Cyclic trimer substitution-polymerization

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

Linear poly(organophosphazenes) are now synthesized by six different methods. These are (a) The ring-opening polymerization of (NPC12)3 mentioned above, followed by macromolecular substitution (b) Ring-opening polymerization of organic substituted phosphazene cyclic trimers, usually followed by macromolecular substitution ... 

Thus, the second approach to the synthesis of poly(organophosphazenes) involves the introduction of the organic (or organometallic) side groups at the cyclic trimer level, followed by ring-opening polymerization of the substituted cyclic trimer to the high polymer (reaction (ll)).23... 

Poly(phosphazenes) are also synthesized by a ring-opening polymerization of the cyclic trimer followed by substituting the chlorines with nucleophiles as shown below ... 

Compounds RB(0H)2 polymerize to cyclic trimers only, in contrast to R2Si(OH)2 which give polymeric linear siloxanes compare the formation of only one cyclic metaborate ion, 8306 . The formation of 6-membered rings is a prominent feature of boron chemistry, as in boroxine (p. 862) and the numerous substituted... 

The linear species are accessible mainly via two reaction pathways — a ringopening polymerization followed by macromolecular substitution, or a living cationic condensation polymerization usually also followed by macromolecular substitution. The most common manifestation of both of these routes is to use either cyclic trimeric (2) (see Scheme 1), or monomeric (3) starting materials that have chlorine atoms linked to phosphorus, and to replace these chlorine atoms in... 

These isocyanurates, normally called trimers, exhibit the characteristic spectra of the isocyanurate carbonyl groups in the infrared, the main band of which occurs at 5 85-5 92 fim. Other interesting and useful features of the isocyanates include their ability (i) to form thermally labile adducts (ii) to give higher molecular weight adducts in which some free isocyanate groups remain and (iii) to give rise to cyclic dimers and trimers. Anionic polymerization of aryl isocyanates to yield substituted polyamides is also possible ... 

Decomposition products of this latter reaction are the corresponding borazines, and polymeric or cyclic dimeric and trimeric B—N compounds, depending on the side chain substitution pattern. 

So far, discussions of the ROP of cyclic phosphazenes have been limited to halo-genated rings. Yet, there was a desire to develop a simplified route to poly(organophosphazenes) by performing nucleophilic substitution chemistry on the more labile trimer followed by polymerization this had the advantage that, in general, the substitution chemistry would be quicker and easier when performed... 

Substitution of the bidentate ferrocenyl fluorinated trimer with sodium 2,2,2-trifluoroethoxide yielded the expected trimer with the fluorines completely displaced (Scheme 4.12). Subsequent direct polymerization of this trimer at 250°C for 14 days failed to yield any polymer, although higher oligomeric cyclic compounds were detected. However, the addition of 1 mol% hexachlorocyclotriphosp-hazene as a catalyst resulted in polymerization of the trimer. 

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