Microwave-Assisted Ring-Opening Polymerization of D,L-Lactide: A Probe for the Nonexistence of Nonthermal Microwave Effects

Ring-opening polymerization of D,L-lactide is critically reevaluated under both microwave dielectric heating and conventional conduction/convection heating in order to probe the nonexistence of nonthermal microwave effects. All experiments are conducted in toluene by resorting to a fiber-optic sensor that allows for accurate internal reaction temperature measurements. For a given temperature, the results obtained either with a temperature control microwave heating mode or with a power control procedure can well be reproduced through conventional thermal heating. Microwave irradiation does not induce any alteration of the polymerization kinetics or livingness, clearly demonstrating the absence of any specific nonthermal effect in the microwave-assisted process.