Tandem ROMP

In apparent contradiction with our results, however, no catalyst decomposition was observed over the course of two tandem ROMP-ATRP polymerisations (Scheme 10) mediated by a difunctional ruthenium complex 9 incorporating both a ROMP and an ATRP initiator [27]. Furthermore, halogen exchange has not been reported. In the preparation of these PMMA-PBD diblock copolymers, ROMP and ATRP occurred simultaneously provided that excess PCy3 be added to the reaction mixture. With this in mind, the stability of catalyst 9 over the course of the polymerisations may be related to the observation that additional PCy extends the longevity of the catalyst [25]. 

In contrast with the Osborn rhodium catalysts, in which the exclusive formation of the product arises from a cis-addition to the alkyne due to the difference of coordination power of the substrates, in these osmium complexes, the strong tendency of the alkyne to undergo insertion to yield the observable styryl intermediate is the step that determines the selectivity (83-85). Complex Os-HCl(CO)(P Prs)2 is also active in tandem ROMP-hydrogenation of norbomene and 2,5-norbornadiene (86). 

Scheme 2.3 Synthesis of homopolymer blend particles and graft-copolymer particles by tandem ROMP-ATRP.

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... 

Figure 7.11 ROMP-derived monolith based on tris(methyl carboxylate)ethane (a) containing PONBE and PNBE, and (b) containing PONBE and poly(cyclooctene) (PCC ). (c) Neo-glycopolymer synthesized via tandem ROMP-hydrogenation.

Long-chain, highly branched polymers have also been synthesized via a tandem ROMP and ADMET polymerization approach in which a telechelic polymer was first made by chain-transfer ROMP and then utilized as an A2B2 -type monomer for ADMET polymerization [187]. 

Figure 10. Saturated neoglycopolymers for tissue engmeering, prepared via tandem ROMP-hydrogenation.

Poly(l,4-butadiene) segments prepared by the ruthenium-mediated ROMP of 1,5-cyclooctadiene can be incorporated into the ABA-type block copolymers with styrene (B-106) and MMA (B-107).397 The synthetic method is based on the copper-catalyzed radical polymerizations of styrene and MMA from the telechelic poly(butadiene) obtained by a bifunctional chain-transfer agent such as bis(allyl chloride) or bis-(2-bromopropionate) during the ROMP process. A more direct route to similar block copolymers is based on the use of a ruthenium carbene complex with a C—Br bond such as Ru-13 as described above.67 The complex induced simultaneous or tandem block copolymerizations of MMA and 1,5-cyclooctadiene to give B-108, which can be hydrogenated into B-109, in one pot, catalyzed by the ruthenium residue from Ru-13. 

Scheme 42. Tandem RCM-ROMP for the Preparation of Chiral Poljrmers...

Dajnoki, A., Muhl, A., Fekete, G., Keutzer, J., Orsini, J., Dejesus, V., et al. (2008) Newborn screening for Rompe disease by measuring acid alpha-glucosidase activity using tandem mass spectrometry. Clin. Chem., 54, 1624-1629. 

Different types of olefin metathesis, all proceeding according to the Chauvin mechanism and catalyzed by Schrock-type or Grubbs-type metathesis catalysts. Tandem, domino and cascade metathesis reactions couple several of these reactions (in particular ROMP + ROM). 

Gnanou s group has extensively explored the use of ROMP in emulsion and miniemulsion in addition to dispersion and suspension. The use of ROMP in tandem with ATRP in miniemulsion has proven to be an effective route for making biphasic or Janus particles, consisting of polynorbornene and poly(methyl methacrylate) domains. They were able to use the same ruthenium-based catalyst for both, achieving simultaneous ROMP of norbornene and ATRP of MMA, using miniemulsion polymerization. Stable latexes with minimal... 

It has been demonstrated that these ruthenium complexes are also effective precatalysts for hydrogenation reactions. In 2001, Louie et al. reported the first example of ruthenium-catalyzed tandem RCM/hydrogenation and RCEM/hydrogenation (Scheme 5.1) [1]. Tandem RCM/isomerization [2], RCM/Kharasch addition [3], RCM/dihydroxylation [4], enyne metathesis/Claisen rearrangement [5], enyne metathesis/cyclopropanation [6], ROMP/hydrogenation [7], and CM/aza-Michael addition [8] have also been developed successfully. 

---