Synthesis of Vinyl Polymer Bundles at Single-Chain Level via Metal–Organic Framework Templating

Bundling polymer chains into few-strand assemblies remains an unresolved synthetic challenge in polymer chemistry. Here, we report a metal–organic framework (MOF)-templated strategy for the synthesis of vinyl polymer bundles. Cross-linking polymerization of methyl methacrylate (MMA) within one-dimensional MOF nanopores yielded covalently linked PMMA bundles with a controlled average number of strands per bundle ( N ). Small-angle neutron scattering analysis using an adapted flexible cylinder model quantitatively determined N, revealing that MOF pore diameter systematically tuned N across a range spanning approximately two to four strands at the single-chain level. In addition, bundle compactness was controlled by varying the cross-linker feed ratio. Rheological analysis showed that highly cross-linked compact bundles exhibit a distinct change in temperature-dependent viscoelastic behavior when N exceeds two, indicating a nonlinear dependence on N . These findings demonstrate that our MOF-templated approach provides access to few-strand polymer bundles and establishes “bundling” as a variable for polymer materials design.