Coordination polymerization Grubbs

The development of novel titanium carbene complexes by Grubbs has opened up a route to living polymer systems, using coordinating polymerizations as opposed to those derived from ionic initiators, which can be used to form block copolymers or produce chains with a functionalized end group. The initiating species are formed by the reaction of norbomene with a titanocyclobutane derived from 3,3-dimethyl cycloprene... 

Simple nonfunctional hydrocarbon polymers such as polyethylene (PE), polypropylene, poly-a-olefins and their copolymers are synthesized by uncontrolled high-pressure-high-temperature radical, metathesis or transition-metal-catalyzed coordination polymerization (Natta, 1956 Ziegler et al, 1955 Wu and Grubbs, 1994 Chanda and Roy, 1993). Although catalysts of exceptional efficiency that produce polymers on a huge scale are in common use, control that approaches a hving polymerization for these methods has not been realized. 

ROM has been used to prepare phosphine-containing polymer supports (Scheme 20). Norbornyl-substituted monomer 22 was prepared in two steps from d-bromo-iodobenzene. This was then polymerized with diene 23. It was initially envisioned that it would be necessary to convert the phosphine to the borane adduct in order not to poison the metathesis catalyst. Although protection was needed when using the Grubb s type 1 complex as a catalyst, when employing the more active second-generation complex 24, the free phosphine monomer could be used. This has been attributed to the lower affinity of the active form of the catalyst toward coordination of phosphines due to the presence of the electron-rich heterocyclic carbene ligand. 

Cycloalkenes undergo ring-opening polymerization in the presence of coordination initiators based on transition metals to yield polymers containing a double bond, for instance, cyclo-pentene yields polypentenamer [lUPAC poly(pent-l-ene-l,5-diyl)] [Amass, 1989 Cazalis et al., 2000, 2002a,b Claverie and Soula, 2003 Doherty et al., 1986 Ivin, 1984, 1987 Ivin and Mol, 1997 Ofstead, 1988 Schrock, 1990, 1994 Tmka and Grubbs, 2001]. The... 

A further approach for making available a vacant coordination site for olefins at the metal was the synthesis of various bimetallic complexes with a weakly bond metal fragment (30a-c) by Grubbs [188]. These complexes displayed high activity in ROM polymerizations [188]. Herrmann et al. reported a series of analogous NHC complexes (30d-f) [193-195] with improved activity [194,220] and stability [220]. A comparative report on the stability of various metathesis initiators in RCM is given in Ref. [220]. 

A different system for chelating at Ru, i.e. a bidentate carbene-pyridine, was devised by Van der Schaaf et al. , the resulting catalyst being used in polymerization of dicyclopentadiene (DCPD) the idea was extended by Grubbs et al. to yield the second-generation catalyst 35. Fiirsmer et aL incorporated a coordinating carbonyl ester on the bidentate carbene and... 

Ru-carbene Grubbs I catalyst did not polymerize 5-trimethylsilylnorbomene in a living manner (/p 1, Table 2). At the same time, it was shown that the presence of functionalized substituents in monomer molecule is able to coordinate the catalyst, decrease to some extent its activity, and lead a living process [156]. Thus, block-copolymers of 5-(dicarbazolylmethylsilyl)norbomene and 5-(trimethylsilyloxymethyl)norbomene (NBCHaOSiMes) were obtained by living polymerization in the presence of Grubbs 1 complex [190]. 

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