Structure and properties of the polyelectrolyte complex of chitosan with poly(methacrylic acid)

The structure and properties of the polyelectrolyte complex composed of chitosan (CS) and poly(methacrylic acid) (PMAA) were studied in aqueous solutions using UV‐visible transmittance measurements, a fluorescence probe technique, and transmission electron microscopy. The thermal properties of the solid complex were measured using differential scanning calorimetry. The results showed that the complex optimum molar ratio (in monomer unit) of CS to PMAA is 1:4 at pH = 4.0, that is, there is an optimum complex between CS and PMAA when the feed ratio (in molar monomer unit) of CS to PMAA is 1:4 and an ionic bond between the amino ion group and carboxylate group can be formed on average every four carboxylate (or carboxyl) groups. The conformation of PMAA changed from a hypercoiled to a loose coil on complexation, and the pH‐ and salt‐sensitive range of the polyelectrolyte complex was obviously different from that of CS or PMAA. The formation process of the complex under various external conditions is discussed in detail. Transmission electron microscopy revealed that the sizes of CS–PMAA complex particles increased with increasing pH or salt concentration, and a change in morphology of the complex was observed. Thermal analysis further revealed that there was a change of structure and properties on blending in aqueous solutions.