ROMP modification

ROMP is not the most suitable method if fatty acids are used as feedstock because of the low ring strain of the ensuing unsaturated cyclic monomers. Thus, for vegetable oils to participate in ROMP, modification of fatty-acid chains is necessary, and this can be achieved by coupling fatty-acid derivatives with conventional unsaturated cyclic building blocks [18, 56]. 

Figure 7. Synthesis of ROMP neoglycopolymers by post-ROMP modification.

In the present study PPO-AGE copolymers have been obtained using as initiators TIBA H20 and various cocatalysts, in a first step, and then grafted by ROMP with cyclooctene in the presence of Grubbs first-generation Ru catalyst, in a subsequent step. Future experiments will be directed at grafting other cycloolefins by ROMP onto PPO-AGE copolymer, and also at extending the same ROMP modification approach to copolymers prepared from epichlorohydrine-AGE and epichlorohydrine-PO-AGE. 

Recently, Caster et al. described the surface modification of multifilament fibers such as nylon or Kevlar [70]. Coating techniques using preformed ROMP-based polymers and process contact metathesis polymerization (CMP), initially described by Grubbs et al. [71], were both used. The latter involves a procedure where the initiator is physisorbed onto the surface of a substrate and fed with a ROMP-active monomer that finally encapsulates the substrate. These modified fibers showed improved adhesion to natural rubber elastomers. 

Triphenyl phosphine is an example of a gel modification additive that acts to retard the rate of reaction, when the catalyst has tricyclo-alkylphosphine ligands. The catalyst with tricycloalkylphosphines ligands is much more active in ROMP than when the ligands would be triphenyl phosphines. 

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. 

Poly(p-arylene vinylene)s were synthesized with low molecular weight via the Horner-Emmons modification of the Wittig reaction [12] and via the precursor route [13]. Efforts to synthesize poly(p-anthrylene vinylene) via a Heck reaction failed [15]. We chose ROMP followed by a dehydrogenation step to produce poly(2-alkyl-9,10-anthrylene vinylene) as has been shown before for poly(l,4-naphthylene vinylene) by Pu et al. [16]. The initiator used was the Schrock molybdenum carbene shown in Figure 1 and our goal was to produce a soluble poly(anthrylenevinylene). 

It has been demonstrated that ROMP represents a highly versatile tool in the preparation and modification of functional polymer supports. The use of well-defined initiators allows the highly reproducible preparation of tailor-made materials in particular in terms of functionalization. Various polymerization techniques such as precipitation- and graft-polymerization may be applied. In due consequence, the use of suitable polymerizable ligands allows the synthesis of well-defined heterogeneous supports. 

H roguez et al. [17] carried out a tandem ROMP of NBE and ATRP of MMA in aqueous heterogeneous systems (Scheme 2.4). In contrast to a mini-emulsion route, this approach avoids the modification step of the initiator 6 to render it water soluble. Despite incomplete monomer conversions (60-80%), well-defined particles with diameters ranging from 20 to 50 nm were prepared. PNBE/PMM A homopolymer blend particles showed a core - shell structure, while... 

Due to it s highly efficient and orthogonal nature, copper-catalyzed click chemistry is an attractive route to post-polymerization functionalization of ROMP copolymer backbones yielding amphiphilic micellar nanoparticles [103, 104]. However, it should be noted that post polymerization modification is necessary to yield azide or acetylene modified polymers, as azide and acetylene functionalities are not compatible with current ROMP catalysts. Ohe and coworkers [104] have synthesized amphiphihc triblock copolymers capable of assembly into discrete micellar nanoparticles by clicking an acetylene-modified hexaethylene... 

Figure 8.5 Strategies to combine AAC and ROMP, (a) A prefunctionalized monomer that contains a metathesis-compatible triazole can be employed, (b) Post-polymerization modification of a halogenated polymer with sodium azide and further elaboration...

The copper-catalyzed azide/alkyne click reaction has found the broadest application in the modification of ROMP polymers, with the first reported example in 2004 by Binder and Kluger [13]. Since then, the copper-catalyzed click reaction has been used for the preparation of block copolymers [24, 29, 37], stars [18, 26], cycles [23], networks [25], and graft copolymers [27, 28, 38, 56, 57], as well as for end- [16] and side-chain-functionalized polymers [13, 17, 19-22, 48]. The most often used catalysts and bases for the azide/alkyne click reaction include copper(l) iodide, copper(l) bromide, trisftriphenylphosphine) copper(l) bromide, or copperfll) sulfate/sodium ascorbate as catalyst and diisopropylethylamine (DIPEA), pentamethyldiethylenetriamine (PMDETA), or 2,2 -bipyridine (bPy) as base. 

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