SORPTION OF LOW-MOLECULAR-WEIGHT ANIONS INTO THIN POLYCATION LAYERS GRAFTED ONTO A FILM

We have investigated the sorption of low-molecular-weight anions, which have different numbers of -SO3 groups per molecule, into a polycation thin layer grafted onto the surface of a poly(ethylene terephthalate) (PET) film a simultaneous UV irradiation method. The anions used are dyes including C.I. Acid Orange 7 (mono-SO3), C.I. Acid Red 26 (di-SO3), and C.I. Acid Red 27 (tri-SO3). The cationic monomers used for surface graft polymerization are N-[3-(N,N-dimethylamino)propyl]acrylamide (DMA-PAA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The sorption of anions to the cationic polymer layer grafted onto the film surface was carried out at different temperatures and pH's using PET films with various graft densities. The sorption isotherms followed the Langmuir equation. The interaction between the cationic units in the grafted layer and the -SO3 groups in the anions proceeded quantitatively at a 1:1 ratio, even for the tri-SO3 anion which contains three -SO3 groups per molecule. The activation energy of sorption for mono-SO3 into the cationic grafted layer was as small as 9 kcal.mol-1. These results indicate that the densely grafted polycation chains on the surface of PET film are highly mobile in the water-swollen state, allowing the 1:1 binding of the low-molecular-weight anions to the cationic chains. The surface density of cationic polymer chains grafted onto the PET film determined by gravimetry was in good accordance with that determined spectrophotometrically after sorption of anions to the grafted PET film.