| Institution: | 1. Department of Chemistry, Columbia University, New York, NY 10027, USA
Present address: Institut Curie, Section de Recherche;2. Laboratoire PCC/UMR 168 11, rue Pierre et Marie Curie;3. 75231 Paris Cedex 05, France;4. Department of Chemical Engineering, Columbia University, New York, NY 10027, USA;5. Department of Chemistry, Columbia University, New York, NY 10027, USA |
| Abstract: | We have developed a method to measure living chain molecular weight distributions (MWDs) in free radical polymerization (FRP). By laser photolysis of photoinhibitor molecules included in the polymerizing mixture, the living chains are instantaneously flooded with small molecule radicals carrying fluorescent labels. These radicals react with living chain radical end groups, kinetically freezing growth of living chains and simultaneously end -labelling them: the living chain population has been photocopied. The living MWD is obtained from subsequent analysis by GPC equipped with fluorescence detection. We have measured low conversion thermally initiated PMMA living MWDs, Exponential behaviour is found for large chain length N, in accord with classical Flory-Schultz theory, but at smaller N we establish strong deviations, consistent with the stretched exponential predicted by modern FRP theory incorporating first principles chain length dependencies of termination rate constants. However, this behaviour may derive at least partially from distortions produced by the photocopying technique which can generate power law or logarithmic forms at small N. |
