Polyelectrolytes are a useful class of macromolecules as they are capable of binding oppositely charged species under various conditions and exhibit stimuli-responsive properties. Different polymer structures and arrangements of charges can be achieved, including homopolymers and copolymers, such as polyampholytes, that offer responsive properties to changes in temperature, ionic strength, and pH. Polyampholytes are capable of complexing via both intra- and intermolecular interactions in complexes such as simple coacervates, where complex coacervates are a result of mixtures of different polyelectrolytes with opposite charges (i.e., polyanion-polycation complexation). In addition to selection of different functional groups and general polymer composition, it has been previously demonstrated that the arrangement of charges in polyelectrolytes used in PECs has a significant impact on the physical properties.<br/>Here, we investigate various polyelectrolyte complexes (PECs) using different charge arrangements ranging from one-component, charge-balanced polyampholytes to mixtures of polyanion-polycation homopolymers. Using methacrylic acid and N-(3-aminopropyl)methacrylamide as comonomers, a series of homopolymers and polyampholytes of different compositions were prepared and used in PECs demonstrating physical properties that are dependent on the arrangement of charges. The different PEC ionic associations were explored using techniques including turbidimetric titration, UV-visible light spectroscopy, and optical microscopy. Different charge arrangements offer different sensitivity to various stimuli, generally improving PEC stimuli-responsiveness with less separation of charges. A brief investigation of coacervates indicate these materials are useful in binding model compounds such as ionic dyes and are also capable of covalent crosslinking using naturally-occurring genipin. These polymers have the potential to be useful models for better understanding polyelectrolytes in various biological systems.

Investigating the effects of charge arrangement in stimuli-responsive polyelectrolytes

ACS Fall 2021

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