Rheological and thermomechanical properties of long-chain-branched polyethylene prepared by slurry polymerization with metallocene catalysts

摘要

A series of polyethylene (PE) samples were prepared in a slurry polymerization with bis(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2)/modified methylaluminoxane (MMAO) using a semibatch reactor. The samples had long-chain branch densities (LCBDs) of a 0.03-1.0 branch per 10,000 carbons and long-chain branch frequencies (LCBFs) up to a 0.22 branch per polymer molecule. The rheological and dynamic mechanical behaviors of these long-chain branched PE samples were evaluated. Increasing the LCBF significantly increased the eta(0)'s and enhanced shear thinning. Long-chain branching (LCB) also influenced the loss modulus and storage modulus. Increasing the LCBF led to enhanced G' and G" values at low shear rates and broader relaxation spectrums. The samples exhibited thermorheologically complex behavior. LCB also played a significant role in the dynamic mechanical behavior. Increasing the LCBF increased the stiffness of the polymer and enhanced the damping or energy dissipation. However, LCB had little influence on the crystalline structure of the PE. The alpha- and gamma-relaxations showed little dependence on the LCBF. 2004 Wiley Periodicals, Inc. J. Appl Polym Sci 92: 307-316, 2004. [References: 26]