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Ternary poly (A-Block-B-Block-C) block copolymers as structurally controlled matrices of new polymeric transition metal complexes

This project deals with complex formation of transition metal compounds in polydienes, when the polydienes are one block of a ternary triblock copolymer, namely polystyrene-block-polybutadiene-block-poly(methyl methacrylate). Only few work has been done in the field of ternary triblock copolymers, so that in addition to the modification of the already synthesized triblock copolymers by transition metal compounds, some theoretical work on the morphological behaviour of these systems had to be carried out.

The initial idea of this project was the introduction of catalytically active sites into microdomains of a ternary block copolymer. However, it turned out that already small amounts of transition metal compunds are sufficient to alter the thermodynamic balance between the different adjacent blocks completely. Rather than maintaining the morphology of the original unmodified block copolymer, the modified block copolymer showed another morphology. While an unmodified block copolymer with a polybutadiene middle block showed a lamellar morphology of the outer polystyrene and poly(methyl methacrylate) blocks with polybutadiene spheres between them, the same system showed a gyroid morphology, when being modified slightly by a Palladium complex and transformed into a cylindrical morphology when being modified with an Iron complex. This experimental result was interpreted as an indication of induction of an increasing curvature into the intermaterial dividing surface by an increasing asymmetry of the interactions between the middle and the outer blocks.

Theoretical work dealt with the influence of one block onto the miscibility of the two other blocks in an ABC triblock copolymer. This was done by two different approaches. While in one case a simple approach in the strong segregation limit was used to show an increasing compatibility between the two outer blocks due to a conformational entropy gain of the strongly incompatible middle block, another work in the weak segregation limit analysed the phase behaviour for diblock copolymers attached to a strongly incompatible point like third block (where this third block could be located both at the end of the diblock or betwenn the two blocks). Also in these cases situations could be found, where the third block enhances miscibility of the two other blocks. These theoretical works confirmed the experimental results, according to which the morphologies in ternary block copolymers are much more sensitive towards chemical modifications as compared to the morphologies of diblock copolymers.

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