Graft terpolymers consist of a polymer backbone onto which are grafted two series of chemically dissimilar sidechains. Depending on monomer incompatibility, such terpolymers either order into periodic morphologies or remain microscopically mixed. Addition of a small quantity (<2 wt %) of dibenzylidene sorbitol, a smallmolecule gelling agent which self-associates through hydrogen bonding, to a homogeneous (Le., disordered) amphiphilic graft terpolymer results in a physical gel that exhibits two levels of structural organization. In this initial study, we report on the nature and evolution of such hierarchical order. Interactions between the gellant and terpolymer result in the formation of a fine percolation network comprised of fibrillar strands measuring 10-20 nm in diameter, as determined from scanning electron micrographs. Amorphous micrometersize spherules, similar in appearance to crystalline spherulites, subsequently develop through nucleation. Dynamic rheological measurements reveal that these two distinct levels of microstructural organization are (i) responsible for deformation mechanisms manifested at different strain levels and (ii) recoverable upon mechanical and thermal recycling. These polymer-rich gels constitute a new family of responsive materials which show promise in biomedical applications.Block and graft colterpolymers continue to receive considerable attention because they can be used commercially as adhesives,' compatibilizing agents,2 surface coating^,^ monoporous filters: and delivery system^.^ These materials, comprised of at least two dissimilar contiguous monomer sequences covalently bonded together, have also provided tremendous insight into the self-assembly of condensed matter.6-9 If the blocks or grafts are sufficiently incompatible, they undergo phase separation similar to that of the parent homopolymers. Due to the interblock covalent linkages, segmental mobility is restricted, and phase separation occurs on a much smaller size scale than that of immiscible blends.'O As a result of such enthalpy-or entropy-' driven microphase separation, a periodic microstructure forms, imparting the material with properties of its constituent blocks or grafts. If the contiguous monomer sequences are thermodynamically compatible, microphase segregation does not occur, and the colterpolymer remains disordered (i.e., microscopically homogeneous). Even in this state, however, the discrete blocks or grafts can strongly influence the morphology and localized interactions of an additive, such as a parent homopolymer.In contrast to the numerous studies of diblock and triblock copolymers, relatively few efforts have explored the phase behavior of block or graft terpolymers, composed of three chemically dissimilar monomer species, which are also capable of ordering into a variety of periodic morphologie~'~-'~ or remaining disordered. In this work, we have examined the effect of adding a small-molecule gelling agent, dibenzylidene sorbitol (DBS), to a homogeneous amphiphilic graft terpolymer which can be e...