Feed-Programmed Backbone RAFT-Site Organization Directs Graft Copolymer Colloidal Morphology

Abstract

Controlling polymer-colloid morphology through a synthetic variable that does not alter the principal monomer chemistry remains challenging. Here, monomer feed sequence was used to generate distinct feed-defined, ensemble-averaged organizations of pendant trithiocarbonate sites along methacrylate backbones and thereby regulate graft-growth-driven nanoassembly. One-pot reverse atom transfer radical polymerization of poly(ethylene glycol) methyl ether methacrylate and a trithiocarbonate-bearing methacrylate afforded simultaneous-feed, end-enriched, and center-enriched multifunctional macro-RAFT agents with the same target composition and comparable apparent molar masses. The pendant trithiocarbonate-containing side groups were subsequently used to mediate grafting-from RAFT dispersion polymerization of styrene. At [St]/[macro-RAFT] = 150, the three precursors produced compact particles, interconnected vesicle-like assemblies, and multicompartment-like nanoassemblies, respectively, under otherwise identical conditions. This pronounced morphology differentiation demonstrates that the feed-programmed RAFT-site organization strongly influences graft-growth-driven colloidal assembly. Time-resolved 1H NMR spectroscopy, transmission electron microscopy, dynamic light scattering, and size-exclusion chromatography linked increasing styrene conversion and graft growth to aggregate growth, particle association, and the development of apparent internal domains. Repeated feed-conversion cycles extended the approach to nominal 7-, 5-, and 3-segment backbones, with feed-stage characterization supporting sequential monomer consumption and population-level chain extension. These results establish feed history as a practical synthetic variable for controlling graft-copolymer colloidal morphology and internal organization, which may support the future development of polymer nanoassemblies for encapsulation, compartmentalized reaction media, and adaptive material platforms.