Organolithium compounds functionalized chains

Other Organolithium Compounds. Organoddithium compounds have utiHty in anionic polymerization of butadiene and styrene. The lithium chain ends can then be converted to useflil functional groups, eg, carboxyl, hydroxyl, etc (139). Lewis bases are requHed for solubdity in hydrocarbon solvents. 

The alkyllithium-initiated, anionic polymerization of vinyl and diene monomers can often be performed without the incursion of spontaneous termination or chain transfer reactions (1). The non-terminating nature of these reactions has provided methods for the synthesis of polymers with predictable molecular weights and narrow molecular weight distributions (2). In addition, these polymerizations generate polymer chains with stable, carbanionic chain ends which, in principle, can be converted into a diverse array of functional end groups using the rich and varied chemistry of organolithium compounds (3). 

No carboxylic acid functionality was detected either by thin-layer chromatographic analyses or by end-group titration. Therefore, procedures are now available to control the carbonation of polymeric organolithium compounds to efficiently produce either the carbox-ylated chain ends or the corresponding ketone dimer. 

The repertoire of reactions possible with organolithium compounds is well documented in the literature 4). The application of these functionalization reactions to polymers is also described in the anionic polymer review literature 314 316). Unfortunately, many of the reported applications of these functionalization reactions to anionic polymers have not been well characterized. Accordingly, one is faced with the situation in which a variety of useful chain end functionalization reactions is potentially possible, but whose application to polymers is not well defined in terms of specifics such as side reactions, yields, solvent effects, etc. The following discussion of representative functionalization reactions is not meant to be exhaustive, but can be regarded as typical of the state-of-the-art in this area. 

In addition to being a synthetic route to unusual graft copolymers, the metalation technique offers a way to add functional groups to the chain by reactions characteristic of organolithium compounds. Hydroxyl or carboxyl groups, for instance, can be added by treating the metalated polyisoprene or polybutadiene (22) solution with ethylene oxide or C02, respectively. The lithium alkoxide and carboxylic salt obtained (23) in... 

Functionalizations via Silyl Hydride Functionalization and Hydrosilation A new general functionalization method based on the combination of living anionic polymerization and hydrosilation chemistry has been developed as illustrated in Scheme 7.26 [281]. First, a living polymeric organolithium compound is quantitatively terminated with chlorodimethylsilane to prepare the corresponding co-silyl hydride-functionalized polymer. The resulting co-silyl hydride-functionalized polymer can then react with a variety of readily available substituted alkenes to obtain the desired chain-end functionalized polymers via efficient regioselective transition-metal-catalyzed hydrosilation reactions [282-284]. 

In conclusion, the addition reactions of simple and polymeric organolithium compounds with substituted 1,1-diarylethylenes provide a general method for the synthesis of a and co end-functionalized and labeled polymers. With this method in conjunction with appropriate protecting groups and reaction conditions, a wide variety of well-characterized, quantitatively functionalized and labeled polymers and copolymers can now be prepared with diverse molecular structures. Polymers can be prepared with functional groups either at the initiating chain end or at the terminating chain end. ... 

The reaction of polymeric organolithium compounds with substituted 1,1-di-phenylethylene derivatives (16) has been shown to be an excellent methodology for anionic synthesis of chain-end functionalized polymers (18) (Eq. 35)... 

Polymeric organolithium compounds react simply and quantitatively with 1,1-diphenylethylenes [3, 109]. These reactions have provided a new methodology for the synthesis of star-branched polymers, internally-functionalized polymer chains and stars, as well as heteroarm, star-branched polymers via living linking reactions as shown in Scheme 33 [3, 202, 203, 207]. 

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