Carbon‐13 NMR of ethylene‐1–olefin copolymers: Extension to the short‐chain branch distribution in a low‐density polyethylene

As model polymers for isolated short‐chain branches in low‐density polyethylene, a series of ethylene–1‐olefin copolymers was examined by use of 13C NMR at 25.2 MHz. An array of 13C resonances was observed that could be associated independently with methyl through amyl branches. The 13C chemical shifts became insensitive to branch length with hexyl and longer branches. Assignments of the various carbon resonances associated with branching were accomplished by using off‐resonance decoupling techniques and the behavior of alkane chemical shifts previously observed by other investigators. The ratio of certain backbone and branch resonances could be used to establish the short‐chain branch distribution in a low‐density polyethylene.