Effect of long chain branching on the properties of polyethylene synthesized via metallocene catalysis

Abstract

In this research, the effect of long chain branching (LCB) and polymerization conditions on thermal, mechanical, and rheological properties of polyethylene synthesized via a metallocene polymerization was studied. The LCB was varied in the range of 0.64–1.14 per 104 atoms of C. 13C NMR spectra showed that the distributions of both short as well as long chain branches in the polymer backbone chain are influenced by polymerization conditions. The increase in ethylene pressure leads to rise in polymer yield, catalyst activity, molecular weight, and narrowing of molecular weight distribution. In contrast, the increase of polymerization duration results in broadening of MWD and a decrease in catalyst activity. In addition, the influence of frequency and LCB on dynamic shear and extensional melt rheology has been reported. The polymer crystallization was discussed in light of Avrami model and modified Hoffman-Lauritzen theory. LCB promoted the transport of chain segments but retarded the nucleation in polyethylene crystallization. The tensile strength decreased with the increase in LCB content. The different macroscopic properties were correlated to LCB content.