Fractionation and characterization of linear low‐density polyethylene at a lower critical solution temperature (LCST)

Abstract

AbstractThe composition and molecular weight distribution of linear low‐density polyethylenes (LLDPE) have been determined by fractionation and characterization at a lower critical solution temperature (LCST). The fractionation in 2,4‐dimethyl pentane takes advantage of the fact that the LCST is sensitive to the side‐group content as indicated by the 70 K difference between the LCSTs of PE and polypropylene at the same molecular weight (MW). Temperature‐rising elution fractionation (TREF) and LCST fractions are compared by IR and SEC and also by a new method based on turbidity at an LCST. It is found that the LCST fractionation is sensitive to MW and TREF largely depends on a comonomer content. Calibration of the LCST method for MW distribution and effect of the nature of the comonomer on the LCST are discussed. The LCST technique associated with IR analysis is found to be quite effective for characterizing LLDPE.