Quantitative adiabatic-refocused INEPT (QA-RINEPT) as a tool for fast and reliable characterization of polyols

¹³ C nuclear magnetic resonance (NMR) is a powerful tool for the detailed characterization and structure elucidation of polymeric samples. The low natural abundance and sensitivity of the ¹³ C isotope, however, lead to very long acquisition time, therefore limiting the use of such technique. We report here the implementation of a quantitative method, quantitative adiabatic-refocused insensitive nuclei enhanced by polarization transfer (QA-RINEPT), for the characterization of polyol samples. The method, based on the well-known insensitive nuclei enhanced by polarization transfer sequence, allows the boost in sensitivity of the carbon resonances without sacrificing the quantitative aspects of the analysis. This is achieved controlling the polarization transfer mechanism and introducing a response factor to calculate precisely the sensitivity gain of the different carbon signals. Compared with the standard single pulse quantitative experiment, the QA-RINEPT method produces up to 4.7× signals enhancement per unit of time. An in-depth statistical analysis was conducted to confirm the reliability of the QA-RINEPT method. We show that there is excellent agreement between the new and old ¹³ C-NMR methods for the quantitative determination of several important polyol properties such as the comonomer and initiator content as well as the ratio of primary and secondary hydroxyl groups.