Polystyrene chemical reactivity

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

Despite the current success and popularity of polymer reagents, the availability of functional resins has been a severe limitation in recent years. For many synthetically important transformations, reliable reagents were not available. Moreover, polymer-assisted synthesis was usually restricted to small scale apphcations, and also suffered from the inherent limitations of the standard support material (e.g., cross-linked polystyrene) such as solvent incompatibihty, adsorption of reagents,14 or the chemical reactivity of the resin backbone. 

Ethylbenzene is a colorless aromatic liquid. It is only slightly soluble in water, but infinitely soluble in alcohol and ether. Additional properties are listed in Table 1. Ethylbenzene is chemically reactive with the most important reaction being its dehydrogenation to form styrene. Styrene is used to produce polystyrene, which is used in the manufacture of many commonly used products such as toys, household and kitchen appliances, plastic drinking cups, housings for computers and electronics, foam packaging, and insulation. In addition to polystyrene, styrene is used to produce acrylonitrile-butadiene-styrene polymer (ABS), styrene-acrylonitrile polymer (SAN), and styrene-butadiene synthetic rubber (SBR). 

Styrene is chemically reactive with the most important reaction being its polymerization to form polystyrene. Styrene can also copolymerize with other monomers, such as butadiene and acrylonitrile, to produce a variety of industrially important copolymers. 

The widespread applications of polystyrene derived resins is due to the fact that styrene consists of a chemically inert aUcyl backbone carrying chemically reactive aryl side chains that can be easily modified. As discussed earlier, a wide range of different types of polystyrene resins exhibiting various different physical properties can be easily generated by modification of the crosslinking degree. In addition, many styrene derived monomers are commercially available and fairly cheap. Polystyrene is chemically stable to many reaction conditions while the benzene moiety, however, can be funtionalised in many ways by electrophilic aromatic substitutions or lithiations. As shown in Scheme 1.5.4.1 there are principally two different ways to obtain functionalised polystyrene/DVB-copolymers. 

The copolymerization of styrene with maleic anhydride creates with a copolymer (SMA) which has a higher glass transition temperature than polystyrene and is chemically reactive with certain functional groups. Thus, SMA polymers are often used in blends or composites where interaction or reaction of the maleic anhydride provides for desirable interfacial effects. The anhydride reaction with primary amines is particularly potent. 

One of the most important methods for controlling the yield behaviour of polymers is rubber modification, which is widely used to increase fracture resistance. The technique was first used in 1948 to modify the properties of polystyrene, and has since been extended to most of the major plastics, including polypropylene, polycarbonate, and rigid PVC, and to a number of the less highly crosslinked thermosets, notably epoxy resins. Between S and 20 % of a suitable rubber is added in the form of small particles, which are typically between 0.1 and S /im in diameter. Chemically reactive rubbers are preferred, because they form bonds with molecules of the surrounding matrix which can withstand tensile stress. The rubber particles have low moduli, and therefore act as stress concentrators. Accelerated deformation in the matrix adjacent to the rubber particles results in a lowering of the yield stress. 

Lactic acid is a linear, aliphatic thermoplastic polyester with a rigidity and clarity similar to polystyrene and poly(ethylene terephthalate) (PET Martin and Averous, 2001). It is a hydroxycarboxylic acid having a chiral center on its second carbon. Because of the presence of fxmctional groups in a 3-carbon molecule, a lot of chemical reactivity can be incorporated. The carboxylic acid group is mildly acidic, and the stereochemistry of the second carbon is very important in the PLA chemistry (Garlotta, 2001 Gupta and Kumar, 2007). The major characteristics of lactic acid are presented in Table 14.2. Lactic acid comprises two optical isomers of lactic acid L (+)-lactic acid and D(-)-lactic acid. 

Widespread chlorine-containing polymers would include, 1) stable molding material for practical use such as polyvinyl chloride (PVC), polyvinylidene chloride and poly(epichlorohydrin)(PECH) and, 2) reactive polymers capable to introduce additional functional groups via their active chlorines such as chloromethyl polystyrene, poly (3-chloroethyl vinyl-ether) and poly (vinyl chloroacetate). While the latter, especially the chloromethyl polystyrene, has been widely used recently for the synthesis of variety of functional polymers, we should like to talk in this article about the chemical modification of the former, mainly of PVC and PECH, which was developed in our laboratory. 

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