Organometallic oligomers

Sita, L. R. (1992) A new strategy for the synthesis of homologously pure linear polystannane oligomers, Organometallics 11,1442-1444. 

The reactions that predominate during the post-induction period where rapid polymerization occurs are given in Scheme 5.3 by eqn (5.3.1)-(5.3.4). Radicals (R ) entering solution from V-70 initiate polymerization of MA (eqn (5.3.1)), and the radicals in solution exchange with radicals in the dormant (TMP)Co-P complex by dissociative and associative pathways (eqn (5.3.2), (5.3.4)). In the specific case of the methyl acrylate oligomer organometallic complex ((TMP)Co-PMA) homolytic dissociation at 333 K is sufficiently fast to account for the observed low polydispersity. 

Oligomers Oppolzer s camphor sultam (see also camphor derivatives) Organometallics Organosilicon Organosulfur Organozirconocenes Orthoquinodimethanes Oxabutadienes Oxanorbornadiene(s) Oxazinolactams Oxazinones Oxazoles... 

The first series of soluble oligo(para-phenylene)s OPVs (20) were generated by Kern and Wirth 1331 and shortly thereafter by Heitz and Ulrich [34]. They introduced alkyl substituents (methyls) in each repeat unit and synthesized oligomers (20) up to the hexamer. Various synthetic methods, like copper-catalyzed Ullmann coupling, copper-catalyzed condensation of lithium aryls, and twofold additon of organometallic species to cyclohexan-l,4-dione, have been investigated. 

The authors developed two general methodologies for the synthesis of these monodisperse, defined oligomers. They can be built up stepwise, e. g. via additon of organometallic species to cyclohexan-1,4-dione, followed by aromatization to the oligoarylene (e.g. for 21). 

There is a current drive in microlithography to define submicron features in bilevel resist structures. The introduction of organometallic components, most notably organosilicon substituents, into conventional resists is one promising approach. To this end, organosilicon moieties have been primarily utilized in starting monomers (1-4) or in post-polymerization functionalization reactions on the polymer (5,6). Little work has been done on the reaction of preformed reactive oligomers to synthesize block copolymer systems. 

The first results of anionic polymerization (the polymerization of 1,3-butadiene and isoprene induced by sodium and potassium) appeared in the literature in the early twentieth century.168,169 It was not until the pioneering work of Ziegler170 and Szwarc,171 however, that the real nature of the reaction was understood. Styrene derivatives and conjugated dienes are the most suitable unsaturated hydrocarbons for anionic polymerization. They are sufficiently electrophilic toward carbanionic centers and able to form stable carbanions on initiation. Simple alkenes (ethylene, propylene) do not undergo anionic polymerization and form only oligomers. Initiation is achieved by nucleophilic addition of organometallic compounds or via electron transfer reactions. Hydrocarbons (cylohexane, benzene) and ethers (diethyl ether, THF) are usually applied as the solvent in anionic polymerizations. 

Organometallic macro cycles and cyclic polymers were prepared by the photolytic ring opening of a silicon-bridged ferrocenophane with a bipyridine initiator. The relative amounts of cyclic oligomers and cyclic polymer, as well as the molecular weight of the cyclic polymer, can be controlled by the reaction temperature [228]. 

In conclusion, for the most part, polymers incorporating phosphole units are still rare. However, the work described above demonstrates that they are accessible via a number of diverse synthetic routes including organometallic coupling or electropolymerization processes. The general property-structure relationships established with well-defined small oligomers have been shown to extend to the corresponding polymeric materials. 

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