Highly Defined ABC Triblock Cooligomers and Copolymers Prepared by ROMP Using an N-Heterocyclic-Carbene-Substituted Ruthenium Benzylidene Initiator Christian Slugovc,* Silvia Riegler, Gertraud Hayn, Robert Saf, Franz Stelzer Institute for Chemistry and Technology of Organic Materials (ICTOS), Graz University of Technology, Stremayrgasse 16, A-8010 Graz, Austria Fax: þ43 316 873 8951; E-mail: slugi@ictos.tu-graz.ac.at Keywords: block copolymers; living polymerization; MALDI; ROMP Introduction Ring-opening metathesis polymerisation (ROMP) is a powerful tool to prepare well-defined and highly function- alised polymers. [1] Schrock-type initiators are very active and provide complete initiation, although they suffer from a poor functional-group tolerance compared to ruthenium initiators. This issue was solved, in part, by using (PCy 3 ) 2 (Cl) 2 Ru CHPh, the ‘‘1 st generation Grubbs’’ initia- tor, and related complexes as initiators for ROMP. However, this was at the expense of lower activity. With the introduction of the ‘‘2 nd generation Grubbs’’ catalyst (H 2 IMes)(PCy 3 )(Cl) 2 Ru CHPh (H 2 IMes ¼ N,N-bis(mesi- tyl)-4,5-dihydroimidazol-2-ylidene) and related initiators, a new tool for polymer chemistry became accessible. Activities comparable with Schrock-type initiators and even higher functional-group tolerance with respect to (PCy 3 ) 2 (Cl) 2 Ru CHPh could be combined, but with the drawback of poor initiation. [1] Very recently, Grubbs et al. published that the initiation rate for (H 2 IMes)(3-bromopyr- idine) 2 (Cl) 2 Ru CHPh (1) in the polymerisation of cyclooctene is 6 orders of magnitude higher than that for (H 2 IMes)(PCy 3 )(Cl) 2 Ru CHPh. [2] Our own results reveal- ed a complete initiation of (H 2 IMes)(pyridine) 2 (Cl) 2 - Ru CHPh in the ROMP of norbornenes meaning that every initiator molecule starts a polymer chain. [3] These two reports are promising, indicating that NHC/pyridine based ruthenium carbenes will further enlarge the scope of ROMP. We now want to demonstrate that 1 is an ideal initiator for the synthesis of triblock copolymers with very narrow molecular-weight distributions in a living manner. The presented example of an ABC triblock copolymer would neither be accessible by using (PCy 3 ) 2 (Cl) 2 Ru CHPh (not compatible with cyano groups [4] ) nor by (H 2 IMes)- (PCy 3 )(Cl) 2 Ru CHPh (produces polymers with rather high polydispersities and does not provide complete initiation [5] ). Communication: The ‘‘3 rd generation Grubbs’’ initiator (H 2 IMes)(3-bromopyridine) 2 (Cl) 2 Ru CHPh (1) accom- plishes the synthesis of ABC triblock copolymers via living ring-opening metathesis polymerisation (ROMP) of norbor- nene derivatives. Complete initiation and an outstanding tolerance of functional groups are provided, which is proven by a combined study by means of matrix-assisted laser desorption/ionisation mass spectrometry, gel permeation chromatography and NMR spectroscopy on an ABC triblock cooligomer. Gel permeation chromatograms of oligoA, oligoAB, and oligoABC. Macromol. Rapid Commun. 2003, 24, 435–439 435 Macromol. Rapid Commun. 2003, 24, No. 7 ß WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2003 1022-1336/2003/0705–435$17.50þ.50/0