Postpolymerization conductivity

The preparation of polyacrylamides and postpolymerization reactions oti polyacrylamides arc usually conducted in water. Reactions on the amide groups of polyacrylamides are often more complicated than reactions of simple amides because of neighboring groups effects. 

Structural modifications of polyaniline have mainly been exploited to achieve improved processability and environmental stability. In general, the substituted polyanilines can be obtained via oxidative polymerization of the corresponding monomer. However, inductive and steric effects can make such monomers difficult to polymerize [42]. Several substituted polyanilines have been prepared by varying the nature (alkyl, alkoxy, halogen, etc.) and the position (2- vs 3-, 5-positions) of the substituent [24, 27-32, 34, 37, 43, 44]. These studies have shown that regardless of the nature and position of the substituent group, there is an adverse effect on polymerization and the properties of the polymer such as conductivity and electroactivity. To overcome these limitations, various synthetic methods have been developed to prepare self-doped sulfonated polyanilines. These methods involve controlled postpolymerization modifications by synthetic reactions on the whole polymer and copolymerization of less reactive monomers with aniline as described below. 

In addition to sulfonic acid groups, carboxylic acid groups as ring substituents results in self-doping of polyaniline and influence properties such as solubility, pH dependent redox activity, conductivity, thermal stability, etc. Sulfonated polyanilines are typically obtained by postpolymerization modifications such as electrophilic and nucleophilic substitution reactions. However, carboxylic-acid-functionalized polyanilines are typically synthesized directly by chemical and electrochemical polymerization of monomer in the form of homopolymer or copolymer with aniline. In contrast to sulfonated polyaniline, very few monomers are available for the synthesis of carboxyl acid functionalized polyaniline. Anthranilic acid (2-aminobenzoic acid) is an important monomer and is often used for the synthesis of carboxyl acid functionalized polyanilines. 

For example, in situ conductivity probes were used to monitor incorporation of ionic comonomers in aqueous copolymerization reactions [73,74], and to directly monitor counterion condensation during copolymerization [75]. Conductivity probes immersed in flow-coupled mixing chambers were used on ACOMP-extracted streams during organic phase polymerization, and for aqueous copolymerization where the reactor ionic strength was too high for direct conductivity measurements. In situ pH probes have been coupled with ACOMP data to monitor hydrolysis during postpolymerization modifications. 

Free radical polymerization reactions are conducted under an inert atmosphere. Initiation with thermal or redox free-radical initiators is common [9,14], Industrial processes are designed to reduce residual monomer levels to below regulated limits [24, 25], This is achieved by pushing the reaction to completion by increasing the reaction temperature or increasing the initiator levels toward the end of the reaction. Also postpolymerization strategies have been employed, such as an enzymatic treatment with amidase [26]. 

Recently, much interest has been shown in enhancing the order and consequent conducting properties of conducting polyaniline salts via postpolymerization treatment with an appropriate "secondary dopant." In particular, much attention has focused on the influence of w-cresol 1 solvent or... 

Linear poly(A/-methyl-3,6-carbazolylen) (64c) has been prepared by the reaction of 3,6-dibromo-9-methylcarbazole (67a) with the Grignard reagent (67b) in the presence of a complex nickel catalyst [436-438], A brittle film of (67c) can be cast from nitrobenzene solution which shows a conductivity, when doped with I2 or NOBF4, as high as 6 S cm . Doping with iodine induces a postpolymerization reaction which increases its molecular weight and improves mechanical stability. 

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