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      Permanent link:
      https://www.ias.ac.in/article/fulltext/jcsc/127/04/0717-0728

    • Keywords

       

      Metallocene catalyst; MWD and CCD deconvolution; active centre distribution; ethylene-1-hexene chain end unsaturation; chain termination probability.

    • Abstract

       

      Polymerization chain termination reactions and unsaturation of the polymer backbone end are related. Therefore, in this study, the parameters resulting from the modelling of the active centre distribution of the supported catalyst—silica/MAO/(nBuCp)2ZrCl2—were applied to evaluate the active-centredependent ethylene homo- and copolymerization rates, as well as the corresponding chain termination rates. This approach, from a microkinetic mechanistic viewpoint, elucidates better the 1-hexene-induced positive comonomer effect and chain transfer phenomenon. The kinetic expressions, developed on the basis of the proposed polymerization mechanisms, illustrate how the active site type-dependent chain transfer phenomenon is influenced by the different apparent termination rate constants and momoner concentrations. The active centrespecific molecular weight Mni (for the above homo- and copolymer), as a function of chain transfer probability, pCTi, varied as follows: log(pCTi) = log(mwru)−log(Mni) where mwru is the molecular weight of the repeat unit. The physical significance of this finding has been explained. The homo- and copolymer backbones showed all the three chain end unsaturations (vinyl, vinylidene, and trans-vinylene). The postulated polymerization mechanisms reveal the underlying polymer chemistry. The results of the present study will contribute to develop in future supported metallocene catalysts that will be useful to synthesize polyethylene precursors having varying chain end unsaturations, which can be eventually used to prepare functional polyethylenes.

    • Author Affiliations

       

      Muhammad Atiqullah1 Mamdouh A Al-Harthi2 Siripon Anantawaraskul3 Abdul-hamid M Emwas4

      1. Center for Refining and Petrochemicals, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
      2. Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
      3. Department of Chemical Engineering, Kasetsart University, Jatujak, Bangkok 10900, Thailand
      4. NMR Core Laboratory, King Abdullah University of Science & Technology, Thuwal 23955-6900, Saudi Arabia
    • Dates

       
  • Journal of Chemical Sciences | News

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