Ring-opening polymerization cycloalkene

Fig. 4. Kinetic model of Calderon applied to the ring-opening polymerization of cycloalkenes.

Crotonaldehyde, hydrogenation of, 43-48 Cubane, isomerization of, 148 Cyclic dienes, metathesis of, 135 Cyclic polyenes, metathesis of, 135 Cycloalkenes, metathesis of, 134-136 kinetic model, 164 ring-opening polymerization, 143 stereoselectivity, 158-160 transalkylation, 142-144 transalkylidenation, 142-144 Cyclobutane configuration, 147 geometry of, 145, 146 Cyclobutene, metathesis of, 135 1,5,9-Cyclododecatriene, metathesis of, 135... 

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... 

Ivin, K. J., Cycloalkenes and Bicycloalkenes, Chap. 3 in Ring-Opening Polymerization, Vol. 1, K. I. Ivin and T. Saegusa, eds., Elsevier, London, 1984. 

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. 

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 ... 

It is generally accepted that ring-opening polymerization of cycloalkenes proceeds via metallocarbenes. Although less extensively studied, metathesis of alkynes... 

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. 

Most polymerizations of cyclic monomers are ionic processes. Coordination catalysts are effective only for some heterocycles (oxirane and its derivatives, lactones). Ziegler-Natta catalysts can only be used for cycloalkene polymerization by metathesis heterocycles act as a catalytic poison. Smooth radical polymerization of hydrocarbon monomers with ring strain is unsuccessful [304], The deep-rooted faith that ring strain represents a major contribution to the driving force in ring opening (polymerization) has to be revised [305, 306]. 

In the course of time it appeared that many olefinic substrates could undergo this reaction in the presence of a transition metal compound, such as substituted alkenes, dienes, polyenes, and cyclic alkenes, and even alkynes. Calderon et al. were the first to realize that the ring-opening polymerization of cycloalkenes, which they observed with their tungsten-based catalyst system [4], and the disproportionation of acyclic olefins are, in fact, the same type of reaction. They introduced the more general name metathesis [2], The metathesis reaction has now become a common tool for the conversion of unsaturated compounds. In view of the limited space this intriguing reaction is reviewed only briefly more information can be found in a detailed and extensive monograph [5]. 

The subjects Include fundamental and applied research on the polymerization of cyclic ethers, slloxanes, N-carboxy anhydrides, lactones, heterocycllcs, azlrldlnes, phosphorous containing monomers, cycloalkenes, and acetals. Block copolymers are also discussed where one of the constituents is a ring opening monomer. Important new discussions of catalysis via not only the traditional anionic, cationic and coordination methods, but related UV Initiated reactions and novel free radical mechanisms for ring opening polymerization are also Included. 

Ivin KJ, Saegusa T (1984) Cycloalkenes and bicycloalkenes ring-opening polymerization,... 

A similar mechanism has been postulated for reactions involving cycloalkenes. It has been shown that a copolymer of cyclooctene and cyclopentene (labelled on its double bond with is predominantly labelled in the C5 fragment, this result being obtained by reductive ozonolysis of the polymer [9j. The radioactivity found in the C5 diol proves that ring opening polymerization also proceeds via scission on the double bonds rather than cleavage of carbon—carbon single bonds. 

The disproportionation of olefins first reported by Banks and Bailey ) and - as a special case - the ring-opening polymerization of cycloalkenes 3) comprise a re-arrangement of the carbon skeleton of the olefins by opening and closure of double bonds. Thus the reaction - generally referred to as inetathosls reaction - is a trans-alkylidenation reaction. 

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. 

It has been shown that [(r]6-arene)RuCl2]2 6 and [(r 6-arene)RuCl2] PR3 7 complexes can be activated in situ to afford active metathesis catalysts, either on treatment with diazoalkanes [15] or by UV irradiation [16]. The structure of the active species thus formed is unknown, but it initiates the ring opening metathesis polymerization reactions (ROMP) of various cycloalkenes very efficiently. Therefore these in situ recipes may also be useful in the context of preparative organic chemistry. 

Polymerization of cycloalkenes through the double bond without ring opening occurs when initiators other than the ROMP initiators are used, including initiators based on various early transition (Ti, Zr, Hf, V), late transition (Pd, Ni), central transition (Cr, Co), and rare-earth (Ln) metals [Janiak and Lassahn, 2001]. This mode of polymerization is discussed in Secs. 8-lf and 8-6a. 

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. 

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