Norbornene functional monomers

In 2010, Buchmeiser [56] developed a similar system that capitalized on the thermally reversible carboxylation [11] of NHCs (Scheme 31.13, inset). By employing the NHC-CO2 adduct (which essentially is a protected NHC), the reaction conditions did not have to be stringently air- and moisture-free to prevent NHC decomposition. Synthesis of the norbornene-functionalized monomer 37 allowed the molybdenum-catalyzed ROMP with l,4,4a,5,8,8a-hexahydro-l,4,5,8-exo-ewdo-dimethanonaphthalene (a ditopic norbornene) to produce crossHnked polymer 38 with pendant CO2-masked NHCs (Scheme 31.13). Upon heating in the presence of Rh, Ir, or Pd species, the NHC-metal-functionalized polymers 39 were formed and found to contain >20mol% metal, as determined with inductively coupled plasma optical emission spectrometry (ICP-OES). The C02-masked NHC material was found to catalyze the carboxylation of carbonyl compounds and the trimerization of isocyanates upon thermal deprotection (i.e., decarboxylation). Moreover, the NHC-metal-crosslinked materials were found to catalyze Heck reactions, transfer hydrogenations, and also the polymerization of phenylacetylene (M = 8.4 kDa, PDI = 2.45, as determined with GPC in DMF against PS standards). This modular system provides an array of options for catalysis from simple modifications of polymer-supported, C02-masked NHCs. 

BF Goodrich s patents US 5,569,730 (29 Oct 1996) and US 5,571,881 (5 Nov 1996) further erode the mystique of metallocene catalysts in making specially polyolefins, specifically for norbornene-functional monomers. Unique catalyst systems that catalyze the insertion of chain-transfer agents exclusively at a terminal end of a polymer chain are used to produce addition polymers from norbornene-functional monomers. These catalyst systems, in common with DuPont s, are based on nickel or palladium. There are two noteworthy factors firstly, the nickel or palladium can be present as simple compounds such as the bromides, oxides, acetylacetonates, or 2-ethylhexanoates secondly, and perhaps more surprisingly, these catalysts are activated by the same activators as are the metallocenes. 

The first documented example of the living ROMP of a cycloolefin was the polymerization of norbornene using titanacyclobutane complexes such as (207) 510-512 Subsequent studies described the synthesis of di- and tri-block copolymers of norbornenes and dicyclopentadiene.513 However, functionalized monomers are generally incompatible with the highly electrophilic d° metal center. 

Alternatively a non-metallated chelating monomer such as (227) or (228) may be copolymerized with (223) and the metal introduced post-polymerization. Using this strategy nanoclusters of silver,615 gold,616 ZnS617 and CdS618 have been prepared. A related approach has recently been adopted with the ROMP of norbornenes functionalized with crown ether, (229),619 and triazacy-clononane, (230),620 substituents. 

Sinner and Buchmeiser prepared a new class of functionalized monolithic stationary phases (norbornene monoliths) by a ROMP process that tolerates a huge variety of functional monomers [69]. They used this approach in order to chemically attach (3-cyclodextrin onto the monomer prior... 

In the same way, dipyridyl amide-functionalized supports suitable for the SPE of metal ions from aqueous solutions can be prepared. The resins are synthesized via the copolymerization of the functional monomer endo-norbornene-5-yl-N,N-di-2-pyridyl carboxylic amide with a molybdenum-based catalyst (42). Essentially no loss of performance was observed after extensive use over more than twenty cycles. After exposure to air for at least 2 months, a change in color from bright white to yellow was observed. However, this change in color did not influence the characteristic properties of the resins. 

The (co-)polymerization of functional monomers was also explored with the Ni and Pd catalyst systems. The multi-component Ni catalyst (Ni(O2CR)2 -i-HSbFg-i-OBFs LlyO-i-lOAlLlj) works very well for the copolymerization of norbornene and 5-triefhoxysilylnorbornene. The copolymerization of norbornene and with 5-10 mol% 5-triethoxysilylnorbomene monomers yields a high molecular weight copolymer of fhe same molar composition in excellent yield (85%) at a 4000 1 monomer to nickel molar ratio. 

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). 

A series of patents were issued to DuPont in the mid-1970s that covered the terpolymerization of ethylene, propylene, and functional monomers. The catalyst employed was a soluble VCl4/AlEt2Cl in combination with hexachloropropene as a catalyst activator. The functional comonomers studied included 2-hydroxy-5-norbornene, 2-hydroxymethyl-5-norbornene, allylsulfonyl chloride, 2-allylphenol, and... 

A series of [2.2.1]bicycloheptenyl (norbornene) functional prepol)nners have been prepared via the cycloaddition reaction of cyclopentadiene monomer with corresponding acrylics. When these materials are formulated with an appropriate multifuntional thiol crosslinker and photoinitiator and irradiated, a rapid, exothermic, crosslinking reaction takes place. When the acrylic precursors are organic resins, the derived polymers behave like toughened plastics. The choice of a norbornene functional polydimethylsiloxane precursors gives elastomeric products. 

Figure 2.7 Synthesis of HBP with pendent norbornene functionalities via RAFT polymerisation of a novel asymmetrical divinyl monomer. Adapted with permission from Z-M. Dong, X-H. Liu, X-L. Tang and Y-S. Li, Macromolecules, 2009, 42, 13, 4596. 2009, American Chemical Society [49]...

Figure 6 Polymerization of bioactive functionalized monomers using polar mixed reaction solvents, (a) Polymerization of unprotected carbohydrate-functionalized oxanorbornene monomers, (b) Poiymerization of cyclooctene monomers bearing sulfated carbohydrates using highly active catalyst 9. (c) Peptide-functionalized norbornene monomers were polymerized using defined cataiyst 10. DCE, 1,2-dichloroethane Pbf, 2,2,4,6,7-pentamethyl-dihydrobenzofuran-5-sulfonyi.

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... 

The first report of ROMP activity by a well-characterized Mo or W species was polymerization of norbornene initiated by W(CH-t-Bu)(NAr)(0-f-Bu)2 [122]. In the studies that followed, functionality tolerance, the synthesis of block copolymers, and ring-opening of other monomers were explored [30, 123]. Two important issues in ROMP concern the cis or trans nature of the double bond formed in the polymer and the polymer s tacticity. Tacticity is a consequence of the presence of two asymmetric carbons with opposite configuration in each monomer unit. The four ROMP polymers (using polynorbornene as an example) that have a regular structure are shown in Scheme 3. 

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]. 

Monomers with UV-absorbing functionality, such as shown in Figure 1.11 can be copolymerized with norbornene to have the UV-absorber bond to the polymeric backbone. (4-(Bicyclo[2.2.1]hept-5-en-2-ylmethoxy)-2-hydroxyphenyl)phenyl-methanone is prepared by first synthesizing 4-allyl-2-hydroxyphenyl-phenyl-methanone... 

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]. 

---