Self-Assembly Assisted Polypolymerization (SAAP) of Diblock Copolymer Chains with Two Reactive Groups at Its Insoluble End

Abstract

Preparation of diblock copolymers, (≡,N₃)-poly­(<i>N</i>-isopropylacrylamide)-<i>b</i>-poly­(<i>N</i>,<i>N</i>-dimethylacrylamide) [(≡,N₃)-PNIPAM<i>-<i>b</i>-</i>PDMA] and (≡,N₃)-polystyrene<i>-<i>b</i>-</i>PNIPAM [(≡,N₃)-PS<i>-<i>b</i>-</i>PNIPAM], with reactive alkyne and azide at one end using a trifunctional agent enables us to study how their self-assembly in a selective solvent affects interchain coupling, i.e., the self-assembly assisted polypolymerization (SAAP). As expected, (≡,N₃)-PNIPAM<i>-<i>b</i>-</i>PDMA chains self-assemble into a micelle-like core–shell structure with a PNIPAM core in water at 50 °C. The coupling of as many as 17 PNIAPM ends together led to star-like chains, independent of the copolymer concentration, while the coupling efficiencies at lower temperatures (with no self-assembly) and in good solvents are much lower. These star-like chains remember their “birth” state in water and undergo the intrachain contraction to form single-chain micelles instead of large multichain aggregates. On the other hand, (≡,N₃)-PS<i>-<i>b</i>-</i>PNIPAM exists as individual chains in THF, a mixture of unimers and micelles in 2-propanol, the core–shell micelles in methanol, and irregular aggregates in water. Only in methanol, the coupling efficiency is notably improved. The addition of water into 2-propanol enhances the self-assembly and so does the interchain coupling. The current study shows that even the solvophobic interaction makes the insoluble blocks less mobile inside the core and decreases the collision probability of reactive chain ends, the self-assembly still concentrates the reactive ends together and assists the coupling if the selective solvent is properly chosen