Anionic solution polymerization

The original SBR process is carried out at. 50° C and is referred to as hot polymerization. It accounts for only about 5% of aU the mbber produced today. The dominant cold polymerization technology today employs more active initiators to effect polymerization at about 5°C. It accounts for about 85% of the products manufactured. Typical emulsion polymerization processes incorporate about 75% butadiene. The initiators are based on persulfate in conjunction with mercaptans (197), or organic hydroperoxide in conjunction with ferrous ion (198). The rest of SBR is produced by anionic solution polymerization. The density of unvulcanized SBR is 0.933 (199). The T ranges from —59" C to —64 C (199). 

The Anionic Solution Polymerization of Butadiene in a Stirred-Tank Reactor... 

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. 

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... 

Figure 3 Effect of the temperature on the overall heat rate for the anionic solution polymerization ofL6 using the one-shot method of contacting the catalytic species. In the insets, the reaction temperatures and gravimetric conversions are given. Reaction conditions solvent, mixture of aliphatic hydrocarbons with bp. 140 - 160 °C initial concentration ofL6, 3 mol L catalyst, NaH = 3% mol mol L6 Cl/catalyst ratio = 1...

Figure 6 Effect of the amount of Cl on the overall heat for the anionic solution polymerization of L6 at 105 °C using the successive injections method of contacting the catalytic species...

Figure 11 Effect of stirring level on the heat rate (a) and overall heat (b) for the anionic solution polymerization of L6 at 120 °C...

Manufacture Styrene-diene copolymers are produced by anionic solution polymerization, typically using i-butyl lithium in cyclohexane at 60-120°C. The system may also be promoted by small amounts of an amine such as tetramethylethylene diamine or an ether, such as tetrahydrofuran. Polymerization solids are in the range of 20-25%. 

At Shell, research on anionic solution polymerization systems commenced in mid-1955 and covered a broad area. One of the outgrowths of this work was the first commercial production of high cis-polyisoprene (IR) in 1959 at the Torrance, California, plant. In this case, our confidence in this polymerization system was such that we went directly from bench scale to commercial scale. The very strong analytical background, particularly in GLC, developed at the Emeryville Research Center, was a great strength in all of this anionic research. 

Alkali Metals The direct use alkali metals and alkaline-earth metals as initiators for anionic polymerization of diene monomers as first reported in 1910 is primarily of historical interest because these are uncontrolled, heterogeneous processes [4]. One of the most significant developments in anionic vinyl polymerization was the discovery reported in 1956 by Stavely and coworkers at Firestone Tire and Rubber Company that polymerization of neat isoprene with lithium dispersion produced high di-l,4-polyisoprene, similar in structure and properties to Hevea natural rubber [47]. This discovery led to development of commercial anionic solution polymerization processes using alkyllithium initiators. 

SBR may also be produced by anionic solution polymerization of styrene and butadiene with alky-llithium initiator (e.g., butyllithium) in a hydrocarbon solvent, usually hexane or cyclohexane. In contrast to emulsion SBR, which may have an emulsifier (soap) content of up to 5% and nonrubber materials sometimes in excess of 10%, solution SBR seldom has more than 2% nonrubber materials in its finished form. Solution SBR has a narrower molecular weight distribution, higher molecular weight, and higher cis-1,4-polybutadiene content than emulsion polymerization SBR. 

These thermoplastic elastomers are prepared by anionic solution polymerization with or-ganometallic catalysts. A typical example of such preparation is polymerization of a 75/25 mixture of butadiene/styrene in the presence of jec-butyllithium in a hydrocarbon-ether solvent blend. At these reaction conditions butadiene blocks form first, and when all the butadiene is consumed styrene blocks form. In other preparations, monomers are added sequentially, taking advantage of the living nature of these anionic polymerizations. 

The NIR in situ process also allowed for the determination of intermediate sequence distribution in styrene/isoprene copolymers, poly(diene) stereochemistry quantification, and identification of complete monomer conversion. The classic one-step, anionic, tapered block copolymerization of isoprene and styrene in hydrocarbon solvents is shown in Figure 4. The ultimate sequence distribution is defined using four rate constants involving the two monomers. NIR was successfully utilized to monitor monomer conversion during conventional, anionic solution polymerization. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerization conditions. Despite the presence of the NIR probe, the living nature of the polymerizations was maintained in... 

In anionic solution systems the feed stocks are typically dried over various types of dessicants because the systems are sensitive to water contamination. When using continuous anionic solution polymerization systems, it is necessary to employ low (ppm) concentrations of a chain-transfer agent in order to discourage gelation and fouling 1,2-butadiene is often used for this purpose in commercial applications. Alkyl-lithium-initiated polybutadiene is less prone to contain gel and does not contain the heavy metal catalyst residues associated with Ziegler-Natta catalyzed products. 

In conclusion, the characteristic features of the active centers in anioiuc polymerization of EO in ether solvents are (1) tight ion pairs with extremely low dissociation constants (10" -10" moir in THF) (2) formation of ion triplets and higher associates and (3) competitive interaction of the growing chains with monomer units sequences, monomer, and electron-pair donors such as crown ethers or crjqjtands. Thus, the complex character of the growing species is the fundamental problem in the anionic solution polymerization of EO, PO, and other oxiranes. An upper limit (up to 50 000) for the MWs has been repotted. ... 

Figure 12 GPC trace of the product of the anionic solution polymerization of 8-caprolactone in THF. Conditions of polymerization [s-caprolactone]o = 6.1 x 10 " moir initiator [(CH3)3SiONa]...

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