Acrylonitrile-butadiene-styrene polymerization

Styrene [100-42-5] (phenylethene, viaylben2ene, phenylethylene, styrol, cinnamene), CgH5CH=CH2, is the simplest and by far the most important member of a series of aromatic monomers. Also known commercially as styrene monomer (SM), styrene is produced in large quantities for polymerization. It is a versatile monomer extensively used for the manufacture of plastics, including crystalline polystyrene, mbber-modifted impact polystyrene, expandable polystyrene, acrylonitrile—butadiene—styrene copolymer (ABS), styrene—acrylonitrile resins (SAN), styrene—butadiene latex, styrene—butadiene mbber (qv) (SBR), and unsaturated polyester resins (see Acrylonithile polya rs Styrene plastics). 

ABS (acrylonitrile—butadiene-styrene) resins are two-phase blends. These are prepared by emulsion polymerization or suspension grafting polymerization. Products from the former process contain 20—22% butadiene those from the latter, 12—16%. 

We have considerable latitude when it comes to choosing the chemical composition of rubber toughened polystyrene. Suitable unsaturated rubbers include styrene-butadiene copolymers, cis 1,4 polybutadiene, and ethylene-propylene-diene copolymers. Acrylonitrile-butadiene-styrene is a more complex type of block copolymer. It is made by swelling polybutadiene with styrene and acrylonitrile, then initiating copolymerization. This typically takes place in an emulsion polymerization process. 

Uses Copolymerized with methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride, or 1,1-dichloroethylene to produce acrylic and modacrylic fibers and high-strength fibers ABS (acrylonitrile-butadiene-styrene) and acrylonitrile-styrene copolymers nitrile rubber cyano-ethylation of cotton synthetic soil block (acrylonitrile polymerized in wood pulp) manufacture of adhesives organic synthesis grain fumigant pesticide monomer for a semi-conductive polymer that can be used similar to inorganic oxide catalysts in dehydrogenation of tert-butyl alcohol to isobutylene and water pharmaceuticals antioxidants dyes and surfactants. 

Emulsion polymerization is used for 10-15% of global polymer production, including such industrially important polymers as poly(acrylonitrile-butadiene-styrene) (ABS), polystyrene, poly(methyl methacrylate), and poly (vinyl acetate) [196]. These are made from aqueous solutions with high concentrations of suspended solids. The important components have unsaturated carbon-carbon double bonds. Raman spectroscopy is well-suited to address these challenges, though the heterogeneity of the mixture sometimes presents challenges. New sample interfaces, such as WAI and transmission mode, that have shown promise in pharmaceutical suspensions are anticipated to help here also. 

When polymerization proceeds in the presence of modifiers, the mechanochemical process enhances cross-linking and, correspondingly, improves the physicochemical properties of final plastics. For example, mechanochemical treatment of acrylonitrile butadiene styrene (ABS) plastic in the presence of tolnene diisocyanate improves thermal oxidative stability of the plastic (Chetverikov et al. 2002). 

In Table 8.4 we see that most butadiene is polymerized either by itself or with styrene or acrylonitrile. The most important synthetic elastomer is styrene-butadiene rubber (SBR). SBR, along with polybutadiene, has its biggest market in automobile tires. Specialty elastomers are polychloroprene and nitrile rubber, and an important plastic is acrylonitrile/butadiene/styrene (ABS) terpolymer. Butadiene is made into adiponitrile, which is converted into hexamethylenediamine (HMDA), on of the monomers for nylon. 

Polymerization Reactions. The polymerization of butadiene with itself and with other monomers represents its largest commercial use. The commercially most important polymers are styrene—butadiene rubber (SBR), polybutadiene (BR), styrene—butadiene latex (SBL), acrylonitrile—butadiene—styrene polymer (ABS), and nitrile rubber (NR). The reaction mechanisms are free-radical, anionic, cationic, or coordinate, depending on the nature of the initiators or catalysts (194—196). 

Chemical processes are far more varied and may involve either the formation of radicals or ions along a polymeric backbone. Both cationic processes3 as well as radical processes have been widely used for graft copolymerization of vinyl monomers onto various polymers. Radical graft copolymerization has been reported for many polymers including styrene-butadiene block copolymers, and acrylonitrile-butadiene-styrene terpolymer, ABS.3 7 9... 

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. 

Another widely used copolymer is high impact polystyrene (PS-HI), which is formed by grafting polystyrene to polybutadiene. Again, if styrene and butadiene are randomly copolymerized, the resulting material is an elastomer called styrene-butadiene-rubber (SBR). Another classic example of copolymerization is the terpolymer acrylonitrile-butadiene-styrene (ABS). Polymer blends belong to another family of polymeric materials which are made by mixing or blending two or more polymers to enhance the physical properties of each individual component. Common polymer blends include PP-PC, PVC-ABS, PE-PTFE and PC-ABS. 

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... 

Acrylonitrile-butadiene-styrene A blend of polymeric materials... 

