Norbornenes ring-opening metathesis polymerization

Scheme 5.12 Chain-end control in norbornene ring-opening metathesis polymerization.

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

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... 

Scheme 6. Ring-opening metathesis polymerization of norbornene in C02 [144,145]...

Much better results were obtained when dendronized structures were prepared via ring opening metathesis polymerization (ROMP) of norbornene... 

The living character of the ring opening metathesis polymerization described earlier in this review enables a simple preparation of functionalized norbornene-based monoliths. Adding one more in situ derivatization step that involves functional norborn-2-ene and 7-oxanorborn-2-ene monomers that react with the surface-bound initiator, the pores were provided with a number of typical functional groups such as carboxylic acid, tertiary amine, and cyclodextrin [58,59]. 

Ring-Opening Metathesis Polymerization (ROMP) of Norbornene by a Group VIII Carbene Complex in Protic Media, S.T. Nguyen, L.K. Johnson, R.H. Grubbs, et al, J. Am. Chem. Soc. 1992, 114, 3974-3975. 

The norbornene derivative is polymerized by a ring opening metathesis polymerization, followed by a hydrogenation reaction. The polymers can be used for optical disks, optical lenses, and optical films or sheets. 

With the discovery of ruthenium carbene complexes as highly effective catalysts for olefin metathesis under mild reaction conditions [233,234], the scope of ring-opening metathesis polymerization could be extended to include functionalized and sensitive monomers. The resulting (soluble) polymers have been used as supports for simple synthetic transformations [235-237]. Insoluble polymers have been prepared by ringopening metathesis copolymerization of norbornene with l,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene. These polymers have been used as supports for ruthenium carbene complexes [238]. 

Rhenium complex (37) has been used in the ring-opening metathesis polymerization of strained alkenes such as norbornene.37 The alkenes of the polymer backbone are predominantly Z, the polymer exhibiting high molecular weight and poly-dispersity. 

Norbornene polymerization was initiated selectively on the surface of SWCNTs via a specifically adsorbed pyrene-linked ring-opening metathesis polymerization initiator (Fig. 1.20). The adsorption of the organic precursor was followed by cross-metathesis with a ruthenium alkylidene, resulting in a homogeneous noncovalent poly (norbornene) (PNBE) coating [249]. 

Fig. 12. Cationic norbornene as a charged-tag for detection by ESI-MS of ruthenium species involved in ring-opening metathesis polymerization (69].

Enholm [13] has also described the synthesis of soluble designer supports by the ring-opening metathesis polymerization (ROMP) of norbornyl derivatives. Reduction of norbornene-l-carboxaldehyde 88 to the corresponding alcohol 89, followed by treatment with either 2-bromopropionic acid or 2-bromo-2-phenylacetic acid in the presence of DCC, provided the esters 90 or 91 respectively (Scheme 19). Polymerization of 90 and 91 was carried out with Grubbs catalyst and halted after 25 s by capping with excess ethyl vinyl ether to give polymers 92 and 93 respectively. 

There are three different mechanisms by which the cyclic olefin norbornene can be polymerized to reasonably high molecular weights ring-opening metathesis polymerization (or ROMP), vinyl addition copolymerization with acyclic olefins such as ethylene, and vinyl addition homopolymerization (see Fig. 4.2). Carbocationic and free-radical initiated polymerizations are ignored since they yield only low molecular weight oligomers [8]. 

The sheer activity of these new nickel norbornene polymerization catalysts and their very rapid polymerization rates makes them potential catalysts for a new nor-bornene-RIM (reaction injection molding) technology to afford a saturated, oxidatively stable RIM part rather than the unsaturated ROMP (ring-opening metathesis polymerization) polymer that is the current commercial Telene or Metton . Fig. 4.6 illustrates the concept and also exemplifies the very rapid polymerization rates that are observed. 

Complex 17 shows versatile reactivity in both catalytic and stoichiometric reactions. It is a catalyst for olefin metathesis, in which a metallacyclobutane is proposed to be a key intermediate [52]. Grubbs et al. successfully isolated titanacyclobutanes 18 by treatment of 17 with alkenes in the presence of a Lewis base such as dimethylaminopy-ridine [56,57]. When cyclic olefins such as norbornene are treated with a catalytic amount of 18, ring opening metathesis polymerization occurs [58]. 

The ring opening metathesis polymerization (ROMP) of norbornene by the OsO. complex has been reported recently [261]. The key intermediate is considered to be an oxaosmacyclobutane whose C—C and Os—O bonds can open to form an osmium alkylidene species (Scheme 10.30). 

Grubbs and co-workers reported the ring-opening metathesis polymerization (ROMP) of norbornene derivatives in water using Ru(H20)6(ts)2 as the catalyst [127, 128]. More recently, these authors have described the first example of a homogeneous living polymerization in water using a water-soluble ruthenium carbene [Eq. (24)] [129]. 

Matyjaszewski et al. demonstrated that living ring opening metathesis polymerization (ROMP) could also be combined with ATRP to produce novel block copolymers [292]. ROMP of norbornene (NB) and dicyclopentadiene (CPD) were performed using an Mo-alkylidene complex, followed by reaction with p-(bro-momethyl) benzaldehyde to generate a benzyl bromide terminated polymer capable of being used as a macroinitiator for ATRP (Scheme 41). 

Ring-opening metathesis polymerization was also used recently for the preparation of amphiphilic star-block copolymers [25]. Mo (CH-f-Bu) (NAr) (0-f-Bu)2 was used as the initiator for sequential polymerization of norbornene-type, unfunctionalized and functionalized, monomers. The living diblocks were reacted with endo-ris-endo-hexacyclo- [ 10.2.1.1.3/115>8.02>l 1. O 1-9] heptadeca-6,13-diene, a difunctional monomer in a scheme analogous to the use of DVB in anionic polymerization, to form the central core of the star (Scheme 10). 

Polymers for use in 193 nm lithography are co-, ter-, and tetra-polymers of 1) methacrylates, 2) norbornenes, 3) norbornene-maleic anhydride, 4) nor-bornene-sulfur dioxide, and 5) vinyl ether-maleic anhydride (Fig. 39). While 1), 3), 4), and 5) are prepared by radical polymerization, all-norbornene polymers 2) are synthesized by transition-metal-mediated addition polymerization [166-168].Norbornenes (Fig.40) are sluggish to undergo radical [168,169] and cationic [170] polymerizations. Their ring-opening metathesis polymerization (ROMP, Fig. 40) [ 171 ] has never produced worthy resist polymers. The C=C double bonds introduced in the ROMP polymer backbone must be hydrogenated to reduce the 193 nm absorption and the ROMP polymers tend to have low Tg. However, the major problem for the ROMP polymers was their unacceptable swelling in aqueous base development. While polymethacrylate systems contain etch-resistant alicyclic structures in the ester side chain, norbornene-based systems carry the alicyclic unit in the backbone. Essentially all the 193 nm re-... 

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