Living metal halide-based

Living polymerization by metal halide-based metathesis catalysts... 

The general formula of metal halide-based living polymerization catalysts is expressed as MO,jCl ,-co-catalyst-ROH (M = Mo or W, = 0 or 1, m = 5 or 4). The most important feature of these catalysts is ease of preparation, but their initiation efficiency is low. A typical living polymerization by metal halide-based catalysts has been achieved with 1-chloro-l-octyne as monomer and using MoOCl -w-Bu Sn-EtOH (1 in Table 15.2) as catalyst [41]. Specifically, poly(l-chloro-l-octyne) with a narrow MWD < 1.2) is obtained, and the... 

The last decades have witnessed the emergence of new living Vcontrolled polymerizations based on radical chemistry [81, 82]. Two main approaches have been investigated the first involves mediation of the free radical process by stable nitroxyl radicals, such as TEMPO while the second relies upon a Kharash-type reaction mediated by metal complexes such as copper(I) bromide ligated with 2,2 -bipyridine. In the latter case, the polymerization is initiated by alkyl halides or arenesulfonyl halides. Nitroxide-based initiators are efficient for styrene and styrene derivatives, while the metal-mediated polymerization system, the so called ATRP (Atom Transfer Radical Polymerization) seems the most robust since it can be successfully applied to the living Vcontrolled polymerization of styrenes, acrylates, methacrylates, acrylonitrile, and isobutene. Significantly, both TEMPO and metal-mediated polymerization systems allow molec-... 

Another target was to reexamine a wide range of metal halides for living polymerization. FeCU is less hard as an acid than the Al-based adds, and has advantages, such as low toxicity, for industrial use. However, FeCU has never been used for living cationic polymerization of any monomers, although there have been several examples of its use in cationic polymerization of VEs, Sts, and dienes. The combination of FeCU with a Lewis base also allowed fast living polymerization of IBVE. For example, a time period of 15 s was required for quantitative cationic polymerization of IBVE when IBVE-Cl/FeCU was used in toluene in the presence of 1,4-dioxane at 0 °C. In addition, the product polymer had a very narrow MWD (Mw/Mn = 1.06). ... 

Diverse combinations of metal halides and Lewis bases also allowed living/controlled polymerization of monomers with high and poor reactivities. For example, polymerization of NVC was controlled under conditions milder than those of the previous report. The combination of ZnCU with a rdatively strong Lewis base, tetrahydrofuran (THF), produced polymers with a narrow MWD (Mw/A n[Pg.534]

In the past 15 years, several new living cationic poljrmerizations, based on stabilization of unstable growing carbocations, have been developed. For example, living polymerization of vinyl ethers, initiated by protonic acid/ vinyl halide combined system proceeds via reversible and heterolytic cleavage of a carbon—halogen terminal bond mediated by the metal halide [111] ... 

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