Abstract
Materials with ultimately thin (2D) or narrow (1D) structures have gained significant attention due to their exceptional properties. However, decreasing the dimensionality of soft polymer materials has been a formidable challenge due to the lack of rational synthetic methodology. Here, we performed cross-linking polymerization inside metal-organic frameworks (MOFs) as nanoporous scaffolds to afford poly(N-isopropylacrylamide) (PNIPAm) with unprecedented 1D and 2D network topologies: double strands and monolayer sheets. Remarkably, these polymer networks exhibited unique thermoresponsive properties in water that were strongly correlated with their specific topologies. Note that the transition temperature of double-stranded PNIPAm is among the lowest of known PNIPAm materials. The monolayer PNIPAm sheets exhibit a markedly slow thermal response over a wide temperature range. The dimensional constraint imposed on cross-linking by MOF-templated polymerization enables precisely controlling the chain orientation and proximity, providing new insights into the mechanism of the PNIPAm phase transition.