Investigation of Interpolymer Complexation Between Poly(Vinylcaprolactam) and Poly(Maleic Acid-Alt-Styrene)

The interactions between two synthetic polymers used in biomedical applications, maleic acid-styrene copolymer (MAc-St) and poly(vinylcaprolactam) (PVCL), were investigated in dilute aqueous solution considering the influence of the pH, the added salt and the ratio between the components in the mixture. Hydrogen-bonding interactions between the COOH groups of MAc-St and the C═O groups of PVCL, together with hydrophobic interactions are involved in the formation of the interpolymer complex. The complex is insoluble below pH = 2.85 in aqueous solution, but the addition of NaCl enlarged the pH domain where the precipitation of the complex occurred. When the ratio between the polymers was varied, two maxima of the optical density were obtained: at a 1:1 ratio between the COOH and caprolactam groups, and also at a lower ratio (1:3). Other investigations, like the measurements of the turbidity in situ during mixing, and fluorescence, viscometric and potentiometric measurements were performed in order to understand these interactions. The phase separation of the thermosensitive poly(vinylcaprolactam) in the presence of MAc-St was also studied. The cloud point and the phase transition profile were found to be influenced by the amount of polyacid, as well as by the pH.