Shaping a Predictive Model for the Organocatalytic Ring-Open Polymerization Ability of Cyclic Carbonate Monomers

Predicting the potential of newly designed cyclic monomers toward catalytic ring-opening polymerization (ROP) under mild conditions remains challenging and often only achieved after extensive empirical efforts. Here, we describe a computer-guided mechanistic model based on a widely applied N-heterocyclic organocatalyst (TBD) and a standard initiator (BnOH). The developed model allows to use two key parameters to predict the influence of the positional and functional substitution of five-, six- and seven-membered cyclic carbonates on their ROP potential to form polycarbonates. More specifically, the computed model determines the energy requirement (δE) of the key initiation and two following propagation steps for a large series of known and unknown cyclic carbonate monomers thereby extracting important trends in terms of the number, position and type of substituent present on the heterocyclic rings. It also provides an assessment of the relative thermodynamic stability (delta-GD) of the resting state prior to each of the propagation steps. In combination with the δE of the process, the probability of the ROP event for each monomer can be estimated. The computational data and model have been validated with a large number of reported experimentally data available for the TBD/BnOH-promoted ROP of various five-, six- and seven-membered cyclic carbonates, and are further complemented by a series of ROP experiments.