Self-assembly of acrylic triblock hydrogels by vapor-phase solvent exchange

We investigate the self-assembly of poly(methyl methacrylate)-poly(methacrylic acid)-poly(methyl methacrylate) triblock copolymers by a vapor-phase solvent-exchange mechanism. Two acrylic triblock copolymers were synthesized with different hydrophilic/hydrophobic block ratios. Hydrogels were formed by exposing the solutions to saturated water vapor. As water diffuses into the solution, the hydrophobic end-blocks form aggregates that are bridged by the hydrophilic mid-blocks. Structure formation in the gels was characterized by small angle X-ray scattering, and swelling was measured in controlled pH buffer solutions. The solvent exchange process occurs while the methacrylic acid group remains in the protonated state. After swelling to equilibrium in water or controlled pH buffers, strong gels are formed with polymer-weight fractions between 0.01 and 0.15, and with shear moduli between 0.6 kPa and 3.5 kPa. Porous gels were produced by adding salt crystals to the polymer solution prior to solvent exchange. Salt was then leached out by immersing the gel into water. Structures of the porous hydrogels were characterized by confocal laser scanning microscopy.