Organic-Organometallic Block Copolymers

Issues regarding the self-assembly of organic-organometallic block copolymers in thin films and applications of the resulting nanoperiodic patterns are discussed in this section. 

Lammertink, R.G.H., Hempenius, M.A., van den Enk, J.E., Chan, V.Z.H., Thomas, E.L., Vancso, G.J. Nanostructured thin films of organic-organometallic block copolymers one-step lithography with poly(ferrocenylsilanes) by reactive ion etching. Adv. Mato. 12, 98 (2000)... 

Fig. 16 Tapping mode AFM height image of an etched PI-6-PFS organic-organometallic diblock copolymer film. The dots are a result of the block copolymer phase separation. Reprinted with permission from [7]. Copyright 2000, American Chemical Society...

Acrylate monomers do not generally polymerize by a cationic mechanism. However, the anionic polymerization of acrylic monomers to stereoregular or block copolymers is well known. These polymerizations are conducted in organic solvents, primarily using organometallic compounds as initiators. 

Polyferrocenylsilane block copolymers in which the blocks are immiscible (which is generally the case) would be expected to self-assemble to form phase-separated organometallic domains in the solid state. Based on the classical behavior of organic block copolymers, thin films of polyferrocene diblock copolymers would be expected to form domains such as spheres, cylinders, double diamonds (or gyro-ids) (or their antistructures), or lamellae (Chapter 1, Section 1.2.5). The preferred domain structure would be expected to be controlled by the ratio of the blocks, their degree of immiscibility (as defined by the Flory-Hu ins interaction parameter x), and the overall molecular weight of the block copolymer [159]. 

Phosphazene polymers comprise a class of several hundred different macromolecules with the general formula shown in Structure 1, where R represents organic, organometallic or inorganic side groups. Two structural factors can be varied for these polymers. First, the basic skeletal architecture varies from linear polymers or block copolymers to stars, dendrimers, combs, cyclolinear or cyclomatrix structures. Second, more than 250 different side groups have been linked to the various skeletons. Most of the polymers that have been studied in detail are linear macromolecules of type 1 or block copolymers formed between 1 and classical organic polymers. 

Synthesis of Organometallic—Organic Block Copolymers Well-defined block copolymers can be synthesized by sequential anionic polymerizations. The living end of the first polymeric block must be reactive enough to initiate the polymerization of the second block. 

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