Selectivity of Thermal Analysis in the Branching Analysis of Low Density Polyethylene

Abstract

Abstract Low density polyethylene (LDPE) exhibits a complex branching architecture that is characterized by the numbers and lengths of the branches. In previous work, it has been demonstrated that comprehensive microstructural information on LDPE can only be obtained via multiple preparative fractionations and subsequent advanced analysis of the fractions. In this work, microstructural differences of LDPE with similar molar masses but different melt flow indexes are addressed. The samples are fractionated using the multiple preparative fractionation concept to generate narrowly distributed branch and molar mass fractions, respectively. The individual fractions are cross‐fractionated by stepwise recrystallization using successive self‐nucleation and annealing to obtain endotherms with multiple peaks (seeds). Each seed represents a population of chains with similar branching structure or crystallizable methylene sequences. The methylene sequence lengths (MSLs) and the seed contents of the seeds with the highest population are compared for fractions with similar fractionation characteristics. Fractions showing significant differences in their MSL and/or seed content are investigated further using advanced analytical techniques and 2D liquid chromatography (2D‐LC), to correlate MSL or seed content to the branching structure.