STATISTICAL N-BUTYL ACRYLATE (SULFOPROPYL)AMMONIUM BETAINE COPOLYMERS.5. PLASTICIZATION STUDIES

The influence of additives of strongly different polarities such as di butyl phthalate (DBP), ethylammonium nitrate (EAN), or water on the mo rphology of zwitterionomers of n-butyl acrylate (A) and (3-methacrylam idopropyl)-1-(3-sulfopropyl)ammonium betaine (B) has been studied by d ifferential scanning calorimetry (DSC) and small-angle X-ray scatterin g (SAXS). In the case of a clustered copolymer (F(B) (molar fraction) = 0.11), addition of DBP as a selective solvent of A units (W(DBP) (we ight fraction) < 0.7) results in simultaneous plasticization of the so ft matrix (T(g)S,p approximately 237-183 K) and of the hard zwitterion ic domains (T(g)H,P approximately 330-260 K) without significant redis tribution of A and B units: the DBP partition coefficient K, which mea sures the plasticizer fraction located in the matrix, is always in fav or of a weakly preferential sorption of the additive by the matrix and slightly increases with the overall DBP content (K approximately 0.84 -0.96). According to SAXS analysis (Bragg spacings corresponding to th e ''ionic'' peak in the range 6-10 nm), the plasticization process dif fers only slightly from an isotropic homogeneous swelling of the syste m. Addition of EAN or water as a selective solvent of B units (number of polar additive molecules per zwitterionic unit <2.2) results in a f airly similar and nearly selective plasticization of the zwitterionic domains (T(g)S,p approximately 237-232 K, T(g)H,p approximately 330-25 0 K) with simultaneous reorganization of the B units: the rather stron g increase of the Bragg spacings (d approximately 6-10 nm) suggests a reduction of the number of zwitterionic multiplets and an increase of their size and of their aggregation number.