Polymers, unsaturated aromatic groups

Another important use of BCl is as a Ftiedel-Crafts catalyst ia various polymerisation, alkylation, and acylation reactions, and ia other organic syntheses (see Friedel-Crafts reaction). Examples include conversion of cyclophosphasenes to polymers (81,82) polymerisation of olefins such as ethylene (75,83—88) graft polymerisation of vinyl chloride and isobutylene (89) stereospecific polymerisation of propylene (90) copolymerisation of isobutylene and styrene (91,92), and other unsaturated aromatics with maleic anhydride (93) polymerisation of norhornene (94), butadiene (95) preparation of electrically conducting epoxy resins (96), and polymers containing B and N (97) and selective demethylation of methoxy groups ortho to OH groups (98). 

Among the polymers containing aromatic rings and unsaturated hydrocarbon groups in the backbone are poly(phenylene-ethynylenes) (PPE). This type of polymer has been synthesized by alkyne metathesis of 1,4-dipropynylated benzenes [11] and has applications in optical and electronic industry. A comprehensive study on thermal decomposition of several poly(substituted p-phenylene-ethynylenes) is available [12], The general formula for this group of polymers is the following ... 

Polymers with aromatic side groups smoke heavily, even when flaming. The most important representative of this group is polystyrene (the conventional unsaturated polyester products are also rated here by their styrene content). 

The reasons for the use of maleic anhydride instead of other anhydrides or unsaturated carboxylic acids is not clearly stated in Chapter 10. If you possess an extensive knowledge of chemistry, you will know that maleic anyhydride is a cheap, safe, readily reactive compound which puls carbor lic acid sites onto a polymer by formation of a carbon carbon bond. The reaction is specific as long as aliphatic or aromatic groups are the only functional groups in the polymer being grafted. 

Many of the studies of multiphase polymers are conducted on unsaturated rubbers which are adequately stained by osmium tetroxide, which reveals the nature of the dispersed phase domains. Polymers with activated aromatic groups have been selectively stained by reaction with mercuric trifluoroacetate (Section 4.4.8). Hobbs [262] has successfully used this technique to provide contrast in blends of poIy(2,6-dimethyl-l,4-phenylene oxide) and Kraton G (SBS block copolymer). Although this stain is effective in enhancing contrast, a drawback of the method is that the material is not hardened or fixed by the stain. 

The products formed by hydrolysis are effective primary and secondary antioxidants. Polyfunctional antioxidants are formed during the application of cyclic arylene phosphites and various HD and chain breaking moieties which autosynergetically enhance their antioxidative activity. In addition to decomposing hydroperoxides, aromatic phosphites can also react with unsaturated (vinyl) groups in the polymer, coordinate with transition metal residues, help to preserve the hindered phenol, and prevent discoloration by reacting with quinoidal compounds. 

Polycarbosilanes are polymers in which organosilicon moieties as silanes, disilanes, and trisilanes and carbon as aliphatic or aromatic units lie in the polymer backbone. The general formula for this class of material may be represented by structure 33. Polycarbosilanes may be linear, cyclic, polycyclic, extended networks, or any combination thereof R and R are the usual substituents found in organo-silanes, and (C) represents difimctional aliphatic (saturated or unsaturated) or aromatic groups that can serve as bridges between the silicon moieties. Consequently, a... 

Because of the commercial availability and relatively low cost of the starting acid anhydrides, and the ease of preparation of the unsaturated imides, aromatic chain segments and low-M polymers end-capped with these reactive groups are most common. Although exotic unsaturated end-caps appear on occasion in the patent literature, the most common unsaturated reactive groups are maleimide [417-419,567-570], nadimide [417,419,567,571,572], methylnadimide [417,419, 567, 571] and itaconimide [573]. The maleimide end-group is prepared by the condensation of an amine with maleic anhydride, followed by cyclization ... 

Unsaturated groups are very interesting for application development because this specific functionality opens up a broad range of possibilities for further (chemical) modification of the polymer structure, and therefore its physical and material properties. The direct microbial incorporation of other functional substituents to the polymer side chains, e.g. epoxy-, hydroxy-, aromatic-, and halogen functional groups, influences the physical and material properties of poly(HAMCL) even further [28,33,35,39-41]. This features many possibilities to produce tailor-made polymers, depending on the essential material properties that are needed for the development of a specific application. 

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