Determination of reactivity ratios for the anionic copolymerization of ethylene oxide and propylene oxide in bulk

Abstract

Reactivity ratios have been determined for the anionic copolymerization of ethylene oxide and propylene oxide in bulk over the temperature range 0–80°C. The ratios were obtained by two methods, the first using the variation of copolymer composition with monomer feed composition according to the Mayo-Lewis equation, and the second using the triad sequence distribution derived from 13C-NMR spectra. In both methods, the ratios were obtained by a computer search for the values giving the best fit between simulated and experimental data. The program took composition drift into account by numerical simulation of the copolymerization as a series of small steps, the feed composition being adjusted after each step. The reactivity ratios were independent of temperature within experimental error, with average values r E = 2.8 ± 0.6 and r p = 0.25 ± 0.07 from the Lewis-Mayo equation, and r E = 3.1 ± 0.4 and r p = 0.30 ± 0.04 from the triad distribution.