Poly metathesis catalyst

Initially alkynes were polymerised by trial and error with the use of Ziegler type recipes and the mechanism for these reactions may well be an insertion type mechanism. Undefined metathesis catalysts of ETM complexes were known to give poly-acetylene in their reaction with alkynes (acetylene) [45] and metallacycles were proposed as intermediates. Since the introduction of well-defined catalysts far better results have been obtained. The mechanism for this reaction is shown in Figure 16.24 [46], The conductive polymers obtained are soluble materials that can be treated and deposited as solutions on a surface. 

Poly (acetylenes) [16], There are several catalysts available for polymerization of substituted acetylenes. Whereas Ziegler-Natta catalysts are quite effective for polymerization of acetylene itself and simple alkylacetylenes, they are not active towards other substituted acetylenes, e.g. phenylacetylenes. Olefin-metathesis catalysts (Masuda, 1985 Masuda and Higashimura, 1984, 1986) and Rh(i) catalysts (Furlani et al., 1986 Tabata, 1987) are often employed. In our experience, however, many persistent radicals and typical nitrogen-containing functional groups serve as good poisons for these catalysts. Therefore, radical centres have to be introduced after construction of the polymer skeletons. Fortunately, the polymers obtained with these catalysts are often soluble in one or other organic solvent. For example, methyl p-ethynylbenzoate can be polymerized to a brick-coloured amorph- See the Appendix on p. 245 of suffixes to structural formula numbers. 

In 1975, it was discovered that WCk, which is a typical metathesis catalyst, is capable to catalyze the polymerization of phenylacetyl-ene. Subsequently, various substituted acetylenes have been polymerized by this type of catalyst. In 1983, poly(l-(trimethylsilyl)-l-propyne)) was synthesized in the presence of Tads and NbCls (35). The alkyne polymerization has many similarities with ROMP. 

Scheme 17. Formation of poly(arylenethynylene)s via a tungsten-carbyne metathesis catalyst.

Scheme 12.3 The homodifunctional unimolecular cyclization of poly(THF) using Grubbs metathesis catalyst [27].

Poly(alkenamers) are produced by ring-opening polymerization of cycloolefins with metathesis catalysts (see Chapter 19). The industrially used name for this class of compounds is based on a lUPAC nomenclature that has since been superceded. These compounds are classified as poly( 1-alkenylenes) according to present lUPAC nomenclature. Poly(pentenamers) and poly-(octenamers) are presently being developed. 

Matron and Grubbs formed block copolymers by combining ring opening metathesis polymerization with ATRP [437]. Use was made of fast initiating ruthenium metathesis catalyst to form three different monotelechelic poly(oxa)norbomenes. The ends were functionized and ATRP polymerizations of styrene and ferf-butyl acrylate followed. 

The monomer 7-methylnorbornadiene (7-MeNBD) also undergoes polymerization in the presence of several conventional metathesis catalysts to form poly(7-MeNBD). It is noteworthy that the catalyst OSCI3 (in 1 1 EtOH/PhCl) leads to polymer stereochemistry that is significantly different from that of poly(fl fi-7-MeNB). The OsC -derived polymer of the monoolefin contains predominantly atactic trans olefin structures, whereas the analogous diolefin polymer is composed of nearly exclusively cis alkene structures (97%) and predominantly syndiotactic dyads (r m = 75 25 through the NMR signals of the methyl substituent at 8 16.2-17.0 ppm)." The catalysts Reds... 

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