Styrenes copolymers

Automotive plastic waste components are, in addition to PP and PVC, styrene copolymers, rubber, polyamides and polyurethanes. 

Plastics copolymerized from styrene, butadiene and acrylonitrile offer a wide application scope, thus high-impact polystyrene (HIPS, styrene-butadiene copolymer), styrene- 

In HIPS the butadiene content is in general low, the chemical structure of the polymer kept of vinyl type, thus the pyrolysis product distribution is very much like that of PS. However, some negligible components of PS pyrolysate such as toluene, a-methylstyrene, and 1,3-diphenylpropane are markedly produced from HIPS. These compounds originate directly from those volatile radicals which have been produced by the p-scission of the PS chain end. Presumably the intramolecular radical transfer necessary for the stabilization of the volatile radicals is facilitated due to the presence of butadiene segments in the copolymer. 

Styrene-co-MA resins were first introduced in the 1960s by Sinclair Petrochemicals and called SMA resins. There are two commercial producers of SMA-type copolymers, Monsanto and ARCO Chemical. ARCO s SMA resin series have styrene to MA ratios of 1 1, 2 1, and 3 1, with molecular 

Monsanto s Lytron resins are marketed as partially esterified styrene-MA copolymers, available as fine, white powders. These resins are insoluble in water, hexane, and toluene, but soluble in bases such as ammonia, sodium hydroxide, potassium hydroxide, and in ketones, alcohols, and ester solvents. 

Monsanto also markets a product called Stymer S , which is the sodium salt of a styrene-MA resin. The free-flowing, fine powder picks up moisture readily and is very soluble in water, exhibiting a pH of 7.5-8.5. This product has also been called at various places Sodium Stymer, Vinylite SYHM, Polyco 328, Styromol, and Polvimal resins. SMA resins are easily converted to Stymer 

Form White powder White powder White powder 

Partial esters of the SMA 1000 base resins, with the degree of esterification approximately 35-50%. 

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Other products such as butadiene and styrene copolymers have been commercialized. 

Chains of polybutadiene were trapped in the network formed by cooling a butadiene-styrene copolymer until phase separation occurred for the styrene, effectively crosslinking the copolymer. At 25°C the loss modulus shows a maximum which is associated with the free chains. This maximum occurst at the following frequencies for the indicated molecular weights of polybutadiene ... 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

The organic and aqueous phases are prepared in separate tanks before transferring to the reaction ketde. In the manufacture of a styrenic copolymer, predeterrnined amounts of styrene (1) and divinylbenzene (2) are mixed together in the organic phase tank. Styrene is the principal constituent, and is usually about 90—95 wt % of the formulation. The other 5—10% is DVB. It is required to link chains of linear polystyrene together as polymerization proceeds. DVB is referred to as a cross-linker. Without it, functionalized polystyrene would be much too soluble to perform as an ion-exchange resin. Ethylene—methacrylate [97-90-5] and to a lesser degree trivinylbenzene [1322-23-2] are occasionally used as substitutes for DVB. 

Functionalization. Copolymers do not have the abiHty to exchange ions. Such properties are imparted by chemically bonding acidic or basic functional groups to the aromatic rings of styrenic copolymers, or by modifying the carboxyl groups of the acryHc copolymers. There does not appear to be a continuous functionalization process on a commercial scale. 

Many synthetic latices exist (7,8) (see Elastomers, synthetic). They contain butadiene and styrene copolymers (elastomeric), styrene—butadiene copolymers (resinous), butadiene and acrylonitrile copolymers, butadiene with styrene and acrylonitrile, chloroprene copolymers, methacrylate and acrylate ester copolymers, vinyl acetate copolymers, vinyl and vinyUdene chloride copolymers, ethylene copolymers, fluorinated copolymers, acrylamide copolymers, styrene—acrolein copolymers, and pyrrole and pyrrole copolymers. Many of these latices also have carboxylated versions. 

