Segmental Dynamics of Poly(acrylic acid) in Polyelectrolyte Complex Coacervates Studied by Spin-Label EPR Spectroscopy

The dynamics of spin-labeled poly(acrylic acid) (PAA) in polyelectrolyte complexes (PECs) has been studied by EPR It has been found that the segmental mobility of the PAA in the PECs is nearly constant in the pH range 10 to 5 but decreases dramatically for pH < 5. Recently, we have studied the dynamics of spin-labeled poly(ethylene-alt-maleic acid) (P(E-alt-MA)) in PECs. The rotational mobility of the P(E-alt-MA) has been observed to depend on pH, which has been related to the formation of hydrogen bonds of the maleic acid units at low pH [Macromolecules 2015, 48, 3577]. To test this hypothesis, in the present study, P(E-alt-MA) has been replaced with PAA, which is a structural isomer of P(E-alt-MA). Now with the results for PAA at hand, we can conclude that the low mobility of the P(E-alt-MA) at low pH cannot be exclusively attributed to the presence of maleic acid units. Nevertheless, it has been confirmed that the dynamics in the PECs is strongly influenced by the degree of dissociation of the weak polyacid.