Parallel reactions in polymerization of ethylene/methyl methacrylate by late-transition-metal catalysts (α-diimine nickel)

Polymerization of ethylene (E)/methyl methacrylate (MMA) was carried out by late-transition-metal catalyst and co-catalysts such as methylaluminoxane (MAO), ethylaluminum sesquichloride (Al2Cl3Et3), and modified methylaluminoxane (MMAO). Moreover, for precise study and profound understanding of the reactions, polymerization of MMA was performed with co-catalysts in the absence of ethylene and catalyst. The samples were analyzed using differential scanning calorimetry (DSC) to determine glass transition temperature (Tg) and melting temperature (Tm). Molecular weights (Mw) were determined by methods of gel permission chromatography (GPC) and rheometric mechanical spectroscopy (RMS). 13C NMR was applied for recognition of molecular structure, the number of branches, and tacticity. At first, the formation of E/MMA copolymer was expected but in the resulting polymer, two homopolymers of polyethylene and polymethyl methacrylate were obtained instead of E/MMA copolymer. After analyzing the results, it was found that two separate reactions govern the polymerization system, one coordination catalytic polymerization of ethylene, and the second Lewis acid cationic polymerization of MMA. Also, highly branched PE (315 branches per 1000 carbon atoms) with the highest Mw (180,500 g/mol) was obtained at 30 oC, 1 bar ethylene pressure, and 15 mL MMA. The highly syndiotactic PMMA was achieved by co-catalyst of MAO and Al2Cl3Et3 with Tg about 130 oC whereas PMMA generated from MMAO has Tg about 110 oC or less than 110 oC.