Anionic polymerization living’ polymers

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]. 

Immediately after the discovery of the living character1 of anionic polymerization,2 polymer chemists started synthesizing well-defined linear homopolymers and diblock copolymers with low molecular... 

In the anion-cation transformation reaction, the anionically generated living polymer chain is end-capped with a hahde, producing a chain that can be isolated for subsequent reaction. This can be used to initiate a cationic polymerization of a suitable monomer by activating the end with a silver or hthium salt according to the general scheme shown in Equation 5.20a to Equation 5.20c. 

Szwarc, M., 1983. Living polymers and mechanisms of anionic polymerization. Adv. Polym. Sci. 49, 1-177. 

Jagur-grodzinski J (2002) Functitmal polymers by living anionic polymerization. J Polym Sci A Polym Chem 40 2116-2133... 

Boor J, Jr (1979) Ziegler-Natta Catalysts and Polymerization. Acadetrric Press, New York. Szwarc M (1968) Carbanions, Living Polymers, and Electron Transfer Processes. Interscience, New York see also (1983) Living Polymers and Mechanisms of Anionic Polymerization, Adv Polymer Sci 49 1-175,... 

HIR Hirao, A., Inushima, R., Nakayama, T., Watanabe, T., Yoo, H.-S., Ishizone, T., Sugiyama, K., Kakuchi, T., Carlotti, S., and Deffieux, A., Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization, Eur. Polym. J., 47, 713, 2011. 

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.

In ionic polymerizations termination by combination does not occur, since all of the polymer ions have the same charge. In addition, there are solvents such as dioxane and tetrahydrofuran in which chain transfer reactions are unimportant for anionic polymers. Therefore it is possible for these reactions to continue without transfer or termination until all monomer has reacted. Evidence for this comes from the fact that the polymerization can be reactivated if a second batch of monomer is added after the initial reaction has gone to completion. In this case the molecular weight of the polymer increases, since no new growth centers are initiated. Because of this absence of termination, such polymers are called living polymers. 

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). 

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] ... 

One of the earliest examples of this methodology involves the reaction of a polymeric anion (formed by living anionic polymerization) with molecular oxygen to form a polymeric hydroperoxide which can be decomposed either thermally or, preferably, in a redox reaction to initiate block polymer formation with a second monomer (Scheme 7.25). However, the usual complications associated with initiation by hydroperoxides apply (Section 3.3.2.5). 

---