Polymerization metal acrylates

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-... 

Enolate Initiators. In principle, ester enolate anions should represent the ideal initiators for anionic polymerization of alkyl methacrylates. Although general procedures have been developed for the preparation of a variety of alkali metal enolate salts, many of these compounds are unstable except at low temperatures (67,102,103). Useful initiating systems for acrylate polymerization have been prepared from complexes of ester enolates with alkali metal alkoxides (104,105). 

Acetyl ligands, in niobium complexes, C-H BDEs, 1, 298 Achiral phosphines, on polymer-supported peptides, 12, 698 Acid halides, indium compound reactions, 9, 683 Acidity, one-electron oxidized metal hydrides, 1, 294 Acid leaching, in organometallic stability studies, 12, 612 Acid-platinum rf-monoalkynes, interactions, 8, 641 Acrylate, polymerization with aluminum catalysts, 3, 280 Acrylic monomers, lanthanide-catalyzed polymerization,... 

Another method is based on the metal-catalyzed polymerization from carbon—halogen bonds in the main-chain units, which was applied for the synthesis of C-3 and C-4.430 For C-3, the main chain polymers with controlled molecular weights were prepared via the copper-catalyzed radical polymerization of tri-methylsilyl-protected HEMA followed by the transformation of the silyloxyl group into 2-bromoisobu-tyrate. The pendant C—Br bonds were subsequently activated by the copper catalysts to polymerize styrene and nBA. A more direct way is employed for C-4 i.e., via conventional radical polymerization of 2-[(2-bromopropinonyl)oxy]ethyl acrylate followed by the copper-catalyzed graft polymerization of styrene and nBA from the C—Br substituent. 

What is fhe implication of our work wifh respect to the metal-catalyzed polymerization of polar vinyl monomers FirsL for fhe late metal compounds, fhe polar vinyl monomers can clearly outcompete efhene and simple 1-alkenes wifh respect to insertion. However, fhe ground-state destabilization of the alkene complex that favors the migratory insertion of fhe polar vinyl monomers is a two-edged sword because it biases the alkene coordination towards ethene and l-alkenes. Indeed, we have observed fhe near quantitative displacement of vinyl bromide by propene to form 7 from 3 (Scheme 9.1). Thus, the extent of incorporation of fhe polar vinyl monomer in fhe polymer will depend on the opposing trends in alkene coordination and migratory insertion. The above discussion does not take into account the problem of functional group coordination for acrylates or halide abstraction for vinyl hahdes. 

There is also a considerable body of literature on the use of late metals to polymerize acrylates and styrene, but those atom-transfer radical polymerizations are beyond the scope of this review. 

The rate of polymerization increases in this series of metals Mg(II) < Sr(II) < Ba(II) < Ca(II), The nature of the cation is likely to have a significant effect on the kinetics of the polymerization of salts of unsaturated acids in ionizing environments [68-70]. These differences are attributed to a different charge density at the macroradical anion, which influences the rate of interaction in the propagating macroradical-monomeric anion system. In comparable conditions the rate of radical polymerization of transition metal acrylates is lower than that of acrylic acid (AA) and decreases in the series (Fig. 4-7) [71] AA > Co(II) > Ni(II) > Fe(III) > Cu(II) (see Experiment 4-1, Section 4.6). The resulting metallopolymers are insoluble in any organic solvent, which indicates... 

Thus, the polymerization of transition metal acrylates can be accompanied by redox reactions that involve metal ions and cause termination of the propagating chain. 

The kinetic analysis indicates (35) that polymerization of transition metal acrylates proceeds by the same elementary prxx esses as that of their metal-free" analogs. HOft/ever, in many cases the polymerization may be complicated by an individual effect of the. transition metal ion. In particular, the kinetic scheme for the Ti (4+)-containing MCM (36) can be described by the follov/ing system of equations (see Fig. 4) ... 

The best results are obtained by preirradiation of polymer supports in the air with a subsequent deconposition of the hydroperoxides formed the resulting immobilized radicals initiate graft polymerization of the transition metal acrylates (Fig. 5), MX acrylamide complexes and their complexes with allyl-type monomers (49, 50). MCM graft polymerization is essentially oharacterized by the same... 

A parallel development was initiated by the first publications from Sawamoto and Matyjaszweski. They reported independently on the transition-metal-catalyzed polymerization of various vinyl monomers (14,15). The technique, which was termed atom transfer radical polymerization (ATRP), uses an activated alkyl halide as initiator, and a transition-metal complex in its lower oxidation state as the catalyst. Similar to the nitroxide-mediated polymerization, ATRP is based on the reversible termination of growing radicals. ATRP was developed as an extension of atom transfer radical addition (ATRA), the so-called Kharasch reaction (16). ATRP turned out to be a versatile technique for the controlled polymerization of styrene derivatives, acrylates, methacrylates, etc. Because of the use of activated alkyl halides as initiators, the introduction of functional endgroups in the polymer chain turned out to be easy (17-22). Although many different transition metals have been used in ATRP, by far the most frequently used metal is copper. Nitrogen-based ligands, eg substituted bipyridines (14), alkyl pyridinimine (Schiff s base) (23), and multidentate tertiary alkyl amines (24), are used to solubilize the metal salt and to adjust its redox potential in order to match the requirements for an ATRP catalyst. In conjunction with copper, the most powerful ligand at present is probably tris[2-(dimethylamino)ethyl)]amine (Mee-TREN) (25). 

