Vinyl anionic polymerizability

The ability to ionically polymerize apparently correlates in many cases with the capacity of the substituents to act as electron acceptors (anionic polymerizability) or as electron donors (cationic polymerizability) on the rt-bond of the vinyl group. These relationships should be visible in carefully chosen quantum chemical parameters. 

Figure 5.1 Cyclic monomers capable of anionic polymerization. Table 5.1 Anionic polymerizability of vinyl monomers.

Phenyl vinyl sulfoxide (8) shows a high anionic polymerizability, similar to that of (meth)acrylates and N,N-dialkylacrylamides [158-160]. Hogen-Esch first reported that 8 underwent anionic polymerization in TH F at — 78 °C to afford polymers with relatively narrow molecular weight distributions (Mw/M = 1.1-1.5) [158]. AnAB diblock copolymer, PS-b-poly(8), was also synthesized by the sequential addition of styrene, followed by 8. Subsequently, the anionic polymerization was improved by using 4-methylphenyl vinyl sulfoxide (9) with l,l-diphenyl-3-methylpentyllithium in the presence of a 20-fold excess of liCl in THF at —78°C [161]. In this way. 

Various substituted styrenes also anionically polymerize readily. These include methyl, methoxy, dimethylamino, t- butyl and other groups which are electron donating to the benzene ring and do not themselves react with carbanion centers. Substituents such as chloro or nitro can be anionically polymerized only at imder very carefolly controlled conditions. 2,3, or 4 vinylpyridine can also be anionically polymerized. Any aromatic or condensed aromatic compounds with a vinyl substituent is potentially anionically polymerizable, or co polymerizable with any other anionically polymerizable monomer. 

One of the limitations of anionic polymerization is the types of monomers which can be polymerized without termination and chain transfer. The most well-behaved systems are the vinyl monomers based on styrene and butadiene which are available primarily from petroleum feedstocks. Several years ago we began a search for anionically polymerizable monomers which would be available from renewable natural resources. One of the monomers uncovered (rediscovered) in this search was myrcene (4) 7-methyl-3-methylene-1,6-octadiene,... 

The anionic polymerizability of vinyl monomers cannot be deduced from the thermodynamics of polymerization since almost all vinyl monomers exhibit negative free energies of polymerization that is, if a suitable pathway exists, the polymerization will proceed spontaneously to form the polymer from the monomer. This is exemplified by the fart that cyclopropane does not undergo anionic polymerization in spite of its high ring strain and exothermic energy of polymerization (AG = -22.1 kcalmol" ). The proviso that there exists a suitable pathway provides the major limitation on the... 

It might be noted that most (not all) alkenes are polymerizable by the chain mechanism involving free-radical intermediates, whereas the carbonyl group is generally not polymerized by the free-radical mechanism. Carbonyl groups and some carbon-carbon double bonds are polymerized by ionic mechanisms. Monomers display far more specificity where the ionic mechanism is involved than with the free-radical mechanism. For example, acrylamide will polymerize through an anionic intermediate but not a cationic one, A -vinyl pyrrolidones by cationic but not anionic intermediates, and halogenated olefins by neither ionic species. In all of these cases free-radical polymerization is possible. 

Recently it has been shown that anionic functionalization techniques can be applied to the synthesis of macromonomers — macromolecular monomers — i.e. linear polymers fitted at chain end with a polymerizable unsaturation, most commonly styrene or methacrylic ester 69 71). These species in turn provide easy access to graft copolymers upon radical copolymerization with vinylic or acrylic monomers. 

Our investigations agree with arguments in earlier articles by other authors, namely that empirical reactivity indices provide the best correlation with the goal values of the cationic polymerization (lg krel, DPn, molecular weight). On the other hand, the quantum chemical parameters are often based on such simplified models that quantitative correlations with experimental goal values remain unsatisfactory 84,85>. But HMO calculations for vinyl monomers show, that it is possible to determine intervals of values for quantum chemical parameters which reflect the anionic and cationic polymerizability 72,74) (see part 4.1.1) as well as grades of the reactivity (see part 3.2). 

