Real-time monitoring of ring-opening polymerization of tetrahydrofuran via in situ Fourier Transform Infrared Spectroscopy

ABSTRACT The polymerization of tetrahydrofuran (THF) was carried out in CH2Cl2 by using phosphotungstic heteropolyacid as initiator and epichlorohydrin as promoter. This cationic ring‐opening polymerization process was monitored by in situ mid‐infrared spectroscopy system (ReactIR) to further study the thermodynamics and kinetics of THF polymerization. It was observed that the sharp infrared peak of COC stretching vibrations will shift from about 1068 to 1109 cm−1 in THF ring‐opening step. The changes in absorbance intensity of the two characteristic peaks were used for determining instantaneous concentration of linear polymer and ring monomer. The experimental results demonstrated that the kinetics of THF polymerization proved to be typically first‐order. Thermodynamic parameters were determined from the temperature dependence of the monomer equilibrium concentration [M]e over the range from −5 to 25°C. The values of kapp were obtained via the plots of ln{([M]0−[M]e)/([M]t−[M]e)} vs reaction time, for polymerization under specific conditions. The apparent activation energy (Ea) and frequency (A) were determined from the Arrhenius plot of kapp vs. T−1. Besides, the in situ kinetic investigation revealed that more chain‐transfer occurred at higher temperatures, leading to a reduction in propagation species concentration and a deviation from first‐order propagation at the later stage of polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40503.