Switchable vesicles formed by diblock random copolymers with tunable pH- and thermo-responsiveness

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Thermo-responsive polymers change properties with temperature.
• pH-responsive polymers change properties with acidity/alkalinity.
• Block copolymers can self-assemble into complex structures like vesicles.

Purpose of the Study:

• To synthesize and characterize novel diblock random copolymers with both pH- and thermo-responsiveness.
• To investigate the self-assembly behavior of these copolymers in aqueous media.
• To explore the "schizophrenic" behavior and tunable vesicle formation.

Main Methods:

• Sequential reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize well-defined block copolymers.
• The copolymers were composed of N-n-propylacrylamide (nPA), 2-(diethylamino)ethyl methacrylate (DEAEMA), and N-ethylacrylamide (EA).
• Vesicle formation and structural changes were studied in aqueous solutions at varying pH and temperature, with hydrodynamic diameter measured.

Main Results:

• The synthesized block copolymers exhibited "schizophrenic" behavior in aqueous solutions.
• Vesicles were formed with tunable membrane core and corona structures depending on pH and temperature.
• At pH 7 and 37 °C, poly(nPA0.8-co-EA0.2) formed the core (Dh = 148 nm). At pH 10 and 25 °C, poly(nPA0.8-co-DEAEMA0.2) formed the core (Dh = 60 nm).
• Two-step phase transitions were observed, corresponding to the individual block's lower critical solution temperatures.

Conclusions:

• The combination of random sequences and specific comonomers allows fine-tuning of thermo-responsiveness and pH-sensitivity.
• The synthesized copolymers enable the creation of vesicles with switchable membrane core and corona structures in aqueous solutions.
• This provides a versatile platform for developing smart materials with responsive properties.