A new decoupling method for accurate quantification of polyethylene copolymer composition and triad sequence distribution with 13C NMR

C-13 NMR is a powerful analytical tool for characterizing polyethylene copolymer composition and sequence distribution. Accurate characterization of the composition and sequence distribution is critical for researchers in industry and academia. Some common composite pulse decoupling (CPD) sequences used in polyethylene copolymer 13C NMR can lead to artifacts such as modulations of the decoupled 13C NMR signals (decoupling sidebands) resulting in systematic errors in quantitative analysis. A new CPD method was developed, which suppresses decoupling sidebands below the limit of detection (less than 1:40,000 compared to the intensity of the decoupled signal). This new CPD sequence consists of an improved Waltz-16 CPD, implemented as a bilevel method. Compared with other conventional CPD programs this new decoupling method produced the cleanest C-13 NMR spectra for polyethylene copolymer composition and triad sequence distribution analyses. (c) 2007 Elsevier Inc. All rights reserved.