Polystyrene, copolymers chemical reactivity

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. 

Low molecular weight reactants such as phthalic anhydride and dimethylsuccinic anhydride were used as model compounds for trimellitic anhydride terminated polystyrene and styrene-maleic anhydride (SMA) copolymer. As amine functional species, benzyl-amine and 1,2 diphenylethylamine, were employed, the transposal of the knowledge gained from model compounds to a real polymer blend system reacted in the melt under shear was only slightly instmctive. The low reactivity observed in the case of the reactive polymers has been ascribed to a chemically different environment and not to a diffusion-controlled process as is generally considered. 

The vector fluid concept was first suggested for a polyethylene (PE)/polyamide (PA) reactive blending system [12], as mentioned earlier in this chapter. This concept is interesting because it has the potential to provide a compatibilization method for polymers that have no chemical functionalities suitable for copolymer formation during melt blending (e.g. the case of polyolefin and polystyrene). It has been seen that the blends of polyolefin/polystyrene are difficult to compatibilize in situ by simply adding a free radical initiator into the blending process. Usually, flie pre-made block or reactive polymers or copolymers, which can be expensive, are needed for polyolefin/polystyrene compatibilization [15-17]. If a suitable vector fluid can be found for the polyolefin/ polystyrene/peroxide in situ compatibilization, the process could become more controllable and more cost efficient. 

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