Polymerization ROMP process

Olefin metathesis (olefin disproportionation) is the reaction of two alkenes in which the redistribution of the olelinic bonds takes place with the aid of transition metal catalysts (Scheme 7.7). The reaction proceeds with an intermediate formation of a metallacyclobutene. This may either break down to provide two new olefins, or open up to generate a metal alkylidene species which -by multiple alkene insertion- may lead to formation of alkylidenes with a polymeric moiety [21]. Ring-opening metathesis polymerization (ROMP) is the reaction of cyclic olefins in which backbone-unsaturated polymers are obtained. The driving force of this process is obviously in the relief of the ring strain of the monomers. 

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... 

Metathesis of alkenes is essentially a class of reactions where an interchange of C atoms between pairs of double bonds takes place. A few representative examples are shown by the reactions listed in Fig. 7.10. The industrial use of metathesis reactions so far has been limited mainly to exchange metathesis (Fig. 7.10, top, backward reaction) as in the SHOP process, and ring-open metathesis polymerization (ROMP). As already mentioned (Section 7.5), Vas-tenamer is a polymer made by Hulls by ROMP from cyclooctene. Similarly, the polymer from norborene by ROMP is manufactured by CdF Chemie and is sold by the trade name of Norsorex . 

The reaction is applied in industrial processes (Phillips triolefin process. Shell higher olefin process) and has importance in ring opening-metathesis polymerization (ROMP) in polymer chemistry [1]. In the past, olefin metathesis was not commonly applied in organic synthesis [2] because of the reversibility of the reaction, leading to olefin mixtures. In contrast, industrial processes often handle product mixtures easily. In ROMP, highly strained cyclic olefins allow the equilibrium of the reaction to be shifted towards the product side. 

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. 

These compounds are of particular interest as they have been shown to be active Ring Opening Metathesis Polymerization (ROMP) catalysts (see Metathesis Polymerization Processes by Homogeneous Catalysis). They are not, however, as effective as imido-based alkylidene systems (see next section). 

W(NAr)(=CHBuO(OR)2 (R = CMe(CF3)2, 50) are highly active catalysts for the metathesis of internal alkenes (equation 16), and also effect the stereoselective olefmation of hydroxy ketones (equation 17). The reactivity of these catalysts can be tuned by varying the aUcoxide ligands for example, when R = Bn, the complex acts only upon strained cyclic alkenes and is a highly effective ring-opening metathesis polymerization (ROMP) catalyst (see Metathesis Polymerization Processes by Homogeneous Catalysis). 

Figure 6.1 Examples of olefin metathesis processes. Ring-closing metathesis (RCM), cross metathesis (CM), acyclic diene metathesis polymerization (ADMET), and ring-opening metathesis polymerization (ROMP).

Grubbs, R. H., Khosravi, E. Ring-opening metathesis polymerization (ROMP) and related processes. Mater. Sci. Technol. 1999, 20, 65-104. 

Poly(l,4-butadiene) segments prepared by the ruthenium-mediated ROMP of 1,5-cyclooctadiene can be incorporated into the ABA-type block copolymers with styrene (B-106) and MMA (B-107).397 The synthetic method is based on the copper-catalyzed radical polymerizations of styrene and MMA from the telechelic poly(butadiene) obtained by a bifunctional chain-transfer agent such as bis(allyl chloride) or bis-(2-bromopropionate) during the ROMP process. A more direct route to similar block copolymers is based on the use of a ruthenium carbene complex with a C—Br bond such as Ru-13 as described above.67 The complex induced simultaneous or tandem block copolymerizations of MMA and 1,5-cyclooctadiene to give B-108, which can be hydrogenated into B-109, in one pot, catalyzed by the ruthenium residue from Ru-13. 

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