Norbomenes living polymerization

The ring-opening metathesis polymerization (ROMP, cf. Section 2.3.3) of strained-ring cyclic alkenes has attracted considerable attention in recent years due to the discovery that well-characterized metallacyclobutane [24] and metal alkylidene [25] complexes catalyze the living polymerization of monomers such as norbomene. Unfortunately, these catalysts often sulfer deactivating side reactions... 

It was found that 6 (a variant of the latter Grubbs catalyst [34]) would catalyze the living polymerization of norbomene in organic solvents. Although not soluble in water, complex 6 will initiate aqueous emulsion polymerizations. To date, all attempts to solubilize 6 in aqueous solution by the incorporation of sulfonated phosphine ligands have failed to yield active catalysts. 

The ROM polymerization of norbomene, catalyzed by Schrock catalyst D, is a living polymerization that can be halted by the addition of benz-aldehyde. This gives a polymer terminated at one end by CH=CH-Ph and at the other end by CH=CH-r-Bu. The byproduct is a tungsten oxide complex. Propose an explanation for the chain termination step.117... 

Due to the water insolubility of these metal carbenes, aqueous polymerizations represent heterogeneous multiphase mixtures. Investigation of ROMP of the hydrophilic monomer 8 or of a hydrophobic norbomene in aqueous emulsion (catalyst precursor 7 b added as methylene chloride solution) or suspension demonstrated that the polymerization can occur in a living fashion. For example, at a monomer to catalyst ratio 8/7b = 100 with 78% yield, poly-8 of Mw/Mn 1.07 vs. polystyrene standards was obtained [68]. Using water-soluble carbene complexes of type 9 and water-soluble monomers 10, living polymerization can be carried out in aqueous solution, without the addition of surfactants or organic co-solvents [69]. 

Robert (Bob) Howard Grubbs main interests in organometallic chemistry and synthetic chemistry are catalysts, notably Gmbbs catalyst for olefin metathesis and ring-opening metathesis polymerization with qrdic olefins such as norbomene. He also contributed to the development of so-called living polymerization. ... 

The rate of norbomene polymerization is first order in catalyst and first order in NBE over greater than three half lives when the catalyst concentration is less than 10 mM (correlation coefficients > 0.995). At higher catalyst concentrations we suspect that bimolecular decomposition reactions that destroy the alkylidene ligand compete with polymerization. We have found that kp = 0.027 (3) M ls l at 23 °C. Since kp/ki = 5 (0.5), ki = 0.0050 M ls l. PolyNBE can be cleaved from the metal by adding a large excess of benzaldehyde (e.g., 50 equiv). GPC analysis showed the samples to be essentially monodisperse, indicative of a well-behaved living polymerization. By proton NMR we can say that the double bonds in the polymer are -- 60% cis,... 

CHBu CH(C5HgCH) ] (structurally characterized) formed from norbomene acts as a living polymerization catalyst for the formation of polynorbomene." Kinetic studies show that the rate determining step is ring opening of the metallacycle. 

Living Polymerization of Norbomene with a/wa-Dimethysilylene(fluorenyl)(amido)-... 

The most important role of living polymerization is to synthesize block copolymers. The Ti complexes 2—5 activated by dMAO or dMMAO were found to conduct living polymerization of propene, higher l-aUcene, and norbomene as well as their random living copolymerization. Thus, we can synthesize tailor-made copolymers composed of l-aUcene and norbomene with this catalytic system. 

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]. 

Calderon was the first to find a catalyst system that would initiate both ring-opening polymerization of olefins (subsequendy named ROMP by Tim Swager when he was a student at Caltech) and acydic metathesis of simple olefins. Up until his findings, most catalysts for acydic metathesis were heterogeneous systems, and metal salts were used to polymerize strained olefins such as norbomenes. Beautiful work was carried out using the poorly defined systems to work out the stereochemistry and mechanism of metathesis. This beautiful work provides an excellent backdrop for the work described here. This section will focus on the use of well-defined complexes as initiators for the living polymerization of cydic olefins. 

Ring-Opening Metathesis Polymerization. Several new titanacyclobutanes have been shown to initiate living ring-opening metathesis polymerization (ROMP) systems. These have been used to make diblock and triblock copolymers of norbomene [498-66-8] (N) and its derivatives (eg, dicyclopentadiene [77-73-6] (D)) (Fig. 2) (41). 

New kinds of living polymer systems result from the reactions of transition metals with cyclic, strained olefins 16). These polymerizations proceed through the intermediacy of metal carbenes and are exemplified by the polymerization of norbomene initiated by bis(cyclopentadienyl)-titane-cyclobutane described recently by Grubbs17>. 

The validity of the non-steady state assumption is shown in Figure 1, where the molecular weight of the copolymerization mixture increases with conversion at the beginning of copolymerization. The long lived radical is observed from the ESR spectrum in Figure 2, measured at room temperature for polymerization in toluene this agrees with the S02 radical similar to the norbomene-S02 system (16). 

If the living ROMP of norbomene is terminated with a 9-fold excess of terephthalaldehyde, the chains formed carry an aldehyde end-group which, when activated by ZnCl2, can be used to initiate the aldol-group-transfer polymerization of tert-butyldimethylsilyl vinyl ether621. 

Coupling of living anionic polymerization and living ROMP may be achieved by terminating living anionic polymer chains with norborn-2-ene-5-carboxylic chlo-ride425 or norbomene-2,3-dicarboxylic chloride. 6 427 This end-functionalized polymer may then be polymerized via ROMP (Scheme 47). 

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... 

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