Study on molecular chain heterogeneity of linear low-density polyethylene by cross-fractionation of temperature rising elution fractionation and successive self-nucleation/annealing thermal fractionation

The molecular chain heterogeneity of commercial linear low-density polyethylene (LLDPE) was investigated by cross-fractionation of temperature rising elution fractionation (TREF) and successive self-nucleation/annealing (SSA) thermal fractionation by use of DSC. The results indicate that the linear relationships between crystallinity or melting temperature and the elution temperature are confirmed by TREF fractions. Intermolecular heterogeneity exists in the original LLDPE, whereas there is less intermolecular heterogeneity in the TREF fractions. After SSA thermal fractionation, the multiple endothermic peaks for both LLDPE and their TREF fractions are mainly attributed to the heterogeneities of ethylene sequence length (ESL) and lamel lar thickness. The statistical terms, including weighted mean L̄ _ẃ arithmetic mean L̄_ń and broad index L̄_w/L̄_ń were introduced to evaluate the heterogeneities of ESL and lamellar thickness of polyethylene. The difference of broadness index indicates that TREF fractions of LLDPE have less inter- and intramolecular heterogeneities of both ESL and lamellar thickness than, those of the original LLDPE.