Linear low-density polyethylene synthesis promoted by homogeneous and supported catalysts Griselda B Galland,* Marcus Seferin, Raquel S Mauler and Joa ˜o Henrique Z Dos Santos Instituto de Quı´mica, UFRGS, Av. Bento Gonc ¸alves 9500, Porto Alegre, 91509-900 Brazil Abstract: Linear low-density polyethylenes (LLDPEs) were obtained through the copolymerization of ethylene with 1-hexene using (nBuCp) 2 ZrCl 2 co-catalyzed by methylaluminoxane (MAO). For com- parative reasons, the same metallocene was supported on silica (0.85 wt%Zr/SiO 2 ) by grafting. The copolymerizations were performed in toluene, at 1.6 bar of ethylene, 60 °C and in an Al/Zr molar ratio of 2500. The 1-hexene concentration varied from 0 to 0.50 mol L 1 . The resulting copolymers were characterized by GPC, DSC and 13 C NMR. The catalytic activities remained close to 2  10 7 and 7  10 6 (g pol) mol Zr 1 bar 1 h 1 for the homo- geneous and supported systems, respectively. For the homogeneous system, the catalytic activity and the comonomer incorporation increased with the 1-hexene concentration up to 0.30 mol l 1 . Higher comonomer concentrations led to a decrease in catalytic activity in the case of the homogeneous system. The highest comonomer incorporation (6.3 mol%) was achieved with 0.50 mol l 1 of 1-hexene in the reaction medium. The supported system afforded lower comonomer incorporations (maximum 4.0 mol%). The effect of the 1-hexene incorporation can also be evaluated through the polymer properties, namely, crystallinity, melting temperature, molecular weight and polydispersity. # 1999 Society of Chemical Industry Keywords: linear low-density polyethylene; LLDPE; copolymerization; metallocene catalyst; 1-hexene; supported catalyst INTRODUCTION The development of metallocene catalysts activated by methylaluminoxane (MAO) afford a combination of high activity with excellent stereoregularity and co- monomer distribution producing polyole®ns which are inaccessible through heterogeneous Ziegler±Natta catalysts. 1 Moreover, metallocenes permit the copoly- merization of ethylene with a-ole®ns, forming linear low-density polyethylenes (LLDPEs), which, because of the short branching from the incorporated a-ole®ns, present lower melting points, lower crystallinities and lower densities, making ®lms formed from these materials more ¯exible and better processable. 2 These copolymers have a great industrial interest and can ®nd applications in packing, in shrink ®lms, in cable coatings, just to mention a few. Nevertheless, these soluble catalysts are unsuitable for industrial applications, where heterogeneous cata- lyst systems are required for gas-phase and slurry polymerization processes or for large-scale polymer production. One approach to overcome this problem consists of the heterogenization of such catalysts, by supporting them on inorganic carriers. Several routes, employing different supports, are described in the scienti®c and patent literature (see, for example, refs 3±6). The majority of these preparations have involved silica supports. Among the metallocene complexes, some patents report the properties of supported (nBuCp) 2 ZrCl 2 in ethylene homo- and copolymerization. Properties such as high melt tension polyethylene 7 or reduction of fouling and sheeting in the reactor during ethylene homopolymerization 8 are claimed with supported (nBuCp) 2 ZrCl 2 on modi®ed silicas. Concerning co- polymerizations, for instance, linear ethylene-1- hexene copolymer, the applicability of which was tested in retort containers for medical and food packaging purposes because their melting point (T m ) is higher than the sterilization temperature, was obtained with a catalyst resulting from the mixture of silica support, (nBuCp) 2 ZrCl 2 , MAO and alkyl- aluminium compounds. 9 Bimodal molecular weight Polymer International Polym Int 48:660±664 (1999) * Correspondence to: Griselda B Galland, Instituto de Quı ´mica, UFRGS, Av. Bento Gonc ¸alves 9500, Porto Alegre 91509-900, Brazil Contract/grant sponsor: CNP q Contract/grant sponsor: FINEP Contract/grant sponsor: FAPERGS (Received 10 June 1998; accepted 5 February 1999) # 1999 Society of Chemical Industry. Polym Int 0959±8103/99/$17.50 660