The effect of an unsymmetric branched branch on the 13C NMR chemical shifts of main chain carbons in polyethylene

✍ Scribed by Antoni Jurkiewicz; Nancy W. Eilerts; Eric T. Hsieh

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 100 KB
• Volume: 38
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(20000415)38:8<1210::aid-pola3>3.0.co;2-9

✦ Synopsis

The 13 C NMR spectra of copolymers of ethylene with 4-methyl-1-hexene and 4-methyl-1-pentene, respectively, were compared. The 4-methyl-1-hexene/ethylene copolymer, which contains an unsymmetric 2-methylbutyl branch, exhibits two distinct 13 C NMR peaks for each of the pairwise methylenes spaced one, two, and three carbons from the backbone methine. The chemical shift differences for these pairwise methylenes are 57.4 Hz, 18.7 Hz, and 4.3 Hz, respectively, with chemical shift differences decreasing with increasing distance from the asymmetric carbon. The frequency differences for carbons farther from the branch were not distinguishable. The magnitude of the chemical shift difference also varies with temperature, with the first and second methylene carbon chemical shift differences decreasing with increasing temperature. The third carbon is almost unaffected by temperature variations. In contrast, the 4-methyl-1-pentene/ethylene copolymer exhibits a single peak for each of the pairs of methylenes in the branch's vicinity. This is the first reported observation of a branched branch affecting the chemical shifts of main chain carbons in polyethylene containing short chain branches.