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 sca ttering (SAXS). Both series of materials have monodisperse polybutadie ne (PB) backbones and monodisperse polystyrene (PS) graft blocks. In o ne series there are on average five trifunctional junction points rand omly distributed along the PB backbone. Each junction point grafts one PS block to the backbone. In the other series there are on average fo ur tetrafunctional junction points randomly distributed along the PB b ackbone. Each junction point grafts two PS blocks to the backbone. A r ange of overall PB and PS volume fractions was investigated for both s eries. These materials simulate a controlled and known degree of archi tectural disorder. Current theory cannot rigorously predict the morpho logical behavior for these complex molecular architectures. However, i t 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 morphol ogy in these materials. The materials form the domain shape (spheres, cylinders, or lamellae) which is predicted by theory, but spherical an d cylindrical morphologies lack the long-range lattice order found in diblocks and other simpler block copolymer molecular architectures. Wh en lamellar morphologies are formed, however, at least some long range order is always present due to the space filling requirements of the lamellar domains.