Polymerization reactions relaxation techniques

The advances in the molecular design of new polymeric materials with targeted properties require advanced molecular characterization of the polymers. ESR techniques are among the methods under continuous development in the quest for more comprehensive physical and chemical information that could correlate microscopic properties with materials performance. ESR spectroscopy has been used in various areas of polymer science, with different goals, such as to study mechanisms of chemical reactions in polymerization and radiation effects, to identify intermediate species, to observe decay and conversion of different species, or to investigate relaxation phenomena of polymer chains by observing temperature-dependent ESR spectra of radical species trapped in solid and liquid polymers. 

In the condensation reaction between a trifunctional alcohol and a difunctional isocyanate, gel formation is marked by significant changes in the velocity and attenuation in the MHz region. The relaxation in the isolated monomers can be ascribed to a combination of intra- and inter-molecular processes. Intermolecular relaxation occurs in the hydrogen-bonded structure formed as a result of hydroxyl interactions. Reaction between the isocyanate and alcohol leads to the possibility of normal mode contributions to the relaxation spectrum and consequent increase in the ultrasonic attenuation. Detailed analysis of the data is difficult because of the complex topography generated by the reaction of di- and tri-functional monomers. This study does however once more illustrate the possibility of using ultrasonic techniques to monitor polymerization processes. 

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