Direct Assembly of Micrometer-Long Polymeric Cylinders in Water via Supramolecular Sticker Engineering

We report a direct, solvent-free method to produce micrometer-length, well-organized polymer nanocylinders in water. To achieve this, a hydrophilic poly(N,N-dimethylacrylamide) (PMDAc) was functionalized at one chain-end with a perylene diimide (PDI) sticker using RAFT polymerization. Two PDI RAFT agents were prepared and studied: one featuring two tri(ethylene glycol) (TEG) units at the PDI bay-positions and one without. The corresponding PDI-PDMAc conjugates spontaneously self-assembled in water, driven by π-π interactions made of H-aggregates, and showed a morphological evolution from cylinders to spheres when increasing the polymer chain length. The introduction of TEG units was found to be important to avoid the clustering of nanocylinders or the formation of ill-defined assemblies, which were observed in the TEG-free system. Moreover, we found that the PDI-TEG₂-PDMAc with degrees of polymerization (DP_n) below 24 self-assembled into micrometer-long nanocylinders. By heating the aqueous polymer solution, this process can be accelerated and is accompanied by a large increase in viscosity. Fluorescence spectroscopy revealed an excimer emission signal for the PDI polymers in water, with a higher emission for cylinders, suggesting better organization within the PDI H-aggregates. This strategy provides a sustainable approach for developing functional nanomaterials with precise morphological control, eliminating organic solvents and complex processing.