Synthesis of ethylene/propylene elastomers containing a terminal reactive group: The combination of metallocene catalysis and control chain transfer reaction

This article discusses a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as φ-CH ₃ and OH. The chemistry involves metallocene-mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent - a mixture of hydrogen and styrene derivatives carrying a CH ₃ (p-MS) or a silane-protected OH (St-OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St-f) at the polymer chain end, in other words, altering the St-f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C ₅Me ₄)SiMe ₂N( ^tBu)]TiCl ₂ and rac-Et(Ind) ₂ZrCl ₂, under certain H ₂ pressures, were found to be suitable catalyst systems to perform the combined task. A broad range of St-f terminated EP copolymers (EP-t-p-MS and EP-t-St-OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St-f]/[monomer].