Project Details:

Establishment of quantitative reliability of electron spin resonance techniques for polymerization kinetics

(1) An international collaboration to identify the key sources of error that have led to discrepancies between propagation rate coefficients (k_p(T)) measured by electron spin resonance (ESR) and pulsed laser polymerization techniques in free radical polymerizations.

(2) To use the results of this study to develop techniques for the reliable quantitative use of ESR techniques in such systems to add to the data base produced by the IUPAC projects on polymerization kinetics.

The ability of electron spin resonance spectrometers to directly identify the nature and environment of free radicals in free radical polymerizations (including the propagating radicals) has long been recognized. Appropriate treatment of the spectra of the propagating radicals allows the measurement of the propagating radical concentration, which in principle allows the measurement of the propagation rate coefficient. However, other than a few exceptions, the propagation rate coefficients (for numerous monomers) measured by this technique have differed significantly from those measured by the IUPAC method of choice (pulsed laser polymerization, PLP).

The establishment of reliable techniques for the measurements of these rate coefficients by ESR is of high importance for high weight-fraction polymer systems, where the PLP methods are not applicable.

The objective of this project is to measure propagation rate coefficients for a monomer (or monomers) not previously investigated by either ESR or PLP techniques (effectively a "double-blind" experiment), and to use this study to investigate the major sources of error in the ESR techniques. Expected outcomes include the establishment of techniques for the reliable measurement of the propagation rate coefficient by ESR techniques, the development of guidelines for experimental design that allows the avoidance of the main potential sources of error, and guidelines for testing the consistency and reliability of the rate coefficients thus measured.