WATER SORPTION BEHAVIOR AND SOME PROPERTIES OF POLY(L-LYSIN) POLY(GLUTAMIC ACID) COMPLEX FILMS

Polyion complex films of poly(L-lysine) (PL) with poly(glutamic acid) (PGA) were prepared by casting from 60% aqueous formic acid solution. Their water-sorption behavior and some physical properties were examined. The degree of swelling in water was minimal when the molar ratio of the repeating units of PL/PGA was 5/5. The larger the molar ratio of PL, the larger the degree of swelling in acidic solution, whereas in basic solution the film with large molar ratio of PGA showed little increase in the degree of swelling. The addition of electrolytes in water influenced the water absorption behavior of polyion complex films. Especially for the films of 3/7 and 1/9 ratios, the degree of swelling decreased remarkably with the addition of CaCl2. IR-Spectra showed a new absorption band at 1630 cm-1 for the complex films of 3/7, 5/5, and 7/3 ratios, which was assigned to cross-linking bond formation. In C-13 NMR spectra, the broadest widths at half-height of the peaks at 50 and 170 ppm were observed for the complex film of 5/5 molar ratio, which meant motion restriction by cross-linking of the PL-PGA complex. DSC studies showed that the larger PL content samples had higher temperatures of solidification and melting, and also showed the presence of bound water absorbed in the films of 3/7 approximately 7/3 molar ratios.