Monomers butyllithium

A kinetic study has been carried out on the system butyllithium plus styrene in benzene. Although published reports by Tobolsky (85) and Welch (88) differ in their interpretations, it appears that these differences may be due to the fact that Welch examined a wider range of initiator concentrations. Welch showed that no termination occurs in this system and that the molecular weight was a linear function of the ratio monomer/ butyllithium. The rate results showed... 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

Bifunctional Initiator Arising from Butyllithium and Diunsaturated Monomers... 

Reaction Mechanism. The reaction mechanism of the anionic-solution polymerization of styrene monomer using n-butyllithium initiator has been the subject of considerable experimental and theoretical investigation (1-8). The polymerization process occurs as the alkyllithium attacks monomeric styrene to initiate active species, which, in turn, grow by a stepwise propagation reaction. This polymerization reaction is characterized by the production of straight chain active polymer molecules ("living" polymer) without termination, branching, or transfer reactions. 

The alkyl methacrylate monomers were available from various sources. Isobutyl methacrylate (IBMA) (Rohm and Haas) and t-butyl methacrylate (TBMA) (Rohm Tech) may be purified first by distillation from CaH, followed by distillation from trialkyl aluminum reagents as described in detail earlier (20,21). In particular, t-butyl methacrylate (b.pt. 150°C) was successfully purified by distillation, from triethyl aluminum containing small amounts of diisobutyl aluminum hydride. The trialkyl aluminum and dialkyl aluminum hydride reagents were obtained from the Ethyl Corporation as 25 weight percent solutions in hexane. The initiator, -butyllithium, was obtained from the Lithco Division of FMC, and analyzed by the Gilman "double titration" (22). 

However, vinyltin monomers are readily polymerized or copolymerized with butyllithium at 0 and 20 °C respectively by an anionic mechanism51). 

A bulky methacrylate, triphenylmethyl methacrylate (TrMA), is a unique monomer which gives an almost 100% isotactic polymer in anionic polymerization with n-butyllithium both in nonpolar and polar solvents. Moreover, even free-radical polymerization affords a highly isotactic polymer from this monomer.23 The isotactic specificity of TrMA polymerization is ascribed to the helical formation of the main chain. When TrMA is polymerized in toluene at —78°C... 

In 1866 AD a polymeric product was formed from styrene and sulphuric acid. Another breakthrough was the production of synthetic rubber from butadiene by using metallic sodium or potassium by German scientists during 1911 -22. In 1929, Ziegler reported polymerisation of vinyl monomers using butyllithium. 

Methyl sorbate and analogous monomers were polymerized in the presence of (/ )-2-methylbutyllithium or of complexes between butyllithium and optically active Lewis bases (329, 330) (see formulas 32 and 33) the polymers show weak optical activity. The prevailing configuration of the — CH(CH3)— group was determined by the sign of rotation of the methylsuccinic acid obtained from the polymer after ozonization. The low optical purity ( = 6%) found is related to the presence of a remarkable stereochemical disorder (115, 116) and to the fact that the chiral agent is active, at least in the case of methylbutyllithium, only in the initiation reaction. 

The initiation and propagation reactions typically show fractional orders of dependence of rate on alkyllithium. The situation is quite complex. The fractional orders for initiation and propagation are seldom the same and often vary depending on the monomer, solvent, and initiator and their absolute as well as relative concentrations. For styrene polymerization by n-butyllithium in aromatic solvents, the initiation and propagation rates are proportional to only the and -powers of n-butyllithium concentration, respectively. These results have been interpreted in terms of the following association equilibria... 

The situation is similar qualitatively but differs quantitatively for isoprene and 1,3-buta-diene. The dependence of Rp on initiator varies from g- to -order depending on the specific reaction system. The reaction orders for all monomers are affected hy the relative as well as absolute concentrations of initiator and monomer. Thus the dependence of Rp on initiator for the n-butyllithium polymerization of isoprene in benzene at 30°C is -order at initiator concentrations above 10-4 M but -order at initiator concentrations below 10 4 M [Van Beylen et al., 1988]. Higher initiator concentrations yield higher degrees of aggregation and lower kinetic orders. The excess of monomer over initiator is also important. Higher kinetic orders are often observed as the monomer initiator ratio increases, apparently as a result of breakup of initiator and propagating ion-pair associations by monomer. 

