Urea Anions: Simple, Fast, and Selective Catalysts for Ring-Opening Polymerizations

Abstract

Aliphatic polyesters and polycarbonates are a class of biorenewable, biocompatible, and biodegradable materials. One of the most powerful methods for accessing these materials is the ring-opening polymerization (ROP) of cyclic monomers. Here we report that the deprotonation of ureas generates a class of versatile catalysts that are simultaneously fast and selective for the living ring-opening polymerization of several common monomers, including lactide, δ-valerolactone, ε-caprolactone, a cyclic carbonate, and a cyclic phosphoester. Spanning several orders of magnitude, the reactivities of several diaryl urea anions correlated to the electron-withdrawing substituents on the aryl rings. With the appropriate urea anions, the polymerizations reached high conversions (∼90%) at room temperature within seconds (1-12 s), yielding polymers with narrow molecular weight distributions (Đ = 1.06 to 1.14). These versatile catalysts are simple to prepare, easy to use, and exhibit a range of activities that can be tuned for the optimal performance of a broad range of monomers.

Stoichiometric Reactions of CO2 and Indium‐Silylamides and Catalytic Synthesis of Ureas

“…The series of compounds In(N(SiMe 3 ) 2 ) 3 ( 1 ), In(N(SiMe 3 ) 2 ) 2 Cl⋅THF ( 2 ) and In(N(SiMe 3 ) 2 )Cl 2 ⋅(THF) n ( 3 ) were prepared by minor modifications of the literature method involving a salt metathesis reaction of Na(N(SiMe 3 ) 2 ) and InCl 3 –. In the case of compounds 2 and 3 crystallographic studies confirmed the formulations (Figure ).…”

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

“…This approach was inspired by the use of monourea or bis(thio)urea catalysts in small molecule transformations . Neutral bisureas were readily prepared in one step from the commercially available isocyanates and bisamines at room temperature . The results of 1 H and 13 C NMR spectra, FTIR, element analysis confirmed the success synthesis of bisurea catalysts.…”

DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

“…The thioimidate catalyst demonstrated good catalytic activity in lactide polymerization, but lower activity in TMC ROP and low productivity in polymerization of lactones. The novel simple and promising catalysts, the close structural analogs of TU-derived thioamidate, were studied in the few past years [138][139][140][141][142]. These catalysts, which represent the metal derivatives of disubstituted ureas, demonstrated high activities in ROP of cyclic esters of all actual structure types-lactide, lactones, TMC, and ethylene phosphates.…”