was a founding member and first programme leader of the Polymers and Composites Group. Through the OCMR, students may receive special scholarships and also work on collaborative research with scientists at major Canadian industrial research laboratories such as Xerox, DuPont, Polysar, ICI, Nova and Bell Northern Research.

Research underway in the chemistry department covers topics ranging from theoretical studies of chain conformation and diffusion of macromolecules, polymer photochemistry and photophysics, colloidal and membrane interfaces, polymerization kinetics, structure-property relationships, and the synthesis of novel organic, inorganic and biopolymers. Brief descriptions of the research interests of faculty members are given below.

Masad Jose Damha

Masad Jose Damha and his students have begun a programme to answer several questions regarding the mechanism of splicing and catalysis of ribonucleic acid (RNA). One research goal is to demonstrate that these complex biological processes can be studied by a combination of spectroscopy, x-ray diffraction, and molecular biology techniques. By combining synthesis and in-vitro splicing reactions they can study the relationships between structure and biological activity.

They are also pursuing new aspects of nucleotide structures for use in novel strategies for drug design. The applicability of nucleotide analogues in chemotherapy depends largely on the stability of the drug in organisms. Two new classes of nucleotide analogues are being developed in Damha's laboratory in which degradation of nucleosidic and phosphoric acid ester linkages is made impossible by stereochemical alterations. These analogues have physical properties similar to natural DNA/RNA oligomers, but at the same time are restricted in their interactions with most enzymes which catalyze degradative processes. The degree of base pairing between these analogues and the complementary sequences of normal DNA and RNA chains is being investigated by UV absorption measurements. This feature is important to the development of new "antisense" antiviral oligo-nucleotides.

James E. Guillet, FCIC

The research interests of James Guillet have been mainly in the field of photophysics and radiation and photochemistry of large synthetic macromolecules.

These studies have been related to a number of practical concerns: the synthesis of photo- and biodegradable plastics; photo and radiation studies of plastics used in photoresists for microcircuitry; and the development of solar processes for the synthesis of useful chemicals or for the photodestruction of harmful materials in the environment (eg., PCBs). In the latter category, Guillet and his students have developed new water-soluble photocatalysts called |photozymes', specially constructed synthetic macromolecules mimicking some essential features of biological macromolecules such as enzymes and photosynthetic bacteria.

A major objective is to produce a polymer molecule capable of carrying out many functions of chloroplasts in green plants. This involves the study of very fast energy-transfer processes along polymer chains, and the conversion of this electronic excitation to chemical energy via the reduction of water or carbon dioxide. A photochemical membrane system has also been developed to produce hydrogen peroxide, a potential non-polluting fuel.

Another area of study in Guillet's laboratory involves the use of molecular probe techniques (inverse gas chromatography) to study the thermodynamics of interactions in polymer systems. Similar studies are underway using luminescent probes.

Mark Lautens, MCIC

The research group of Mark Lautens is interested in the development of metal-promoted reactions in organic chemistry. Several aspects of this work are related to the synthesis and reactions of new polymeric materials. Lautens and his students are attempting to bring advances from modern methodology in organic and organometallic synthesis to polymer chemistry.

Specifically, in the past two years they have been using the method of ring-opening metathesis polymerization (ROMP) for the synthesis of polyolefinic hydrocarbons. The ROMP reaction is currently under intense investigation because of its ability to control molecular weight and polymer microstructure. Lautens's contribution to the field has focused on the synthesis of novel monomers using a cobalt-catalyzed cycloaddition reaction between norbornadiene and an acetylene to generate compounds known as deltacyclenes. Lautens group members have demonstrated that ring-opening polymerization of deltacyclenes is extremely facile, giving rigid and highly-strained polymers which undergo interesting thermal transitions above 150 degrees C. Studies are in progress to understand the mechanism and to prepare modified monomers and polymers to adjust their thermal and mechanical properties.

Peter M. Macdonald, MCIC

The investigation of electrostatics at the surface of polymer particles is the main interest of Peter Macdonald. Particle surface charge is a major contributor to the stability of colloidal latex dispersions because of the resulting interparticle electrostatic repulsions. Macdonald and his students have developed a new method for measuring particle surface charge, based on (2)H-NMR spectroscopy. They discovered that choline behaves like a |molecular voltmeter' in that it responds to, and via the (2)H-NMR spectrum, reports on surface charge in lipid bilayer membranes. This technology has now been transferred to latex dispersions by first attaching the molecular voltmeter to a long alkyl chain and then binding the resulting surfactant molecule to the surface of a polymer particle. Macdonald and his students are also probing the effects on particle surface charge of varying the density of covalently attached charged groups, and the composition of surface bound surfactants. Many of the concentrated, coagulated or flocculated states assumed by such particle suspensions are intractable to classical methods of determining surface charge. The molecular voltmeter approach, however, has no such limitations because it is derived from solid-state NMR methodologies.

