Copolymerization of isoprene with ethylene catalyzed by cationic half-sandwich fluorenyl scandium catalysts

Isoprene polymerization and copolymerization with ethylene can be carried out by using cationic half-sandwich fluorenyl scandium catalysts in situ generated from half-sandwich fluorenyl scandium dialkyl complexes Flu'Sc(CH₂SiMe₃)₂(THF)_n, activator, and AlⁱBu₃ under mild conditions. In the isoprene polymerization, all of these cationic half-sandwich fluorenyl scandium catalysts exhibit high activities (up to 1.89 × 10⁷ g/mol_Sc h) and mainly cis-1,4 selectivities (up to 93%) under similar conditions. In contrast, these catalysts showed different activities and regio-/stereoselectivities being significantly dependent on the substituents of the fluorenyl ligands in the copolymerization of isoprene with ethylene under an atmosphere of ethylene (1 atm) at room temperature, affording the random copolymers with a wide range of cis-1,4-isoprene contents (IP content: 64 - 97%, cis-1,4-IP units: 65 - 79%) or almost alternating copolymers containing mainly 3,4-IP-alt-E or/and cis-1,4-IP-alt-E sequences. Moreover, novel high performance polymers have been prepared via selective epoxidation of the vinyl groups of the 1,4-isoprene units in the IP-E copolymers.