Telechelic controlled radical polymerizations

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... 

Among the controlled radical polymerization methods discussed here, ATRP is the most applied route for the preparation of telechelics since besides the initiator functionalization, the terminal halogen produced in ATRP can easily be converted to many useful functionalities, eg by nucleophilic substitution (82). 

The synthesis of telechelics via radical polymerization techniques has been extensively reviewed. Telechelics are typically synthesized free radically by controlling the structure of the end groups either by using a large amount of initiator (dead end polymerization), or by... 

End-functional polymers, including telechelic and other di-end functional polymers, can be produced by conventional radical polymerization with the aid of functional initiators (Section 7,5.1), chain transfer agents (Section 7.5.2), monomers (Section 7.5.4) or inhibitors (Section 7.5.5). Recent advances in our understanding of radical polymerization offer greater control of these reactions and hence of the polymer functionality. Reviews on the synthesis of end-functional polymers include those by Colombani,188 Tezuka,1 9 Ebdon,190 Boutevin,191 Heitz,180 Nguyen and Marechal,192 Brosse et al.rm and French.194... 

The goal of producing low cost ( 1—5/lb.) acrylic block, comb, star, and telechelic polymers by GTP and anionic polymerization has not been met. Free radical polymerization of acrylics and other vinyl monomers on the other hand requires little purification of materials, works in water and other protic solvents, and is low cost. Considerable efforts are presently under way therefore to develop controlled free radical polymerization methods. 

This article describes the general techniques for the preparation of telechelics. A special emphasis has been placed on controlled radical and metathesis polymerization methods. 

Conventional Radical Polymerization. Telechelics can be synthesized by radical polymerization (qv) in two ways End groups can be controlled using a large concentration of (functional) initiator (dead-end pol3unerization), or polymerization can be conducted in the presence of suitable transfer agents (telomer-ization) (10-14). 

The major differences between the polymers prepared by ATRP and prior art polymers prepared by a conventional radical polymerization (RP) are the additional degrees of control over architecture, MW, MWD, and telechelic functionality provided by GRP. 

For nitroxide-mediated radical polymerizations and in the RAFT process, the same synthetic strategy as for ATRP can be used in the synthesis of AB and ABA block copolymers. The first step is coupling a functionalized alkoxyamine with a telechelic or monofunctional nonvinylic polymer to give a macroinitiator. This macroinitiator can be used in standard controlled free-radical polymerization procedures. This approach is best illustrated by the preparation of PEO-based block copolymers [81-84]. One example is the preparation of macroinitiator LMI-7 by the reaction of a monohydroxy-terminated PEO with sodium hydride followed by reaction with the chloromethyl-substituted alkoxy amine as shown in Scheme 3.16. 

In addition to the initiator-controlled polymer functionalization, transfer reactions may result in functional polymers. In free-radical polymerization, thiols are often employed as chain transfer agents. Chain transfer reactions involving thiols proceed via atom abstraction, as illustrated in Scheme 3. Consequently, these molecules do not offer any scope for introducing functionalities at both ends. However, monofunctional telechelics have been successfully prepared by using thiols. For example, Boutevin and co-workers [39,40] introduced polymerizable vinyl groups to polyvinylchloride accord-... 

Matyjaszewski, K., Ga5mor, S. G., and Coca, S. (1998). Controlled atom or group-transfer radical pol5mierization, coupling of molecules, multifunctional polymerization initiators, and formation of telechelic functional material. In PCT Int. Appl. WO 9840415, Carnegie Mellon University, USA, 230 pp. 

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