Reaction temperature and solvent influence reactivity ratios in the copolymerization of ethylene oxide and propylene oxide
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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 1H 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 rPO = 0.26 and rEO = 3.78 at 40 °C to rPO = 0.31 and rEO = 3.21 at 60 °C. A similar pattern is observed in anisole, with the reactivity ratios shifting from rPO = 0.28 and rEO = 3.52 at 40 °C to rPO = 0.30 and rEO = 3.32 at 60 °C, respectively. In contrast, the reactivity ratios in DMSO are generally slightly more similar, with rPO = 0.32 and rEO = 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.
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Macromolecules, 58, 24, ACS Publ., Washington, DC, 2025, https://doi.org/10.1021/acs.macromol.5c02759