Alkyl lithium compounds anionic polymerization

The syntheses of siloxanes with vinyl groups at the silicon atoms of the chain was performed by anionic ring-opening polymerization of vinyl group-containing cyclotri- or cyclotetrasiloxanes (03, 04 ) with alkyl lithium compounds as initiators. The polymerizations were terminated by chlorosilanes with additional silico- or carbofunctional groups or octyl groups. In the block copolymerizations we used 03 or 04 and hexamethylcyclotrisiloxane (D3) (Scheme 1 and 2). 

Solution-polymerized SBR is made by termination-free, anionic/live polymerization initiated by alkyl lithium compounds. Other lithium compounds are suitable (such as aryl, alkaryl, aralkyl, tolyl, xylyl lithium, and ot/p-naphtyl lithium as well as their blends), but alkyl lithium compounds are the most commonly used in industry. The absence of a spontaneous termination step enables the synthesis of polymers possessing a very narrow molecular weight distribution and less branching. Carbon dioxide, water, oxygen, ethanol, mercaptans, and primary/secondary amines interfere with the activity of alkyl lithium catalysts, so the polymerization must be carried out in clean, near-anhydrous conditions. Stirred bed or agitated stainless steel reactors are widely used commercially. 

It should be noted that the preparation of n-type (reduced) polyacetylene using strong organic bases (e.g., alkyl lithium compounds) or more commonly electron transfer reagents (e.g., sodium naphthalide radical anion) employs the two major classes of initiators used in anionic polymerization of monomers such as styrene and butadiene. Reductive doping can also be accomplished by deprotonation of, for example, acetylene/butadiene copolymers and related phenylenepentadienylenes." ... 

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. 

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). 

Organolithum compounds (lithium alkyls) are the most valuable initiators in anionic polymerization.120168 169172-175 Since living anionic polymerization requires the fastest possible initiation, sec- or ferf-butyllithium is usually used. Lithium alkyls add readily to the double bond of styrene [Eq. (13.32)] or conjugated dienes and form free ions or an ion pair depending on the solvent ... 

Anionic polymerization of vinyl monomers can be effected with a variety of organomciallic compounds alkyllithium compounds are the most useful class. A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds ate soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. 

The methodology to synthesize polymer hybrids by living anionic polymerization is shown in Fig. 3 [30]. Polyolefins containing p-tolyl groups have been used to initiate anionic polymerization by the lithiation of the methyl moiety using alkyl lithium and amine compounds system. 

The initiation of methyl methacrylate polymerization by alkyl- and aryl-lithium compounds is a very complex process which has not been completely elucidated so far. Even less information is available on the efects of or-ganometals not containing lithium. Recently, the interest of some authors has centred on the application of Grignard reagents for the initiation of anionic polymerizations, especially of MMA [171, 172],... 

Additionally, if the initiation reaction is more rapid an the chain propagation, a very narrow molecular weight distribution, MJM = 1 (Poisson distribution), is obtained. Typically living character is shown by the anionic polymerization of butadiene and isoprene with the lithium alkyls [77, 78], but it has been found also in butadiene polymerization with allylneodymium compounds [49] and Ziegler-Natta catalysts containing titanium iodide [77]. On the other hand, the chain growth can be terminated by a chain transfer reaction with the monomer via /0-hydride elimination, as has already been mentioned above for the allylcobalt complex-catalyzed 1,2-polymerization of butadiene. 

The activity of transition metal allyl compounds for the polymerization of vinyl monomers has been studied by Ballard, Janes, and Medinger (10) and their results are summarized in Table II. Monomers that polymerize readily with anionic initiators, such as sodium or lithium alkyls, polymerize vigorously with allyl compounds typical of these are acrylonitrile, methyl methacrylate, and the diene isoprene. Vinyl acetate, vinyl chloride, ethyl acrylate, and allylic monomers do not respond to these initiators under the conditions given in Table II. 

---