Lithium styrene

This has been studied much less frequently and appears to be a rather more complex reaction. The first results obtained, for the butyl-lithium, styrene reaction in benzene have already been described. In a similar way the addition of butyllithium to 1,1-diphenylethylene shows identical kinetic behaviour in benzene (26). Even the proton extraction reaction with fluorene shows the typical one-sixth order in butyllithium (27). It appears therefore that in benzene solution at least, lithium alkyls react via a small equilibrium concentration of unassociated alkyl. This will of course not be true for reactions with polar molecules for reasons which will be apparent later. No definite information can be obtained on the dissociation process. It is possible that the hexamer dissociates completely on removal of one molecule or that a whole series of penta-mers, tetramers etc. exist in equilibrium. As long as equilibrium is maintained, the hexamer is the major species present and only monomeric butyllithium is reactive, the reaction order will be one-sixth. A plausible... 

Examples of the introduction of metals into polymer chain side groups by polymer analog conversions are the synthesis of poly(p-lithium styrene) [see (3-11)] and the conversion of poly(p-chloromethyl styrene) with sodium tungsten pentacarbonyl ... 

N,N-dimethyl-p-phenylenediamine by the method of Bernthsen33 to give poly( -vinyl Methylene Blue), This polymer acts as a hydrogen acceptor in the enzymatic dehydrogenation of ethanol. The carbinol form (XVIl) of polymeric Malachite Green may be prepared by the. nucleophilic attack of poly(p-lithium styrene) on Michler s ketone 3 acidification gives the colored dye (XVIIl). 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Aromatic radical anions, such as lithium naphthalene or sodium naphthalene, are efficient difunctional initiators (eqs. 6,7) (3,20,64). However, the necessity of using polar solvents for their formation and use limits their utility for diene polymerization, since the unique abiUty of lithium to provide high 1,4-polydiene microstmcture is lost in polar media (1,33,34,57,63,64). Consequentiy, a significant research challenge has been to discover a hydrocarbon-soluble dilithium initiator which would initiate the polymerization of styrene and diene monomers to form monomodal a, CO-dianionic polymers at rates which are faster or comparable to the rates of polymerization, ie, to form narrow molecular weight distribution polymers (61,65,66). 

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. 

Ring Additions Catalyzed by Alkali Metals. The addition of tributyltin chloride and olefins such as styrene, isoprene, or butadiene to sulfolane is cataly2ed by alkah metals, including sodium and lithium, and by sodium amide (10—13). The addition of tributyltin chloride to sulfolane in the... 

Many random copolymers have found commercial use as elastomers and plastics. For example, SBR (62), poly(butadiene- (9-styrene) [9003-55-8] has become the largest volume synthetic mbber. It can be prepared ia emulsion by use of free-radical initiators, such as K2S20g or Fe /ROOH (eq. 18), or in solution by use of alkyl lithium initiators. Emulsion SBR copolymers are produced under trade names by such companies as American Synthetic Rubber (ASPC), Armtek, B. F. Goodrich (Ameripool), and Goodyear (PHoflex) solution SBR is manufactured by Firestone (Stereon). The total U.S. production of SBR in 1990 was 581,000 t (63). 

The styrene-diene triblocks, the main subject of this section, are made by sequential anionic polymerisation (see Chapter 2). In a typical system cc-butyl-lithium is used to initiate styrene polymerisation in a solvent such as cyclohexane. This is a specific reaction of the type... 

Initiating polymerisation of styrene with sec-butyl-lithium. 

When the styrene has been consumed, to give living polymers of narrow molecular mass distribution, more styrene and more catalyst is added. The styrene adds to the existing chains and also forms new polymer molecules initiated by the additional sec-butyl-lithium. 

The earliest SIS block copolymers used in PSAs were nominally 15 wt% styrene, with an overall molecular weight on the order of 200,000 Da. The preparation by living anionic polymerization starts with the formation of polystyryl lithium, followed by isoprene addition to form the diblock anion, which is then coupled with a difunctional agent, such as 1,2-dibromoethane to form the triblock (Fig. 5a, path i). Some diblock material is inherently present in the final polymer due to inefficient coupling. The diblock is compatible with the triblock and acts... 

Of the amorphous block copolymers, styrenic block copolymers are the vast majority. These are synthesized anionically in solution, with butyl lithium commonly employed as the initiator [4]. There are three processes for this polymerization ... 

Sequential one styrene block is polymerized, then the mid-block monomer is added and polymerized, then more styrene is added and the second styrene block polymerized. This process is used to produce 100% triblock rubbers, for maximum strength [5]. Termination is commonly with alcohols, which produces a lithium alkoxide salt as the by-product. 

The styrene double bond in 9(ll)-dehydroestradiol 3-methyI ether (1) or its 8-dehydro counterpart is reduced by potassium or lithium in ammonia without affecting the aromatic ring estradiol 3-methyl ether (2) is formed from both compounds. Reduction of the corresponding 17-ketones occurs with partial or complete reduction of the carbonyl group. Lithium... 

