122 ISSN 1560-0904, Polymer Science, Series B, 2018, Vol. 60, No. 1, pp. 122–129. © Pleiades Publishing, Ltd., 2018. Ethylene/1-Hexene Copolymerization and Synthesis of LLDPE/Nanocarbon Composite through In Situ Polymerization 1, 2 Nikoo Nabizadeh a , Gholam Hossein Zohuri a, *, Mostafa Khoshsefat b , Navid Ramezanian a , and Saeid Ahmadjo b a Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran b Department of Catalyst, Iran Polymer and Petrochemical Institute, Tehran, Iran *e-mail: zohuri@um.ac.ir Received April 7, 2017; Revised Manuscript Received July 21, 2017 Abstract—Copolymerization of ethylene/1-hexene using a modified ZN-type catalyst was carried out in the presence of triethylaluminium as cocatalyst. The optimum copolymerization activity was obtained at Al : Ti = 357 : 1, 60°C and the comonomer concentration of 0.6 mol/L in the range studied. Copolymer/nanocarbon (including multiwalled carbon nanotube, graphene nanoplatelet) composites were prepared via in-situ polymerization. The copolymerization activity decreased by addition of the nanocarbon into the reactor. The presence of graphene nanoplatelet in nanocomposites reduced the melting temperature and increased heat of fusion, crystallinity and density of the obtained polymer. In the copolymer/carbon nanotube nanocompos- ites, decreasing of melting temperature was observed in comparison to pure copolymer, whereas, heat of fusion, crystallinity and density increased. The results of TGA analysis showed that the addition of nanocar- bons has improved the thermal stability of obtained copolymers. DOI: 10.1134/S1560090418010104 INTRODUCTION Nowadays, polyolefins play an important role in many applications, particularly linear low-density polyethylene (LLDPE). LLDPE is very attractive polymer due to its excellent properties, such as low density, good mechanical properties, easy fabrication and recycling [1–3]. LLDPE is a copolymer of eth- ylene with C 4 –C 8 α-olefins. Because it contains a small amount of short-chain branches along the back- bone of polymer chains, the crystallinity, melting tem- perature, and density are lower than for ethylene homopolymer. Introduction of α-olefin comonomer into the polyethylene chain alters the structure, and consequently the properties of the polymer product obtained. This effect is dependent on the type of cata- lytic system used, polymerization conditions as well as the comonomer type that is introduced [4–8]. Among all of PE grades, the LLDPE offers many interesting properties; however, its relatively low creep resistance, barrier of oxygen, poor stiffness and elec- trical conductivity may limit its application in some fields. Based on this, addition of small amounts of nanoparticles have proved to play a beneficial role in 1 The article is published in the original. 2 Supplementary materials are available for this article at 10.1134/S1560090418010104 and are accessible for authorized users. improving of its applications in packaging, electronics industries, etc. [9–14]. Synthesis of nanocomposites can be carried out by three main methods; in situ polymerization, solution and melt mixing [14–19]. Among these methods, in situ polymerization is one of the most promising and efficient methods to synthesize polyolefin nanocom- posites [14]. The nanocarbons such as carbon nano- tube, graphene nanoplatelets, etc. with their striking features of the polymer properties have captured attention of numerous researchers. For instance, Kaminsky et al. used multi-walled carbon nanotubes (CNTs) through in situ polymerization method for ethylene and propylene homopolymerization. Activi- ties of single site metallocene catalysts decreased as the percentage of nanotubes increased. They also observed increasing in crystallization temperature and variations in molecular weight polyethylene and poly- propylene composites. Moreover, the presence of CNTs in polymer matrices resulted in a significant improvement in electrical conductivity as well as improved mechanical strength [20]. Boggioni synthe- sized ethylene-co-norbornene copolymers grafted CNTs composites by in situ polymerization in the presence of Ti-based catalyst and MAO as co-catalyst. Based on the results, the grafted CNTs caused increas- ing in glass transition temperature and Young’s mod- ulus in comparison neat ethylene/norbornene copoly- mer [21]. COMPOSITES