The binding of dodecyltrimethylammonium bromide (DTAB) to poly(maleic acid-co-alkyl vinyl ether) has been investigated by means of potentiometry and fluorescence probing, using pyrene as a probe, as a function of the length of the copolymer alkyl chain (methyl, ethyl, butyl, hexyl, decyl, and hexadecyl; these copolymers being referred to as PS1, PS2, PS4, PS6, PS10, and PS16, respectively) and for PS1, PS2, and PS4 as a function of the copolymer neutralization degree, alpha, concentration, and the ionic strength. The binding has been found to be cooperative for PS1 and PS2 in the whole range of alpha. It is still cooperative with PS4 at alpha greater-than-or-equal-to 0.75 but becomes anticooperative at alpha less-than-or-equal-to 0.5. It is anticooperative for PS6, PS10, and PS16 even at alpha = 1.00. For PS1 and PS4 the cooperativity parameter, u, and the binding constant, K, are independent of the copolymer concentration, within the experimental error. Upon increasing ionic strength, u increases for PS1 but appears to decrease for the more hydrophobic PS4. These results are compared to those reported in the literature. The change in the nature of the binding with the copolymer alkyl chain length is discussed in terms of the difference in free energies for the binding of an oncoming surfactant ion to a copolymer site where it interacts with another bound surfactant and for a binding site where it interacts with copolymer alkyl chains. This difference decreases and changes sign as the length of the alkyl chain increases. The existence of hydrophobic microdomains in the solutions of copolymers with long alkyl chains is taken into account.
