Methacrylates, alkyl living anionic polymerization

Sugimoto, H., Aida, T., and Inoue, S,. 1994, Lewis Acid-Promoted Living Anionic Polymerization of Alkyl Methacrylates Initiated with Aluminum Porphyrins. Importance of Steric Balance between a Nucleophile and a Lewis Acid, Macromolecules, 27 3672... 

Controlled/Living Anionic Polymerization of Alkyl Methacrylates Using Flow Microreactor Systems... 

Similarly, MF synthesis offers crucial benefits for living anionic polymerization [39b,46]. For example, for polymerization of alkyl methacrylates conducted in a flow microreactor system, control over molecular weight distribution was achieved under easily accessible conditions at temperatures of —28 °C (methyl methacrylate, Mw/Mn = 1.16), 0°C (butyl methacrylate, M /M = 1.24), and 24°C (t-butyl methacrylate, M /M = 1.12) [39b]. The molecular weight of the polymer increased with increasing monomer to initiator ratio. Furthermore, a subsequent reaction of a reactive polymer chain with alkyl methacrylate yielded a block copolymer with a narrow molecular weight distribution. 

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)... 

A new technique was developed recently, by introducing cationic to anionic transformation. A living carbocationic polymerization of isobutylene is carried out first. After it is complete, the ends of the chains are transformed quantitatively to polymerization-active anions. The additional blocks are then built by an anionic polymerization. A triblock polymer of poly(methyl methacrylate)-polyisobutylene-poly(methyl methacrylate) can thus be formed. The transformation involves several steps. In the first, a compound like toluene is Friedel-Craft alkylated by a,6t>"di-rerr-chloro-polyisobutylene. The ditolylpolyisobutylene which forms is lithiated in step two to form a,cu-dibenzyllithium polyisobutylene. It is then reacted with 1,1-diphenylethylene to give the corresponding dianion. After cooling to -78 °C and dilution, methyl methacrylate monomer is introduced for the second polymerization in step three. 

Although organometallic catalysts have attracted the most attention lately with regard to the anionic polymerization of alkyl methacrylates, it is important to recognize that alkali metal alkoxides in a variety of media can initiate the polymerization of both alkyl methacrylates and alkyl acrylates. Especially in view of the recent discovery and reporting of controlled, living acrylate and methacrylate polymerizations via group transfer... 

Polymers of alkyl methacrylates are important materials that have many industrial uses. In anionic polymerization of an alkyl methacrylate, however, the initiator or the living end of the propagating polymer can undergo a nucleophilic reaction with the ester carbonyl group. With the need to suppress such side reactions, anionic polymerization of methacrylates has been more difficult than anionic polymerization of styrenes [11, 12]. The flow microreactor system allows anionic polymerization of methacrylates under the conditions that are easily accessible in industrial production (-30 °C or above) [13-15]. 

Alkyllithium initiators are primarily used as initiators for polymerizations of styrenes and dienes. They effect quantitative living polymerization of styrenes and dienes in hydrocarbon solution. In general, these alkyllithium initiators are too reactive for alkyl methacrylates and vinylpyridines. n-Butyllithium is used commercially to initiate anionic homopolymerization and copolymerization of butadiene, isoprene, and styrene with linear and branched structures. Because of its high degree of association (hexameric), n-butyllithium-initiated polymerizations are often effected at elevated temperatures (>50 °C) and in the presence of small amounts of Lewis base to increase the rate of initiation relative to propagation and thus obtain polymers with narrower molecular weight distributions [55, 57]. 

The preparations by anionic mechanism of A——A type block copolymers of styrene and butadiene can be carried out with the styrene being polymerized first. Use of alkyl lithium initiators in hydrocarbon solvents is usually a good choice, if one seeks to form the greatest amount of c/s-1,4 microstructure [346]. This is discussed in Chap. 4. It is more difficult, however, to form block copolymers from methyl methacrylate and styrene, because living methyl methacrylate polymers fail to initiate polymerizations of styrene [347]. The poly(methyl methacrylate) anions may not be sufficiently basic to initiate styrene polymerizations [345]. 

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