Polyolefin microstructures, e.g., short chain branching (SCB) and short chain branch distribution (SCBD), have direct impact on properties and thus ultimately influence end-use applications. The 1H NMR approach to analyze SCB and SCBD is particularly useful when only a limited amount of sample is available, e.g., polyolefin film layers or the fractions from polyolefin separation techniques, such as gel permeation chromatography (GPC), crystallization elution fractionation (CEF), high temperature liquid chromatography (HTLC) and thermal gradient interaction chromatography (TGIC).
In this paper, we discuss the best approach to find a good decoupling frequency and propose an improved 1H pulse sequence with homonuclear decoupling for better measuring SCB. With this new pulse it is possible to reach a S/N of 10 (level of quantification) for the methyl signal from SCB in an ethylene-hexene copolymer (EH, 3.6 mol% H) in 3.5 min with 0.5 g sample.
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