Polyacetylenes procedures

Polyacetylene, (CH),(, is a simple, conjugated polymer which may have either a trans or a cis configuration (Fig. 9.1). Free-standing films of polyacetylene can be easily obtained by catalytic polymerisation of gaseous acetylene, the most common procedure being the Shirikawa... 

Electrochemical doping of insulating polymers has been attempted for polyacetylene, polypyrrole, poly-A/-vinyl carbazole and phthalocyaninato-poly-siloxane. Significantly, Shirota et al. [91] claim to have achieved the first synthesis of electrically conducting poly(vinyl ferrocene) by the method of electrochemical deposition (ECD) [91]. This is based on the insolubilization of doped polymers from a solution of neutral polymers. A typical procedure applied [91] for polyvinyl ferrocene is to dissolve the polymer in dichlorometh-ane and oxidize it anodically with Ag/Ag+ reference electrode under selective conditions. The modified polymer [91] (Fig. 28) is a partially oxidized mixed valence salt containing ferrocene and ferrocenium ion pendant groups with C104 as the counter anion. 

Of various homocoupling procedures derived from the original Glaser process that are still used today, Hay s procedure [4] using catalytic amounts of the biden-tate complexing base TMEDA in polar solvents (e.g. acetone, dichloromethane or o-dichlorobenzene) is most utilized and is the method favored for preparing linear oligo- and polyacetylenes, as outlined in Scheme 2 [5]. 

Scheme 2. Preparation of polyacetylene 2 (n 32) using the coupling procedure described by Hay. (ODCB o-dichloroben-zene, TMEDA N,N,N, N -tetramethylethylenediamine.)...

This review describes the synthesis and properties of polyacetylenes with substituents (substituted polyacetylenes) mainly on the basis of our recent studies At first, Sections 2 and 3 survey the synthesis of substituted polyacetylenes with group 6 (Mo, W) and group 5 (Nb, Ta) transition metal catalysts respectively, putting emphasis on new, high-molecular-weight polyacetylenes. Then, Section 4 refers to the behavior and mechanism of the polymerization by these catalysts. Further, Section 5 explains the alternating double-bond structure, unique properties, and new functions of substituted polyacetylenes. Finally, Section 6 provides detailed synthetic procedures for substituted polyacetylenes. 

To our mind, except for bivalent biopolymers, the terminally functionalyzed conformational-rigid molecules such as polyphenylenes, polyacetylenes, perfluoroalkyls etc. seem to be promising spacers for this procedure. 

Using such a procedure, a sample of the microporous polypropyl-ene/polyacetylene structure consisting of 5.7% polyacetylene was doped to the maximum level. 

The appearance of the sample was quite different from that in Procedure 7. After only one exposure, the sample was dark in color, indicating a more uniform deposition of polyacetylene throughout. Multiple exposures gave an even darker membrane. 

Procedure 12 Attempt to Prepare a Nylon 6/Polyacetylene Structure. 

Most of the research was done with 0.2 micrometer rated porous polypropylene (Accurel ) membrane, and the concentration of polyacetylene in the composite could be varied from 4 to 43 percent. Larger percentages should be possible. The membranes did not lose their flexibility, and membrane properties such as flux rates and bubble point pressure were not altered (see Experimental Procedure 1). As is the case for polyacetylene alone, the conductivity of these membranes could be varied depending upon the type and amount of dopant. Iodine doped laminates were the most stable of the two doped laminates investigated in this study. 

The all-dry box procedures resulted in another interesting visual effect. By controlling the solvent removal step that is, how long a vacuum was applied to the polymerization vessel, the location of the polyacetylene within the membrane structure could be regulated. For example, sandwich structures could be created by immediately applying a vacuum to a membrane sample wet with catalyst solution. This technique caused the solution to move into the center of the membrane s cross section thus polyacetylene formed only in the center of the cross section as well. The presence of polyacetylene, then, was hidden by the membrane s surface. Consequently, the surface of the membrane appeared almost white when dry (opaque) but instantly turned very dark when wet with solvent (transparent - polyacetylene then could be seen). Upon drying, the membrane again turned white. The phenomenon could be observed countless times with the same sample. 

The experimental procedure for the preparation of the-polyacetylene/styrene-diene triblock polymer blend was essentially the same as that of the EPDM/polyacetylene blend. The polyacetylene/styrene-diene triblock polymer was doped with either I2 or FeClg in nitromethane. 

Samples containing more than 2% of sulfur did not pick up any iodine even after a 72-hour period. The completely saturated EPDM portions of the blend seem to prevent any iodine molecules from permeating into the polyacetylene moieties. In order to circumvent this problem, we have doped the blend with iodine prior to the crosslinking procedure. Subsequently, the doped material having a conductivity of 60 ft-1 cm-1 was reacted with sulfur monochloride in a toluene solution for 10 minutes. The color of the solution turned from pale yellow to dark red while the polymer film remained insoluble in the toluene solution. 

When well-defined, less Lewis-acidic metathesis polymerization catalysts are used to polymerize COT, a lower level of detectable sp defects are formed. Also, although the polyacetylene produced is still insoluble, the reaction proceeds slowly enough to allow manipulation of the liquid reaction solution before hardening. In this way, one can obtain films in a desired shape and location, e.g., on a semiconductor [123]. This procedure was found to result in better electrical contact than can be obtained when a free-standing film prepared via the Shirakawa route is simply pressed against an electrode. 

Earlier investigators used a standard polymerization procedure for gaseous monomers that involves bubbling acetylene gas through the catalyst solution with stirring, and produced polyacetylene in the form of a black powder. Since the latter is oxidatively unstable, insoluble in all solvents and infusible, detailed investigation of its properties was unsuccessful. 

---