Pyrroles continued structure

The pi bonding structure of pyrrole. The pyrrole nitrogen atom is sp2 hybridized, with a lone pair of electrons in the p orbital. This p orbital overlaps with the p orbitals of the carbon atoms to form a continuous ring. Counting the four electrons of the double bonds and the two electrons in the nitrogen p orbital, there are six pi electrons. 

A mechanism involving the coupling of cation radicals has also been considered for the electropolymerization of benzene compounds [306,313]. This mechanism occurs by a sequence of events similar to those proposed for the electropolymerization of pyrroles. The first step is the oxidation of benzene to a cation radical (471). Two of these cation radicals combine to form a dication dimer (478). The neutral aromatic dimer (479) is formed upon loss of two protons. This dimer is then reoxidized to a cation radical (480). Chain growth is accomplished by the coupling reaction of this cation radical with other cation radicals followed by deprotonation to form aromatic structures. Polymer growth continues by this sequence of steps until precipitation from solution occurs (Fig. 72). 

Pyrroles and their Benzo Derivatives Structure Table 12 (continued)... 

Caprolactam for use as fibers is hydrolytically polymerized in batches as 80%-90% aqueous solutions with 0.2%-0.5% acetic acid and ethylene diamine at 250-280° C. The acetic acid acts as chain stabilizer (see above). The ethylene diamine increases the amine equivalent of PA 6 so that mixed weaves of Perlon and wool can be evenly dyed. The water is removed as steam in the polymerization progresses. Caprolactam is also polymerized continuously by what is known as the VK process (vereinfacht-A ontinuierliche, or simplified continuous, process). This process is carried out without pressure with, for example, 6-amino caproic acid or AH salt as initiator. In contrast to the production of nylon 6,6, this process can proceed continuously the melt can be directly spun from the reactor. Polyamide 6 fibers have good properties but they yellow slowly since pyrrole structures are formed at the chain ends. 

Besides using an in situ polymerization of pyrrole to form an electrically conductive textile, other researchers have adopted a two-step process. The major advantage of the two-step process is that it can be easily adapted into a continuous process for industrial applications. However, the structure of the polypyrrole may be different to that obtained from the in situ polymerization process. Several variations to the a two-step process include first immersing the textile support in a solution containing the oxidant and desired dopant anion and then exposing the impregnated textile to either pyrrole vapor [87-89] or pyrrole dissolved in an aliphatic solvent [90] to initiate the polymerization reaction. Alternately, the textile support may be first exposed to pyrrole vapor and then immersed into an aqueous solution containing the oxidant and desired dopant anion [91]. 

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