Cationic Zirconocene‐Mediated Catalytic H‐Shuttling Polymerization of Polar Vinyl Monomers: Scopes of Catalyst, Chain‐Transfer Agent, and Monomer

Abstract

Summary: This study investigates the characteristics of the recently developed catalytic H-shuttling polymerization (HSP) of polar vinyl monomers mediated by cationic zirconocenium catalysts, through examining the scopes of chain transfer agent, catalyst, and monomer. Amongst the three classes of chain transfer agents (metal hydrides, metal aryl/alkyls, organics) investigated for the MMA polymerization catalyzed by C s -ligated catalyst 1, the Lewis acid B(C 6 F 5 ) 3 , metal hydrides MH (M ¼ K, Na, Li) and the organic PhNMe 2 promote efficient catalytic polymerization, while metal alkyls such as Et 3 Al and Et 2 Zn serve only as the scavenger and/or monomer activator and thus do not promote chain transfer. In the presence of 5 equivalents of KH, both C s -ligated catalyst 1 and achiral C 2v -ligated catalyst 3 promote catalytic MMA polymerization through effective chain transfer, whereas C 2 -ligated catalyst 2 shows no chain transfer. Of several other conjugated polar vinyl monomers investigated, including acrylamides and a-methylene-g-butyrolactones, only N,N-diphenylacrylamide (DPAA) exhibits catalytic polymerization behavior. Thus, in the presence of enantiopure pre-catalyst (S,S)-4 and excess B(C 6 F 5 ) 3 , DPAA is polymerized catalytically and asymmetrically to optically active poly(DPAA) with a narrow MWD of 1.02.

Reactivity of Bridged and Nonbridged Zirconocenes toward Biorenewable Itaconic Esters and Anhydride

“…It has been well established that coordination–addition polymerization of polar vinyl monomers by cationic zirconocenium catalysts occurs through a labile eight-membered-ring chelate intermediate (resting state, exemplified by B in Scheme ) formed upon Michael addition of the growing ester enolate chain end onto the conjugated CC of the incoming monomer (active species, exemplified by A in Scheme ). − ,− ,,,,− Moreover, it has been determined that the ring opening of the resting state to accommodate the coordination of the new incoming monomer is the rate-determining step (rds) of the polymerization reaction. In this work, we have shown that DMIA, D i PrIA, and MMA were not capable of ring opening the eight- and seven-membered-ring chelate complexes formed after the first monomer addition took place, effectively prohibiting the polymerization reaction.…”