Determination and Temperature Dependence of Plateau Modulus for Polymerization of Propylene to Isotactic Polypropylene with Ultra-high Molecular Weight under Catalysis of Ziegler-Natta Catalyst

Abstract

Abstract: The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight (UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G") plots at 180 and 200 ℃ versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0.01-100 rad/s for Ziegler-Natta catalyzing ethylenepropylene random copolymerization (PPR) with a conventional molecular weight and broad MWD.The fact indicates that the high molecular weight is responsible for a maximum peak of G"(ω) vs.lnω curves for UHPPH.This makes it possible to determine the plateau modulus (G_N⁰) of UHPPH from a certain experimental temperature G"(ω) curve directly.For UHPPH, the G_N⁰ determined to be 4.28×10⁵ and 3.62×10⁵ Pa at 180 and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G_N⁰ has no relation to the molecular weight.

Key words: Isotactic polypropylene, Ultra-high molecular weight, Broad molecular weight distribution, Plateau modulus

DING Jian, DING Xue-jia, XU Ri-wei, YU Ding-sheng. Determination and Temperature Dependence of Plateau Modulus for Polymerization of Propylene to Isotactic Polypropylene with Ultra-high Molecular Weight under Catalysis of Ziegler-Natta Catalyst[J]. Chemical Research in Chinese Universities, 2005, 21(2): 227-231.

References

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