Cycloalkenes polymers

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 of alkyl- or aryl-substituted cycloalkenes provides a route to certain perfectly alternating copolymers. For example, metathesis of 5-methylcyclooctene leads to a polymer that may be considered as a... 

A chloro-substituted cycloalkene, 1-chloro-l, 5-cyclooctadiene, has also been converted by metathesis into a polymer, the perfectly alternating copolymer of butadiene and chloroprene (29). 

The inhibitory effects of polar functional groups are not nearly as pronounced when the substituent is attached to a strained cycloalkene, where the release of ring strain provides a significant driving force for its metathesis. The norbornene ring system polymerizes easily by ring opening thus, numerous functionalized polymers have been prepared by the sequence depicted in Eq. (61). Many of these polymers hold some potential for commercialization and hence the bulk of this work is reported in the patent literature. 

Initially the polymer molecular weight distribution obeys a Poisson distribution, typical of a chain growth reaction without chain transfer. Since the reactions are reversible, at a later stage, also the equilibration between the polymers becomes important and a broad distribution of molecular weights is obtained. As can be seen from Figure 16.5 the presence of linear alkenes causes chain termination (chain transfer) and thus low molecular weights are produced if the cycloalkenes are not sufficiently pure. 

ROM-RCM of cycloalkene-yne 119 having a substituent at the 3-position of the cycloalkene would give a polymer because ruthenium carbene complex XVlll generated in this reaction could react with the starting alkyne. If this reaction is carried out under ethylene gas, the cyclized compound 120 should be formed by the reaction of XVlll with ethylene [Eq. (6.88)]. On the basis of this idea, ROM-RCM-CM of cycloalkene-yne 119 was carried out under ethylene gas " ... 

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... 

The polymerization of the alkyne triple bond (Secs. 5-7d and 8-6c) and ring-opening metathesis polymerization of a cycloalkene (Secs. 7-8 and 8-6a) yield polymers containing double bonds in the polymer chain. Cis-trans isomerism is possible analogous to the 1,4-polymer-ization of 1,3-dienes. 

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... 

The stereochemistry of ring-opening polymerizations has been studied for epoxides, episul-fides, lactones, cycloalkenes (Sec. 8-6a), and other cyclic monomers [Pasquon et al., 1989 Tsuruta and Kawakami, 1989]. Epoxides have been studied more than any other type of monomer. A chiral cyclic monomer such as propylene oxide is capable of yielding stereoregular polymers. Polymerization of either of the two pure enantiomers yields the isotactic polymer when the reaction proceeds in a regioselective manner with bond cleavage at bond 1. 

In the polymerization of cycloalkenes, not only linear polymers, but also cyclic oligomers are formed. These reactions are thus examples of ring/chain equilibriums, but their mechanism is not yet fully clarified. 

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. 

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 ... 

According to this mechanism, olefin metathesis is a chain reaction with the carbene as chain carrier. It predicts complete randomization of alkylidene fragments from the first turnover. An important additional feature is that both metathesis and ringopening polymerization of cycloalkenes can be explained by this mechanism, which provides ready explanation of polymer molecular weight. 

Ziegler-Natta catalysts are not active at all in polymerization of disubstituted acetylenes.415 Mo- and W-based systems (for alkynes with small substituents) and Nb- and Ta-based catalysts (for alkynes with bulky groups), in turn, are very effective catalysts used to convert disubstituted acetylenes into polymers with very high molecular weight.414 415 A polymerization mechanism similar to that of metathesis polymerization of cycloalkenes are supported by most experimental observations.414 423 424... 

The extent of HT bias in the polymers of substituted cycloalkenes is very dependent on (i) the location and nature of the substituent(s), and (ii) the catalyst. Monomers with a substituent at the double bond generally give strongly biased polymers with most catalysts. For example, 1-methylcyclobutene with W(=CPh2)(CO)5 gives an 85% cis polymer with HH HT TT = 1 8 l294. The presence of one or two substituents at the a-position results in fully biased polymers with some but not all catalysts. When the substituent(s) are further removed from the double bond there is usually very little HT bias in the polymer. 

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. 

Oxidations of hydrocarbons (cycloalkanes, cycloalkenes, aromatics) photo-catalyzed by metallotetrapyrroles lead to the formation of epoxides, aldehydes, ketones, alcohols, and carboxylic acids both in solutions and polymer matrices. These processes frequently occur as selective (one-product formation) reactions. Irradiation with visible light has a pronounced accelerating effect on such important industrial processes as the oxidation of thiols to disulfides (Merox process [265]) in a treatment of petroleum distillates or waste water cleaning. 

In 1970, Chauvin and Herisson presented a study of the co-metathesis of cycloalkene/alkene mixtures using a WOCLj/SnBuj pro-catalyst mixture [12]. Whilst the fully quantitative analysis of the product mixtures was made complicated by the range of techniques that were required for the low, medium and high molecular weight products (mono alkenes, telomers and polymers), it became clear that product ratios were not consistent with what would be predicted by either mechanism in Scheme 12.14. The analysis and associated mechanistic interpretation were seminal and worthy of consideration in some detail here. The key point is that both mechanisms in Scheme 12.14 are pairwise, i.e. each turnover of the catalyst cycle involves two alkenes that undergo concerted alkylidene exchange. When a single alkene, e.g. pent-2-ene (C5), is considered, the products of alkylidene metathesis... 

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. 

An interesting case is the coordination polymerisation of acetylene and higher alkynes. It may proceed by a mechanism quite similar to the metathesis polymerisation of cycloalkenes involving metal carbene and metallacycle (metallacyclobutene) species [45], The initiation and propagation steps in alkyne polymerisation (leading to a polymer of cis structure) in the presence of a catalyst with a diphenylcarbene initiating ligand are as follows ... 

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). 

Alternating polymers can be produced by taking advantage of the functional group tolerance, high activity, and chemoselectivity of 3. Copolymerization of cycloalkenes such as cyclooctene or cyclopentene with diacrylates affords regular alternating polymers (Eq. 15) [32]. Based on the different reactivity of the two monomers (class 1 and class 2, respectively) the more... 

Remarkable development over the last 10-15 years in the synthesis of well-defined functional-group-tolerant ruthenium carbenes (Grubbs-related catalysts) also caused real development of the metathesis-based reactions in organosilicon polymers. For recent reviews on metathesis of organosilicon compounds see Refs. [6,7]. Unsaturated organosilicon polymers can be synthesized via ruthenium carbene catalyzed ring-opening metathesis polymerization (ROMP) of silylsubstituted cycloalkenes (Eq. 113). 

By ring-opening polymerization, polymers can formed from cycloalkenes, but mostly from simple and more complicated heterocycles containing heteroatoms such as O, N, S, P and Si. Ring-opening polymerizations are mostly initiated by the ionic mechanism. 

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