Graft copolymers with regularly spaced, tetrafunctional branch points: Morphology and grain structure

An investigation of the morphological behavior of a series of graft copolym ers having multiple regularly spaced, tetrafunctional branch points has bee n carried out. The behavior of these materials, comprised of polyisoprene b ackbones with two polystyrene arms grafted to the backbone at each branch p oint, is shown to be effectively modeled by considering the behavior of sma ller, architectural subunits based on the local environment of each junctio n point (constituting block copolymer). Morphological behavior was characte rized using TEM and SAXS. Well-ordered cylindrical and lamellar morphologie s were observed. Several samples appear to form cylindrical domains in diso rdered arrangements. Samples predicted to form spheres form instead a micro phase-separated "mesh" morphology. Lamellar grain size and shape were also investigated, and lamellar grain orientation correlation lengths were deter mined. These measurements show a decrease in grain size with increasing num ber of branch points per molecule. They also indicate that the grains forme d are anisotropic in shape.