Quantification of mesopore infiltration in a polymer-grafted metal-organic framework

Abstract

Polymer-grafted metal-organic frameworks (MOFs) address the powder form and poor processability of crystalline MOFs by forming free-standing self-assembled MOF monolayers (SAMMs). However, to date, SAMMs have been limited to microporous MOFs. Herein, we report the first successful synthesis of polymer-grafted mesoporous PCN-222 nanorods using chain transfer agents (CTA)-anchored reversible addition-fragmentation chain transfer polymerization (RAFT) polymerization of methyl acrylate (MA) and methyl methacrylate (MMA), extending SAMMs beyond microporous frameworks. Monodisperse PCN-222 nanorods were surface-functionalized and polymer grafts were grown from the particles using optimized photocatalyst conditions. PMMA grafting yields free-standing SAMMs with tunable 1D-2D rod alignments through thick external brushes and partial mesopore infiltration, while flexible PMA causes aggregation and SAMMs failure due to thin surface coverage. Quantitative 13C solid-state nuclear magnetic resonance (ssNMR) reveals polymer-MOF ratios consistent with PMMA’s dual surface/partial pore filling (perturbed linker peaks and relaxation), while 1H-13C HetCor with spin diffusion shows rapid initial cross-peaks from proximal polymer. Simulations confirm thicker PMMA brushes (~2x PMA thickness) and significant pore filling, explaining assembly differences when compared to SAMMs derived from other MOFs (e.g., UiO-66). This work establishes polymer rigidity-mesopore interplay as a design principle for high-porosity MOF hybrids, providing a foundation for future development of functional, free-standing SAMMs for catalysis, separation and large-molecule transport applications.