The need for solvation in anionic polymerization manifests itself in some instances by other deviations from the normal reaction rate expressions. Thus the butyllithium polymerization of methyl methacrylate in toluene at — 60°C shows a second-order dependence of Rp on monomer concentration [L Abbe and Smets, 1967]. In the nonpolar toulene, monomer is involved in solvating the propagating species [Busson and Van Beylen, 1978]. When polymerization is carried out in the mixed solvent dioxane-toluene (a more polar solvent than toluene), the normal first-order dependence of Rp on [M] is observed. The lithium diethylamide, LiN(C2H5)2, polymerization of styrene at 25°C in THF-benzene similarly shows an increased order of dependence of Rp on [M] as the amount of tetrahydrofuran is decreased [Hurley and Tait, 1976]. 

Sequential addition of monomer works well in anionic polymerization for producing well-defined block copolymers [Morton, 1983 Morton and Fetters, 1977 Quirk, 1998 Rempp et al., 1988]. An AB diblock copolymer is produced by polymerization of monomer A to completion using an initiator such as butyllithium. Monomer B is then added to the living polyA carbanions. When B has reacted completely a terminating agent such as water or... 

Compounds containing two or more carbon-carbon double bonds also act as coupling agents and also as multifunctional initiators [Hadjichristidis et al., 2001 Quirk et al., 2000]. Such compounds can also be used to synthesize multifunctional initiators that subsequently produce star polymers. Consider l,3,5-tris(l-phenylethenyl)benzene (XL). Reaction with r-butyllithium produces a trifunctional initiator XLI, which initiates polymerization of a monomer such as styrene to form a 3-arm star polystyrene [Quirk and Tsai, 1998]. The 3-arm... 

There are few studies of the effect of temperature on monomer reactivity ratios [Morton, 1983]. For styrene-1,3-butadiene copolymerization by r-butyllithium in rc-hexane, there is negligible change in r values with temperature with r — 0.03, r2 = 13.3 at 0°C and n = 0.04, r% = 11.8 at 50°C. There is, however, a signihcant effect of temperature for copolymerization in tetrahydrofuran with r — 11.0, r2 = 0.04 at —78°C and r — 4.00, r2 = 0.30 at 25° C. The difference between copolymerization in polar and nonpolar solvents is attributed to preferential complexing of propagating centers and counterion by 1,3-butadiene as described previously. The change in r values in polar solvent is attributed to the same phenomenon. The extent of solvation decreases with increasing temperature, and this results in... 

Polymerization of the bulky monomer chloral yields an optically active product when one uses a chiral initiator, e.g., lithium salts of methyl (+)- or (—)-mandelate or (R)- or (S)-octanoate [Corley et al., 1988 Jaycox and Vogl, 1990 Qin et al., 1995 Vogl, 2000], The chiral initiator forces propagation to proceed to form an excess of one of the two enantiomeric helices. The same driving force has been observed in the polymerization of triphenyl-methyl methacrylate at —78°C in toluene by initiating polymerization with a chiral complex formed from an achiral initiator such as n-butyllithium and an optically active amine such as (+)-l-(2-pyrrolidinylmethyl)pyrrolidine [Isobe et al., 2001b Nakano and Okamoto, 2000 Nakano et al., 2001]. Such polymerizations that proceed in an unsymmetrical manner to form an excess of one enantiomer are referred to as asymmetric polymerizations [Hatada et al., 2002]. Asymmetric polymerization has also been observed in the radical... 

Metallation of a polymer by treatment with strong base, for example, t-butyllithium, yields polymeric anions that initiate the grafting of monomers such as styrene, acrylonitrile, and... 

Well developed is the anionic polymerization for the preparation of olefin/di-olefin - block copolymers using the techniques of living polymerization (see Sect. 3.2.1.2). One route makes use of the different reactivities of the two monomers in anionic polymerization with butyllithium as initiator. Thus, when butyl-lithium is added to a mixture of butadiene and styrene, the butadiene is first polymerized almost completely. After its consumption stryrene adds on to the living chain ends, which can be recognized by a color change from almost colorless to yellow to brown (depending on the initiator concentration). Thus, after the styrene has been used up and the chains are finally terminated, one obtains a two-block copolymer of butadiene and styrene ... 

Studies on the Anionic Polymerization of Methyl Methacrylate Initiated with Butyllithium in Toluene by Using Perdeuterated Monomer... 

The formation of butane, detected by gas chromatography, when initiating with butyllithium in hexane and THF was attributed by Kawabata and Tsuruta (51) to the metallation of the monomer by the initiator, leading to an allylic anion ... 

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