We report a high-throughput study of the kinetics of a multicomponent polymerization reaction in a microfluidic reactor integrated with in situ attenuated total reflection Fourier transform infrared spectroscopy. The technique was used to study the kinetics of an exemplary free-radical polymerization reaction of N-isopropylacrylamide, which was initiated by ammonium persulfate in the presence of the accelerator N,N,N′,N′- tetramethylethylenediamine in water. By monitoring the rate of disappearance of the monomer double bonds, we determined the effects of the concentration of the monomer, initiator, and accelerator on the rate of polymerization and the effect of the pH of the reaction system on the reaction kinetics. This work opens the way for the kinetic studies of complex polymer systems in a microfluidic format. © 2012 American Chemical Society.