Conductivity alkylated thiophenes

The conductive properties of alkylated thiophenes are known to be unstable, particularly at elevated temperatures. The mechanism of thermal undoping has been associated with thermal mobility. Consequently, various workers126 have considered synthesis of random copolymers (e.g., thiophene and 3-octylthiophene), with well-distributed octyl side groups leaving space around the main chains to accommodate dopants. 

An alternative approach52 involves polymerization of conventional polymer in the presence of a soluble conducting polymer (alkylated thiophene) to form a semi-interpenetrating network. The polythiophene was dissolved in solutions of styrene and divinyl benzene conductivities in the range 0.01-0.10 S cm-1 were obtained. 

Thin film field-effect transistors have been prepared of poly(3-alkyl-thiophenes) by using spin-coating techniques. The devices are used in the determination of the charge carrier mobility p, dc conductivity a, and the carrier concentration p. Poly(3-hexylthiophene) is characterized in a wide temperature range T = 130 - 430 and possible transport mechanisms are discussed. ... 

Elsenbaumer, R. L., Jen, K.Y., Miller, G. G., Eckhardt, H., Shacklette, L. W., and Jow, R., 1987. Poly [alkyl thiophenes] and poly (substituted heteroaromatic vinylenes] versatile, highly conductive, processible polymers with tunable properties, in Electronic Properties of Conjugated Poiymers, Kuzmany, H., Mehring, M., and Roth, S. [Eds.], Springer, Berlin. ISBN 0-387-18582-8. 

As an extension of our earlier work we have studied soluble conductive polymers (sulfonic acids doped polyaniline (4), poly(3-alkyl thiophenes) (5)) for the design of a new generation of microwave absorbing materials (6). These studies have own that microwave properties were very dependent on minor changes in e q)erimental procedures. Therefore it was necessary to determine how synthetic conditions effects influence structural parameters of polymers, and how these structural parameters influence electrical, optical properties and stability over time. In the case of poly(a]kylthiophene)s, solubility of polymers permits a complete structural characterization and then a better understanding of links between... 

S. -A. Chen and J.-M. Ni, Structure/properties of conjugated conductive polymers. 1. Neutral poly(3-alkyl-thiophene)s. Macromolecules 25 6081 (1992). 

Template syntheses yielding complexes of poly(styrene)/poly(3-alkyl-thiophene) (P(Sty)/P(3AT)) claimed to be full interpenetrating polymer networks (IPN, all polymer components part of a crosslinked network) have been effected by the Rubner group [133], with conductivities in some cases up to 0.5 S/cm. In this case, however, the P(3AT) actually forms the template The pendant groups of a vinyl derivatized P(3AT) are first crosslinked with styrene monomer. The resulting compound is then polymerized and crosslinked at the styrenes. As however the resulting complexes are insoluble, intractable, less conductive and generally less stable than P(3AT) s, their utility is not made clear by the authors of the work. 

A lot of poly(3-alkyl-thiophenes) were known at that time, and some of these special polythiophenes exhibited a remarkable conductivity in the doped state. A comprehensive overview about polythiophenes and their electronic properties available at that time can be foimd in the Handbook of Oligo- and PolythiophenesP The fundamental drawback of all these polythiophenes was the instability of the highly conductive form. In particular, humid air was destructive. 

The synthesis involves the nickel-catalyzed coupling of the mono-Grignard reagent derived from 3-alkyl-2,5-diiodothiophene (82,83). Also in that year, transition-metal hahdes, ie, FeCl, MoCl, and RuCl, were used for the chemical oxidative polymerization of 3-substituted thiophenes (84). Substantial decreases in conductivity were noted when branched side chains were present in the polymer stmcture (85). 

The synthetic utility of o-quinodimethane generated by cheletropic elimination of S02 has been amply demonstrated by Oppolzer and Nicolaou, who have conducted an intramolecular cycloaddition coupled with the alkylation of 1,3-dihydrobenzo[c]thiophene 2,2-dioxide122. When 1,3-dihydro-l-(4-pentenyl)benzo[c]thiophene 2,2-dioxide (201) prepared from 1,3-dihydrobenzo[c]thiophene 2,2-dioxide and 4-pentenyl bromide is heated in di-n-butyl... 

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