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

An investigation of the morphological behavior of a series of graft copolymers having multiple regularly spaced, tetrafunctional branch points has been carried out. The behavior of these materials, comprised of polyisoprene backbones with two polystyrene arms grafted to the backbone at each branch point, is shown to be effectively modeled by considering the behavior of smaller, architectural subunits based on the local environment of each junction point (constituting block copolymer). Morphological behavior was characterized using TEM and SAXS. Well-ordered cylindrical and lamellar morphologies were observed. Several samples appear to form cylindrical domains in disordered arrangements. Samples predicted to form spheres form instead a microphase-separated 'mesh' morphology. Lamellar grain size and shape were also investigated, and lamellar grain orientation correlation lengths were determined. These measurements show a decrease in grain size with increasing number of branch points per molecule. They also indicate that the grains formed are anisotropic in shape.