Guanidinium as bifunctional organocatalyst for ring-opening polymerizations

Abstract

Typical organocatalyst promoted ring-opening polymerization (ROP) by activation of monomer or polymer chain end via the acidic or basic mechanism. Dual activating of both the monomer and the propagating polymer chain end suggested an ideal strategy of widely tuneable catalysis of high efficiency. Stoichiometric Brønsted acid–base adduct was rarely employed in ROPs since general Brønsted acid and Brønsted base quench each other. We proposed that an acid–base adduct may work bifunctionally in catalysis. The cationic part of the acid–base adduct as H-bond donor activated the monomer, and the counter anion part as H-bond acceptor activated initiator/chain end. A series of guanidiniums, derived from commercially available Brønsted acids and guanidine, were employed as catalysts in ROPs of carbonate, lactide, and lactone. Guanidinium triazabicyclodecene hydrochloride exhibited outstanding catalytic performances in the respect of the rate and controlled in the ROPs of l-lactide, trimethylene carbonate, and δ-valerolactone with nearly full conversions, predicted molecular weights, as well as narrow dispersity of Đ = 1.07. These experimental results indicated that guanidinium is an efficient organocatalyst in controlled/living ring-opening polymerization.