MOLECULAR, THERMAL AND MORPHOLOGICAL CHARACTERIZATION OF NARROWLY BRANCHED FRACTIONS OF 1-OCTENE LINEAR LOW-DENSITY POLYETHYLENE .1. MOLECULAR AND THERMAL CHARACTERIZATION

A 1-octene linear low-density polyethylene (LLDPE) with a bimodal short-chain branching (SCB) distribution has been fractionated with respect to the SCB content using preparative temperature-rising elution fractionation (PTREF). The average SCB content of the fractions obtained ranges from 2.9 to 28.2 branches per 1000 C atoms. Their weight-average molecular weight decreases with increasing degree of branching, while the polydispersity remains rather broad. The fractions exhibit a broad single melting endotherm in contrast to the multiple melting endotherms of the unfractionated copolymer. Dynamic crystallization of the fractions from the melt results in two separate exotherms.