Polymerization of Polar Vinyl Monomers

Several polymers based on 1,3-dienes are used as elastomers. These include styrene-1,3-butadiene (SBR), styrene-1,3-butadiene terpolymer with an unsaturated carboxylic acid (carboxylated SBR), acrylonitrile-1,3-butadiene (NBR or nitrile rubber) (Secs. 6-8a, 6-8e), isobutylene-isoprene (butyl rubber) (Sec. 5-2i-l), and block copolymers of isoprene or 

About 1.5 billion pounds of rxv-l, 4-poly(l, 3-butadiene) were produced in the United States in 2001. This polymer has a lower Tg and, therefore, higher resilience hut poorer tear resistance and tensile strength than does natural ruhher. For this reason, cis- 

4- polybutadiene is not used alone but is blended with either natural ruhher or SBR to produce tires for trucks and passenger automobiles. Considerable amounts of cis-1,4-polybutadiene are also used in producing ABS materials (Sec. 6-8a). 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity 

TABLE 8-12 Effect of Counterion, Solvent, and Temperature of Polymerization of Methyl Methacrylate 

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

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. 

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)... 

R 118 M. Kang, A. Sen, L. Zakharov and A.L. Rheingold, Trends in Alkene Insertion in Late- and Early-Transition Metal Compounds Relevance to Transition Metal-Catalysed Polymerization of Polar Vinyl Monomers , p. 143... 

Organoaluminum porphyrins with axial alkyl groups (la, lb) are effective for the living polymerization of unsaturated monomers such as acrylates (20)- and methacrylates (21),-2 whereas chloride, alcoholate, phenolate and carbox-ylate complexes (Ic-f) are totally inert for the polymerization of these monomers. In contrast to the polymerization of polar vinyl monomers, controlled polymerization of nonpolar vinyl monomers such as styrene with aluminum porphyrins has been unsuccessful. 

Chen EY-X. Coordination polymerization of polar vinyl monomers by single-site metal catalysts. Chem Rev 2009 109 5157-5214. 

A patent disclosure claims the polymerization of polar vinyl monomers in a constant electric field.No details were available to the authors on this method of polymerizing MA. 

Recent reviews on the coordination polymerization of polar vinyl monomers constitute excellent and comprehensive accounts regarding the latest developments in Al-mediated alkyl methacrylate polymerization [67-69]. Noteworthy results in this area are highlighted in this section. 

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