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

该奖项将支持马里兰大学的Sandra Greer博士与下列法国科学家在实验物理化学方面的合作研究：巴黎-南大学物理化学实验室的Pierre Pfeuty教授，以及法国格勒诺布尔Leon Brillouin实验室的R.Bellissend博士和F.Boue博士。这项研究的目的是通过中子散射对活性聚合物进行结构和动力学研究。活性聚合物是与其单体保持动态化学平衡的有机聚合物。活性聚合物中的单体来来去去。单体向聚合物的转化取决于温度，只有在一定的“最高温度”以下才能开始。在上限温度以下，聚合物的摩尔分数和平均链长随着温度的降低而增加。研究人员建议通过中子散射来研究这些聚合物的静态和动态性质。格里尔博士和她的研究小组在制备活的聚合物样品方面拥有专业知识，这些样品将无限期地“活着”。Pfeuty博士是活聚合物统计力学方面的专家，而Leon Brillouin实验室的研究人员在中子散射和聚合物研究方面拥有丰富的经验。在这个项目中，样品将在马里兰大学准备，然后运往萨克雷和格勒诺布尔的核反应堆。将在Saclay进行的活体聚苯乙烯在氚代环己烷中的低角中子散射将为研究人员提供聚合附近和三临界点附近聚合物链的结构信息，以及平衡链分布的松弛速率。格勒诺布尔的自旋回波中子谱仪的研究将提供有关链运动动力学的信息。由于缺乏高通量小角中子散射设施，拟议中的实验目前不能在美国进行。

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.