Simultaneous measurements of T1 and T2 during fast polymerization reaction using continuous wave‐free precession NMR method

Abstract

Continuous wave-free precession (CWFP) pulse sequence employing time domain nuclear magnetic resonance spectroscopy (TD-NMR) was used to measure longitudinal (T(1)) and transverse relaxation times (T(2)), during the cure of a commercial epoxy resin (Araldite(TM)) with a 10-min solidification time. The intensity of the NMR signal after the first pulse and in the CWFP regime were used to monitor the concentration of the monomers, and the relaxation times were used to monitor the chain mobility. The main advantage of CWFP over the standard methods to measure relaxation times, inversion recovery (inv-rec) for T(1) and Carr-Purcell-Meiboom-Gill (CPMG) for T(2), is that the measurement of both relaxation times can be performed in a fast and single NMR experiment and, therefore, using a single reaction batch. CWFP is also as fast as the CPMG measurement but at least fivefold faster than the method to obtain T(1) using null point approximation in the inv-rec method. Therefore, the CWFP sequence can be used as a fast and general method to measure relaxation times in polymerization reactions, even with fast solidification time. As a TD-NMR technique, CWFP can be employed in any low-cost bench top TD-NMR equipment commonly used in an academic or industrial laboratory.