Polymerization of Aniline Derivatives

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Electropolymerization in acidic media affords free-standing films that are believed to contain varying degrees of cross-linking [267,292,304]. The miscibility of aniline with water allows for a variety of aqueous oxidants, such as ammonium peroxydisulfate, to be used [305]. Chemical polymerization of aniline can also be performed in chloroform through the use of tetrabutyl ammonium periodate [306]. Accordingly, a number of alkyl [301] and alkoxy-substituted [307] aniline derivatives have been chemically polymerized. Unfortunately, functionalization of the aniline nucleus often leads to a decrease in performance in the resulting polymers [308,309]. 

Aniline and its derivatives were oxidatively polymerized by peroxidase catalyst. HRP catalyzed the polymerization of aniline in aqueous organic solvents to produce the polymer with a complicated structure in low yields.65 The resulting polymer showed good third-order nonlinear optical properties.66... 

Y-J. Liu and M. G. Kanatzidis, Postintercalative polymerization of aniline and its derivatives in layered metal phosphates, Chem. Mater., 7, 1525-1533 (1995). 

Y. Wei, G. W. Jang, K. F. Hsueh, R. Hariharan, S. A. Patel, C. C. Chan, C. Whitecar, Effects of p-phenylenediamine and other additives on polymerization of aniline and its derivatives and on the properties of resultant polymers, Polymeric Materials Science and Engineering 1989, 61, 905. 

Ext ive investigations on polyaniline (PAn) and its derivatives have be carried out (i) since they possess a moderate conductivity upon doping with protonic acid and an excellent stability under ambient conations (2,3). PAn is simply prepared by the chemical and electrochemical oxidation of aniline or its derivatives in aqueous solution. In general, however, the chemical and electrochemical polymerization of aniline monomer lead merely to an insoluble powder and a thin brittle film, respectively. Hence, it is very difficult to process PAn for a practical use. In order to deal well with this problem, the improvement of processability of PAn has been studied by preparing polymer composites (4) and soluble PAn (5,6) and using plasma polymerization (7) and postsulfonation of PAn (8,9). Another approadi to the preparation of processible PAn is to apply a precursor polymer, e.g., PAn can be produced by the thermal treatment of poly(anthranilic acid) 0 ANA) (10). This mefliod is particularly useful for the preparation of processible PAn or its composites with other insulating polymers since it does not use external dopants that often cause an inconvenient situation associated with a practical use of the conducting polymer. 

The materials discussed in this section are polyaromatic polymer/anion composite films prepared electrochemically by the polymerization of the derivatives of pyrrole, aniline, thiophene, azulene and benzene. The films are normally used directly as grown on the metal substrate where they have good adhesion and electrical contact. The switching properties of these materials are described with more detail in the first section which describes polyaniline. However, it should be understood that these characteristics are generally common to all of the materials. 

PANI and its derivatives can be synthesized by the electrochemical polymerization or chemical polymerization of aniline although some other approaches have also been reported such as solid-state polymerization [313], electroless polymerization [314], plasma polymerization [315], and emulsion polymerization [307], Various oxidants were used for oxidation of aniline monomer, such as ammonium peroxy-disulfate, sodium peroxydisulfate, potassium bichromate, and hydrogen peroxide. 

Enzymatic polymerization of a series of aniline derivatives was studied in aqueous and aqueous organic solvents. Phenylenediamines and aminophenols were polymerized in ambient conditions by the catalysis of horseradish peroxidase (HRP) in dioxane without the presence of templates [15,16]. The products were soluble in DME and DMSO. The structures were analyzed by ET-IR and NMR. The larger molar excess of hydrogen peroxide was necessary in reaching a higher polymer yield. Poly(2-aminophenol) and poly(4-aminophenol) resulting from these reactions have been shown to have electroactive properties. 

Electroactive polyaniline films were synthesized by the catalysis of biUru-bin oxidase (BOD, a copper-containing oxidoreductase). The polymerization of aniline was carried out on the surface of a sohd matrix such as glass sUde, plastic plate, or platinum electrode to form homogeneous films [33]. The BOD was immobilized on the surface by physical absorption. The optimum pH was around 5.5. Some aniline derivatives such as p-aminophenol and p-phenylenediamine were good substrates for BOD. Structural analysis suggested the BOD synthesized polyanihne possessed partially 1,2-substititued structures. Cyclic voltammetric studies demonstrated that the PANl films were electrochemically reversible in redox properties, but differed from that of chemically or electrochemically synthesized PANl. The difference was attributed to the partial 1,2-substitution. Laccases are known to oxidize phenolic compounds in nature in the presence of oxygen and are capable in polyaniline synthesis in vitro [34-36]. 

Isocyanates. The commodity isocyanates TDI and PMDI ate most widely used in the manufacture of urethane polymers (see also Isocyanates, organic). The former is an 80 20 mixture of 2,4- and 2,6-isomers, respectively the latter a polymeric isocyanate obtained by phosgenation of aniline—formaldehyde-derived polyamines. A coproduct in the manufacture of PMDI is 4,4 -methylenebis(phenyHsocyanate) (MDI). A 65 35 mixture of 2,4- and 2,6-TDI, pure 2,4-TDI and MDI enriched in the 2,4 -isomer are also available. The manufacture of TDI involves the dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Separation of the undesired 2,3-isomer is necessary because its presence interferes with polymerization (13). 

A number of dihydroquinolines have been prepared by treating aniline derivatives with acetone or mesityl oxide in the presence of iodine. In these cases aromatization to the fully unsaturated quinoline would require the loss of methane, a process known as the Riehm quinoline synthesis. Such Skraup/Doebner-von Miller-type reactions are often low yielding due to large amounts of competing polymerization. For example, aniline 37 reacts with mesityl oxide to give dihydroquinolines 39, albeit in low yield. ... 

Studies on the Bischler-Napieralski cyclization of A -acetyltryptamine in the presence of indole have led to the isolation of numerous products, among which the indolocarbazole 186 could be found in 3.5% yield. This outcome was rationalized as a result of the intermediacy of a spiroindolenine species formed under these conditions [89H(28)175]. During detailed studies on the polymerization of indole, formation of a low yield of the related indolo[3,2-h]carbazole 187 was discovered in the product mixture originating from the treatment of indole with p-toluenesulfonic acid at elevated temperature [88JCS(P1)2387]. In an investigation of the condensation of p-benzoquinone with 4-substituted anilines, an indolo[3,2-h]carbazole derivative has been reported to be formed in 2% yield (80JOC1493). 

Ring fluorination is observed in reactions of protected aniline derivatives, with the ojp ratio of the products, e.g. 11-13, being dependent on the substituent 5 nitrobenzene is unreactive towards electrophilic substitution. The polymerization process may be studied by di-fluorobis(fluoroxy)methane reactions with variousfluoro-substituted benzene derivatives (hexa-... 

---