1. a Laboratoire de Chimie theorique Appliquee Facultes , Universitatires Notre-Dame de la Paix , Namur, Belgium
2. d Belgian National Science Foundation (Aspirant FNRS)
3. b Polymer Laboratory Allied Corporation , Morristown, N.J., 07960
4. c Department of Chemistry , MASSACHUSETTS INSTIITUTE OF TECHNOLOGY , Cambridge, MA 02139