Emulsion-polymerized styrene-butadiene

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

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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. 

Production of emulsion-polymerized styrene-butadiene rubber... 

Most, if not all, of the large-toimage grades of emulsion-polymerized styrene-butadiene rubbers are produced by continuous emulsion polymerization. The advantages over batch and setni[Pg.684]

TYPICAL POLYMERIZATION RECIPES FOR HOT AND COLD EMULSION POLYMERIZED STYRENE-BUTADIENE RUBBERS... 

Abex LIV 30 Disponil SLS 2010 Non-oxynol-10 Nonoxynol-12 Nonoxynol-14 POLYSTEP B-24 POLYSTEP F-4 emulsifier, emulsion polymerization styrene-butadiene Colonial STDES... 

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. 

A modified latex composition contains a phosphorus surface group. Such a latex is formed by emulsion polymerization of unsaturated synthetic monomers in the presence of a phosponate or a phosphate which is intimately bound to the surface of the latex. Thus, a modified latex containing 46% solids was prepared by emulsion polymerization of butadiene, styrene, acrylic acid-styrene seed latex, and a phosphonate comonomer in H20 in the presence of phosphated alkylphenol ethoxylate at 90°C. The modified latex is useful as a coating for substrates and as a binder in aqueous systems containing inorganic fillers employed in paper coatings, carpet backings, and wallboards [119]. 

Over 5.5 billion pounds of synthetic rubber is produced annually in the United States. The principle elastomer is the copolymer of butadiene (75%) and styrene (25) (SBR) produced at an annual rate of over 1 million tons by the emulsion polymerization of butadiene and styrene. The copolymer of butadiene and acrylonitrile (Buna-H, NBR) is also produced by the emulsion process at an annual rate of about 200 million pounds. Likewise, neoprene is produced by the emulsion polymerization of chloroprene at an annual rate of over 125,000 t. Butyl rubber is produced by the low-temperature cationic copolymerization of isobutylene (90%) and isoprene (10%) at an annual rate of about 150,000 t. Polybutadiene, polyisoprene, and EPDM are produced by the anionic polymerization of about 600,000, 100,000, and 350,000 t, respectively. Many other elastomers are also produced. 

Figure 15. Molecular weight distribution of anionically polymerized styrene-butadiene random copolymer and emulsion polymerized SBR.

A series of latex samples with varying stage ratios (LS-1 to LS-4) was prepared at 90°C by emulsion polymerizing styrene and butadiene monomer mixes (S/B/AA/CHBr3 59/40/1/0.5) in the pre-... 

As discussed in Chapter 4, emulsion polymerization received a significant boost in the United States during the Second World War. When Japan overran countries that supplied natural rubber to the West, a crash program to manufacture synthetic rubber was initiated in the United States and Canada. The product was called Government Rubber-Styrene (GR-S), and was produced by the emulsion polymerization of butadiene and styrene. The fundamental recipe for GR-S is still used as a teaching tool for those learning the art and science of emulsion polymerization. 

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. 

Emulsions Emulsions have particles of 0.05 to 5.0 pm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce massive polymers. Figures 2Z-2Zd and 2Z-2Ze show bead and emulsion processes for rinyl chloride. Continuous emulsion polymerization of butadiene-styrene rubber is done in a CSTR battery with a residence time of 8 to 12 h. Batch treating of emulsions also is widely used. 

Equation (2.26) leads to a solution for from available knowledge of the rate R, the concentration of monomer in the monomer-polymer particles [M], and the number of particles, N. This method has been applied to several monomers and has been especially useful in the case of the dienes, where the classical method of photoinitiation poses difficulties. Some of these results are shown in Table 2.4 in the form of the usual kinetic parameters. The results obtained for styrene by photoinitiation techniques are included for comparison. It can be seen that the agreement is remarkably good, considering the widely different experimental methods used. Recent studies of the emulsion polymerization of butadiene have shown that the rate constant for propagation is even higher than previously estimated (see Table 2.1) (Weerts et al., 1991). 

CAS 151-21-3 EINECS/ELINCS 205-788-1 Uses Surfactant, emulsifier for emulsion polymerization, styrene acrylics, acrylics, vinyl chloride and styrene butadiene emulsions defoamer in food-contact paper/paperboard in food-contact textiles in resinous/ polymeric food-contact coatings Features No formaldehyde present... 

Carr C.W., Kolthoff I.M., Meehan E.I., Williams D.E., Studies on the rate of the emulsion polymerization of butadiene-styrene (75-25) as a function of the amount and kind of emulsifier used. 2. Polymerizations with fatty acid soaps, rosin soaps, and various synthetic emulsifiers, 7. Polym. Sci, 5(2), 1950, 201-206. 

Emulsion polymerization requires free-radical polymerizable monomers which form the structure of the polymer. The major monomers used in emulsion polymerization include butadiene, styrene, acrylonitrile, acrylate ester and methacrylate ester monomers, vinyl acetate, acrylic acid and methacrylic acid, and vinyl chloride. All these monomers have a different stmcture and, chemical and physical properties which can be considerable influence on the course of emulsion polymerization. The first classification of emulsion polymerization process is done with respect to the nature of monomers studied up to that time. This classification is based on data for the different solubilities of monomers in water and for the different initial rates of polymerization caused by the monomer solubilities in water. According to this classification, monomers are divided into three groups. The first group includes monomers which have good solubility in water such as acrylonitrile (solubility in water 8%). The second group includes monomers having 1-3 % solubility in water (methyl methacrylate and other acrylates). The third group includes monomers practically insoluble in water (butadiene, isoprene, styrene, vinyl chloride, etc.) [12]. 

This is in general a heterogeneous free radical polymerization that involves the emulsification of the relatively hydrophobic monomer in water and sometimes an organic phase-in-water emulsifier, followed by the initiation reaction with either a water soluble initiator e.g. sodium persulfate (NaPS)) or an oil-soluble initiator e.g. 2-20-azobisisobutyronitrile (AIBN)) [266]. Typical monomers used in the emulsion polymerization include butadiene, styrene, acrylonitrile, acrylate ester and methacrylate ester, vinyl acetate, and vinyl chloride, but also biopolymers are now obtained by this versatile technique in several mesodimensionate morphologies [267]. 

In North America approximately 5-10 % of the dispersions used for labels are based on styrene-butadiene rubber (SBR) [24]. SBR used in pressure sensitive adhesives are produced by emulsion polymerization with butadiene contents typically between 25 and 45 %. With carefijl control of process conditions (temperature, styrene and butadiene feed rates) and ingredient feed levels (chain transfer agent, initiator, monomers), intermediate molecnjlar weight, lightly cross-linked elastomers having an excellent balance of cohesive and adhesive properties can be obtained. 

Acrylics. Acetone is converted via the intermediate acetone cyanohydrin to the monomer methyl methacrylate (MMA) [80-62-6]. The MMA is polymerized to poly(methyl methacrylate) (PMMA) to make the familiar clear acryUc sheet. PMMA is also used in mol ding and extmsion powders. Hydrolysis of acetone cyanohydrin gives methacrylic acid (MAA), a monomer which goes direcdy into acryUc latexes, carboxylated styrene—butadiene polymers, or ethylene—MAA ionomers. As part of the methacrylic stmcture, acetone is found in the following major end use products acryUc sheet mol ding resins, impact modifiers and processing aids, acryUc film, ABS and polyester resin modifiers, surface coatings, acryUc lacquers, emulsion polymers, petroleum chemicals, and various copolymers (see METHACRYLIC ACID AND DERIVATIVES METHACRYLIC POLYMERS). 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

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