Sains Malaysiana 40(7)(2011): 771–779

Chromium(III) Based Ziegler-Natta Catalysts for Olefin Polymerization

(Mangkin Ziegler-Natta Berasaskan Kromium(III) untuk Pempolimeran Olefin)

J.X. Wong* & S.N. Gan

Department of Chemistry, Faculty of Science, University Malaya, Kuala Lumpur, Malaysia

M.J. Aishah

Chemistry Division, Centre for Foundation Studies in Science, University Malaya,

Kuala Lumpur, Malaysia

Received: 23 October 2009 / Accepted: 21 October 2010

ABSTRACT

Four chromium based oxo-trinuclear carboxylate complexes were prepared by reacting chromium(III) nitrate nonahydrate with acetic acid and substituted carboxylic acids. They were characterized using infrared spectroscopy (FT-IR). Chromium content of the complexes was determined by titrimetry method. The chromium(III) monochloroacetate complex, [Cr3O(ClCH2COO)6.3H2O]NO3.3H2O in combination with diethylaluminium chloride formed heterogeneous catalyst system for ethylene polymerization. Both Al/Cr ratio and temperature influenced the catalytic activity. The maximum activity was 1768 gPE/gCr/hr/atm, achieved by polymerizing at 29°C and monomer pressure around 1 atm, with Al/Cr ratio 30.8. Effect of chloro-substituent groups on carboxylic ligand was studied by comparing the catalytic acitivities of chromium(III) monochloroacetate, chromium(III) dichloroacetate, chromium(III) trichloroacetate and chromium(III) acetate.The polymerization reaction was found to be first order with respect to the monomer during the initial stage. The activity decreases very rapidly presumably due to fast decay of the active sites. The polyethylene was characterized using FT-IR and DSC, and the results showed that it was of high density and crystallinity.

Keywords: Chromium based complexes; ethylene polymerization; Ziegler-Natta catalyst

ABSTRAK

Empat kompleks kromium berasaskan okso-trinuklear karboksilat telah dihasilkan melalui tindak balas antara Cr(NO3).9H2O dengan asid asetik dan asid karboksilik tertukarganti. Kompleks kromium yang disediakan telah dikaji dengan spektroskopi inframerah dan kaedah penitratan. Kompleks kromium(III) mono-kloro asetat [Cr3O(ClCH2COO)6.3H2O]NO3.3H2O bergabung dengan di-etilaluminium klorida untuk membentuk sistem mangkin heterogenous bagi pempolimeran etilena. Aktiviti pemangkinan dipengaruhi oleh nisbah Al/Cr dan suhu. Aktiviti maksimum bagi pempolimeran etena tercapai apabila suhu pempolimeran adalah 29°C dan nisbah Al/Cr 30.8, iaitu 1768 gPE/gCr/j/atm. Faktor pengaruh kumpulan kloro tertukarganti pada ligan karboksilat telah dikaji dengan menggunakan kompleks kromium(III) di-kloro asetat, kromium(III) tri-kloro asetat dan kromium(III) asetat sebagai mangkin. Pempolimeran etilena dalam kajian ini adalah linear terhadap etilena pada permulaan tindak balas. Plot aktiviti lawan masa tindak-balas menunjukkan graf jenis lengkung menurun. Polietilena yang dihasilkan dikaji dengan FT-IR dan DSC dan keputusan menunjukkan bahawa polietilena yang terhasil mempunyai darjah ketumpatan yang tinggi.

Kata kunci: Kompleks berasaskan kromium; mangkin Ziegler-Natta; pempolimeran etilena

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*Corresponding author; email: junxuan@perdana.um.edu.my