Morphology of model graft copolymers with randomly placed trifunctional and tetrafunctional branch points

The morphologies of two series of model graft copolymers were studied using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Both series of materials have monodisperse polybutadiene (PB) backbones and monodisperse polystyrene (PS) graft blocks. In one series there are on average five trifunctional junction points randomly distributed along the PB backbone. Each junction point grafts one PS block to the backbone. In the other series there are on average four tetrafunctional junction points randomly distributed along the PB backbone. Each junction point grafts two PS blocks to the backbone. A range of overall PB and PS volume fractions was investigated for both series. These materials simulate a controlled and known degree of architectural disorder. Current theory cannot rigorously predict the morphological behavior for these complex molecular architectures. However, it is found that an approximate extension of existing theory utilizing the constituting block copolymer (fundamental building block) concept allows a rational explanation of the effect of architecture on morphology in these materials. The materials form the domain shape (spheres, cylinders, or lamellae) which is predicted by theory, but spherical and cylindrical morphologies lack the long-range lattice order found in diblocks and other simpler block copolymer molecular architectures. When lamellar morphologies are formed, however, at least some long range order is always present due to the space filling requirements of the lamellar domains.