Ian Manners, MCIC

Ian Manners and his students emphasize research in the synthesis, properties, and applications of new classes of inorganic polymers with backbones consisting of elements such as silicon, sulphur, boron, phosphorus, and transition metals. Species I-III are typical examples of the polymers being investigated. These materials are expected to display a variety of properties such as electronic conductivity and non-lineary optical activity, and also unusual thermal, mechanical, or preceramic characteristics often difficult or impossible to achieve using conventional organic systems.

William F. Reynolds, ACIC

Nuclear magnetic resonance spectroscopy is the most widely used spectroscopic method with applications in all areas of science from physics to medicine. In Reynold's laboratory, he and his students are working on both the development of new two-dimensional NMR methods for characterization of complex organic compounds, and their applications to structure elucidation of natural products and stereoregular polymers.

One- and two-dimensional MNR are being used in Reynolds's laboratory to determine the tacticity of stereoregular polymers. The relative stereochemistries of as many as seven adjacent monomer units can be determined, allowing development and testing of improved statistical models for mechanisms of polymerization. As part of this project new methods have been developed for synthesis of polymers of constant molecular weight and continuously varying tacticity. Experiments using a variety of physical and spectroscopic techniques are planned to investigate the relationship between polymer microstructure and bulk physical properties of these polymers.

Thomas T. Tidwell, MCIC

Conducting organic polymers of the polyacetylene type are the object of research in the laboratory of Thomas Tidwell. Polyacetylene, or (CH=CH)(n), can be doped so as to be an excellent electrical conductor, but suffers from the drawback of difficult processibility because of poor solubility and low air stability. The use of acetylenic monomers bearing fluorine substituents is under study, and it has been found that the resulting polymers do have greatly improved solubility and stability. The use of bisketenes as unique difunctional substrates for the preparation of polyesters and polyamides is also under examination.

G. Julius Vancso

The general focus of Julius Vancso's research is to understand and predict how atomic-scale characteristics influence the properties of polymeric materials. This work is closely related to the design of advanced, high-value-added polymers. Three levels of structural organization are emphasized: isolated macromolecules; solid, well relaxed glassy polymers; and solid, oriented polymers.

Various light scattering experiments are used to investigate the size, shape, conformation and dynamics of individual polymer molecules. Research on scaling studies of neutral and charged macromolecules is in progress.

Special attention, motivated by many unanswered problems, is devoted to interdependence between macromolecular architecture and thermophysical properties of solid, glassy polymers. Vancso and his colleagues use x-ray and synchrotron radiation scattering experiments to describe the microscopic structure. On the basis of the atomic arrangement and interparticle potentials, they calculate the functional form of thermodynamic parameters. For comparison, these parameters can be measured independently by various techniques. Computer-aided molecular modelling and design is extensively applied to bring theory and experiment into harmony. Studies underway focus on polymers with different polarity and on polyesters containing metal ions.

The anisotropy in solid, oriented polymers is also being investigated, with emphasis on the molecular aspects of orientation. This research is stimulated by applications of oriented-macromolecular systems, including the aircraft and space industry.

Stuart G. Whittington

Experimental work in polymer science is complemented by the theoretical efforts to Stuart Whittington and his students. Their interests focus on the statistical mechanics of dilute polymer solutions. At high temperatures, or in good solvents, the system is dominated by entropic effects. But, as the temperature is lowered, energetic terms become important and can lead to a collapse transition. The details of this transition have been studied in a variety of models. The resulting changes in the average shape of the molecule can lead to dramatic differences in energy transfer processes along the polymer chain and topological effects, such as self-entanglements, play a delicate role in this collapsed state.

Related problems include polymer adsorption and the behaviour of polymers in restricted geometries, such as pores. In particular, how does the architecture of the polymer affect its behaviour in a confined environment.

Mitchell A. Winnik, MCIC

There are many times when the advancement of a technology is retarded by the lack of fundamental scientific information. When such situations raise questions about polymer surfaces and interfaces, Mitchell Winnik and his research group like to get involved. They specialize in designing new experiments using fluorescence spectroscopy to provide this information. It is very difficult, for example, to measure the diffusion of polymer molecules across an interface. This diffusion is the key to understanding polymer welding and the formation of films from latex particles. The Winnik group devised a way to measure this diffusion by labelling the polymers on either side of the interface with a pair of fluorescent dyes (eg., phenanthrene (Phe) and anthracene (An) able to undergo energy transfer. One observes, for instance, much faster Phe* fluorescence decay in a latex film after heat treatment. Phe and An, originally in separate latex particles, could mix only through the process of polymer diffusion. Using the fluorescence decay technique, diffusion processes as fast as 50 Angstrom/s or as slow as 10 Angstrom/day can be measured and applied to problems of technological and scientific significance.
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Title Annotation:Plastics in Canada: the state of the art; University of Toronto
Author:Guillet, James, E.
Publication:Canadian Chemical News
Article Type:Cover Story
Date:Jan 1, 1991
Previous Article:McMaster Institute for Polymer Production Technology.
Next Article:Polymer research at Waterloo.

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