Polymeric organolithium compounds

We have previously reported the results of careful investigations of the solution carbonation (8) and oxidation (9) of polymeric organolithium compounds. These studies have been extended to the investigation of solid-state carbonation reactions and these results are reported herein. In addition, a new method has been developed for the synthesis of telechelic polymers with primary amine end-group... 

Carbonation. The carbonation of polymeric organolithium compounds using carbon dioxide is one of the most useful functionalization reactions. However, there are special problems associated with the carbonation of polymeric organolithium compounds. For example,... 

Wyman, Allen and Altares (20) reported that the carbonation of poly-(styryl)lithium in benzene with gaseous carbon dioxide produced only a 60% yield of carboxylic acid the acid was contaminated with significant amounts of the corresponding ketone (dimer) and tertiary alcohol (trimer) as shown in eq. 6. A recent, careful, detailed investigation of the carbonation of polymeric organolithium compounds has... 

Since Lewis base additives and basic solvents such as tetrahydrofuran are known to deaggregate polymeric organolithium compounds, (21,23,26) it was postulated that ketone formation would be minimized in the presence of sufficient tetrahydrofuran to effect dissociation of the aggregates. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium (eq. 9), poly(isoprenyl)-lithium, and poly(styrene-b-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the carboxylic acid chain ends (8 ). 

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. 

Adogen 464, coupling reagent, poly(phenylene oxide), 190 Amination, polymeric organolithium compounds, 139-145... 

Lewis bases effect dramatic changes in microstructure, initiation rates, propagation rates, and monomer reactivity ratios for alkyllithium—initiated polymerizations of vinyl monomers (1-6). Some insight into the molecular basis for these observations has been provided by a variety of NMR, colligative property, and light-scattering measurements of simple and polymeric organolithium compounds in hydrocarbon and basic solvents... 

In general, simple alkyllithiums exist predominantly as either hexamers (for sterically unhindered RLi) or tetramers (for sterically hindered RLi) in hydrocarbon solvents and as tetramers in basic solvents (9-12). Polymeric organolithium compounds such as poly(styryl)lithium exist as dimers in hydrocarbon solution and are unassociated in basic solvents such as tetrahydrofuran (13-15). The state of association of poly-(dienyl)lithiums in hydrocarbon solution is a subject of current... 

This supposition is supported by results for linking reactions of polymeric organolithium compounds which indicate that the steric requirements of a poly(styryl) chain end are larger than those for a poly(dienyl) chain end ( 4,25). Since a larger sensitivity to base steric requirements is exhibited by poly-(isoprenyl)lithium and it is known that the coordination process for poly(styryl)lithium involves coordination to give the unassociated species (eq 1), it is concluded that tetrahydrofuran coordination with poly(isoprenyl)lithium must involve interaction with an associated species (presumably the dimer) to explain the large sensitivity to the steric requirements of the base. 

The most dramatic effects of Lewis bases in organolithium chemistry are observed in polymerization reactions. Aside from colligative property measurements, there is little direct quantitative information on the nature of the organolithium-base interactions responsible for the observed effects. The calorimetric method has been used also to examine the fundamental nature of the interaction of bases with polymeric organolithium compounds 83,88,89). Information is now available on the ground-state interaction of bases with poly(styryl)lithium (PSLi), poly(isoprenyl)lithium (PILi) and poly(butadienyl)lithium (PBDLi). 

With this background, the following range of products could be forme in the oxidation of a polymeric organolithium compound (Eq. (89)) as illustrated for polystyrene. q... 

Any rigorous study of the oxidation of polymeric organolithium compounds should consider these products and their variation in yield with reaction conditions. To date, few of these reaction products have been considered, let alone identified and analyzed. However, the presence of the macroperoxide has been identified recently among the products of the oxidation of poly(styryl)lithium 352). Lithium aluminium hydride reduction followed by SEC analysis of the dimer fraction before and after reduction... 

Polymeric organolithium compounds exhibit good stability in hydrocarbon solutions at ambient temperatures and for short periods at elevated temperatures [101, 102]. The principal mode of decomposition is loss of lithium hydride to form a double bond at the chain end as illustrated in Equation 7.22 for poly(styryl)lithium. 

Polymeric organolithium compounds exhibit limited stability in ether solvents similar to alkyllithium compounds. Living carbanionic polymers react with ether solvents such as THF in a pseudo-tirst-order decay process and the rate decreases in the order Li > Na > K. For example, a 10 M solution of poly(styryl)lithium in THF at 25 °C exhibited a rate of decay of a few percent per minute, but poly(styryl)cesium was found to be exceptionally stable [96], Metalation and decomposition reactions can also occur in the presence of amines such as TMEDA. 

There have been two general approaches that have been used to increase the efficiency of linking reactions of polymeric organolithium compounds with multifunctional silyl halides. The first procedure is to add a few units of butadiene to either the poly(styryl)lithium or poly(isoprenyl)lithium chain ends to effectively convert them to the corresponding less sterically hindered poly(butadienyl)lithium chain ends. For example, after crossover to butadienyllithium chain ends, the yield of four-armed star polyisoprene with silicon tetrachloride was essentially quantitative in cyclohexane [255]. The second method is to utilize a polychlorosilane compound in which the silyl halide units are more separated to reduce the steric repulsions in the linked product. 

Scheme 7.25 Branching chemistry of polymeric organolithium compounds with divinylbenzenes.

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]. 

The reaction of polymeric organolithium compounds with ethylene oxide (EO) is a model specific functionalization reaction. For example, the functionalization of PSLi with 4 equivalents of EO in benzene at 25 ° C proceeds quantitatively with no oligomerization to produce the corresponding co-hydroxyl-ftmctionalized polymer in the absence of polar additives (eqn [4]) ... 

The functionalization of polymeric organolithium compounds with 3,4-epoxy-1-butene (EPB) provides the potential to prepare a polymer molecule with dual functionality as well as a potential precursor to a diene-functionalized macromonomer. It has been shown that the reaction of EPB with methyllithium results in three modes of addition to the... 

Another useful and efficient hydroxyl functionalization procedure is the reaction of polymeric organolithium compounds... 

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