U.S.-France Cooperative Research: Structural and Dynamical Studies of Living Polymers by Neutron Scattering

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This award will support collaborative research in experimental physical chemistry between Dr. Sandra Greer, University of Maryland, and the following French scientists: Professor Pierre Pfeuty, Laboratoire de Physique des Solides, University of Paris-Sud, and Drs. R. Bellissent and F. Boue, Laboratoire Leon Brillouin, Grenoble, France. The objective of the proposed research is to carry out structural and dynamical studies of living polymers by neutron scattering. Living polymers are organic polymers which remain in dynamical chemical equilibrium with their monomers. The monomers come and go from the active polymers. The conversion of monomers to polymers depends on temperature, commencing only below a certain "ceiling temperature". Below the ceiling temperature, the mole fraction and the average chain length of the polymers increase as the temperature is decreased. The investigators propose to study the static and dynamic properties of these polymers by neutron scattering. Dr. Greer and her research group have expertise in the preparation of samples of living polymers which will remain "alive" indefinitely. Dr. Pfeuty is an expert on the statistical mechanics of living polymers, while the investigators at the Laboratoire Leon Brillouin have extensive experience in neutron scattering and polymer research. In this project, samples will be prepared at the University of Maryland and transported to the nuclear reactors at Saclay and Grenoble. Low angle neutron scattering from living polystyrene in deuterated cyclohexane to be carried out at Saclay will provide the investigators with information on the structure of the polymer chains near the polymerization and near the tricritical point, and on the rate of relaxation to the equilibrium chain distribution. Studies with the spin echo neutron spectrometer at Grenoble will provide information on the dynamics of the chain motions. The proposed experiments cannot presently be carried out in the US, because of a lack of high-flux small angle neutron scattering facilities.