It is well known that anionic samples tend to adsorb on poly(styrene-divinylbenzene) resins. However, cationic samples tend to be repelled from the resins. The mechanism seems to be an ionic interaction, although the poly(styrene-divinylbenzene) resin should be neutral. The reason is not well clarified. Therefore, it is recommended to add some salt in the elution solvent when adsorption or repulsion is observed in the analyses of polar samples. For example, polysulfone can be analyzed successfully using dimethylformamide containing 10 mM lithium bromide as an elution solvent, as shown in Fig. 4.42. 

A mixture containing 186 g (0.20 mol) of 2-aminopyridine, 0.55 g of lithium amide and 75 cc of anhydrous toluene was refluxed for 1.5 hours. Styrene oxide (12.0 g = 0.10 mol) was then added to the reaction mixture with stirring over a period of ten minutes. The reaction mixture was stirred and refluxed for an additional 3.5 hours. A crystalline precipitate was formed during the reaction which was removed by filtration, MP 170°C to 171°C, 1.5 g. The filtrate was concentrated to dryness and a dark residue remained which was crystallized from anhydrous ether yield 6.0 g. Upon recrystallization of the crude solid from 30 cc of isopropyl alcohol, 2.0 g of a light yellow solid was isolated MP 170°C to 171°C. 

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

Chlorotris(diethylamino)titanium24 is prepared directly from diethylamine, lithium and tilani-um(IV) chloride in the presence of styrene as reducing agent25. However, a metathesis reaction between tetrakis(diethylamino)titanium26 28 and titanium(lV) chloride gives a cleaner product and is thus preferred. Bromotris(diethylamino)titanium is prepared similarly7,29. 

The Laboratory prepn for amorph styrene involves thermal conditions or the use of butyl-lithium at 50°. Crystalline polystyrene can be... 

The effect of penultimate units on the rate constants of anionic propagation is observed also in other systems. For example, the addition of styrene to the lithium salt of 1-phenyl-n-hexyl anion is 4 times faster than to polystyryl lithium 51). Similarly, the addition of monomer to the lithium salt of 1,1-diphenyl-n-hexyl lithium is faster than the addition to 1,1,3-triphenyl-n-octyl lithium or 2-poly-sty ry 1-1,1-diphenyl ethyl lithium, the latter two salts having comparable reactivities52 . See also Ref.53)... 

The mechanism of anionic polymerization of styrene and its derivatives is well known and documented, and does not require reviewing. Polymerization initiated in hydrocarbon solvents by lithium alkyls yields dimeric dormant polymers, (P, Li)2, in equilibrium with the active monomeric chains, P, Li, i.e. 

Table 3. Pseudo-first order rate constant kapp of propagation of lithium o-methoxy styrene in toluene at 20 °C. The values collected in the first two columns are taken from Table 2 of Ref. 69)...

The initiation of polymerization of styrene and isoprene in benzene by t-butyl lithium reveals some complexities129) (e.g. zero order kinetics in monomer) not observed in the reaction proceeding in cyclohexane. Further studies of that system are needed. 

Some new initiators soluble in hydrocarbons were described during the last few years. Organo-lithium compounds form 1 1 complexes with alkyls of Mg 134,135), Zn 136) or Cd l36), and their usefulness as initiators of anionic polymerization of styrene and the dienes was established 137). 

The order of reactivities could be also reversed by a change of solvent. For example, in THF styrene is more reactive than butadiene towards salts of polystyryl anions, whereas in hydrocarbon solvents butadiene is more reactive than styrene towards lithium polystyrene. This reversal of reactivities presumably is caused by a change in the mechanism of propagation. The monomers react directly with carbanions in THF, but become coordinated to Li+ in hydrocarbon solvents. 

The correct explanation of the peculiar behaviour of the butadiene-styrene system was provided by O Driscoll and Kuntz 144). As stated previously, under conditions of these experiments butadiene is indeed more reactive than styrene, whether towards lithium polystyrene or polybutadiene, contrary to a naive expectation. This was verified by Ells and Morton 1451 and by Worsfold 146,147) who determined the respective cross-propagation rate constants. It is germane to stress here that the coordination of the monomers with Li4, assumed to be the cause for this gradation of reactivities, takes place in the transition state of the addition and should be distinguished from the formation of an intermediate complex. The formation of a complex ... 

The observation of Tsuji et al. 148) concerned with copolymerization of 1- or 2-phenyl butadiene with styrene or butadiene illustrates again the importance of the distinction between the classic, direct monomer addition to the carbanion, and the addition involving coordination with Li4. The living polymer of 1- or 2-phenyl butadiene initiated by sec-butyl lithium forms a block polymer on subsequent addition of styrene or butadiene provided that the reaction proceeds in toluene. However, these block polymers are not formed when the reaction takes place in THF. The relatively unreactive anions derived from phenyl butadienes do not add styrene or butadiene, while the addition eventually takes place in hydrocarbons on coordination of the monomers with Li4. The addition through the coordination route is more facile than the classic one. 

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