The macroester ⇄ macroion equilibrium in the cationic polymerization of THF observed directly by 300 MHz1 H NMR

Two isomeric forms of active chain ends were observed simultaneously in the living cationic polymerization of tetrahydrofuran (THF) initiated with derivatives of trifluoromethanesulphonic acid (CF3SO2OH). These forms are magnified image the macroion and the macroester. Concentrations of both species were determined in the polymerization of THF conducted in CCl4, CH2Cl2, and CH3NO2, by using 300 MHz 1H NMR spectroscopy. In CCl4 the macroester form dominates (96%), and in CH3NO2 only 8% of macroester could be detected. In CH2Cl2 both species coexist in comparable concentrations ([macroion]:[macroester] = 1:3). The present direct measurements are in agreement with our previous determination of the proportions of macroester and macroions based on kinetics data. Therefore, this also confirms our earlier conclusion, that if an equilibrium between the macroions and macroester is involved in the polymerization of THF, the chain growth proceeds almost exclusively on the macroions.