Synthesis of Narrowly Distributed Cyclic Polymers by Suzuki Cross-Coupling Polycondensation Under Nanoconfinement

Cyclic polymers have gained significant attention due to their intriguing physical and biological properties in comparison to their linear counterparts with similar molecular weights. Cyclic polymers are commonly synthesized through ring-expansion and ring-closure polymerizations, but these methods have limited structural variability and can lead to broad dispersity in the resulting products. To this end, a new strategy has been developed by confining the step-growth polymerization (SGP) of monomers with a flexible ester linkage within nanopores. The spatial confinement effect is believed to limit the formation of extremely long linear polymers at high conversion of functional groups and facilitate end-to-end cyclization. The synthesis of cyclic polymers with high purity and narrow dispersity through Suzuki coupling polymerization with Pd@SBA-15 as the nanoreactor was confirmed by gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization–time-of-flight (MALDI-TOF) analysis. This approach provides a general and straightforward method for the synthesis of cyclic polymers by simply ushering in the SGP of flexible monomers in nanoreactors.