Influence of counteranion on the thermal and solution behavior of poly (2-(dimethylamino)ethyl methacrylate)-Based polyelectrolytes

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was synthesized and subsequently neutralized with various acids to form PDMAEMA · HCl, PDMAEMA · HBF₄,and PDMAEMA · HOTf polyelectrolytes. In addition, ion exchange of the chloride anion provided polyelectrolytes with NO₃ ^-,N(CN)₂ ^-, PF₆ ^-,and Tf₂N^- anions. The glass transition temperature (T_g) varied significantly with anion in the order Cl ^- > PF₆ ^- > BF₄ ^- >NO₃ ^- >TfO^- >Tf₂N ^-. The polyelectrolytes with larger, weakly coordinated anions required less thermal energy to dissociate ionic interactions, leading to tailored thermal behavior. Solution conductivity of the water-soluble polyelectrolytes decreased in the order Cl^- >NO₃ ^- >BF₄ ^- >N(CN)₂ ^- >TfO-,which was consistent with counteranion mobility. Solution rheology revealed polyelectrolyte behavior for PDMAEMA · HCl, PDMAEMA ₃ HBF₄, and PDMAEMA HOTf. PDMAEMA HCl underwent an electrospraying-electrospinning transition at three times the critical concentration for entanglement (C_e), which was consistent with other cationic polyelectrolytes. However, the BF₄ ^- and TfO ^- polyelectrolytes exhibited an onset of fiber formation at (1.4-1.8)C_e, much closer to the behavior of neutral, nonassociating polymers. Fiber diameters for all polyelectrolytes were 1-2 orders of magnitude smaller than those for neutral polymers due to increased conductivities of the electrospinning solutions.