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Browsing by Author "Marques, M.M."

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  • Homogeneous Ziegler-Natta polymerisation: A kinetic approach .2. Transient-state kinetics
    Publication . Marques, M.M.; Dias, A.R.; Justino, Jorge; Costa, C.; Lemos, F.; Ribeiro, F.R.
    An integrated view is presented of several possible mechanisms applicable to the interpretation of homogeneous Ziegler-Natta polymerisation. In this paper, the transient aspects related to the kinetics of Ziegler-Natta polymerisation are investigated. Extensive data are used to construct kinetic profiles (rM vs. t) from a theoretical approach. Special attention is given to the duration of the transient period as a function of the different kinetic parameters. The kinetic models developed are fitted to experimental data, either directly obtained by the authors or published in the literature. These general models have a broad range of application.
    1997Journal article Open access Show more
  • A kinetic approach to homogeneous Ziegler type polymerization. Transient state
    Publication . Marques, M.M.; Costa, C.; Justino, Jorge; Lemos, F.; Ribeiro, F.R.; Dias, A.R.
    In this paper we present a kinetic approach to the analysis of transient-state homogeneous Ziegler-Natta polymerization activity data. The main features of the experimental data are discussed and fitted to transient kinetic models.
    1997Journal article Open access Show more
  • Polymerization of ethylene using metallocene and aluminoxane systems
    Publication . Justino, Jorge; Dias, A.R.; Ascenso, J.; Marques, M.M.; Tait, P.J.T.
    This paper describes ethylene polymerization using a number of metal-locene and aluminoxane catalyst systems, Cp2MR2 and methylaluminoxane [M = Zr, W, Nb; R = Cl, CH3]. Two types of methylaluminoxane, MAO (1) and MAO (2), were used as cocatalysts. The polymerization activities of the complexes Cp2WCl2 and Cp2NbCl2 were compared with that of Cp2ZrCl2. The Nb and W complexes were found to be less active than the Zr complex. Polyethylene characterization was also carried out by the following methods: gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR).
    1997Journal article Open access Show more
  • Study of low catalytic activity systems (Biscyclopentadienyl complexes-aluminoxane) on olefin polymerization
    Publication . Justino, Jorge; Marques, M.M.; Correia, S.; Dias, A.R.; Lemos, F.; Ribeiro, F.R.
    Olefin polymerization using low activity catalyst systems: Cp2WCl2-methylaluminoxane, [Cp2Mo(CH3)2][PF6]-methylaluminoxane and Cp2Mo(CH3)2-methylaluminoxane, is described. All these catalyst systems were studied in ethylene and propylene polymerization; however, they only showed catalytic activity for ethylene. Only one type of methylaluminoxane (MAO) was used, prepared in an Al/H2O ratio of 2. The kinetics of polymerization were examined and the experimental data (either presented here or in previous papers) were fitted to the kinetic models developed previously and now extended to account for the methylaluminoxane effect.
    1997Journal article Open access Show more