Polymerization polar vinyl monomer

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Uses. Magnesium alkyls are used as polymerization catalysts for alpha-alkenes and dienes, such as the polymerization of ethylene (qv), and in combination with aluminum alkyls and the transition-metal haUdes (16—18). Magnesium alkyls have been used in conjunction with other compounds in the polymerization of alkene oxides, alkene sulfides, acrylonitrile (qv), and polar vinyl monomers (19—22). Magnesium alkyls can be used as a Hquid detergents (23). Also, magnesium alkyls have been used as fuel additives and for the suppression of soot in combustion of residual furnace oil (24). 

To be eligible to living anionic polymerization a vinylic monomer should carry an electron attracting substituent to induce polarization of the unsaturation. But it should contain neither acidic hydrogen, nor strongly electrophilic function which could induce deactivation or side reactions. Typical examples of such monomers are p-aminostyrene, acrylic esters, chloroprene, hydroxyethyl methacrylate (HEMA), phenylacetylene, and many others. 

Some polar vinyl monomers such as MMA can be polymerized. 

Rare Earth Metal-Initiated Polymerization of Polar Vinyl Monomers... 

Kinetics in Non-Polar Media. Polymerization of vinyl monomers in non-polar solvents, i.e., hydrocarbon media, has been almost entirely restricted to the organolithium systems (7), since the latter yield homogeneous solutions. In addition, there has been a particularly strong interest in the polymerization of the 1,3-dienes, e.g., isoprene and butadiene, because these systems lead to high 1,4 chain structures, which yield rubbery polymers. In the case of isoprene, especially, it is possible to actually obtain a polymer with more than 90% of the eis-1,4 chain structure (7, 8, 9), closely resembling the microstructure of the natural rubber molecule. 

Solvent polarity and temperature also influence ihe results. The dielectric constant and polarizability, however, are of little predictive value for the selection of solvents relative to polymerization rates and behavior. Evidently evety system has to he examined independently. In cationic polymerization of vinyl monomers, chain transfer is the most significant chain-breaking process. The activation energy of chain transfer is higher than that of propagation consequently, the molecular weight of the polymer increases with decreasing temperature. 

Kuran, W., Polar Vinyl Monomer Polymerization and Copolymerization with Olefins Promoted by Organometallic Catalysts , Polimery, 42, 604-609 (1997). 

Catalysts of the Ziegler-Natta type are applied widely to the anionic polymerization of olefins and dienes. Polar monomers deactivate the system and cannot be copolymerized with olefins. J. L. Jezl and coworkers discovered that the living chains from an anionic polymerization can be converted to free radicals by the reaction with organic peroxides and thus permit the formation of block copolymers with polar vinyl monomers. In this novel technique of combined anionic-free radical polymerization, they are able to produce block copolymers of most olefins, such as alkylene, propylene, styrene, or butadiene with polar vinyl monomers, such as acrylonitrile or vinyl pyridine. 

In anionic polymerization of vinyl monomers (nondiene), low temperatures and polar solvents favor the preparation of syndiotactic polymers.21 Nonpolar solvents tend to favor isotactic polymerization. In the case of diene monomers such as butadiene and isoprene, the use of lithium based initiators in nonpolar... 

These monomers usually polymerize by classical methods, i.e. radical or ionic, more readily than ethylene. On the other hand, they are too good as electron donors in coordination polymerizations they act as catalytic poisons. The group of polar vinyl monomers is very large. Mostly these compounds are of only theoretical interest. Many of them are, however, technically and socially important, and the exploitation of others is anticipated. 

The high polar group tolerance of co-catalyst-free ylide nickel catalysts makes them interesting candidates for fhe polymerization of polar monomers. In fact, quite a number of polar vinyl monomers can be homo- and copolymerized quite effectively. The mechanisms of initiation and chain propagation have not been elucidated yet. Especially, acrylic monomers are well suited. It is fhus possible to produce, for example, poly(methyl methacrylate), poly(efhyl acrylate) and poly-(butyl acrylate) in high yield [Eq. (15)]. 

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. 

In the polymerization of vinyl monomers on free anions or solvent separated ion pairs, ring opening in a cyclic intermediate occurs in the conrotatory manner [39]. Hence, anionic polymerization in polar media should tend to form syndiotactic polymers and should be slightly similar in this respect to free-... 

This chapter describes the coordination polymerization of acyclic and cyclic vinylic monomers, conjugated dienes, and polar vinylic monomers with the most important catalytic systems known in this area. A chronological classitication for the development of the main coordination catalyst types is outlined, as well as polymerization kinetics and mechanisms and applications of polymers obtained through different metallic complexes. 

Initiation The mechanism of initiation of anionic polymerization of vinyl monomers with alkyllithium compounds and other organometallic compounds is complicated by association and cross-association phenomena in hydrocarbon solvents and by the presence of a variety of ionic species in polar media [3, 4, 45, 48, 55, 56]. The kinetics of initiation is complicated by competing propagation and the occurrence of cross-association of the alkyllithium initiator with the propagating organolithium [55]. Thus, only the initial rates provide reliable kinetic data. 

Polar Vinyl Monomers The anionic polymerization of polar vinyl monomers is often complicated by side reactions of the monomer with both anionic initiators and growing carbanionic chain ends, as well as chain termination and chain transfer reactions. However, synthesis of polymers with well-defined structures can be effected under carefully controlled conditions. The anionic polymerizations of alkyl methacrylates and 2-vinylpyridine exhibit the characteristics of living polymerizations under carefully controlled reaction conditions and low polymerization temperatures to minimize or eliminate chain termination and transfer reactions [118, 119]. Proper choice of initiator for anionic polymerization of polar vinyl monomers is of critical importance to obtain polymers with predictable, well-defined structures. As an example of an initiator that is too reactive, the reaction of methyl methacrylate (MMA)... 

---