1. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, Florida Agricultural and Mechanical University and Department of Chemical Engineering, Florida State University College of Engineering, Tallahassee, Florida 32310-6046, Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-3015, and Plastics Technology Division, Exxon Chemical Company, Baytown, Texas 77520