Combination techniques such as microscopy—ftir and pyrolysis—ir have helped solve some particularly difficult separations and complex identifications. Microscopy—ftir has been used to determine the composition of copolymer fibers (22) polyacrylonitrile, methyl acrylate, and a dye-receptive organic sulfonate trimer have been identified in acryHc fiber. Both normal and grazing angle modes can be used to identify components (23). Pyrolysis—ir has been used to study polymer decomposition (24) and to determine the degree of cross-linking of sulfonated divinylbenzene—styrene copolymer (25) and ethylene or propylene levels and ratios in ethylene—propylene copolymers (26). 

There has been a marked trend toward concentration of higher styrene (ca 40%) polymers in hot latices, and lower styrene (mostiy 20—30% bound styrene) types in cold latex series. This is a reflection of the fact that lowering the polymerization temperature of high styrene copolymers produces little or no gain in the physical properties of the copolymer. 

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). 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

Acrylonitrile—Butadiene—Styrene Copolymer (ABS). Uses for ABS are in sewer pipes, vehicle parts, appHance parts, business machine casings, sports goods, luggage, and toys. 

Styrene Copolymers. Acrylonitrile, butadiene, a-methylstyrene, acryUc acid, and maleic anhydride have been copolymerized with styrene to yield commercially significant copolymers. Acrylonitrile copolymer with styrene (SAN), the largest-volume styrenic copolymer, is used in appHcations requiring increased strength and chemical resistance over PS. Most of these polymers have been prepared at the cross-over or azeotropic composition, which is ca 24 wt % acrylonitrile (see Acrylonithile polya rs Copolyp rs). 

I ew Rubber-Modified Styrene Copolymers. Rubber modification of styrene copolymers other than HIPS and ABS has been useful for specialty purposes. Transparency has been achieved with the use of methyl methacrylate as a comonomer styrene—methyl methacrylate copolymers have been successfully modified with mbber. Improved weatherability is achieved by modifying SAN copolymers with saturated, aging-resistant elastomers (88). 

To obtain satisfactory moldings with good surface appearance, contamination, including that by moisture, must be avoided. For good molding practice, particularly with the more polar styrene copolymers, drying must be part of the molding operation. A maximum of 0.1 wt % moisture can be tolerated before surface imperfections appear. 

Benzene is alkylated with ethylene to produce ethylbenzene, which is then dehydrogenated to styrene, the most important chemical iatermediate derived from benzene. Styrene is a raw material for the production of polystyrene and styrene copolymers such as ABS and SAN. Ethylbenzene accounted for nearly 52% of benzene consumption ia 1988. 

At the same time, however, considerable research was being done, especially in Germany, on a novel process called emulsion polymerization, in which the monomer was polymerized as an emulsion in the presence of water and soap. This seemed advantageous since the product appeared as a latex, just like natural mbber, leading to low viscosity even at high soHds content, while the presence of the water assured better temperature control. The final result, based mainly on work at the LG. Farbenindustrie (IGF) (10), was the development of a butadiene—styrene copolymer prepared by emulsion polymerization, the foremnner of the present-day leading synthetic mbber, SBR. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Figure 11.18 Influence of styrene content on properties of ethylene-styrene copolymers (based on...

The term ABS was originally used as a general term to describe various blends and copolymers containing acrylonitrile, butadiene and styrene. Prominent among the earliest materials were physical blends of acrylonitrile-styrene copolymers (SAN) (which are glassy) and acrylonitrile-butadiene copolymers (which are rubbery). Such materials are now obsolete but are referred to briefly below, as Type 1 materials, since they do illustrate some basic principles. Today the term ABS usually refers to a product consisting of discrete cross-linked polybutadiene rubber particles that are grafted with SAN and embedded in a SAN matrix. 

Besides the MBS materials, related terpolymers have been prepared. These include materials prepared by terpolymerising methyl methacrylate, acrylonitrile and styrene in the presence of polybutadiene (Toyolac, Hamano 500) methyl methacrylate, acrylonitrile and styrene in the presence of a butadiene-methyl methacrylate copolymer (XT Resin), and methylacrylate, styrene and acrylonitrile on to a butadiene-styrene copolymer. 

One such system involved grafting 70 parts of methyl methacrylate on to 30 parts of an 81-19 2-ethylhexyl acrylate-styrene copolymer. Such a grafted material was claimed to have very good weathering properties as well as exhibiting high optical transmission. 

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