Chain Architecture as an Orthogonal Parameter to Tune Morphologies of Polymer Assemblies: Efficient Synthesis and Self-Assembly of Linear-Branched Block Copolymers via RAFT Dispersion Polymerization

Although the formation of linear block copolymers and the assemblies from polymerization-induced self-assembly (PISA) has been widely investigated, the controlled introduction of branching in the block copolymers and therefore the morphological control of block copolymer assemblies via PISA are virtually unexplored. Herein, a diverse set of linear-branched macromolecular chain transfer agents (macro-CTAs) with similar molecular chemical compositions but with different linear chain lengths or branching degrees were synthesized by a two-stage self-condensing vinyl polymerization (SCVP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) in ethanol. Performing reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) in ethanol using these linear-branched macro-CTAs led to the formation of linear-branched block copolymer assemblies. Effects of the structure of linear-branched macro-CTAs on the morphology of linear-branched block copolymer assemblies were investigated in detail. It was found that increasing the linear chain length or decreasing the degree of branching of linear-branched macro-RAFT agents favored the formation of colloidally stable polymer assemblies but with lower-order morphologies. Besides branching in the stabilizer block, the introduction of branching in the core-forming block was also achieved by adding a chain transfer monomer (CTM) into the RAFT dispersion polymerization. Computer simulations of the synthesis of linear-branched block copolymer assemblies were performed, demonstrating similar morphological transitions in our PISA experiments. We expect that this study not only provides an efficient strategy for controlled synthesis of linear-branched block copolymers and the assemblies but also provides valuable insights into the PISA process of linear-branched (or branched) block copolymers.