Local polymer dynamics in solution will be investigated using Nuclear Magnetic Resonance (NMR) relaxation measurements, time- resolved optical experiments, and computer simulations. NMR measurements will be used to investigate the nonlinear dependence of local polymer motions upon the solvent viscosity in dilute solution. These results will be combined with solvent rotation measurements to test a new hypothesis about the origin of the solvent modification effect first noted in viscoelastic studies. Both optical and NMR experiments will be used to systematically explore the microscopic friction of polymer solutions on varying length scales. Computer simulations will provide new insights into the fundamental nature of local polymer dynamics. The cooperative motion of torsional angles, atomic positions , and other degrees of freedom will be examined. The simulations can be critically tested by the NMR measurements. Together these studies will allow the investigators to address the relationship between molecular structure and local dynamics, the interaction of solvent and polymer motions, and the connection between local and global polymer motions. This research deals with a fundamental investigation of dynamic properties of polymer molecules that are different from those found in molecules of other materials. Hence, the research is fundamental, but of potential significance in technology, (i.e., for viscosity and rubber elasticity).
