Polymerization with ruthenium

Material properties of olefin metathesis polymers made by thermal (ROMP) or photoinduced (PROMP) polymerization with ruthenium (Il)-salts and the later developed ruthenium-phosphines as catalysts are described. The low oxidative stability was improved by copolymerization with so-called "build-in" antioxidants (AOs), i.e. hindered phenols or aromatic amines bearing 2-norbornene units. 

Analogues of chiral Pybox have been reported by other chemists and have been applied to ACP with ruthenium catalysts [37,38]. For example, Pybox substituted by a vinyl group at the 4-position of the pyridine skeleton was polymerized with styrene and divinylbenzene to give immobilized ligands, the ruthenium complexes of which were used to give 85% ee for ACP with EDA and styrene [38]. 

Zirconium is the principal FP to arise in oxidation state (IV). Where Zircaloy clad fuel is involved, nonradioactive zirconium isotopes may also be present from fuel can residues. As with ruthenium, there may be a variety of nitrato complexes present in the solution including the aquated complexes Zr(N03)s where x = 1-6, and hydroxy nitrato complexes. However, species containing ZrO " " are not expected to be present since this ion is unstable in aqueous media and is rapidly hydrated to Zr(OH)2. The extraction chemistry is further complicated by the formation of inextractable polymeric species when the Zr" concentration exceeds ca. 10 M. An example of such oligomerization is afforded by the [Zr(0H)2(H20)4]4 ion which contains four Zr ions in a square arrangement linked by two /u-OH ligands on each square edge. Four water molecules complete the Zr coordination sphere in an approximately D2d dodecahedral geometry. 

As with ruthenium, iron belongs to the group 8 series of elements and can similarly take various oxidation states (—2 to +4), among which Fe(II), Fe-(I), and Fe(0) species have been reported to be active in Kharasch addition reactions.33 For metal-catalyzed living radical polymerizations, several Fe(II) and Fe-(I) complexes have thus far been employed and proved more active than the Ru(II) counterparts in most cases (Figure 2). The iron-based systems are attractive due to the low price and the nontoxic nature of iron. 

A haloalkane with mixed halogens (1-7) led to living polymerization of methacrylates, acrylates, and acrylamides when coupled with ruthenium and nickel complexes.133 135 159 160 The weak C—Br bond is preferentially activated, while multifunctional initiation is possible. However, CCl3Br is the initiator of choice if obtaining narrow MWDs is desired without paying attention to monomer structures. 

Bromoisobutyrate 1-24 (X = Br), a unimer model of poly(methacrylate) with a dormant C—Br terminal, is more versatile for various monomers such as methacrylates, acrylates, and styrenes various metal complexes including Ru, Fe, Cu, and Ni can be employed in this case. Living or controlled radical polymerization of MMA was successfully done with 1-24 (X = Br) coupled with ruthenium,56 iron,7071... 

The dependenee of polymerization rates on the ratio of the eatalyst to amine was investigated next. The obtained data show that varying this ratio from 1 1 to 1 4 has no inflnenee on polymerization rate. Polydispersity indexes and MW do not depend on the eoneentration of amine. These resnlts allow ns to propose that amine does not partieipate in the ehain transfer reactions, but interacts with ruthenium complex to generate in sitn catalyst active for ATRP. 

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