Cyclic dienes ring-opening metathesis polymerization

This intramolecular reaction results in the formation of a cyclic system, and therefore it is called ring-closing metathesis (RCM). In this process a diene 36 is treated with a metal alkylidene 37. Two competing pathways are available via the intermediate metal alkylidene 38 A) RCM will occur to afford cyclic adducts 39 and B) intermolecular reaction can occur to form polymeric structures 40 (acyclic diene metathesis polymerization (ADMET)). The reaction is also complicated because of the possibility of ring-opening metathesis (ROM), the retro reaction of path A, and ring opening metathesis polymerization (ROMP) (path C).13... 

Unsaturated polymers can be produced by means of ring-opening metathesis polymerization (ROMP) of cyclic alkenes. These unique polymers can also be produced via intermolecular Acyclic Diene Metathesis (ADMET). Dienes can also react intramolecularly via Ring Closing Metathesis (RCM) to afford cyclic products. RCM is often applied to synthesis of compounds for fine chemical and pharmaceutical application. Generic examples of these reactions are shown in Figure 2. 

ADMET polymerization is performed on a,co-dienes to produce strictly linear polymers with unsaturated polyethylene backbones, as shown in Scheme 2. This step-growth polymerization is a thermally neutral process driven by the release of a small molecule condensate, ethylene [16-20]. Ring-opening metathesis polymerization (ROMP) is widely used to polymerize cyclic olefins and is performed with the same catalysts as in ADMET polymerizations. 

Recently special interest in the Schrock carbenes, especially those of Ta, Mo, W, Re, and Ru, have been focused on the stereospecific polymerization of the cyclic olefins or dienes which is called a ring opening metathesis polymerization (ROMP), A typical example of ROMP is shown in the following equation [18]. 

A large number of applications involve the synthesis of polymers by either ring-opening metathesis polymerization (ROMP), which transforms cyclic olefins into unsaturated polymers (Fig. 4.14) [46,47], or acyclic diene metathesis polymerization (ADMET), which converts acyclic olehns into polymers (Fig. 4.15)... 

In 1991 we introduced olefin metathesis as a tool for direct synthesis of PV polymers and copolymers [2]. In general, two ways exist for a metathesis chain growth process ring opening metathesis polymerization of a cyclic olefin (ROMP) and metathesis polycondensation of an acyclic diene (ADMET). We have tested both possibilities (s. Eqs. 1 2) [2-5]. A stable, tungsten based Schrock-type alkylidene complex W(=NPh - ) (=CHPh"- ) [OCMe(CF3)2l2 (THF) (described by Grubbs et al [6]) served as catalyst (Scheme 1). 

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... 

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]. 

Provided the double bonds are not conjugated, cyclic dienes undergo ring opening polymerization [9]. The metathesis of cyclopentadiene, 1,3-cyc-looctadiene and 1,3,5-cycloheptatriene has not been achieved. 

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