Complexation between poly (styrene-co-methacrylic acid) and polyquaternium for use in shampoo formulations

The complexation between poly (styrene-co-methacrylic acid) (P(St-co-MAA)) and a series of cationically substituted quaternary ammonium derivatives of hydroxyethylcellulose, JR and LR (polyquaternium) was investigated through the viscosity change of the complexes at different mixing ratios of the two poly-mers. The performance of the shampoo containing the complexes was also evaluated. The results show that the viscosity of the mixed aqueous solution increased as the ratio of (P(St-co-MAA)) to JR or LR increased. The maximum viscosity was obtained when the molar ratio (r) of St in P(St-co-MAA) to cations in polyquaternium was near 1. As the mixing ratio increased further, syneresis occurred when the charge stoichiometry between MAA and the quaternary ammonium cation was 1:1. This result reveals that cation -n electron interactions rather than electrostatic attraction play a key role in forming complexes between polyquaternium and P(St-co-MAA). The higher the molecular weight of polyquaternium is, the higher the viscosity of the complex solution. The complexes maintained a large apparent viscosity at a temperature of 70 degrees C, a shear rate of 1 s-1 and a NaCl concentration of 1.2 mol/L. The complexes had good tolerance to temperature, salt and shearing. The addition of the complexes in shampoo was beneficial to thickening, which is difficult in amino acid anionic surfactant systems. Compared with the shampoo containing the polyquaternium normally, the addition of P(St-co-MAA) helped to generate more flocculation earlier during washing of the hair. Unexpectedly, the wet carding performance of the shampoo was significantly better than that of commercial silicon-containing shampoo (P < 0.01). The complex has potential as a thickener and a conditioner in shampoo formulations.(c) 2023 Elsevier B.V. All rights reserved.