Sizes of long branches in low density polyethylenes

Abstract 13C‐NMR spectroscopy and size exclusion chromatography have been used to determine the mean length of long branches in a number of high pressure process low density polyethylenes (LDPEs). 13C‐NMR analyses count all branches longer than C5 as “long.” The polyethylenes studied all had 2–3 long branches per 1000 carbons. The mean branch length was of the order of 200–300 carbons in length. The size of long branches increases with increasing M̄n of the parent polyethylene, but the size of long branches relative to the overall macromolecular size decreases with increasing M̄n. The mean molecular weight of the long branches is some 5–20% of M̄n of the particular polymer and decreases as M̄n increases. Both autoclave and tubular reactor products were studied.