Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj Amorphous to high crystalline PE made by mono and dinuclear Fe-based catalysts Mostafa Khoshsefat a,b,c, ⁎ , Abbas Dechal b , Saeid Ahmadjo b , S. Mohammad M. Mortazavi b , Gholamhossein Zohuri d , Joao B.P. Soares a a Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada b Department of Catalyst, Iran Polymer and Petrochemical Institute (IPPI), P.O. Box 14965/115, Tehran, Iran c Department of Polymer Engineering, Amirkabir University of Technology, P.O. Box 15785, Tehran, Iran d Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, P.O. Box 91775, Mashhad, Iran ARTICLE INFO Keywords: Optimum bulkiness Cocatalyst Bridge Amorphous Structure-property relation ABSTRACT We designed a series of dinuclear structures (F 1 –F 5 ) bearing different linkers (rigid to flexible) between the Fe centers to investigate that how they could control the catalyst behaviour and polymer properties. The dinculear structures were used for polymerization of ethylene in presence of MMAO and TiBA. Based on initial results, catalyst F 2 containing methyl-substituted phenyl bridge owned the highest activity (4.9 × 10 6 g PE/mol Fe.h) through dinuclearity and optimum bulkiness among the structures studied. This performance was along with the greatest crystallinity (χ c ) of PE made by the catalyst. Polymerization at higher temperature and monomer pressure exhibited high thermal stability and performance of catalyst F 2 , respectively. For further structures, decreasing of effective electronic and steric features led to lower activity. In addition, not only catalyst F 4 bearing the short ethylene bridge exhibited the lowest productivity, but also produced the PE containing high level of short chain branches (37.2 SCB/1000C) affording a branched microstructure of polyethylene in presence of TiBA. It could attribute to low steric and electronic effects and short distance between the centers (ethylene linker) that made it suitable and active for SCB formation. Regarding to it, the electrophilicity index (ω) of F 4 also was greater that led to high capacity or propensity of the specie to accept the (macro) monomer. For this sample, virtually no χ c observed in DSC and SSA thermograms. Moreover, MMAO acted as an effective cocatalyst in comparison to TiBA, according to the kinetic profiles of ethylene polymerization. The observations were in respect of strength and affinity of the cocatalysts in deactivation and reactivation of the centers at prolonged time. 1. Introduction As the polyolefins microstructure has a key role on the physical and chemical properties of final product, the chemistry and structure of li- gand and complex can control the catalyst behavior and polymer ar- chitecture [1–3]. This fact reveals the importance of structure design to reach desired properties [4–8]. There are many papers which have discussed about the catalyst structures from metal effect to ligand nature [9–11]. Late transition metals (LTM) complexes as a group of olefin polymerization catalyst have shown striking features. For in- stance; copolymerization of polar monomers, synthesis of linear to hyperbranched polyethylene, rare short chain branches formation and so on [12–20]. The chain walking mechanism for these structures is the main origin of the observed properties [17–20]. Multinuclear LTM catalysts are also interesting due to the unusual and unique pattern in the polymerization [10]. Among LTM complexes, imino pyridine Fe- based catalysts with high activity competitively to metallocenes are one of the fascinating structures that produce HDPE or oligomers [2,21,22]. This variety of products of bis(imino)pyridine iron based catalysts also is due to ortho-substituent effect and aryl rings that make the active center to produce polymer or oligomer and linear to branched (rarely) polyethylene [21,23]. Totally, catalyst structure lead to different be- haviour of catalyst and thermal and microstructural properties of polymer. High activity and convenient working and ease synthesis of the mononuclear analogues made it to be interested by scientist to focus on the multinuclear ones. The nature of bridge between the centers is important as well as the length of it [24,25]. To clarify, the length and nature of bridge have influence on the catalyst activity, stability and https://doi.org/10.1016/j.eurpolymj.2019.07.042 Received 14 June 2019; Received in revised form 25 July 2019; Accepted 30 July 2019 ⁎ Corresponding author. E-mail address: Mostafa.Khoshsefat@ualberta.ca (M. Khoshsefat). European Polymer Journal 119 (2019) 229–238 Available online 03 August 2019 0014-3057/ © 2019 Published by Elsevier Ltd. T