Thermodynamic analysis of hydrogen-bonded polymer complexation with isothermal titration calorimetry

Rigorous thermodynamic analysis of polymer complexation is challenging due to the possible kinetically frozen state, complicated chain conformation, and slow chain relaxation. In this work, we study the complexation of poly(acrylic acid) (PAA) with poly(vinylpyrrolidone) (PVPON), poly(2-ethyl-2-oxazoline) (PEOX) and poly(ethylene oxide) (PEO) in acidic water and in organic solvents , including protic solvents (methanol (MeOH), ethanol (EtOH)), and aprotic solvents ( N, N -dimethylformamide (DMF), N, N -dimethylacetamide (DMAC), 1-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO)) with isothermal titration calorimetry (ITC). In DMF, complexation of PAA and PVPON has moderate heat releasing and the effect of kinetically frozen structure is negligible, and the ITC data meet the basic standard to be used for analyzing and estimating thermodynamic parameters, and enthalpy, entropy and Gibbs free energy are calculated to be −1.5 kJ/mol, 45 J/(mol⋅K), and −15 kJ/mol respectively. Furthermore, the effects of temperature, chain length contrast, and concentration on the complexation of PAA with PVPON in DMF are studied. The work provides a theoretical method how to evaluate the ITC dada of hydrogen-bonding polymer complexation for thermodynamic analysis and strengthens the understanding of polymer complex.