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

Abstract

SummaryThis 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 Cs‐ligated catalyst 1, the Lewis acid B(C6F5)3, metal hydrides MH (M = K, Na, Li) and the organic PhNMe2 promote efficient catalytic polymerization, while metal alkyls such as Et3Al and Et2Zn 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 Cs‐ligated catalyst 1 and achiral C2v‐ligated catalyst 3 promote catalytic MMA polymerization through effective chain transfer, whereas C2‐ligated catalyst 2 shows no chain transfer. Of several other conjugated polar vinyl monomers investigated, including acrylamides and α‐methylene‐γ‐butyrolactones, only N,N‐diphenylacrylamide (DPAA) exhibits catalytic polymerization behavior. Thus, in the presence of enantiopure pre‐catalyst (S,S)‐4 and excess B(C6F5)3, DPAA is polymerized catalytically and asymmetrically to optically active poly(DPAA) with a narrow MWD of 1.02.