Investigation of the effect of branched structure on the performances of the copolymers synthesized from ethylene and α-olefin with rac-Et(Ind)2ZrCl2/MMAO catalyst system

The branched copolymers prepared from ethylene and α-olefins using rac-Et(Ind)2ZrCl2/MMAO catalyst system were studied. Both the absolute molecular weight (M¯w) and the molecular size (radius of gyration, Rg) of the polymers eluting from gel permeation chromatography (GPC) columns were obtained simultaneously via a high temperature GPC coupled with a two-angle laser light scattering (TALLS) detector. The branched structures and performances of the copolymers display approximate molecular weight and molecular sizes were investigated. Wide angle X-ray diffraction analyses indicate that 16-carbon side branch could co-crystallize effectively with backbone chain at low α-olefin incorporation. The melt behaviors of the copolymers were studied by dynamic rheological measurements. Both branch length and comonomer content affect considerably the loss modulus, storage modulus and complex viscosity of the copolymers. The relationship between the dynamic-mechanical behavior and the comonomer content of the copolymers was also examined by dynamic-mechanical experiments. It is found that the intensity of β-transition raise with comonomer content increasing.