One of the main challenges in the use of metal catalysts is the suppression of undesirable termination reactions, which, for reasons described below, tend to be more prevalent for acrylate systems. Most of the recent developments have thus been seen in the polymerization of methacrylate monomers, especially commercially significant methyl methacrylate (MMA), which is polymerized to the commodity material poly(methyl methacrylate) (PMMA), known by its trademark names Perspex , Plexiglass , andLucite (Scheme 23.1). Much of this chapter, therefore, focuses on tacticity control in the production of PMMA using coordination polymerization catalysts. Though little has been reported on stereocontrolled acrylate polymerization, the basic principles established... 

Yasuda, H. Rare-earth-metal-initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomers. 7. Polym. ScL, Part A Polym. Chem. 2001, 39, 1955-1959. 

The researcher should, however, remember that acrylate monomers and acid-containing binders will react with many metals causing polymerization... 

In 1988 Reetz et al. introduced the concept of metal-free polymerization of acrylates, methacrylates and acrylonitrile [224,225]. Metal-free initiators are salts consisting of a carbanion (A ) having R4N as cationic counterions. They are synthesized by the reaction of neutral CH or NH-acidic compounds such as malonic acid esters, nitriles, sulfones, nitro-alkanes, cyclopentadiene, fluorene derivates, carbazoles and succinimide. Water is removed azeotropically using toluene. 

These initiator systems are capable of initiating the polymerizations of -butyl acrylate, methyl methylacrylate and acrylonitrile (PDI 1.1 1.4 molecular mass 1,500 20,000 g/mole). But it must be mentioned that the metal-free polymerization is not a real living process. Backbiting and Hofmann elimination occur to a small but significant extent [226]. 

Different transition metal salts of acrylate polymerize at 60 °C with AIBN, e.g., in ethanol under dissociation-exeluding conditions [183,184]. The resulting metal-containing polymers are as expected insoluble in organic solvents but they are converted to soluble polyacrylic acid in a methanol-HCl mixture. The reactivity of the metal-acrylates in the homopolymerization decreases as follows Co(II) > Ni(II) > Fe(III) > Cu(II). 

Thermal polymerization of MCMs (with transition metal acrylates as examples) is of interest in at least two aspects. First, the stmcture of these salts contains many dislocations, that facilitate solid-state polymerization. Second, thermal decomposition and polymerization transformations are the stages for a potential method of the synthesis of polsnner-immobilized, highly dispersed nanosize metal particles. 

Finally, it should be noted that MCMs are metal complexes with specific ligands, and polymerization is only one of their functions. Generally, these compounds can participate in all the reactions typical of compounds with double bonds. Thus it was foimd under model conditions that, on hydrogenation, metal acrylates are converted into the corresponding propionates.It should be mentioned that the effective energy of activation and enthalpy of the reaction is higher than that of acrylic acid (Table 7). 

Scheme 15 Various metal-free carbanions used for all l (meth)acrylate polymerization.

Acetyiacetonates of aiuminum, chromium, iron, cobait, copper acetyiacetonates of zinc, copper, iron Polyester, vinyl ester and acrylate polymerization and crosslinking, epoxy/epoxy vinyl ester (catalyzed with metallics) urethane reactions... 

Uses Emulsifier for metal, textile processing, household and industrial cleaners, vinyl and acrylic polymerization Properties Liq. HLB 13.5 cloud pt. 65 C (1% aq.)... 

The addition of alcohols to form the 3-alkoxypropionates is readily carried out with strongly basic catalyst (25). If the alcohol groups are different, ester interchange gives a mixture of products. Anionic polymerization to oligomeric acrylate esters can be obtained with appropriate control of reaction conditions. The 3-aIkoxypropionates can be cleaved in the presence of acid catalysts to generate acrylates (26). Development of transition-metal catalysts for carbonylation of olefins provides routes to both 3-aIkoxypropionates and 3-acryl-oxypropionates (27,28). Hence these are potential intermediates to acrylates from ethylene and carbon monoxide. 

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

The range of uses of mercuric iodide has increased because of its abiUty to detect nuclear particles. Various metals such as Pd, Cu, Al, Tri, Sn, Ag, and Ta affect the photoluminescence of Hgl2, which is of importance in the preparation of high quaUty photodetectors (qv). Hgl2 has also been mentioned as a catalyst in group transfer polymerization of methacrylates or acrylates (8). 

Copolymers with acrylonitrile, butadiene, isoprene, acrylates, piperjiene, styrene, and polyethylene have been studied. The high cost of sorbic acid as a monomer has prevented large-scale uses. The abiUty of sorbic acid to polymerize, particularly on metallic surfaces, has been used to explain its corrosion inhibition for steel, iron, and nickel (14). 

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