Facile Synthesis of CO2-Responsive Nano-Objects: Batch versus Semi-Batch RAFT Copolymerization

Precise polymer architecture and self-assembled morphological control are attractive due to their promising applications, such as drug delivery, biosensors, tissue engineering and "smart" optical systems. Herein, starting from the same hydrophilic units poly(ethylene glycol) (PEG), using CO2-sensitive monomer N, N-diethylaminoethyl methacrylate (DEAEMA) and hydrophobic monomer benzyl methacrylate (BzMA), a series of well-defined statistical, block, and gradient copolymers is designed and synthesized with similar degree of polymerization but different monomer sequences by batch and semi-batch RAFT polymerization process and their CO2-responsive behaviors of these nano-objects is systematically studied. The gradient copolymers are generated by using semi-batch methods with programmed monomer feed rate controlled by syringe pumps, achieving precise control over desired gradient copolymer composition distribution. In aqueous solution, the copolymers could self-assemble into various aggregates before CO2 stimulus. Upon bubbling CO2, the gradient copolymers preferred to form nanosheet-like structures, while the block and statistical copolymers with similar molar mass could only form larger vesicles with thinner membrane thickness or disassemble. The semi-batch strategy to precisely control over the desired composition distribution of the gradient segment presents an emerging trend for the fabrication and application of stimuli-responsive polymers.