Abstract
Summary: Seven branched polyethylenes differing in chain topology from hyperbranched to linear structure were synthesized with chain walking Pd‐diimine catalyst, [(ArNC(Me)C(Me)NAr) Pd(CH~3~)(NCMe)]SbF~6~ (1), and Ni‐diimine catalyst, (ArNC(An)C(An)NAr) NiBr~2~ (2)/MMAO, respectively. An extensive rheological study, employing steady‐shear, creep‐recovery, and dynamic oscillation tests, was conducted to examine and compare the melt rheological properties of this novel series of polymers. It was found that the change of chain topology dramatically affected the polymer flow behavior, flow activation energy, and dynamic moduli (G′(ω), G″(ω)). The hyperbranched polymers exhibited typical Newtonian flow behavior and extremely low viscosity. The polymers with chain topology intermediate between hyperbranched and linear structures, however, were essentially viscoelastic materials. All the polymers obeyed the time‐temperature superposition and exhibited enhanced flow activation energy (43.8∼57.2 kJ/mol) compared to HDPE and LLDPE. In the terminal region, these polymers had different dependencies of dynamic moduli (G′(ω), G″(ω)) on angular frequency (ω) and different master curves in the log(G′) versus log(G″) plot. The hyperbranched polymer was also blended with more linear samples as a rheology modifier and was found to significantly lower the viscosity of the blends.
Structure of the Pd‐ and Ni‐catalysts used in this study.
imageStructure of the Pd‐ and Ni‐catalysts used in this study.