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
Yanling Li, Yingxiang Li, Rifeng Yan, Li Zhang, Hong Liu, Jianbo Tan
Abstract
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.