The stabilizing of aqueous latexes succeeded by using emulsifiers (anionic, nonionic) and/or their mixture, steric stabilizators (polyvinyl alcohol (PVOH), hydroxyethyl cellulose, polyethylene glycol, new protective colloids etc.), and polymerizable surfaces active agents, in general. Vinyl acetate (VAc) emulsion homopolymers and copolymers (latexes) are widely used as binders in water-based interior and exterior architectural paints, coatings, and adhesives, since they have higher mechanical and water resistance properties than the homopolymers of both monomers [2, 4, 7]. 

Some monomers such as acrolein and ketene contain two different types of polymerizable group (C—O and C—C). The polymerization of acrolein has been studied with radical, cationic, and anionic initiators [Calvaryrac et al., 1973 Gulino et al., 1981 Schulz, 1967 Yama-shita et al., 1979]. Radical polymerization proceeds exclusively through the vinyl group... 

To the first category belong the homo- and copolymerization of macromonomers. For this purpose, macromolecules with only one polymerizable end group are needed. Such macromonomers are made, for example, by anionic polymerization where the reactive chain end is modified with a reactive vinyl monomer. Also methacrylic acid esters of long-chain aliphatic alcohols or monofunctional polyethylene oxides or polytetrahydrofurane belong to the class of macromonomers. 

Recently, Higashimura [7] has reviewed the data on elementary rate coefficients (fej, fep, fet and fej) in cationic polymerization of vinyl monomers. Information available on initiation and termination reactions is extremely limited, and virtually no attempt [50] has been made to elucidate, either qualitatively or quantitatively the role of free ions and ion pairs in these processes. Numerical data on the separate contributions to propagation by free ions and ion pairs is slowly becoming available, though in a less ordered fashion than in the case of anionic systems. It seems likely that the most fruitful approach to the problem of absolute reactivity, in initiation processes at least, will be an examination of reactions of non-polymerizable monomer models, where electronic factors... 

The grafting through strategy means the preparation of cylindrical brushes by the polymerization of preformed MMs. This was the first method in the synthesis of cylindrical brushes. For the first time, Tsukahara et al. [108] successfully obtained cylindrical brushes by the radical polymerization of MMs. Short polymer chains with a polymerizable vinyl chain end were first made by anionic polymerization and sequential end-functionalization. Further radical polymerizations of the premade MMs yielded cylindrical brushes with uniform side chains. This method was then further employed by Schmidt et al. [109, 119-121] and Ishizu et al. [122-127] to... 

A patent (71) describes a combination of anionic and radical techniques to produce a variety of graft polymers. The synthesis proceeds via a capped anionic block polymer, the capping producing a polymerizable vinyl end unit. The capped polymer is then free-radical polymerized with a selected vinyl monomer to produce the graft polymer ... 

The preceding sections have dealt with polymerization by either insertion or GTP mechanisms. Of course, vinyl monomers are also polymerizable by radical, anionic, or cationic mechanisms. In this short section, we summarize the processes which are reasonably well understood from a mechanistic viewpoint, and which involve the intervention of transition metal alkyls (or hydrides), either during initiation, propagation, or chain transfer/termination. A much larger class of polymerization reactions where redox-active transition metal complexes are used to mediate radical polymerizations by reversible atom transfer (ATRP) or other means has been extensively and recently reviewed from a mechanistic perspective and will only be briefly mentioned here. 

Among these reactions, the Cu(l)-catalyzed azide-alkyne cycloaddition (CuAAC) is the most widely used. This reaction has been implemented for the preparation of segmented block copolymers from polymerizable monomers by different mechanisms. For example, Opsteen and van Hest [22] successfully prepared poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and PEO-b-PSt by using azide and alkyne end-functionalized homopolymers as the click reaction components (Scheme 11.2). Here, PEO, PSt, and PMMA homopolymers were obtained via living anionic ring-opening polymerization (AROP), atom transfer radical polymerization (ATRP), and postmodification reactions. Several research groups have demonstrated the combination of different polymerization techniques via CuAAC click chemistry, in the synthesis of poly(e-caprolactone)-b-poly(vinyl alcohol) (PCL-b-PVA)... 

In monomers with two or more polymerizable sites the structure of the resulting polymer depends on the initiator. Vinyl isocyanate, CH2=CHNCO, polymerizes via the vinyl group free radically, but via the nitrogen/ oxygen double bond in anionic polymerization. Diketenes polymerize to polyesters, polyketones, or poly(vinyl esters) according to what initiator is used ... 

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