L-Phenylalanine Monomer Coacervation Leads to Well-Controlled Nanocrystal Topochemical Photo-RAFT Polymerization

Abstract

We describe self-coacervation and nanocrystal topochemical photo-RAFT polymerization of ionic phenylalanine acrylamide. The charged monomer molecules undergo self-coacervation through nanoclustering, liquid-liquid phase separation, and crystallization in crowded droplets in water at pH 7.0 at 25 °C, leading to ultrathin lamellar nanocrystal-containing droplets capable of well-controlled topochemical photo-RAFT polymerization. Reaction induces pathway-dependent self-assembly involving one-dimensional (non)covalent polymerization of monomer nanoclusters to fibril bundles. Furthermore, monomer molecules within crystal lattice undergo one-dimensional rearrangements guided by growing polymer segments, leading to the nanocrystal transition to perforated lamellar hollow sieves accompanied by decreased crystallinity, and the subsequent interfacial topochemical polymerization of monomer nanoclusters site-specifically along newly activated sites of sieve edges, leading to sieve-centred parallel-growing fibrils. Further reaction leads to densely-charged ultrathin fibril lamellae physically crosslinked by fibril network knots. Consequently, the well-controlled topochemical photo-RAFT polymerization up to >98% conversion was achieved shortly in 1 h, under ecofriendly ambient aqueous conditions. This work provides a robust platform of topochemical photo-RAFT polymerization that proceeds with unprecedentedly high molecular weight controllability.