Solution-polymerized styrene-butadiene

Styrene-butadiene rubber could be produced by using emulsion and solution process, thus it can be divided into emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR). In this entry, we will describe their development and introduce their synthesis process, relationship between structure and property, processing property, blends, and applications. 

Noguchi, K., Yoshioka, A., Komuro, K. and Ueda, A., Structure and properties of newly developed chemically modified high vinyl polybutadiene and solution polymerized styrene-butadiene rubbers , ACS Rubber Division 129th Meeting May, 1986, Paper No. 36. 

Sun J, Song Y, Zheng Q, Tan H, Yu J, Li H (2007) Nonlinear rheological behavior of silica filled solution-polymerized styrene butadiene rubber. J Polym Sci B Polym Phys 45 2594-2602... 

After the war when natural rubber became available again the consumption of styrene-butadiene rubber began to fall however, the trend was reversed in 1949 with the advent of a copolymer made at low temperature. This product gives a passenger-tyre rubber superior to natural rubber and styrene-butadiene rubbers have remained the most important of the large-tonnage rubbers (Table 20.2). In the early 1960s, solution polymerized styrene-butadiene rubbers became available. These rubbers show further improvements in tyre performance. In 1965, styrene-butadiene thermoplastic elastomers were introduced. 

SBR [17,106] solution prepared copolymer (anionic polymerization) styrene-butadiene (34% vinyl 19% cis and 47% trans) 25 wt% styrene... 

The production and properties resulting from the anionic terpolymerization in solution incorporating styrene, butadiene, and isoprene have been reviewed by Halasa [7]. The product, SIBR, can be tailored by monomer composition to give polymers with single or multiple glass transition temperatures. As noted earlier, block copolymers produced by rhythmic alternation of styrene and butadiene in the feed of anionic polymerization are quite different in mechanical behavior from conventional SBR (see Section 4.5). 

Synthetic. The main types of elastomeric polymers commercially available in latex form from emulsion polymerization are butadiene—styrene, butadiene—acrylonitrile, and chloroprene (neoprene). There are also a number of specialty latices that contain polymers that are basically variations of the above polymers, eg, those to which a third monomer has been added to provide a polymer that performs a specific function. The most important of these are products that contain either a basic, eg, vinylpyridine, or an acidic monomer, eg, methacrylic acid. These latices are specifically designed for tire cord solutioning, papercoating, and carpet back-sizing. 

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, butyUithium, 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/flexibiHty (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). 

The glass-transition temperature in amorphous polymers is also sensitive to copolymerization. Generally, T of a random copolymer falls between the glass-transition temperatures of the respective homopolymers. For example, T for solution-polymerized polybutadiene is —that for solution-polymerized polystyrene is -HlOO°C. A commercial solution random copolymer of butadiene and styrene (Firestone s Stereon) shows an intermediate T of —(48). The glass-transition temperature of the random copolymer can sometimes be related simply as follows ... 

Styrene—Butadiene Rubber (SBR). This is the most important synthetic mbber and represents more than half of all synthetic mbber production (Table 3) (see Styrene-butadiene rubber). It is a copolymer of 1,3-butadiene, CH2=CH—CH=CH2, and styrene, CgH5CH=CH2, and is a descendant of the original Buna S first produced in Germany during the 1930s. The polymerization is carried out in an emulsion system where a mixture of the two monomers is mixed with a soap solution containing the necessary catalysts (initiators). The final product is an emulsion of the copolymer, ie, a fluid latex (see Latex technology). 

The use of palladium(II) sulfoxide complexes as catalyst precursors for polymerization has met with mixed results thus a report of a palla-dium(II) chloride-dimethyl sulfoxide system as a catalyst precursor for phenylacetylene polymerization suggests similar results to those obtained using tin chloride as catalyst precursor (421). However, addition of dimethyl sulfoxide to solutions of [NH fPdCh] decreases the activity as a catalyst precursor for the polymerization of butadiene (100). Dimethyl sulfoxide complexes of iron have also been mentioned as catalyst precursors for styrene polymerization (141). 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

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. 

Various patents on the homopolymerization of BD in the presence of styrene are available [581-590]. According to these patents, St is used as a solvent in which BD is selectively polymerized by the application of NdV/DIBAH/EASC. At the end of the polymerization a solution of BR in St is obtained. In subsequent reaction steps the unreacted styrene monomer is either polymerized radically, or acrylonitrile is added prior to radical initiation. During the subsequent radical polymerization styrene or styrene/acrylonitrile, respectively, are polymerized and ris-l,4-BR is grafted and partially crosslinked. In this way BR modified (or impact modified) thermoplast blends are obtained. In these blends BR particles are dispersed either in poly(styrene) (yielding HIPS = high impact poly(styrene) or in styrene-acrylonitrile-copolymers (yielding ABS = acrylonitrile/butadiene/ styrene-terpolymers). In comparison with the classical bulk processes for HIPS and ABS, this new technology allows for considerable cost reductions... 

Through polymerization of a styrene rubber solution, one obtains SB mass (styrene-butadiene). SB forms a twophase system in which the styrene is the continuous phase and the rubber, usually a butadiene base, is the discontinuous phase. The rubber phase also contains pockets of styrene. The SB polymer, because of its properties, is also known as impact resistant or high impact PS (HIPS). 

Butadiene-Styrene Rubber occurs as a synthetic liquid latex or solid rubber produced by the emulsion polymerization of butadiene and styrene, using fatty acid soaps as emulsifiers, and a suitable catalyst, molecular weight regulator (if required), and shortstop. It also occurs as a solid rubber produced by the solution copolymerization of butadiene and styrene in a hexane solution, using butyl lithium as a catalyst. Solvents and volatiles are removed by processing with hot water or by drum drying. 

The commercial production of acryloritrile-butadiene-styrene (ABS) formulations is accomplished by a number of different methods based on free radical polymerization. The two main methods are based on emulsion or solution polymerization techniques. The solution polymerization is mostly called mass or bulk polymerization because only a low amount of solvent is used. Most of the ABS ( 85%) is made using the emulsion process. Both techniques have been used in combination (emulsion/mass). Other combinations are with suspension polymerization as final step (mass/suspension and emulsion/suspen-sion) [1]. 

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... 

The free-radical kinetics described in Chapter 6 hold for homogeneous systems. They will prevail in well-stirred bulk or solution polymerizations or in suspension polymerizations if the polymer is soluble in its monomer. Polystyrene suspension polymerization is an important commercial example of this reaction type. Suspension polymerizations of vinyl ehloride and of acrylonitrile are described by somewhat different kinetic schemes because the polymers precipitate in these cases. Emulsion polymerizations aie controlled by still different reaetion parameters because the growing macroradicals are isolated in small volume elements and because the free radieals which initiate the polymerization process are generated in the aqueous phase. The emulsion process is now used to make large tonnages of styrene-butadiene rubber (SBR), latex paints and adhesives, PVC paste polymers, and other produets. 

Most emulsion polymerization is based on free-radical reactions, involving monomers (e.g., styrene, butadiene, vinyl acetate, vinyl chloride, methacrylic acid, methyl methacrylate, acrylic acid, etc.), surfactant (sodium dodecyl diphenyloxide disulfonate), initiator (potassium persulfate), water (18.2MQ/cm), and other chemicals and reagents such as sodium hydrogen carbonate, toluene, eluent solution, sodium chloride, and sodium hydroxide. 

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