Living anionic polymerization polymerization

Keywords Anionic polymerization. Living Polymerization, Immortal polymerization, Metalloporphyrin, Lewis acid... 

Perhaps the most controlled method for the direct introduction of functionality is by living anionic polymerization. Such polymerization proceeds with an absence of chain transfer and termination, leading to polymers with predictable MW s, narrow MWD s, defined architectures and a high degree of functional purity. It is not uncommon to prepare linear or star polymers witfi MWD s <1.1 and functional purity > 95%. ... 

A new synthetic route for the preparation of polyisobutylene (PIB) based block copolymers was developed by combining living carbocationic and anionic polymerizations. Living PIB chains were quantitatively end-capped with 1,1-diphenylethylene (DPE) leading to 1,1-diphenyl-l-methoxy (DPOMe) and/or 2,2-diphenyl vinyl (DPV) termini. This end-capping process is very sensitive to temperature, and retroaddition of DPE occurs in an equilibrium reaction above about -70 °C. Both the DPOMe and DPV terminated PIBs, and the mixtures of the two endgroups were quantitatively metalated with K/Na alloy, Cs metal and Li dispersion in THF at room temperature. 

Classification of Polymers Properties 1223 Addition Polymers A Review and a Preview 1225 Chain Branching in Free-Radical Polymerization 1227 Anionic Polymerization Living Polymers 1230 1 Cationic Polymerization 1232... 

Teyssie and coworkers found that the anionic polymerization ( Living Polymer-formation ) of methacrylate and acrylate esters in the presence of lithium chloride along with the anionic initiator results in polymers with particularly uniform molecular weight distributions. By this technique, di-and tri-block copolymers and star-block copolymers may readily be prepared. If rerr-butyl acrylate (or methacrylate) is one of the comonomers, hydrolysis of such copolymers with a small amount of / -toluenesulfonic acid leads to a copolymer containing acrylic (or methacrylic) acid [25-27]. 

Three decades after the discovery of living anionic polymerizations, living carbocationic polymerizations were discovered [19]. Isobutylene was polymerized in the presence of cumyl acetate and boron trichloride. The molecular weight increased with increasing amount of isobutylene. In a typical cationic polymerization, the reaction is initiated by protonation of the alkene to give a carbocation. Termination happens by elimination to form an alkene. 

Keywords. Anionic polymerization. Living anionic polymerization, 1,1-Diphenylalkyl-lithiums. Functionalized polymers. Block copolymers. Macromonomers, Star-branched polymers. Dilithium initiators. Trilithium initiators. Multifunctional initiators. Living linking reactions. Heteroarm star polymers, Miktoarm star polymers... 

Scheme 4.19 Synthesis of 4-arm ABCD miktoarm star polymers by combination of living anionic polymerization, living/controlled radical polymerization, and click reaction.

Lodge [1] reviewed the synthesis, structure, morphology, properties, and processing of block copolymers in a well documented article. The part synthesis is mainly devoted to living anionic polymerization, radical polymerization, and chemical modification, but polycondensation and polyaddition reactions are not mentioned, despite that the above examples show their importance in the production of organic materials. 

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 anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

Cationic Polymerization. For decades cationic polymerization has been used commercially to polymerize isobutylene and alkyl vinyl ethers, which do not respond to free-radical or anionic addition (see Elastomers, synthetic-BUTYLRUBBEr). More recently, development has led to the point where living cationic chains can be made, with many of the advantages described above for anionic polymerization (27,28). 

Group-Transfer Polymerization. Du Pont has patented (29) a technique known as group-transfer polymerization and appHed it primarily to the polymerization of acrylates and methacrylates. It is mechanistically similar to anionic polymerization, giving living chains, except that chain transfer can occur (30). 

Anionic polymerization, if carried out properly, can be truly a living polymerization (160). Addition of a second monomer to polystyryl anion results in the formation of a block polymer with no detectable free PS. This technique is of considerable importance in the commercial preparation of styrene—butadiene block copolymers, which are used either alone or blended with PS as thermoplastics. 

The earliest SIS block copolymers used in PSAs were nominally 15 wt% styrene, with an overall molecular weight on the order of 200,000 Da. The preparation by living anionic polymerization starts with the formation of polystyryl lithium, followed by isoprene addition to form the diblock anion, which is then coupled with a difunctional agent, such as 1,2-dibromoethane to form the triblock (Fig. 5a, path i). Some diblock material is inherently present in the final polymer due to inefficient coupling. The diblock is compatible with the triblock and acts... 

A polymer-bound hindered amine light stabilizer [P-HALS] has been synthesized by terminating the living anionic polymerization of isoprene with 4(2,3-epoxy pro-poxy)-1,2,2,6,6-pentamethylpiperidine followed by hydrogenation of the resulting polymer to E-P copolymer using Zeigler type catalyst [40] ... 

Regarding anion radical transfer, low-molecular weight azo compounds were used as terminating agents in anionic polymerizations. An interesting example is the addition of a living polystyrene chain to one nitrile group of AIBN [71]. The terminal styryl anion is likely to form... 

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