## 4 Supported Catalysts in Ring-opening Metothesis Polymerization (ROMP)
An early report of the use of a PIB-supported catalyst was part of a study of a polyisobutylbenzylidene-supported Ru catalyst that was used in ring closing metathesis. That work showed that this \"boomerang\" catalyst could be used in ROMP with _ca._ 3% leaching of the charged Ru [50]. Subsequently in 2012, a more effective Ru separation was achieved by the use of PIB-supported catalyst **45** in ROMP of norbornene derivatives as described in a report by [PERSON] and [PERSON] [65]. The catalyst **45** can be separated from the polymer product at the end of the reaction by dissolving the dry crude mixture of polymer and PIB-supported catalyst in an equi-volume mixture of DMF and heptane. The catalyst-containing heptane layer was then removed and the DMF layer was then evaporated to dryness to afford the crude polymer as an off-white solid. The crude polymer was dissolved in dichloromethane (DCM) and precipitated into an excess amount of hexane to afford the polymer product ready for analysis for properties and ruthenium contamination level. Polymers prepared from catalyst **45** have a nearly identical \(E/Z\) ratio to those prepared by their low molecular weight counterparts with PDI values ranging from 1.39 to 1.78. The amounts of ruthenium content in the resulting polymers were 111-228 ppm. In subsequent work by [PERSON] and [PERSON], the activities and recoverability of a PIB-supported Grubbs second generation catalyst **63** formed from PIB with an \(M_{\text{n}}\) of 1000 Da (Figure 11) in ROMP was studied [66] in a polymerization of norbornene (Scheme 8). The polymerization rate of norbornene using **63** was 93% which is similar to that of its low molecular weight counterpart **64** (99% conversion, after 60 min). However, complex **63** exhibited a faster ROMP initiation with 70% conversion in 10 min than that of **64** with 30% conversion at the same time period. The PDI values of the polymer products **70-74** analyzed by GPC ranged from 1.11 to 2.34. The removal of catalyst **63** was examined in the ROMP reactions of monomer **65-69**. The process used in separation of residues from catalyst **63** and the polymer product involved dissolving the dry crude mixture of polymer product and Ru catalyst residue in a minimum amount of DCM and precipitating the mixture in hexane affording the homopolymer as a white solid. The Ru contamination level of polymers **70-74** prepared by **63** varied from 71 to 252 ppm. Figure 11: Polyisobutylene (PIB\({}_{1000}\))-supported Grubbs second generation catalysts **63** and Grubbs catalyst **64**. The PE\({}_{\text{olig}}\)-supported ruthenium catalyst **46** has also been used in ROMP reactions of norbornene derivatives [67]. Examples of polymer prepared using **46** are shown in Figure 12. This PE\({}_{\text{olig}}\)-supported catalyst **60** was used to prepare polymers **74-78** using the same solid/liquid separation concept as was used previously in reactions where this catalyst was used to prepare RCM products. In this case, separation of the ROMP products from **46** was performed by filtration of reaction mixture through Celite and 0.2 \(\upmu\)m filter to yield colorless solution containing polymer products. The resulting solution was concentrated and then precipitated in hexane to isolate polymers **74-78**. In reactions with catalyst **46**, it was found that the prior scheme where polyethylene oligomers were shown to be useful cosolvents facilitate Ru residue separations in ROMP chemistry [67]. Adding unfunctionalized polyethylene oligomers as a cosolvent further facilitated separations of the product polymer and catalyst residues. For example, when a commercially available unfunctionalized polyethylene (Polywax) (\(M_{\text{n}}\) = 400) [68] was added as a co-solvent to PE\({}_{\text{olig}}\)-supported catalyst, the leaching of Ru residues from catalyst **60** decreased to 19-26 ppm range (_ca._ 0.5% of the charged Ru catalyst).