Molecular Control of Selectivity in Liquid-Phase Chemical Processes through Polymer-Mediated Solvation

Abstract Controlling selectivity in aqueous-phase biomass conversion over acid catalysts is challenging due to competing parallel and sequential reactions that limit yields. Here, we demonstrate that surface-grafted polyimide (PIM) chains create tunable interfacial solvation environments on acid-functionalized supports, suppressing undesired side reactions by preferentially stabilizing desired product states—analogous to organic co-solvent effects in homogeneous catalysis but without bulk solvent additives. Guided by Hansen solubility parameters, we identified 6FDA-ODA-based polyimides as polymer modifiers that selectively stabilize 5-hydroxymethylfurfural (HMF) over levulinic and formic acids during aqueous fructose dehydration. We synthesized PIM-grafted silica nanoparticles functionalized with propylene sulfonic acid groups or WO3 clusters, showing that HMF hydrolysis at the catalyst surface is reduced by an order of magnitude relative to unmodified catalysts in pure water. However, reaction–diffusion modeling reveals that PIM grafts reduce HMF diffusivity by 3 to 4 orders of magnitude relative to bulk water, introducing a transport barrier that slows HMF release. Consequently, homogeneous HMF degradation—catalyzed by levulinic and formic acid co-products—becomes comparable to the diffusion-limited HMF mass transport rate, limiting yields at high fructose conversion. In monophasic water, HMF selectivity never exceeds that of the bare catalyst at similar conversions, revealing the need to reduce the diffusion barrier through rational chain-length design. Coarse-grained molecular dynamics simulations identify shorter PIM chains (3263 g mol–1) as optimal, reducing HMF residence times without sacrificing preferential solvation. These shorter chains enhance HMF selectivity at all fructose conversions relative to longer PIM chains. Using a 1:1 vol/vol biphasic water/MIBK system to partially bypass bulk HMF degradation further raises HMF selectivity to 84% at 46% fructose conversion, approaching the best reported yields achieved with mixed water/organic solvents, NaCl additives, higher temperatures, or more complex biphasic systems. Demonstrated across two distinct acid catalyst architectures, polymer grafting emerges as a broadly applicable, molecularly tunable strategy for engineering product selectivity in complex liquid-phase reaction networks.