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 morpholog ies or remain microscopically mixed. Addition of a small quantity (<2 wt%) of dibenzylidene sorbitol, a small-molecule gelling agent which s elf-associates through hydrogen bonding, to a homogeneous (i.e., disor dered) amphiphilic graft terpolymer results in a physical gel that exh ibits two levels of structural organization. In this initial study, we report on the nature and evolution of such hierarchical order. Intera ctions 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. A morphous micrometer-size spherules, similar in appearance to crystalli ne spherulites, subsequently develop through nucleation. Dynamic theol ogical measurements reveal that these two distinct levels of microstru ctural organization are (i) responsible for deformation mechanisms man ifested at different strain levels and (ii) recoverable upon mechanica l and thermal recycling. These polymer-rich gels constitute a new fami ly of responsive materials which show promise in biomedical applicatio ns.