Polymeric carbanion

While a planar configuration characterizes the last monomeric unit of a polymeric chain growing by a radical or carbonium ion mechanism, a tetrahedral configuration should be attributed to the end of a growing polymeric carbanion. Hence an isotactic or a... 

The stability of polystyryl carbanions is greatly decreased in polar solvents such as ethers. In addition to hydride elimination, termination in ether solvents proceeds by nucleophilic displacement at the C—O bond of the ether. The decomposition rate of polystyryllithium in THF at 20°C is a few percent per minute, but stability is significantly enhanced by using temperatures below 0°C [Quirk, 2002], Keep in mind that the stability of polymeric carbanions in the presence of monomers is usually sufficient to synthesize block copolymers because propagation rates are high. The living polymers of 1,3-butadiene and isoprene decay faster than do polystyryl carbanions. 

Electrochemical (cyclovoltametric) investigations of the ladder-type poly-(para-phenylene) species 71 support the results of the chemical oxidation (doping) experiments both in solution and in the solid state (film). A reversible oxidation takes place and it is well-separated into two waves especially in the solid-state experiment. These are assigned to the formation of radical cationic (79) and dicationic species (80), respectively. The halfwave potential (E1/2) for the first oxidation wave lies between 0.75 V (solution experiment) and 0.95 V (solid state - film) - versus a standard calomel electrode SCE) [106]. Consequently, one has to search for an alternative synthetic process to generate the ladder-type poly(phenylenemethide)s 77 or polymers containing extended segments of the fully unsaturated structure desired. The oxidation of polymeric carbanions appeared suitable, but it proved necessary to work under conditions which completely exclude water and air. 

The formation of the polymeric carbanions 81 of the fluorenyl-type is successful starting from the poly(para-phenylene) ladder polymer 71 with butyl-lithium as metallating agent. The degree of lithiation lies in the range of 90-95% (NMR). The UV/VIS absorption spectrum of these polymeric anions (81) is comparable with that of the 9-phenylfluorenyl anion and indicates the presence of mostly localized (anionic) sub-structures [101]. 

Most interesting from the standpoint of commercial development is the formation of block copolymers by the living polymer method. Sequential addition of monomers to a living anionic polymerization system is at present the most useful method of synthesizing well-defined block copolymers. Depending on whether monofunctional or difunctional initiators are used, one or both chain ends remain active after monomer A has completely reacted. Monomer B is then added, and its polymerization is initiated by the living polymeric carbanion of polymer A. This method of sequential monomer addition can be used to produce block copolymers of several different types. 

A.A. Shvartz, Anionic Polymerization Carbanions, Living Polymers and Processes with Electron Transfer, Mir, Moscow, 1971, p. 669. 

The carbonation of polymeric carbanions using carbon dioxide is one of the simplest, most useful, and widely used functionalization reactions. However, there are special problems associated with the simple carbonation of polymeric organolithium compounds. Eor example, when carbonations with high-purity, gaseous carbon dioxide are carried out in benzene solution at room temperature using standard high vacuum techniques, the carboxylated polymer is obtained in only 27-66% yield for PSLi, PILi, and poly(styrene-b-isopre-nyl)lithium. The functionalized polymer is contaminated with dimeric ketone (23-27%) and trimeric alcohol (7-50%)... 

According to the second method of carbonate block copolymer synthesis, sequential monomer polymerization is proceeded with transformation of the active center. The block copolymers are prepared in three steps. First, the polymerization of one monomer is carried out. After complete conversion of the first monomer the transformation of active centers is performed, and the initiation of the polymerization of the second monomer is proceeded. For example, this approach was applied for obtaining poly(styrene-l7-neopentyl carbonate).After completion of the styrene living polymerization, carbanionic centers were transformed into alkoxide ones via reaction with EO and then the ROP of neopentyl carbonate polymerization was performed. In the case of block copolymers of methyl methacrylate with neopentyl carbonate living PMMA, prepared according to GTP, was used as a macroinitiator for DTC polymerization. A silyl keteneacetal active center was transformed to an alkoxide one. Depending on the functionality of the macroinitiator (A) used for cyclic carbonate polymerization, two types of block copolymers can be obtained A-B or B-A-B. 

The formed during the polymerization carbanion macrocations may be subject of termination deactivity. The chain transfer can take place ... 

This work describes the direct reaction of living polymeric carbanions to form well-defined trialkoxysilyl functional organic polymers. The macromonomers (/= 1) were subsequently hydrolyzed and condensed to yield narrow molecular weight distribution star polymers. Although telechelic (/= 2) trialkoxysilyl functional oligomers have also been prepared and studied in detail, the product after hydrolysis and condensation is an insoluble network, not a soluble star pol)mier. These crosslinked condensation products are not amenable to structural characterization in solution. 

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