Addition metathesis polymerization

The third class of olefin methathesis in Scheme 21.1 is addition metathesis polymerization (ADMET). This reaction is an alternative method to stitch together olefins into polymers, in this case by a combination of dienes with extrusion of ethylene. Control of molecular weight by the ADMET process is less precise than that by ROMP, but this reaction has been used to make polymers with precise architectures, such as polymers that would be perfectly alternating ethylene-propylene copolymers. ... 

Cyclic Polyolefins (GPO) and Gycloolefin Copolymers (GOG). Japanese and European companies are developing amorphous cycHc polyolefins as substrate materials for optical data storage (213—217). The materials are based on dicyclopentadiene and/or tetracyclododecene (10), where R = H, alkyl, or COOCH. Products are formed by Ziegler-Natta polymerization with addition of ethylene or propylene (11) or so-called metathesis polymerization and hydrogenation (12), (101,216). These products may stiU contain about 10% of the dicycHc stmcture (216). 

We have reported the first example of a ring-opening metathesis polymerization in C02 [144,145]. In this work, bicyclo[2.2.1]hept-2-ene (norbornene) was polymerized in C02 and C02/methanol mixtures using a Ru(H20)6(tos)2 initiator (see Scheme 6). These reactions were carried out at 65 °C and pressure was varied from 60 to 345 bar they resulted in poly(norbornene) with similar conversions and molecular weights as those obtained in other solvent systems. JH NMR spectroscopy of the poly(norbornene) showed that the product from a polymerization in pure methanol had the same structure as the product from the polymerization in pure C02. More interestingly, it was shown that the cis/trans ratio of the polymer microstructure can be controlled by the addition of a methanol cosolvent to the polymerization medium (see Fig. 12). The poly(norbornene) prepared in pure methanol or in methanol/C02 mixtures had a very high trans-vinylene content, while the polymer prepared in pure C02 had very high ds-vinylene content. These results can be explained by the solvent effects on relative populations of the two different possible metal... 

Efforts towards the synthesis of strained polycyclic hydrocarbons have been described. These compounds are of interest as fuels and fuel additives for advancedpropulsion. Chemistry has been devised for the attachment of azido functionality to the strained hydrocarbon nucleus. Highly unsaturated substituted cubanes have been synthesized. Ring-opening metathesis polymerization of basketene and 2,3-diazabicyclo[2.2.1]hept-2-ene has been studied. 

If the metathesis polymerization is performed in solution, the preferred solvents are methylene chloride or chlorobenzene. Preferably, the solvent is aprotic in order to avoid ionic side reactions. The molecular weight is controlled by the addition of an acyclic olefin, such as 1-butene (13). 

Basically, COCs can be manufactured by ring opening metathesis polymerization (ROMP) as described in the chapter about metathesis polymers. However, ROMP offers disadvantages as main chain double bonds must be hydrated after polymerization. Therefore, COCs are more conveniently straightforwardly prepared by addition polymerization. 

Mechanistic studies of the rearrangement activity of the ring-opening metathesis polymerization catalyst [Ru(H20)6]2+ were reported for unfunctionalized alkenes (112). The mechanism was found to be intermolecular, the alkene isomerization proceeding through an addition-elimination mechanism with a metal hydride catalytic species. This interpretation was... 

Experimental observations with the Ti(0- -Bu)4 + Et3Al catalyst support the insertion mechanism versus metathesis polymerization.412 Propagation occurs via the cis opening of the triple bond of the coordinated monomer, leading to addition to the Ti—C bond between the growing polymer chain and the catalyst center ... 

The Durham precursor route to polyacetylene is an excellent example of the application of organic synthesis to produce a precursor polymer whose structure is designed for facile conversion to polyacetylene. Durham polyacetylene was first disclosed by Edwards and Feast, working at the University of Durham, in 1980 227). The polymer (Fig. 6 (I)) is effectively the Diels-Alder adduct of an aromatic residue across alternate double bonds of polyacetylene. The Diels-Alder reaction is not feasible, partly for thermodynamic reasons and partly because it would require the polymer to be in the all m-conformation to give the required geometry for the addition to take placed 228). However, the polymer can be synthesised by metathesis polymerization of the appropriate monomer. 

Dienes are cyclized by intramolecular metathesis. In particular, cyclic alkenes 43 and ethylene are formed by the ring-closing metathesis of the a,co-diene 46. This is the reverse reaction of ethenolysis. Alkene metathesis is reversible, and usually an equilibrium mixture of alkenes is formed. However, the metathesis of a,co-dienes 46 generates ethylene as one product, which can be removed easily from reaction mixtures to afford cyclic compounds 43 nearly quantitatively. This is a most useful reaction, because from not only five to eight membered rings, but also macrocycles can be prepared by RCM under high-dilution conditions. However, it should be noted that RCM is an intramolecular reaction and competitive with acyclic diene metathesis polymerization (ADMET), which is intermolecular to form the polymer 47. In addition, the polymer 47 may be formed by ROMP of the cyclic compounds 43. 

Schrock, Gibson et al. [52d] found that styrene and 1,3-pentadiene could be used as chain transfer reagents for the living ring-opening olefin metathesis polymerization of norbornene with molybdenum based catalyst 35a. Renewed norbornene addition to a polymerization mixture containing initiator 35a and 30 equivalents of styrene resulted in the formation of polynorbomene with a low polydispersity and a molecular weight controlled by the number of norbornene equivalents in each of the individual monomer solutions, Eq. (38). This method allows a more efficient use of the catalyst. 

---