An Integrated Theoretical and Experimental Study of a Free Radical Polymerization and Polymer Reaction Kinetics

An integrated program of experiment and theory is proposed whose objective is fundamental progress in the closely coupled fields of Free Radical Polymerization (FRP) and Polymer Reactions Kinetics. Physics and chemistry play equally central roles in these phenomena. Correspondingly, the program unites and coordinates the efforts of an experimental photochemist (NJT) and a theoretical polymer physicist (BOS) with extensive experience in reacting polymer systems. In the accomplished research during the previous funding period, experiment. theory, chemistry and physics have been inseparable. The complex processes in FRP involve many fundamental aspects of polymer science and radical chemistry. A crucial role is played by reactions between growing polymers carrying radical end groups, known as 'living chains' or 'macroradicals.' For this reason, FRP and the general field of polymer reaction kinetics are deeply intertwined.

Since the living chains in a FRP have short lifetimes, their molecular weight distributions (MWD) have never been measured. In the previous funding period a method was developed to measure FRP living MWDs for the first time. Laser photolysis is used to 'photocopy' the transient living population into a fluorescence-labeled dead chain population, which can be analyzed by standard methods. In the proposed research, living MWDs of linear FRP will be photocopied in pre-prepared dead chain backgrounds of known length and concentration. Photocopies and other spectroscopic measurements will be made of steady state FRP, and of non-steady state FRPs evolving from highly novel initial conditions created by flash photolysis. Theory will attempt to predict the outcome of these experiments, extending the theory developed in the first funding period dealing with very dilute dead backgrounds. The experiments enable direct examination of fundamental unresolved issues in a way, which has not been possible until now. For example, photocopying in entangled and unentangled dead matrices, respectively, will provide a unique examination of the role of entanglements in FRP and the nature of the celebrated gel effect. A second family of projects will address fundamentals of polymer reaction kinetics. If successful, these measurements will have significant impact on the field of reacting polymer systems and polymer physics in general since virtually all theoretical predictions on k and k(t) have never been tested.

With this award the Organic and Macromolecular Chemistry Program is supporting the research of Professors Nicholas J. Turro and Ben O'Shaughnessy of the Department of Chemistry at Columbia University. This research is unique in that it provides an opportunity to apply theoretical and experimental efforts to understanding the mechanism of free radical polymerizations. FRP is of enormous technological importance in the polymer industry, used to synthesize a great number of polymeric materials. The expertise of an experimental photochemist will combine with that of a theoretical polymer physicist to provide an interdisciplinary environment where the students involved will be trained in both aspects of the research.