EVIDENCE OF HIERARCHICAL ORDER IN AN AMPHIPHILIC GRAFT TERPOLYMER GEL

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 small-molecule gelling agent which self-associates through hydrogen bonding, to a homogeneous (i.e., 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 micrometer-size spherules, similar in appearance to crystalline spherulites, subsequently develop through nucleation. Dynamic theological 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.