Organic ring-opening polymerization (ROP) of cyclic monomers is one of the main methods for accessing biocompatible, biorenewable, and biodegradable polymer materials. The development of efficient and innovative organocatalysts for ROPs have received increasing attention. Here, we introduced a kind of bifunctional organophosphine for ROPs. The key phosphorus zwitterion was generated in situ by mixing the phosphine with acrylate, and the obtained enolate could be considered as a H-bonding acceptor. In this way, the zwitterion, composed of a urea moiety that usually used as a H-bonding donor and an enolate, could efficiently promoted the ROP as a bifunctional catalyst. Different combinations of organophosphine and acrylate were evaluated in the ROP of l-lactide (l-LA). The partner of 1-(3,5-bis(trifluoromethyl)phenyl)-3-(2-(diphenylphosphaneyl)ethyl)urea and methyl acrylate showed optimal performance in terms of reactivity and selectivity. It afforded the poly(l-lactide)s with precise molar masses (Mn, GPC = 7.1 kg mol−1) and narrow polydispersity (Mw/Mn = 1.07) in 5 min. The controlled/living nature of the ROPs was supported by kinetics experiments, chain extension experiments, and MALDI-ToF-MS characterizations. A bifunctional catalysis mechanism of organophosphorus zwitterion was elucidated by NMR titrations, in which the urea moiety activated the monomer and the enolate activated the chain end.

Bifunctional organophosphorus zwitterion for ring-opening polymerizations

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