pH-Responsive Copolymer Films Prepared by Surface-Initiated Polymerization and Simple Modification

Area of Science:

• Polymer Chemistry
• Materials Science

Background:

• Poly(norbornene diacyl chloride) (pNBDAC) offers a versatile platform for creating functional polymer films.
• Controlling copolymer composition is key to tuning material properties.

Purpose of the Study:

• To prepare pH-responsive ester/carboxylic acid random copolymer films.
• To investigate the relationship between copolymer composition and pH-responsive behavior.
• To explore the switching of ionic barrier properties based on pH-induced swelling.

Main Methods:

• Surface-initiated ring-opening metathesis polymerization to prepare pNBDAC films.
• Modification of pNBDAC films with water and ethanol mixtures to introduce carboxylic acid and ethyl ester groups.
• Quartz crystal microbalance with dissipation (QCM-D) to assess film swelling and reversibility.

Main Results:

• Copolymer films with tunable carboxylic acid content were successfully prepared.
• Ethanol showed higher reactivity than water in modifying acyl chloride groups.
• A 10^4-fold decrease in ion transfer resistance was observed upon pH change.
• Films exhibited significant pH-dependent water swelling, with a 4x increase in thickness at 34% carboxylic acid content in high pH solutions.
• High reversibility of pH-responsive performance was confirmed.

Conclusions:

• The hydrophilicity of copolymer films, dictated by carboxylic acid content, significantly influences pH-responsive switching of ionic barrier properties.
• These materials demonstrate efficient pH-induced switching from hydrophobic/insulating to swollen/ion-permeable states.
• The developed copolymer films show promise for applications requiring tunable ion permeability and responsiveness to pH changes.