¹³C NMR Characterization of Short Chain Branches of Nickel Catalyzed Polyethylene

Abstract

All peaks in the 13 C NMR spectrum of a sample of nickel-catalyzed polyethylene can be assigned to linear short chain branches having specific spatial arrangements along the polymer backbone. The chain walking mechanism of branch formation controls the specific spacing and conformational arrangements between these linear short chains. Certain unusual short chain branching sequences, involving two branches separated either by two or four methylene backbone carbons, were observed. Invariably one of the two branches in these structures was found to be methyl. The observed frequency of the second branch, whether it be methyl, ethyl, or a longer short chain branch, correlated roughly to the relative overall abundance of each branch in the bulk polymer sample. The existence of “branches on branches” was not confirmed, based on the peaks present in this spectrum. No clusters of short chain branches, i.e., branches separated by one methylene carbon, were found in this polymer sample.