Poly cycloalkenes 195

Poly(cycloalkene)s obtained from the vinyl addition polymerization method exhibit extremely high melting points. The high melting points make the polymers unprocessable. For this reason, comonomers, such as ethene or propene are introduced to lower the melting points. Copolymers of this type are addressed as COCs. 

Terminally unsaturated fluonnated alkenoic acids can be obtained from poly-fluorocycloalkenes by reaction with potassium hydroxide m rert-butyl alcohol [24] (equation 26) The use of a tertiary alcohol is critical because primary and secondar y alcohols lead to ethers of the cycloalkenes The use of a polar aprotic solvent such as diglyme generates enols of diketones [26] (equation 27) The compound where... 

Since then, the metathesis reaction has been extended to other types of alkenes, viz. substituted alkenes, dienes and polyenes, and to alkynes. Of special interest is the metathesis of cycloalkenes. This gives rise to a ring enlargement resulting in macrocyclic compounds and eventually poly-... 

Cycloalkenes undergo ring-opening polymerization in the presence of coordination initiators based on transition metals to yield polymers containing a double bond, for instance, cyclo-pentene yields polypentenamer [IUPAC poly(pent-l-ene-l,5-diyl)] [Amass, 1989 Cazalis et al., 2000, 2002a,b Claverie and Soula, 2003 Doherty et al., 1986 Ivin, 1984, 1987 Ivin and Mol, 1997 Ofstead, 1988 Schrock, 1990, 1994 Tmka and Gmbbs, 2001], The... 

Polymers containing rings incorporated into the main chain (e.g., by double-bond polymerization of a cycloalkene) are also capable of exhibiting stereoisomerism. Such polymers possess two stereocenters—the two atoms at which the polymer chain enters and leaves each ring. Thus the polymerization of cyclopentene to polycyclopentene [IUPAC poly(cyclopen-tane-l,2-diyl)] is considered in the same manner as that of a 1,2-disubstituted ethylene. The... 

A closely related special case of metathesis is the conversion of cycloalkenes under metathesis conditions, known as ring-opening polymerization or metathesis polymerization (see Section 12.2). Macrocyclic polyenes and polymers, called poly-alkenamers, are formed with high stereoselectivity ... 

In poly(l-pentenylene) the chemical shifts of the -carbons are about 0.5 ppm upfield from those in the polymers of the other cycloalkenes, an effect which is attributed to a higher proportion of gauche conformations about the CH2—CH2 bonds arising from the influence of the y-olefinic carbons347. 

On stirring at room temperature ozonides of terminal alkenes (prepared in dichloromethane at — 70 °C) with a polymer-supported tertiary amine obtained from chloromethylated poly(styrene/divinylbenzene) and piperidine, followed by filtration and concentration under reduced pressure, the products (aldehydes or ketones) can be obtained easily in almost pure form in high yields <2003T493>. However, yields are low for cycloalkenes because apparently they form monomeric and polymeric ozonides. 

However, cz s-isotactic and cz s-syndiotactic polymers have been obtained predominantly from common cycloolefins such as cyclopentene the 1,3-insertion isomerisation-polymerisation of cycloalkenes such as cyclopentene farely yields polymers with a trans structure (usually in an amount not exceeding 3%) [15,19,20], Figure 6.2 shows both cw-isomers of poly(l,3-cyclopentylene). 

Pseudonitrosites and a-nitro ketone oximes were identified as intermediates in this process. This route has since been developed to provide access to mono- and poly-cyclic furoxans from readily-available alkenes and cycloalkenes. Treatment of the alkene with dinitrogen trioxide affords the nitro-nitroso adduct, which is readily isolated as its nitroso dimer (pseudonitrosite) thermal isomerization to the a-nitro ketone oxime, followed by dehydration with cyclization leads to the furoxan (Scheme 19). 

With a few exceptions, 1,2-disubstituted alkenes are not polymerized because of steric hindrance. The exceptions include 1-deuteropropene (Sec. 8-4g) and cycloalkenes. Polymers are obtained from some 1,2-disubstituted alkenes, but the reactions involve isomerization of the monomer to a 1-alkene prior to polymerization, e.g., 2-butene yields poly( 1-butene) [Endo et al., 1979]. There is one report of polymerization of frans-2-butene to poly(frans-2-butene) using the a-diimine nickel initiators described in Sec. 8-8b [Leatherman and Brookhart, 2001]. 

The metathesis reaction of cycloalkenes yields linear unsaturated polymers, so-called polyalkenamers. This ROMP is driven by the release of ring strain in the starting material. Several interesting polymers are commercially produced via the ROMP of different types of unsaturated cyclic monomers such as cyclooctene, norbornene, and dicyclopentadiene, using homogeneous catalyst systems [6]. As an alternative process, the cross-metathesis between a cyclic and an acyclic olefin allows to synthesize certain poly-unsaturated compounds for the special chemical market. Shell [7] developed the FEAST process for the manufacture of hexa-l,5-diene via cross-metathesis of cycloocta-1,5-diene with ethene. 

When used with monomers such as alkynes, metathesis initiators afford poly-conjugated polymers. The reaction mechanism is similar to that of cycloalkene polymerization, with the reaction intermediate being here a metalacyclobutene ... 

In spite of the thermal instability of the (E)-isomers, the enantiodifferentiating photoisomerization of smaller-sized cycloalkenes has been investigated to some extent. Photosensitization of (Z)-cyclohexene (13Z) with chiral benzene(poly)carboxylates affords trans-anti-trans-, cis-trans-, and cis-anti-cis-[2 + 21-cyclodimers (16). Interestingly, only the trans-anti-trans product is optically active, and the ee reaches up to 68% ee, for which the enantiodifferentiating photoisomerization of 13Z to optically active (El-isomer 13E and the subsequent stereospecific concerted addition to 13Z are responsible. In contrast, the cis-trans photoadduct is formed through the stepwise cyclization via a biradical intermediate, losing the original chiral information in 13E. ... 

---