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·HBF 4, and PDMAEMA·HOTf polyelectrolytes. In addition, ion exchange of the chloride anion provided polyelectrolytes with NO 3 −, N(CN) 2 −, PF 6 −, and Tf 2 N − anions. The glass transition temperature ( T g ) varied significantly with anion in the order Cl − > PF 6 − > BF 4 − > NO 3 − > TfO − > Tf 2 N − . 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 − > NO 3 − > BF 4 − > N(CN) 2 − > TfO −, which was consistent with counteranion mobility. Solution rheology revealed polyelectrolyte behavior for PDMAEMA·HCl, PDMAEMA·HBF 4, 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 BF 4 − 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.