Understanding catalytic synergy in dinuclear polymerization catalysts for sustainable polymers

Understanding the chemistry underpinning intermetallic synergy and the discovery of generally applicable structure-performances relationships are major challenges in catalysis. Additionally, high-performance catalysts using earth-abundant, non-toxic and inexpensive elements must be prioritised. Here, a series of heterodinuclear catalysts of the form Co(III)M(I/II), where M(I/II) = Na(I), K(I), Ca(II), Sr(II), Ba(II) are evaluated for three different polymerizations, by assessment of rate constants, turn over frequencies, polymer selectivity and control. This allows for comparisons of performances both within and between catalysts containing Group I and II metals for CO2/propene oxide ring-opening copolymerization (ROCOP), propene oxide/phthalic anhydride ROCOP and lactide ring-opening polymerization (ROP). The data reveal new structure-performance correlations that apply across all the different polymerizations: catalysts featuring s-block metals of lower Lewis acidity show higher rates and selectivity. The epoxide/heterocumulene ROCOPs both show exponential activity increases (vs. Lewis acidity, measured by the pK(a) of [M(OH2)(m)](n+)), whilst the lactide ROP activity and CO2/epoxide selectivity show linear increases. Such clear structure-activity/selectivity correlations are very unusual, yet are fully rationalised by the polymerization mechanisms and the chemistry of the catalytic intermediates. The general applicability across three different polymerizations is significant for future exploitation of catalytic synergy and provides a framework to improve other catalysts. Understanding the intermetallic synergy and the structure-performances relationships of catalysts remains challenging. Here, the authors demonstrate a relationship between both the rates, selectivity and the s-block metal acidity in a series of heterodinuclear catalysts based on Co(III) in combination with alkali and alkaline earth metals for three different polymerization reactios.

Automated summary

In this study, a series of heterodinuclear catalysts based on Co(III) combined with alkali and alkaline earth metals were evaluated for three different polymerization reactions. The results show that catalysts with lower Lewis acidity exhibit higher reaction rates and selectivity. These structure-performance correlations apply across different polymerization reactions and provide valuable insights for the future development of catalytic synergy.