Equilibrium swelling of poly(methacrylic acid-g-ethylene glycol) hydrogels - Effect of swelling medium and synthesis conditions

Responsive hydrogel networks comprising a poly(methacrylic acid) (FMAA) backbone and oligomeric ethylene glycol (PEG) grafts were synthesized by free-radical solution polymerization and their equilibrium swelling properties were characterized in aqueous solutions of a homologous series of alcohols. These hydrogels are known to exhibit swelling transitions in response to external stimuli which lead to formation or disruption of hydrogen-bonded complexes between the backbone and the grafts. Swelling studies performed in aqueous mixtures of methanol, ethanol end propanol revealed thar the effectiveness of an alcohol in breaking the PMAA/PEG complexes increased as the aliphatic segment length of the alcohol was increased. These results confirm the importance of hydrophobic interactions for stabilizing the complexes. Studies performed to determine the effect of the synthesis conditions on the equilibrium swelling properties revealed that the equilibrium degree of swelling increased as the solvent fraction during synthesis was increased. Finally, molecular simulations revealed that it is sterically possible to form complexes with a 1:1 stoichiometry between chains of poly(methacrylic acid) and poly(ethylene glycol) with essentially no additional bond strain. (C) 1998 Elsevier Science B.V.