Porous Polymers for Generating Slow-Relaxing Hyperpolarization under Benchtop-DNP Conditions

Dissolution dynamic nuclear polarization (dDNP) is a hyperpolarization method providing an orders-of-magnitude sensitivity boost for liquid-state nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) experiments. We recently introduced a hyperpolarization strategy based on DNP at 1 T and 77 K (instead of 7 T and 1.2 K) and demonstrated two-orders-of-magnitude signal enhancements with a compact and affordable benchtop instrumentation, designed to enable repeated hyperpolarization cycles for multiscan NMR experiments. However, as in conventional dDNP, the required presence of paramagnetic polarizing agents for DNP is a major roadblock to melting the sample without dilution. The introduction of hyperpolarizing porous polymer (HYPOP) matrices achieved the paradoxical goal of generating fast polarization while preserving long relaxation times within the matrix. In this study, we evaluate DNP with HYPOP under benchtop conditions, and we demonstrate how paramagnetic relaxation effects can be minimized before and after dilution-free melting. We report 1 H signal enhancement factors exceeding 45 and 13 C polarization lifetimes over 50 s at 77 K and 18 s at 298 K, while the sample remains impregnated in the matrix. This represents a key milestone toward nondestructive melt DNP for replenishable hyperpolarized solution-state NMR.