Styrene Copolymer Production

We commonly copolymerize styrene to produce random and block copolymers. The most common random copolymers are styrene-co-acrylonitrile and styrene-co-butadiene, which is a synthetic rubber. Block copolymerization yields tough or rubbery products. 

The polymerization rates of styrene and acrylonitrile monomer are not equal. If we were to initiate polymerization in an equimolar solution of the two monomers, the styrene monomer would initially be depleted at a faster rate than the acrylonitrile. Thus, the copolymer molecules initially produced would contain a higher concentration of styrene than acrylonitrile. As the reaction progressed, the styrene would be depleted firom the solution and the comonomer ratio in the copolymer would gradually shift towards a higher acrylonitrile content. The final product would consist of polymer chains with a range of comonomer compositions, not all 

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. 

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MABS polymers (methyl methacrylate-acrylonitrile-butadiene-styrene) together with blends composed of polyphenylene ether and impact-resistant polystyrene (PPE/PS-I) also form part of the styrenic copolymer product range. Figure 2.1 provides an overview of the different classes of products and trade names. A characteristic property is their amorphous nature, i.e. high dimensional stability and largely constant mechanical properties to just below the glass transition temperature, Tg. 

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

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. 

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. 

World polystyrene production in 1997 was approximately 10 million tons. The demand is forecasted to reach 13 million tons by 2002. The 1997 U.S. production of polystyrene polymers and copolymers was approximately 6.6 billion pounds. ABS, SAN, and other styrene copolymers were approximately 3 billion pounds for the same year. 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

Second, the conversion of one of the blocks into another type of structure by a suitable quantitative chemical reaction, allows a broad diversification of the properties of the available block copolymers. The best example of such an opportunity is probably the hydrogenation of poly(butadiene-b-styrene) copolymers, which yields a product close to a low density poly(ethylene-b-styrene) when starting from an anionically prepared diblock (including a certain amount, ca. 10 %, of 1.2 units), while a high density poly(ethy1ene-b-styrene)... 

The hydrogenated products are nitrile rubber, with good heat resistance, and styrene-butadiene-styrene copolymer, with high tensile strength, better permeability and degradation resistance. 

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

The initial product is essentially poly(methyl methacrylate) homopolymer. Little styrene is incorporated into copolymer chains unitl most or all of the methyl methacrylate is exhausted. Reports of significant amounts of styrene in products from anionic copolymerization of styrene-methyl methacrylate are usually artifacts of the particular reaction system, a consequence of heterogeneity of the propagating centers and/or counterion. 

The bulk of polyester production in the United States has gone to the synthetic coatings field in the manufacture of glyptal resin coatings and varnishes, with production between 200,000,000 and 300,000,000 pounds in the postwar years. A recent development has been the use of polyester-styrene copolymers reinforced by Fiberglas for the manufacture of items such as low-pressure molded boats, corrugated structural sheet, and plastic pipe. The 1947 requirements for glycerol in the production of polyester resins and... 

A possibly expl picrate is prepd by reacting a diphenyl ether soln of 4-vinylpyridine styrene copolymer (10 90) with an equivalent of PA, also dissolved in diphenyl ether. The 4-vinylpyridine styrene copolymer picrate product is sol in acet and insol in w (Ref 2)... 

A simple but elegant example of the broad utility of mass chromatography is shown in Figure 6. In this case, a polymer sample was thermally decomposed at 400°C, and the products were analyzed. The molecular weight, retention time, and quantitative analyses of the major products indicated that the sample was a 69% methyl methacrylate-31% styrene copolymer. 

Styrene is one of (he most important aromatic compounds Most styrene production comes from the dehydration of ethyl ben7ctic The mam commercial uses of styrene include poly styrene and various styrene copolymers such a> styrene-butadiene rubber Major styrene producers include Amoco. Dosv, Poster Grant, Monsanto, Shell, Sinclair-Koppers, and Union Carbide Styrene growth should continue to be good... 

Chirality induction can be achieved in homo- and copolymerization of vinyl monomers based on chiral monomer structure [1,3,8,9]. The first example of this type of polymerization was the copolymerization of (S)-a-methylbenzyl methacrylate with maleic anhydride the polymerization product showed [a]D +23° after removal of the chiral side group [73]. For another example, the copolymerization of an optically active styrene derivative (39) with N-phenylmaleimide (17, R = -Ph) followed by removal of the optically active side group and deboronation gave an optically active N-phenylmaleimide-styrene copolymer [74]. 

Complete thermolysis of the azo groups in polyazoesters 56,61) in the presence of monomeric styrene leads to block copolymers of an (AB) -type, whereas, when the added monomer is one that tends to terminate via disproportionation (e.g. MMA), the block copolymer products are of an ABA- or an AB-type ... 

Zitting A, Heinonen T. 1980. Decrease of reduced glutathione in isolated rat hepatocytes caused by acrolein, acrylonitrile and the thermal degradation products of styrene copolymers. Toxicology 17 333-342. 

The discovery of the ability of lithium-based catalysts to polymerize isoprene to give a high cis 1,4 polyisoprene was rapidly followed by the development of alkyllithium-based polybutadiene. The first commercial plant was built by the Firestone Tire and Rubber Company in 1960. Within a few years the technology was expanded to butadiene-styrene copolymers, with commercial production under way toward the end of the 1960s. 

Polymeric catalysts are also developed. For example, phospholene oxide modified divinylbenzene/styrene copolymers, as well as a polystyrene anchored triph-enylarsine oxide catalyst were prepared. The solid phase catalysts can be removed by filtration after partial conversion of an isocyanate to the carbodiimide. Such a catalyst is useful for the preparation of carbodiimide modified liquid MDl (4,4 -diisocyanatodiphenylmethane) products, which are of considerable commercial interest. 

Figure 1.11 Schematic of BASF s stirred tank emulsion polymerization reactors (dated 1940) for the production of styrenic copolymers (courtesy of BASF, Ludwigs-hafen)...

Styrenic copolymers are materials capable of thermoplastic processing which, in addition to styrene (S), also contain at least one other monomer in the main polymer chain. Styrene-acrylonitrile (SAN) copolymers are the most important representative and basic building blocks of the entire class of products. By adding rubbers to SAN either ABS (acrylonitrile-butadiene-styrene) or ASA (acrylate-styrene-acrylonitrile) polymers are obtained depending on the type of rubber component employed. These two classes of products yield blends composed of ASA and polycarbonate (ASA -f PC) or ABS and polyamide (ABS -(- PA). 

Thermoset plastics have also been pyrolysed with a view to obtain chemicals for recycling into the petrochemical industry. Pyrolysis of a polyester/styrene copolymer resin composite produced a wax which consisted of 96 wt% of phthalic anhydride and an oil composed of 26 wt% styrene. The phthalic anhydride is used as a modifying agent in polyester resin manufacture and can also be used as a cross-linking agent for epoxy resins. Phthalic anhydride is a characteristic early degradation product of unsaturated thermoset polyesters derived from orf/io-phthalic acid [56, 57]. Kaminsky et al. [9] investigated the pyrolysis of polyester at 768°C in a fiuidized-bed reactor and reported 18.1 wt% conversion to benzene. 

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