Association in solution and adsorption at an air-water interface of alternating copolymers of maleic anhydride and styrene

The behavior of alternating poly(styrene-maleic anhydride) (SMA) in aqueous solution and at the air-water interface was studied by static and dynamic light scattering, by surface tension measurements, and by transmission electron microscopy (TEM). The variables of interest were the polymer concentration, the molecular weight, and the degree of ionization varied with pH. SMA polymers can associate in aqueous solution. The critical size of SMA in solution ranges from the predicted Gaussian radius of gyration (r(g)) up to 150 nm. The size of the associates increases with decreasing molecular weight. A maximum in associate size was measured at pH = 6.5, which corresponds to the polymer salt under its monosodium form. A mechanism by which SMA molecules zip together forming a macrocoil made of two molecules in cross section was proposed. SMA molecules also adsorb at the air-water interface, very likely as 2D-coils. An equilibrium links the concentration of SMA in solution and at the air-water interface.