1,3-Butadiene, butyllithium polymerization

C-13 NMR Study of the Propagating Live End in the Butyllithium Polymerization of 1,3-Butadiene... 

When butadiene is polymerized with lithium metal or with alkyllithium catalysts, inert solvents like hexane or heptane must be used to obtain high cw-1,4 placement (see Chapter 3). Based on NMR spectra, 1,4-polybutadiene formed with n-butyllithium consists of blocks of cw-1,4 units and trans-XA units that are separated by isolated vinyl structures ... 

Nonpolar hydrocarbon monomers such as styrene, isoprene, and butadiene are polymerized in hydrocarbon solvents such as benzene or cyclohexane. Initiation is achieved with the use of alkyllithiums such as sec-butyllithium and molecular mass is controlled by the ratio of initiator to monomer. The living nature of anionic polymerization allows the syntheses of block copolymers by sequential addition of the monomers. After one monomer is exhausted, the chain remains reactive, or living. The addition of the second monomer then continues the polymerization to form a block copolymer. Such techniques are used to synthesize polystyrene-polyisoprene or polystyrene-polybutadiene copolymers (PS-PI or PS-PB, respectively). 

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. 

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. 

The synthesis and characterization of a series of dendrigraft polymers based on polybutadiene segments was reported by Hempenius et al. [15], The synthesis begins with a linear-poly(butadiene) (PB) core obtained by the sec-butyllithium-initiated anionic polymerization of 1,3-butadiene in n-hexane, to give a microstructure containing approximately 6% 1,2-units (Scheme 3). The pendant vinyl moities are converted into electrophilic grafting sites by hydrosilylation with... 

Auguste S, Edwards HGM, Johnson AF et al. (1996) Anionic polymerization of styrene and butadiene initiated by n-butyllithium in ethylbenzene determination of the propagation rate constants using Raman spectroscopy and gel permeation chromatography. Polymer 37 3665-3673... 

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 ... 

Several workers (l. 2,3,4) have used H nmr to study the propagating chain end in the polymerization of 1,3-butadiene (1,3 BD) with a butyllithium initiator. They concluded that the poly(butadienyl) lithium chain end is virtually ICO percent 1,4 with no 1,2 structures, even though 1,2 units are incorporated in the chain. The lithium is bonded to the carbon, and there is no evidence of a T allyl type of delocalized bonding involving the Y carbon. However, the presence of vinyl in-chain units was taken as evidence for the presence of an undetectable amount of the 7 bonded chain ends in equilibrium with the bonded chain ends. Glaze and coworkers (3) further suggested that the stereochemical course of allyllithium reactions may depend on the aggregation of the reactive species. 

The kinetic effects of THF on alkyllithium has been clearly demonstrated. Morton, Bostick, Livigni and Fetters (44) have studied the polymerization of butadiene and isoprene using butyllithium in THF and in normal hexane. By using a preinitiation technique, the kinetics of the propagation could be determined. In all cases the rate of polymerization was proportional to the monomer concentration. In THF the rate of polymerization was proportional to the alkyl lithium concentration. However, in hexane the rate of polymerization was proportional to the square root of the lithium alkyl concentration. Morton et al. showed that the polymerization in hexane involved the dimer of the alkyllithium which dissociated into two alkyllithium molecules before propagating the polymerization. The THF adduct of the alkyllithium, however, was able to react directly. 

These results show that the 1,2-polymerization of butadiene requires a less anionic catalyst than the anionic polymerization of styrene. Tobolsky and Rogers (58) studied the same effects of catalyst anionicity on the copolymerization of styrene and isoprene. They found that the increased anionic character of the lithium-THF combination relative to butyllithium catalysts increased the styrene content of the polymer as well as decreased the 1.4-structure of the polyisoprene. 

An interesting effect of the ionic factors of the polymerization was found by Kuntz (59). He has shown that the homopolymerization of styrene using butyllithium catalysts is six times as rapid as that of butadiene. However, in copolymerization, butadiene polymerized initially at its own rate with relatively small amounts of the styrene being consumed. Only after 90% of the butadiene had been consumed, the styrene began to polymerize at its own rate. THF increased the rate of the polymerization but had little effect on the rate of butadiene to styrene which is polymerized. The butadiene structure is little influenced by copolymerization. The homopolymer contained 44% cis-1.4, 7% 1.2 and 49% trans-1.4 while the butadiene units of the butadiene copolymers contained 40% cis 1.4, 7% 1.2 and 53% trans-1.4 groups. 

