Anionic chain-functionalized polymers

The application of these functionalization reactions to polymers has been catalogued in the anionic polymer review literature (4-6). Unfortunately, many of the reported applications of these functionalization reactions to anionic chain-ended polymers have not been well characterized (7). In order to exploit these functionalization reactions to their potential, well-defined procedures for quantitative chain end functionalization must be available. 

Both chain-end (telechelic) and in-chain functional polymers can be synthesized by anionic methods. For example, termination of living lithiomacromolecules with electrophilic reagents can, in principle, result in a wide variety of telechelic polymers (Scheme 2). ... 

The addition reaction of the functional DPE derivative to a Hving anionic polymer is not, in itself, a termination reaction. After the reaction, the chain-end anion is changed to a DPE-derived anion, which can initiate an anionic polymerization of additional monomers, such as styrene, 2-vinylpyridine, or methyl methacrylate, to extend the chain or to form a new block (Scheme 5.17). Thus, this reaction offers the potential of providing a quite novel chain-functionalization procedure, with which the functional groups can be introduced at essentially any position in a polymer chain [174]. Accordingly, functionalization using functional DPE derivatives is a versatile procedure, not only for the preparation of chain-end-functionaUzed polymers but also for in-chain-functionalized polymers that are difficult to synthesize by any other method [172-174]. 

Scheme 5.17 Synthesis of in-chain-functionalized polymers by polymerization of additional monomers with polymer anions.

Reaction of Living Anionic Polymers with Flectrophiles Synthesis of Chain-Functionalized Polymers 101... 

Olechnowicz, M. Synthesis of End-Chain and In-Chain Functionalized Polymers by Anionic Polymerization-, The University of Akron Akron, OH, 2008. 

Higashihara, T, Hayashi, M., and Hirao, A. (2002) Synthesis of branched polymers by means of Uving anionic polymerization, 9 Radical coupling reaction of 1,1-diphenylethylene-functionalized polymers with potassium naphthalenide and its application to syntheses of in-chain-functionalized polymers and star-branched polymers. Macromolecular Chemistry and Physics, 203,166-175. 

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

Anionic polymerizations are well suited for the synthesis of polymers fitted at chain end with reactive functions. Block copolymers can result from reactions between suitable functions carried by two different functional precursors. In some cases the carbanionic sites themselves are the reactive functions. In other cases, functional polymers (obtained anionically, or by other methods) can be reacted with low molecular weight coupling agents. Here are a few examples ... 

Functionalization of these reactive anionic chain ends can be achieved by a variety of methods all based on the general concepts of carbanion chemistry. For example, reaction with C02 or succinnic anhydride leads to the carboxy terminated derivatives [10], while hydroxy-terminated polymers can be easily obtained by reaction with ethylene oxide (Scheme 3) [11]. In select functionalization reactions, such as alkylation with p-vinyl benzyl chloride, the nucleophilicity of the carbanionic species may be necessary and this can be achieved by reaction of the chain end with 1,1-diphenylethene followed by functionalization [12,13]. 

Synthesis of well defined functionalized (- telechellc or multifunctional-) macromolecules Is an Important task for polymer chemists. The polymers with P0(0R)2, - Si(0R)3, -OH, - . .. functional groupslrS. are produced In limited quantities. The need for polymeric materials possessing specific properties has led to a renewed Interest Is functional polymers, especially if the initial material Is a common hydrocarbon polymer. One of the techniques that we use in our laboratory to prepare these new molecules Is based on anionic processes. This anionic technique is best suited to control the length of the chains prepared and to obtain samples with low polydlsperslty. Although the functionalization of carbanionic sites with various deactivating reagents Is easier than with other methods because of the long lived species, It Is still necessary to carefully control the deactivation reaction to prevent secondary reactions. 

The use of alkyllithium initiators which contain functional groups provides a versatile method for the preparation of end functionalized polymers and macromonomers. For a living anionic polymerization, each functionalized initiator molecule produces one macromolecule with the functional group from the initiator residue at one chain end and the active carbanionic propagating species at the other chain end. 

The carbonation of dilithium reagents is complicated by the occurrence of gelation phenomena which produce severe mixing problems 145 146-323). In general, lithium derivatives of heteroatoms are highly associated in solution therefore, heteroatom functionalization of polymers with two active anionic chain ends will form an insoluble, three-dimensional network. The beneficial effect of decreasing the effects of association and gelation by solvents with solubility parameters <7.2 has been reported in the literature 140,324). 

In addition to post-functionalizing polymers by bonding the macrocycle to the preformed polymer backbone, macrocycles can be incorporated into polymer matrices by direct polymerization of the macrocycle, either by a step-growth mechanism or a chain-growth mechanism. [46] Polymeric crown ether stationary phases were pioneered by Blasius et al. [34, 59-62] These resins were used to separate both cations (including protonated amines) with a common anion, and anions with a common cation in high... 

A specialty class of carboxyl containing elastomers are the telechelic ionomers. In these systems the carboxyl functionality terminates both ends of the polymer chain. Such polymers range in molecular weight from 1500 to about 6000. These materials can be prepared via several synthetic routes involving anionic or free radical initiated polymeri-zation(32-34). Recently, telechelic sulfonate ionomers of poly-isobutylene have been synthesized(35). These systems offer an unusual opportunity to assess the influence of chain length, chain architecture, cation type, and the Influence of polar additives on ionomer properties. 

We have also observed that, at elevated temperature (50°C), DPE could effectively cap the living anionic polyferrocenylsilane directly.30 Therefore, the addition of DMSB to pump up the activity of PFS anionic chain ends can potentially be omitted, but the yield of the isolated PFS- -PMMA is significantly reduced.31 The living DPE-capped PFS polymers also can react with chloromethyl functionalities of poly(styrene-co-chloromethylstyrene) (PS-co-PCMS), leading to the first PS-g-PFS graft copolymers (see Scheme 3.10).30... 

Recent developments have also been reviewed for the synthesis of telechelic (functional groups at both ends) and semitelechelic (functional group at one end) polymers via anionic methods (54). The use of two basic procedures is reported 1. termination of living anionic chains with suitable electrophiles, and 2. the use of functionally substituted anionic initiators. Two of these latter initiators are acetals that give good molecular weight control and monodispersity ... 

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