Abstract
Statistical copolymers of ethylene oxide (EO) and propylene oxide (PO) are widely used in industry and academia. Despite their decade-long use, the influence of the polymerization conditions on reactivity ratios is underexplored, and surprisingly solution and bulk properties of the resulting polyether copolymers have not been reported in a systematic manner. In this study we examined the copolymerization of EO and PO in a variety of solvents (dimethyl sulfoxide, toluene, anisole) and at different temperatures (25-60 °C), correlating reaction conditions with the thermal and solubility properties of the resulting P-(EO-co-PO) copolymers. The copolymerization was monitored online by in situ (1)H NMR spectroscopy to determine the reactivity ratios for the full conversion range. The results show a temperature-dependent trend in reactivity ratios (r) for different solvents. In toluene, the reactivity ratios converge with increasing temperature, changing from r (PO) = 0.26 and r (EO) = 3.78 at 40 °C to r (PO) = 0.31 and r (EO) = 3.21 at 60 °C. A similar pattern is observed in anisole, with the reactivity ratios shifting from r (PO) = 0.28 and r (EO) = 3.52 at 40 °C to r (PO) = 0.30 and r (EO) = 3.32 at 60 °C, respectively. In contrast, the reactivity ratios in DMSO are generally slightly more similar, with r (PO) = 0.32 and r (EO) = 3.10 at 40 °C. Thermal characterization of the polyether copolymers revealed similar melting points of approximately 10 °C and enthalpies of around 40 J·g(-1). Cloud point measurements of the copolymers showed decreased aqueous solubility as the differences in reactivity ratios decreased. These findings demonstrate that the statistical EO/PO copolymerization reaction conditions affect the gradient and thereby significantly influence copolymer physical properties, highlighting the need to consider these parameters for applications.