Determination of Solution Polymerization Kinetics by Near-Infrared Spectroscopy. 1. Living Anionic Polymerization Processes

Near-infrared (NIR) spectroscopy (1.0–2.5 µm or 10 000–4000 cm⁻¹) was successfully utilized to monitor monomer conversion during conventional, anionic solution polymerization. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10–20% solids) solution polymerization conditions. Despite the presence of the NIR probe, the “living” nature of the polymerizations was maintained in all cases. Both styrene and isoprene polymerization kinetics were investigated in nonpolar and polar solvents, and relative rate constants were compared to values previously reported in the literature. In addition to the need for an inert probe, high sampling frequencies were required since polymerization times ranged from 5 s in tetrahydrofuran to 20 min in cyclohexane. Copolymerization kinetics have also been studied in order to determine the feasibility of NIR as an on-line structural probe. In fact, preliminary data indicate that NIR is capable of detecting sequence distributions for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerization. Future studies will focus on the application of NIR to elucidate polymerization mechanisms and deleterious side reactions.