Mechanism and Effect of Polar Styrenes on Scandium-Catalyzed Copolymerization with Ethylene.

Copolymerization of ethylene (E) and polar vinyl monomers remains a problem because E propagation is hindered. Herein, for the first time, we report the copolymerization of E and polar styrenes (SR ) by using an oxophilic scandium catalyst that exhibits higher turnover frequencies than both E and SR homopolymerizations when R is an electron-withdrawing group. This positive comonomer effect was elucidated through computing reaction profiles of E/SF copolymerization at the DFT (B3PW91) level of theory. It reveals that the secondary interaction between Sc3+ and phenyl of the last and penultimate inserted SF units leads to a decrease of the E insertion barrier, because the electron-withdrawing substituent enhances the electrophilicity of Sc3+ by an inductive effect mediated by the secondary interaction. After three consecutive insertions of the E units, the secondary interaction is lost and the SF insertion is kinetically preferred over the E insertion. This process is in line with the NMR spectrum analyses which show that the resultant copolymers mainly contain SR (E)x SR sequences where x≤3.