Self‐Assembled Acrylic ABA Triblock Copolymer Hydrogels with Various Block Compositions: Water Absorbency,Rheology, and SAXS

A series of well‐defined symmetric poly(methyl methacrylate)‐b‐poly(sodium methacrylate)‐b‐poly(methyl methacrylate) (PMMA‐b‐PSMA‐b‐PMMA) triblock copolymers with various block compositions is synthesized. The amphiphilic ABA triblock copolymers form polyelectrolyte hydrogels in water by self‐assembly. The hydrophobic PMMA endblocks act as physical cross‐links in the form of frozen micelles, while the hydrophilic PSMA midblocks span the 3D network. The influence of various synthetic parameters on the self‐assembly and the macroscopic properties of these hydrogels is systematically investigated by water absorbency, oscillatory shear rheology, and small‐angle X‐ray scattering. The polymer concentration during the hydrogel formation affects the ratio between looping and bridging chains. The number of MMA units per endblock (n_A) determines the size and the relaxation rates of the physical cross‐links and thus, the mechanical stability of the hydrogels. More SMA units in the midblock (n_B) increase the water absorbency, while the mechanical moduli decrease. Even lower G‐moduli are achieved by partly exchanging the symmetric ABA triblock with AB diblock copolymers, which can only form non‐elastic dangling ends.