Abstract
Quantitative 13C NMR serves as a potent tool for determining the microstructure of polyolefin, but it generally requires long experiment times to achieve reliable quantification, for its low natural abundance and sensitivity. We utilized refocused insensitive nuclei enhanced by polarization transfer (RINEPT) here to characterize high-density polyethylene (HDPE) with very low branch contents. Compared with the standard quantitative experiment, this approach drastically reduces the experiment time from more than 20 h to several minutes, and boosts the signal to noise ratio by fivefold per unit of time. We have effectively applied this optimized method to determine short chain branching (SCB) in HDPE with various comonomer incorporations. Using 5 mm prodigy cryoprobe can further reduce the experiment time to approximately one-tenth that obtained by conventional probes. It means the total experiment time saved could be up to 225 times. We have quantified an SCB concentration of 7 branches per 10000 CH2 in just 2 h. Furthermore, our results demonstrated excellent concordance between RINEPT and traditional 13C NMR techniques in quantifying the branch content of HDPE, thereby validating the reliability of this method.
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