Using Differential Scanning Calorimetry to Accelerate Polymerization Catalysis: A Toolkit for Miniaturized and Automated Kinetics Measurements

Understanding catalysts, and improving their future performances, requires quantification of their kinetic and thermodynamic parameters, including measurement of rate constants (<i>k</i> _obs), transition state enthalpy barriers (Δ<i>H</i> ^‡) and polymerization enthalpy and entropy (Δ<i>H</i> _p, Δ<i>S</i> _p). This work presents miniaturized and automated methods, conducted using common differential scanning calorimetry (DSC) instruments using <10 mg sample (polymer, solvent, initiator and catalyst), to reliably, accurately, and rapidly measure all these key catalyst performance parameters. The methods are tested using known and highly successful catalyst/alcohol systems (tin(II)bis(2-ethyl hexanoate), Sn(Oct)₂, and benzyl alcohol, BnOH) for cyclic ester or carbonate ring-opening polymerizations, and a catalyst/ionic cocatalyst ((salcy)CrCl and Bu₄NCl) system for epoxide/cyclic anhydride ring-opening copolymerizations-two growth fields in polymerization catalysis. The DSC-measured kinetic parameters are identical and less error prone than those determined using conventional lab-scale experiments by aliquot removal. The DSC kinetics are measured using significantly smaller amounts of materials, 600x less sample, while being significantly more time-efficient. The methods are successfully demonstrated in both neat monomer (bulk) and in solution phase reactions, both of which are common in catalyst testing and application to yield highly reproducible and accurate quantification of catalyst turn over frequency values, rate constants, activation parameters, and rate-determining transition-state enthalpies. In addition to quantifying kinetic parameters, a second methodology is exemplified for two cyclic carbonates, enabling measurement of polymerization enthalpy and entropy change. The paper outlines key recommendations that should enable researchers to apply the DSC method in polymerization catalysis.