Telechelic and block copolymers

Free-radically initiated polymerizations typically do not possess living characteristics since termination process is unavoidable this is because two free radicals very readily combine to form a stable covalent bond and, therefore, two growing chains would readily terminate, either by combination or by disproportionation. 

One of the major drawbacks of CRPs is the inability to prepare block copolymers of monomers with widely differing reactivities, such as styrene and vinyl acetate, by sequential monomer addition. Thus, the use of chemistries that permit effective coupling between suitably end-functionalized preformed polymer chains is clearly an attractive alternative. Quemener et al. designed two novel RAFT agents that could be used to polymerize styrene and vinyl acetate independently [36] one RAFT agent installed an azide unit at the end of the polyvinyl 

Smeets et al. developed a similar approach to prepare a diblock copolymer carrying two different poly(thiophene) derivatives, namely 3-alkyl and 3-alkoxy polythiophenes, using a CuAAC reaction as the final coupling reaction between the two different polythiophene blocks [41]. 

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Lou X, Detrembleur C, Jerome R (2002) Living cationic polymerization of 5-valerolactone and synthesis of high molecular weight homopolymer and asymmetric telechelic and block copolymer. Macromolecules 35 1190-1195... 

Kennedy and co-workers 2 117) used the changing effect of the initiation ability of the Lewis acids according to Eq. (17) and the termination tendency of the anion formed according to Eq. (18) in order to obtain telechelic polymers , block copolymers and graft copolymers in a controlled manner. Quantum chemical calculations provide the possibility to discuss structural influences which work on the equilibrium Eq. (19) and therefore on the stability of the two adjacent ions. 

The remarkable contrd fliat can be exercised on certain processes. Predetermined DP s, narrow DP distributions, and the synthesis of telechelic polymers and block copolymers are now possible in some instances, and living cationic systems are beii perfected. These achievements close tire gap between anionic and cationic pol5meri-sation. 

All these methods have several disadvantages multistep endgroup derivatizations are required for the synthesis of the telechelic PIB initiator precursor, and lithiation and thus the subsequent initiation of anionic polymerization is not quantitative or it requires extreme conditions. As a consequence of less than 100 % initiating efficiency these methods yielded mixtures of homopolymers and block copolymers. This is indicated by the fact that it was claimed that PMMA-Z -PIB-6-PMMA was only obtained by selective extraction ... 

E. N. Peters, Telechelic polyisobutylene and block copolymer derivatives, U.S. Patent... 

Anionic polymerization, particularly of vinyl monomers, has achieved a position of special importance because the possibility of obtaining a system free of any termination step can often be realised. The attraction of this is two-fold (i) the cleanness of such systems facilitates kinetic study and (ii) the reactive chain ends open valuable synthetic routes to telechelic polymers and block copolymers, possibly stereoregular in structure. 

Advantages of end-group transformation include the ability to incorporate functionality incompatible with the polymerization procedure, to prepare halogen-free materials for subsequent reactive processing, to allow characterization of the initial copolymer prior to further functionalization, and an ability to prepare telechelic polymers, block copolymers, and materials that can be immobilized to surfaces, by a full range of substitution and addition chemistry. The use of a difunctional initiator allowed for the first time in a radical process preparation of functional homo-telechelic polymers with almost any desired chain end functionality (Scheme 33). ... 

Synthesis of complex polymeric molecules such as random and block copolymers, star and graft polymers, hyperbranched and dendritic structures by NMP and other CRP techniques has been reviewed several times. Good overviews of telechelic polymers or the coupling of NMP with other polymerization techniques are available. Synthesis of bioconjugates through CRDRP, including NMP, is treated by Nicolas et... 

The quantum yield of polymerization is 6.72 and for photoinitiation < / = 2.85 x 10 . The polystyrene produced with this initiator shows photosensitivity when irradiated with UV light (A = 280 nm). This polymer, which carries two photosensitive end groups of - SC(S) N(CH3)2, behaves as a telechelic polymer and it is useful for production of ABA block copolymer. 

Depending on the choice of transfer agent, mono- or di-cnd-functional polymers may be produced. Addition-fragmentation transfer agents such as functional allyl sulfides (Scheme 7.16), benzyl ethers and macromonomers have application in this context (Section 6.2.3).212 216 The synthesis of PEG-block copolymers by making use of PEO functional allyl peroxides (and other transfer agents has been described by Businelli et al. Boutevin et al. have described the telomerization of unsaturated alcohols with mercaptoethanol or dithiols to produce telechelic diols in high yield. 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Figure 8 The air-stable 77-conjugated organoboron segmented block copolymer (8) obtained by the hydroboration polymerization of allyl-telechelic polyisobutylene, 1,9-decadiene, and tripylborane. (Adapted from ref. 28.)...

The transformation of the chain end active center from one type to another is usually achieved through the successful and efficient end-functionalization reaction of the polymer chain. This end-functionalized polymer can be considered as a macroinitiator capable of initiating the polymerization of another monomer by a different synthetic method. Using a semitelechelic macroinitiator an AB block copolymer is obtained, while with a telechelic macroinitiator an ABA triblock copolymer is provided. The key step of this methodology relies on the success of the transformation reaction. The functionalization process must be 100% efficient, since the presence of unfunctionalized chains leads to a mixture of the desired block copolymer and the unfunctionalized homopolymer. In such a case, control over the molecular characteristics cannot be obtained and an additional purification step is needed. 

In aqueous solvent a hydrophobic environment was constructed by using a water-soluble and hydrophobic tri-block copolymer (Scheme 7). The central block is hydrophobic and composed of the copolymer of styrene and N-vinylimidazole (PSI), to which Cu ions can coordinate. This central block was synthesized by UV-irradia-tion polymerization bytelechelic initiator of bis(4-carbomethoxy-phenyl)-disulfide. The reaction of telechelic block with poly-(ethyleneoxide) gave the block copolymer PE0-PSI-PE0. 

Anionic and cationic living polymerizations offer routes to block copolymers, star polymers, telechelic polymers, and other polymers [Charleux and Faust, 1999 Hadjichristidis et al., 2002],... 

Block copolymers of isobuylene with styrene, isoprene, and vinyl ethers have been synthesized, often requiring an appropriate adjustment of reaction conditions for the second stage, as described above for styrene-MVE. Another approach is the use of a telechelic polymer (containing the first block) as the initiator for polymerization of the second monomer (Sec. 5-4b). 

Telechelic polymers, containing one or more end groups with the capacity to react with other molecules, are useful for synthesizing block and other copolymers [Fontanille, 1989 Hsieh and Quirk, 1996 Nuyken and Pask, 1989 Pantazis et al., 2003 Patil et al., 1998 Quirk et al., 1989, 1996 Rempp et al., 1988]. Living anionic polymers can be terminated with a variety of electrophilic reagents to yield telechelic polymers. For example, reaction with carbon dioxide, ethylene oxide, and allyl bromide yield polymers terminated with carboxyl, hydroxyl, and allyl groups, respectively. Functionalization with hydroxyl or carboxyl groups can also be achieved by reaction with a lactone or anhydride, respectively. Polymers with amine end... 

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