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Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions
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Upper Critical Solution Temperature Behavior of pH-Responsive Amphoteric Statistical Copolymers in Aqueous Solutions
Komol Kanta Sharker1, Yusuke Shigeta2, Shinji Ozoe2
1Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan.
ACS Omega
|April 12, 2021
Summary
Amphoteric copolymers of 2-vinylpyridine and sodium p-styrenesulfonate show tunable upper critical solution temperatures (UCST) in acidic solutions. Adjusting pH, salt concentration, and polymer properties controls their solubility for various applications.
Area of Science:
- Polymer Chemistry
- Materials Science
- Physical Chemistry
Background:
- Amphoteric copolymers offer unique solution behavior due to balanced acidic and basic groups.
- Controlling copolymer properties is crucial for designing materials with specific functionalities.
- Understanding the factors influencing solubility is key for applications in separation and drug delivery.
Purpose of the Study:
- To synthesize and characterize amphoteric statistical copolymers of 2-vinylpyridine (2VP) and sodium p-styrenesulfonate (NaSS).
- To investigate the factors affecting the upper critical solution temperature (UCST) of these copolymers in aqueous solutions.
- To demonstrate the tunability of UCST for potential applications.
Main Methods:
- Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize P(2VP/NaSS) copolymers.
- Monomer reactivity ratios, time conversion profiles, and NMR diffusion-ordered spectroscopy were employed for characterization.
- UCST was determined by monitoring turbidity changes with varying pH, NaCl concentration, polymer concentration, molecular weight, and solvent (H2O vs. D2O).
Main Results:
- Statistical or near-random copolymers of 2VP and NaSS were successfully synthesized.
- P(2VP/NaSS) copolymers exhibited a UCST in acidic aqueous solutions, driven by electrostatic interactions.
- UCST decreased with increasing pH (due to 2VP deprotonation) and NaCl concentration (due to charge screening).
- UCST increased with higher polymer concentration and molecular weight, attributed to increased chain interactions and entanglement.
- The use of deuterium oxide instead of water increased the UCST due to the isotopic effect.
Conclusions:
- The UCST of P(2VP/NaSS) copolymers is highly sensitive to environmental conditions and polymer characteristics.
- These amphoteric copolymers offer a versatile platform for developing stimuli-responsive materials.
- The ability to tune UCST provides opportunities for applications in areas like smart coatings, separation technologies, and controlled release systems.
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