Substituted PAns

In our laboratories, we have used a related approach to covalently attach chiral camphorsulfonate groups to N centers of PAn, by the reaction of EB with (lS)-(+)-10-camphorsulfonyl chloride in NMP/pyridine.153 The optically active product 13, isolated as the HC1 salt, is believed to preferentially adopt a one-handed helical conformation for its polymer chains. This provides the first example of chiral induction in a PAn species through a covalently attached group. A significant advantage for the product 13 compared to the chiral PAn/HCSA salts described earlier is that it consequently retains its optical activity upon alkaline dedoping in solution to its EB form. 

A factor hindering the expansion of PAn chemistry to date has been the lack of a generic route to variously substituted derivatives. An exciting development in this respect is the recent synthesis of the novel poly(aniline boronic acid).138 Aromatic boronic acids are versatile chemical precursors, undergoing a wide range of transformations and this provides a facile route to a wide range of substituted PAn s that are difficult to synthesize directly from their respective monomers. This approach has been successfully demonstrated for the synthesis of poly(hydroxyaniline) and for poly(halogenoaniline).138 

---

A wide range of alkyl- and alkoxy-substituted PAn s of the general types 6 and 7 have been synthesized by the chemical or electrochemical oxidation of appropriately substituted aniline monomers.133 Such substitution imparts markedly improved solubility in organic solvents to the emeraldine salt products compared to the parent (unsubstituted) PAn/HA salts. The poly(2-methoxyaniline) (POMA) species, in particular, has been the subject of extensive studies.134 137 This species has the additional attractive feature of being soluble in water after being wet with acetone. 

The substituted PAn products often have much lower molecular weights than the parent unsubstituted PAn, although Mw values as high as 400,000 g mol-1 have been reported for POMA by controlled chemical polymerization at -40°C.58 This improvement in processability for substituted PAn s is also generally gained at the expense of a large decrease in electrical conductivity, due to twisting of the polymer chains from planarity by the bulky substituents. 

Electrochromic applications of the PAn and substituted PAn films [307a-h], composite films of PAn or its derivatives with other electrochromic materials [307i-m], silanized PAn films [306o] and photo-induced electrochromic reactions on semiconductor particles [307p]. Again, most other polymers can be used for this purpose as long as their oxidized and reduced states are stable and have different colors from that of neutral polymers. 

Grassie and McGuchan (1970-72) [176-184], using TGA, DTA, TVA (thermal volatilization analysis) and IR, carried out a series of pyrolysis investigations on powder forms of PAN and substituted PAN polymers in order to determine the effect of introducing various copolymers. 

---