SWELLING SYNERESIS PHENOMENA IN GEL-FORMING INTERPOLYMER COMPLEXES/

Grafted poly(methacrylic acid-g-ethylene glycol) (P(MAA-g-EG)) copolym ers were synthesized and their pH sensitivity investigated as a functi on of copolymer composition and PEG graft molecular weight. Interpolym er complexation occurred by hydrogen bonding between carboxylic groups on poly(methacrylic acid) (PMAA) and ether groups on poly(ethylene gl ycol) (PEG). This complexation was sensitive to the surrounding enviro nment as complexes formed at pH levels low enough to insure substantia l protonation of PMAA acid groups. At high pH, the acid groups became neutralized and did not form complexes. P(MAA-g-EG) membranes showed p H-sensitivity due to complex formation and dissociation. Uncomplexed e quilibrium swelling ratios were much higher than those of the complexe d states and varied according to copolymer composition and PEG graft l ength. Mesh sizes in the two states were determined. Swelling under os cillatory pH conditions and constant ionic strength revealed the dynam ic sensitivity of P(MAA-g-EG) membranes. Under changing pH conditions, network syneresis (complexation) occurred more rapidly than network e xpansion (decomplexation) because of the rates of diffusion of specifi c ions causing the responses. No distinct water fronts were observed. Instead, water transport was continuous through the gel. These gels sh ow great promise for a number of biomedical applications where fast bi omaterial response is necessary.