Aromatic carbons substitution polymerization

Copolymers with different amounts of pendant sulfonic acid groups have been synthesized by an aromatic substitution polymerization reaction [129]. 4,4-Difluorodiphenylsulfone, 6,7-dihydroxy-2-naph-thalenesulfonate, and various hydroxyl-terminated monomers were used in the presence of potassium carbonate [130]. 

The polymerizations require the use of dipolar aprotic solvents such as N-methylpyrrolidone (NMP), dimethyl acetamide (DMAC), dimethyl sulfoxide (DMSO) or N,N -dimethylpropylene urea (DMPU). Nucleophilic aromatic substitution polymerizations are t q>ically performed in a high boiling aprotic polar solvent with the monomer(s) reacted in the presence of a base, potassium carbonate, at elevated temperatures (ca. 180 C). Potassium carbonate is used to convert the phenol into the potassium phenolate and since K2CO3 is a weak base, no hydrolytic side reactions are observed. Dipolar aprotic solvents are used in these poly(aryl ether) syntheses, since they effectively dissolve the monomers and solvate the polar intermediates and the final polymer. DMPU has been shown to be an excellent solvent for poly(ether) syntheses, particularly for those polymers which are only marginally soluble in other dipolar aprotic solvents (22). Furthermore, DMPU allows higher reaction temperatures (260 C). We have observed that DMPU, when used in conjunction with toluene as a dehydrating agent, accelerates many nucleophilic substitution reactions. 

The use of NMR spectroscopy to evaluate potential aryl fluoride monomers as candidates for nucleophilic aromatic substitution polymerization has shown to be an accurate and time saving technique. Since the shift is controlled by the electron density of the carbon to which it is attached, the magnitude of the F chemical shift can... 

Na and coworkers reported the preparation of another two difluoro monomers, l,4-bi(3-sodium sulfonate-4-fluorobenzoyl) benzene and l.S-fcisCS-sodium sulfonate-4-fluorobenzoyl)benzene. ° A large number of SPAEKs with different structures were then prepared via aromatic nucleophilic substitution from these sulfonated monomers, nonsulfonated dihalo monomers, and bisphenol monomers in the presence of potassium carbonate in polar solvents. Various types of these sulfonated polymers are illustrated in Figure 5.8. Compared to the postsulfonation method, the DS of SPAEKs by direct polymerization can be controlled very easily and precisely, which enables us to finely tune the properties of membranes and maximizes the overall performance of membranes for applications in PEMFCs and DMFCs. 

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

Styrene is a colorless liquid with an aromatic odor. Important physical properties of styrene are shown in Table 1. Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, -heptane, and ethanol. Polymerization generally takes place by free-radical reactions initiated thermally or catalytically. Styrene undergoes many reactions of an nnsaturated compound, such as addition, and of an aromatic compound, such as substitution. 

Many authors have observed an acceleration of caprolactam polymerization in the presence of A-acetyl-e-caprolactam, isocyanates, thiolactones, organic sulphates, aromatic amides, benzyldioxime carbonate, arylenedicarbamoyllactams, phosphorus oxychlorides and phosphorus pen-tachloride. Activator effectiveness increases with growing substituent electronegativity in N-substituted lactams. 

Side group reactions are common during pyrolysis and they may take place before chain scission. The presence of water and carbon dioxide as main pyrolysis products in numerous pyrolytic processes can be explained by this type of reaction. The reaction can have either an elimination mechanism or, as indicated in Section 2.5 for the decarboxylation of aromatic acids, it can have a substitution mechanism. Two other examples of side group reactions were given previously in Section 2.2, namely the water elimination during the pyrolysis of cellulose and ethanol elimination during the pyrolysis of ethyl cellulose. The elimination of water from the side chain of a peptide (as shown in Section 2.5) also falls in this type of reaction. Side eliminations are common for many linear polymers. However, because these reactions generate smaller molecules but do not affect the chain of the polymeric materials, they are usually continued with chain scission reactions. 

Thermosetting phenolic resins form a separate class of polymers containing aromatic rings and aliphatic carbon groups in the polymeric network. These resins are formed from the reaction of phenol (or substituted phenols) with formaldehyde. The fully crosslinked macromolecule is insoluble and infusible. Other thermosetting resins are known in practice, some derived from the reaction of melamine or of urea with formaldehyde. Because these have a different chemical structure, containing nitrogen, they are included in a different class (see Section 15.3). 

---