In situ Fourier transform near infrared (FTNIR) spectroscopy was successfully used to monitor monomer conversion during copper mediated living radical polymerization with N-(ti-propyl)-2-pyridylmethanimine as a ligand. The conversion of vinyl protons in methacrylic monomers (methyl methacrylate, butyl methacrylate, and N-hydroxysuccinimide methacrylate) to methylene protons in the polymer was monitored with an inert fiber-optic probe. The monitoring of a poly(butyl methacrylate-b-methyl methacrylate-b-butyl methacrylate) triblock copolymer has also been reported with difunctional poly(methyl methacrylate) as a macroinitiator. In all cases FTNIR results correlated excellently with those obtained by H-1 NMR. On-line near infrared (NIR) measurement was found to be more accurate because it provided many more data points and avoided sampling during the polymerization reaction. It also allowed the determination of kinetic parameters with, for example, the calculation of an apparent first-order rate constant. All the results suggest that FTNIR spectroscopy is a valuable tool to assess kinetic data. (C) 2004 Wiley Periodicals, Inc.