Cyano and alkoxycarbonyl groups are favorable in this respect and propeneni-trile and methyl 2-methylpropenoate can be polymerized with sodium amide in liquid ammonia. Ethenylbenzene and 2-methyl-1,3-butadiene undergo anionic polymerization under the influence of organolithium and organosodium compounds, such as butyllithium and phenylsodium. 

Diene Polymers Polymerization of a 1,3-diene yields a polymer having true asymmetric centers in the main chain and ozonolysis of the polymer gives a chiral diacid compound (12) whose analysis of optical purity discloses the extent of chiral induction in the polymerization (Scheme 11.2) [12,35-39], The polymerization of methyl and butyl sorbates methyl and butyl styrylacrylates and methyl, ethyl, butyl, and /-butyl 1,3-butadiene-1-carboxylates using (+)-2-methylbutyllithium, butyllithium/(-)-menthyl ethyl ether, butyllithium/menthoxy-Na, butyllithium/bomeoxy-Na, butyllithium/Ti((-)-menthoxy)4, and butyllithium/bomyl ethyl ether initiators [35-37] and that of 1,3-pentadiene in the presence of... 

The kinetics of the polymerization of butadiene by n-butyllithium in the presence of TMEDA was studied by Hay and McCabe 180). They were unable to distinguish between addition of monomeric n-butyllithium and that of the species (n-BuLi TMEDA) to the monomer as the initiation step. The initiation efficiency varied from 50% at a ratio of [TMEDA] [Li] of 0.9 to 99% at a ratio of 3.35 and it was concluded that propagation involves growth from the loose (solvent separated) ion pair of composition (PBLi 2 TMEDA). The presumption that there is no exchange of TMEDA among the complexed species is not in accordance with the observation of time-averaged signals in the 1H-NMR spectrum 181). 

The most widely used organolithium compound is n-butyllithium (see formulas of related compounds in Table 12.1), used as an initiator for the production of elastomers by solution polymerization, predominantly of styrene-butadiene. 

A few other pertinent observations have been made. Although the effect of temperature on structure in the case of sodium or potassium metal polymerized butadiene was shown to lead to the gradual approach to a nearly random mixture between 0 and 45° (41,32), in the case of phenyllithium in tetrahydrofuran there is observed only a few percent difference between — 78° and + 100° (76). Furthermore, the use of lithium, n-butyllithium, n-amyllithium or isoamyllithium produces polyisoprene of the same microstructure in tetrahydrofuran (77). Kuntz (34) found that polybutadiene prepared with n-butyllithium in... 

A somewhat different situation was found to prevail in the butadiene polymerization initiated by trityl sodium (102). The deep red color of trityl sodium does not disappear upon addition of monomer, but remains the same throughout the polymerization. This phenomenon was shown to be due to an opposite difference in rates than that found in the butyllithium case, namely... 

K-Resin SBC synthesis is a batch anionic solution polymerization of styrene and 1,3-butadiene using an n-butyllithium (NBL) initiator in a process referred to as living polymerization . Although often referred to as a catalyst, each NBL gives rise to a distinct polymer chain. Polymer chains grow by adding monomer... 

Anionic polymerization of 2-triethylsilyl-1,3-butadiene (I) in hexane at room temperature initiated by n-, sec-, or rf-butyllithium gave high yields of ( )-l,4-poly(2-triethylsilyl-l,3-butadiene) ( -11). Neither (Z)-1,4-poly(2-tri-ethylsiIyl-1,3-butadiene) (Z-II) nor 1,2 or 3,4 units were found. The reaction is both regio- and stereospecific. 

Materials. Phillips polymerization grade cyclohexane and butadiene were used. Styrene was a commercial polymerization grade. Solvent was dried over activated Alcoa H151 alumina, and monomers were dried over activated Kaiser 201 alumina before they were transferred to the charge tanks. n-Butyllithium and sec-butyl lithium were purchased from Lithium Corporation of America. Chiorosilanes were vacuum distilled before use. 

Alkyllithium compounds are employed commercially in the polymerization of 1,3-butadiene and isoprene. Initiation proceeds by addition of the metal alkyl, e.g., n-butyllithium, to monomer ... 

The first Soviet investigation on the modeling of MWD in the ionic polymerization of butadiene and isoprene in solution on butyllithium catalyst was published in 1958m).In this study one can already find all the elements in the scheme of utilizing MWD to specify the polymerization mechanism. 

Conjugated Dienes and Other Monomers. Alkyllithiums such as n-butyllithium—and even the growing polyethylene carbon-lithium bond complexed with chelating diamines such as TMEDA—are effective initiators for the polymerization of conjugated dienes such as 1,3-butadiene and isoprene. A polybutadiene of high 1,2-content can be produced from butadiene in hydrocarbon solvents using these N-chelated organolithium catalysts. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyllithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibility (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

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