During weathering, phenolic antioxidants are photooxidized into hydroperoxycy-clohexadienones, such as 59 (Pospisil, 1993 Pospisil, 1980). The presence of peroxidic moieties in 57 and 59 renders them thermolabile at temperatures exceeding 100 °C and photolysable under solar UV radiation. Both processes account for homolysis of the peroxidic moieties. As a result, the oxidative degradation of the polymeric matrix is accelerated by formed free-radical fragments (tests were performed with atactic polypropylene and acrylonitrile-butadiene-styrene terpolymer (ABS) (PospiSil, 1981 PospiSil, 1980). Low-molecular-weight products of homolysis, such as 60 to 63 are formed in low amounts. 

The potential problem of styrene taint in foods is well known and documented in the literature (Saxby 1996). Styrene (see Chapter 2) is the monomer that is polymerized to make polystyrene (PS) (also known as general purpose or GPPS grade). It is also commonly used with butadiene rubber (5-20 % w/w) as a block copolymer to form high impact polystyrene (HIPS). In addition there are less common copolymer grades such as acrylonitrile-butadiene-styrene (ABS) having a mixture of 25 %, 15-25 % and 50-65 % of each monomer respectively or a copolymer with acrylonitrile (styrene-acrylonitrile, SAN). 

This class of additives covers a broad range from butadiene to acrylic polymers. Since these additives are polymeric in nature, diffuse reflection will occur at the polymer-modifier interfaces similar to polymer blends. Again, this will result in colors that appear lighter and duller. Table 23.5 contains three examples of impact-modified colors again in polyester compared to the neat resin without modifier. As expected, the impact-modified colors are lighter and have lower chroma. In practice, acrylonitrile butadiene styrene (ABS) or HIPS would have a more restricted color gamut compared to their transparent SAN and polystyrene (PS) base polymers. 

Styrene is frequently used as part of some terpolymers with large practical utilization. One such copolymer is acrylonitrile-butadiene-styrene terpolymer (ABS). Usually it is made as poly(l-butenylene-graft-l-phenylethylene-co-cyanoethylene). This form of the copolymer can be made by grafting styrene and acrylonitrile directly on to the polybutadiene latex in a batch or continuous emulsion polymerization process. Grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of polybutadiene. The degree of grafting is a function of the 1,2-vinyl content of the polybutadiene, monomer concentration, extent of conversion, temperature and mercaptan concentration (used for crosslinking). The emulsion polymerization process involves two steps production of a rubber latex and subsequent polymerization of styrene and acrylonitrile in the presence of the rubber latex to produce an ABS latex. 

Copolymers are produced by the simultaneous polymerization of two or more dissimilar molecules. Examples include polyvinyl acetate, polyesters, and polyamides. Synthetic elastomers (such as SBR synthetic rubber, made from styrene and butadiene) are also copolymers. This pattern continues with the ter-polymers (such as acrylonitrile-butadiene-styrene (ABS)), which consist of three different monomers. 

Thermoplastics are plastics which undergo a softening when heated to a particular temperature. This thermoplastic behaviour is a consequence of the absence of covalent bonds between the polymeric chains, which remain as practically independent units linked only by weak electrostatic forces (Figure 1.4(a)). Therefore, waste thermoplastics can be easily reprocessed by heating and forming into a new shape. From a commercial point of view, the most important thermoplastics are high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene tereph-thalate (PET), polyamide (PA), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene copolymer (ABS), and styrene-acrylonitrile copolymer (SAN). 

When a mixture of styrene and acrylonitrile is polymerized in the presence of a polybutadiene latex by an emulsion radical process, an acrylonitrile-butadiene-styrene (ABS) copolymer is obtained. This ABS copolymer is actually a mixture of (a) a graft copolymer which contains some of the styrene/acrylonitrile (ST/AN) copolymer chemically bound to the polybutadiene backbone, and (b) a random copolymer, conventionally designated as a linear copolymer, which is not bound to the polybutadiene backbone but which consists of the portion of the styrene/acrylonitrile monomer that has polymerized separately. 

In heterophase polymeric materials such as rubber modified polystyrene or acrylonitrile-butadiene-styrene (ABS) resins, outstanding mechanical properties can be obtained only by regulating the dispersed rubber particle size and by achieving adhesion between the rubber and the resin phase. This can usually be achieved by adding block or graft copolymers, or by their formation in situ, as in industry. 

MAJOR USES Manufacture of chemicals including acrylic fiber, plastics, rubber elastomers, plasticizers, solvents, polymeric materials, dyes, pharmaceuticals, insecticides and nylon formation of high impact resins such as styrene acrylonitrile and acrylonitrile butadiene styrene. 

A number of important commercial resins are manufactured by suspension polymerization, including poly(vinyl chloride) and copolymers, styrene resins [general purpose polystyrene, EPS, high impact polystyrene (HIPS), poly(styrene-acrylonitrile) (SAN), poly(acrylonitrile-butadiene-styrene) (ABS), styrenic ion-exchange resins], poly(methyl methacrylate) and copolymers, and poly(vinyl acetate). However, some of these polymers rather use a mass-suspension process, in which the polymerization starts as a bulk one and, at certain conversion, water and suspending agents are added to the reactor to form a suspension and continue the polymerization in this way up to high conversions. No continuous suspension polymerization process is known to be employed on a... 

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