An Inverse Main Chain-Side Chain Amphiphilic Polymer Architecture: Self-Assembly Fractionation of a Squaramide Condensation Polymer

The focusing of a polymer into the narrow chain length polydispersity regime is important for revealing the chain length-property relationship and presenting definitive target property. The conventional approach in the typical form of discrete-chain fractionation relies on the solubility of individual chains in a solvent-nonsolvent medium as an operation handle. Herein, we have developed a self-assembly fractionation method for the focusing of a polymer, with the transitioning into collective-chain micelles in a solvent-nonsolvent medium as a driving tool. As a proof-of-concept demonstration, a unique inverse main chain-side chain amphiphilic polymer architecture has been designed into a squaramide condensation polymer, with a polar solvophilic main chain and a nonpolar solvophobic side chain. This architecture provides a hitherto elusive contrast to the currently dominating canonical amphiphilic polymer architecture for addition polymers, with a nonpolar solvophobic main chain and a polar solvophilic side chain. As such, the squaramide condensation polymer synthesized herein has showcased the intriguing self-assembly into primary micelle and compound micelle constructs, allowing for fractionation into varied chain length fractions, each with a narrow polydispersity. The superior efficiency and accuracy observed in the four-step sequential fractionation as well as one-step fractionation for five as-synthesized chain lengths and six degradation-engendered chain lengths promise self-assembly fractionation as a powerful mechanistic framework for the precision targeting of diverse polymer structures and functions.