An improved method for distinguishing branches longer than six carbons (B6+) in polyethylene by solution 13C NMR

An alternative method for characterizing longer-than-B6 short chain branches (SCB) in polyethylene (PE) by solution 13C NMR technique was introduced in this communication. Instead of relying on chemical shift values of the methine peak, this new method was based on the chemical shift difference (Δδ) between CH(Bn) and CH(B4) where the subscript “n” denotes the number of branch carbons. In order to take advantage of the reference CH(B4) peak using this method, an ethylene/1-hexene copolymer may have to be mixed in with the unknown sample material. Several examples were given in this manuscript demonstrating this method to be more reliable in distinguishing branch lengths up to B20 than the traditional δ-value based method. Possible application to distinguishing PE long chain branching (LCB) from B6+ SCBs in HDPE and LDPE was also examined.