Zaccaria Francesco, Pucciarelli Andrea, Cipullo Roberta, Busico Vincenzo
Department of Chemical Science, Federico II University of Naples, 80126 Naples, Italy.
Scuola Superiore Meridionale, Largo San Marcellino, 80138 Naples, Italy.
Polymers (Basel). 2025 May 7;17(9):1274. doi: 10.3390/polym17091274.
Formation of long chain branches (LCB) in polyethylene (PE), via incorporation of in situ generated vinyl macromonomers, is known to affect material properties dramatically, making their detection and quantification of primary importance. C NMR spectroscopy is the archetypal technique for the analysis of polymer microstructure, yet it suffers from major limitations in the analysis of LCB in polyethylene, primarily in terms of resolution. Herein, we propose a simple and effective methodology for detecting and quantifying LCB based on the analysis of C atoms in β-position with respect to the branching point. By analyzing model ethylene/α-olefin copolymers bearing methyl, ethyl, butyl, hexyl or tetradecyl chain branches, we show how the C resonances can be used to discriminate between shorter or longer branches. Importantly, the proposed method allows the most critical discrimination between hexyl-type branches and LCB, with an up to three-fold detection enhancement with respect to previously proposed procedures based on the analysis of the methine carbons. The proposed approach is then tested on a representative industrial sample of HDPE, proving that it is suitable to detect very small amounts of LCB.
通过引入原位生成的乙烯基大分子单体在聚乙烯（PE）中形成长链支化（LCB），已知会显著影响材料性能，因此对其进行检测和定量至关重要。碳核磁共振波谱法是分析聚合物微观结构的典型技术，但在分析聚乙烯中的长链支化时存在主要局限性，主要体现在分辨率方面。在此，我们提出一种基于分析支化点β位碳原子来检测和定量长链支化的简单有效方法。通过分析带有甲基、乙基、丁基、己基或十四烷基链支化的模型乙烯/α-烯烃共聚物，我们展示了如何利用碳共振来区分较短或较长的支链。重要的是，所提出的方法能够对己基型支链和长链支化进行最关键的区分，与先前基于次甲基碳分析提出的方法相比，检测增强高达三倍。然后将所提出的方法应用于高密度聚乙烯的代表性工业样品进行测试，证明它适用于检测极少量的长链支化。
