NEW ORDERED MORPHOLOGIES IN ABC TRIBLOCK COPOLYMERS

The morphology of well-defined poly(styrene-b-ethylene-co-1-butene-b-methyl methacrylate) (P(S-b-EB-b-MMA)) triblock copolymers of molecular weights of approximately 2 x 10(5) has been investigated by transmission electron microscopy. The fraction of the midblock varies, while the ratio of the outer blocks is kept approximately constant. A block copolymer with 38 wt % EB shows a lamellar morphology. Hitherto unknown morphologies were observed in the triblock copolymers with lower EB content. Regular EB cylinders located at the interface of PS and PMMA lamellae are formed at a level of 17 wt % EB. The triblock copolymer with 6 wt % EB shows PS cylinders dispersed in a PMMA matrix. The cylinders are covered with small isolated EB rings. These unexpected highly ordered structures result from the strong incompatibility between the EB midblock and the outer blocks compared to the weak incompatibility between the PS and PMMA end blocks. The reduction in interfacial free energy is the driving force which stabilizes these morphologies. Such a dominance of the relative incompatibilites of the components in controlling the overall morphology of triblock copolymers has not been reported so far.