Real-time infrared determination of photoinitiated copolymerization reactivity ratios: Application of the Hilbert transform and critical evaluation of data analysis techniques

The reactivity ratios of various UV-copolymerizing systems were determined employing RT-FTIR spectroscopy, combined with advanced and alternative multivariate-statistical data analysis techniques. For complex mixtures peak identification as well as peak deconvolution has been increased significantly by employment of 2-dimensional correlation spectroscopy, based on the Hilbert transform. As an advantage, kinetic reaction profiles of homo- and copolymerization reactions have been extracted and have been separated without any additional measurement. The following reactivity ratios were obtained: fumarate/vinyl ether r(1) = 0, r(2) = 0; maleate/vinyl ether r(1) = 0, r(2) = 0; fumarate/allyl ether r(1) = 0, r(2) = 0; maleate/allyl ether r(1) = 0, r(2) = 0; fumarate/methacrylate r(1) = 0, r(2) = 1.3; fumarate/acrylate r(1) = 0, r(2) > 50; methacrylate/vinyl ether r(1) = 16, r(2) = 0; methacrylate/allyl ether r(1) > 100, r(2) = 0; methacrylate/acrylate r(1) = 1.6, r(2) = 0.15; methacrylate/N-vinylcaprolactam r(1) = 7.3, r(2) = 0.01; and acrylate/ N-vinylcaprolactam r(1) = 1.3, r(2) = 0.01. Kinetically, the fumarate-vinyl ether copolymerization can be regarded as the homopolymerization of a CT complex while the fumarate allyl ether copolymerization should be regarded as a perfect alternating copolymerization. The HEA-NVC copolymerization has to be regarded as a terpolymerization between HEA, NVC, and the HEA-NVC charge-transfer complex.