Poly (acrylic acid) and poly (sodium styrenesulfonate) compatibility by Fourier transform infrared and differential scanning calorimetry

Blends of poly(acrylic acid) (PAA) and poly(sodium styrene sulfonate) (PSSNa) were prepared from polymer solutions by solvent evaporation. The observed decrease in PAA-solution pH upon addition of PSSNa suggests an inter-penetration of the two polymer chains, thus the polymer compatibility, in solution. The blend compatibility was studied with the attenuated total reflection-Fourier transform infrared (atr-FTIR) and the differential scanning calorimetry (DSC) techniques. The unique and composition-dependent glass transition temperature indicates that the two polymers are compatible, but the ΔTg broadening suggests a certain degree of nano-heterogeneity. The Tg of pure PSSNa which was non-detectable in DSC, was calculated from the Fox equation. From FTIR data, the polymer compatibility could be attributed to the establishment of hydrogen bonds, and dipole–ion interactions between carboxylic groups, sulfonate groups, and sodium ion on the polymer segments.