Feast monomer

As an alternative, copolymerization of alkynes bearing bulky substituents with TCDTF6 (7,8-bis(trifluoromethyl)tricyclo [4.2.2.0 ]deca-3,7,9-triene) was carried out. In the course of this copolymerization, usually referred to as the Durham Route [86-89], the Feast-monomer was introduced into the polymer main chain and subsequently converted into three unsubstituted, conjugated double bonds via a thermally-induced retro-Diels Alder reaction (Scheme 3) [53]. 

The first hving polymerization of cyclic olefins with a high ring strain [28], such as norbomenes, norbornadienes (bicyclohepta-2,5-dienes, NBDs) or the Feast-monomer 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 ]deca-3,7,9-triene (TCDTFj) by W(N-2,6 i Pr2 C6H3)(CH- Bu)(OCMe(CF3)2) [34] was re-... 

A potential drawback of all the routes discussed thus far is that there is little control over polydispersity and molecular weight of the resultant polymer. Ringopening metathesis polymerization (ROMP) is a living polymerization method and, in theory, affords materials with low polydispersities and predictable molecular weights. This methodology has been applied to the synthesis of polyacctylcne by Feast [23], and has recently been exploited in the synthesis of PPV. Bicyclic monomer 12 [24] and cyclophane 13 [25) afford well-defined precursor polymers which may be converted into PPV 1 by thermal elimination as described in Scheme 1-4. 

In agreement with Flory s predictions, hyperbranched polymers based on A,jB monomers reported in the literature exhibit a broad molecular weight distribution (typically 2-5 or more). The polydispersity of a hyperbranched polymer is due to the statistical growth process. A strategy to overcome this disadvantage is to add a By-functional core molecule, or a chain terminator, which Hmits the polydispersity and also provides a tool to control the molecular weight of the final polymer. The concept of copolymerizing an A2B monomer with a B3 functional core molecule was first introduced by Hult et al. [62] and more recently also utilized by Feast and Stainton [63] and Moore and Bharathi [64]. 

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. 

Andrews and Feast d have described a further application of the Patemo-Buchi reaction in which furans are used in step-growth polymerization. Irradiation of m-dibenzoylbenzene and furan produced the monomeric 2 1 adduct (182), which was polymerized further with m-dibenzoylbenzene to produce polymers containing isomeric oxetane units. The step-growth polymerization in this case was limited by low monomer solubility, slow oxetane formation, and hydrogen abstraction processes that led to crosslinking. 

Since little anti-form is present under equihbrium conditions (without irradiation) in Mo(NAr )(CHR)(OCMe(CF3)2)2, and syn- into anti-conversion is slow (ca. 10 s ), cis-polymers are proposed to form from the syn-species of a catalyst via olefin attack on the CNO-face of the initiator [94]. In a t-butoxide system, where interconversion is relatively fast (ca. 1 s ), it was proposed that the anti-form was the only propagating alkylidene species. This proposal was further supported by studies carried out by Feast and co-workers [100]. Using sterically hindered and therefore unreactive monomers such as 1,7,7-trimethylnorbornene, only the reaction of the anti-rotamer at a very slow, monomer concentration-independent rate was observed. Additionally, the calculated rate constant was essentially identical with the one for syn-anti[Pg.165]

Compounds 19 (Makovetsky 1992a), 22 (Gunther 1970) and 23 (Feast 1980) do not polymerize, probably because their free energy of polymerization is positive. However, the fact that 1% of 19 can completely inhibit the polymerization of 20 and 21 indicates that it is likely to add preferentially to the active site forming the head carbene complex, [W](=CMeCH2CH2CH2CH=CHR), which is then unable to add any of these three monomers. It should be capable of copolymerization with norbomene. 3- and 4-Alkenylcyclopentenes have been tested as chain transfer agents for the ROMP of norbomene, but without much success (Schrock 1989). 

The ROMP of the dicyano analogue of 139, also the tricyclic monomer having [CH2C(CN)2C(CN)2CH2] attached to the 5,6-positions, can be initiated by 149a, the latter giving a 97% trans polymer (Feast 1995). 

---