Poly phenylene vinylene P PV

This polymer bears some analogy with the P(TV) discussed above, both structurally and from the synthetic point of view interest in it has been high recently due to its 

The above is a variant of the route originally implemented by Wessling [646], which yields high MWt polymer with claimed conductivities as high as 5,000 S/cm, and 

Wudl et al. [648] have claimed that if in the precursor polymer in the scheme above. Cl is replaced by, e.g., PF, a fiilly doped polymer results in the final thermal treatment step. Pig. 14-16. after Brown et al. [89], summarizes precursor routes to P(PV). 

Some Precursor Routes to P(PV). After Reference [89], reproduced with permission. 

Because of the availability of precursor routes to P(PV), it is a relatively simple matter to prepare and orient or stretch fibers or films of the precursor polymer, and then convert them into P(PV) fibers or films, with fibers sometimes showing some crystallinity. It has been claimed [253, 649] that the 2,5-dialkoxy derivatives of P(PV) with long chain alkyl (e.g. 2,5-dihexyloxy-) are soluble in their fully doped form. 

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The wide variety of coupling methods adapted from organic synthesis to condensation polymerization of just one CP can be appreciated from Fig. 5-12. for poly(pheny-lene). Typical condensations and eliminations adapted to syntheses of such CPs as poly(phenylene) and poly(phenylene vinylene) (P(PV)) are illustrated in Fig. 5-13. Fig. 5-14 shows the variety of precursor routes available to P(PV). More recently, the Yu group [86] has demonstrated application of Pd-catalyzed Stille and Heck reactions to the synthesis of poly(thiophene) (P(T)) derivatives (cf. Fig. 5-15. Besides the Grignard couplings such as shown in Eq. 1.6, Chapter 1, P(T) s can also be prepared via a variety of other procedures, such as Friedel-Crafts alkylation [87], and direct oxidation with FeClj as for P(Py) above. 

Apart from the template-based sulfonated systems above very few examples abound of CP systems that may be considered to be truly soluble in doped and undoped forms. One of these is a poly(phenylene vinylene) (P(PV)) derivative reported by the Wudl group [253]. The polymer, prepared via conventional precursor-polymer routes commonly used for P(PV) s, has protonated and metal-salt forms (Fig. 8-2). Films can be cast readily from solution. The metal salt form yields films that readily redissolve in water, but films of the protonated form do not redissolve, apparently due to crosslinldng. The conductivities of films of the protonated and metal salt forms are, respectively, ca. 10 S/cm and 10 S/cm. 

Soluble polymers can likewise be prepared in the form of thin films by spinning the solution onto a substrate and then evaporating the solvent. Insoluble polymers can in suitable cases be spun in the form of their soluble precursors and then after evaporation of the solvent be converted into the insoluble polymer by elimination of the substituents which rendered them soluble. A well-known example of this is poly(para-phenylene-vinylene) (P PV). 

In a precursor-polymer synthetic approach [288], amphiphiles which formed charged complexes with precursor polymers of poly(p-phenylene vinylene) (P(PV)) and poly(thienylene vinylene) (P(TV)) were spread onto solutions of these precursor polymers. This unique complex is then transferred to an appropriate substrate using standard LB techniques, and then converted to P(PV) or P(TV) via heat treatment. In a similar but rather novel, in-situ polymerization approach from the Rubner group [289], LB films of ferric stearate are exposed sequentially to HCl vapor (generating FeCls oxidant) and pyrrole monomer, yielding conductive LB P(Py) films. 

Polymers of type shown on in Figure 4.28(b) were also investigated. For materials with five PV units, well-defined nanostructures were observed which are spaced 8 nm from center to center and have a length of 80 nm. Electron diffraction measurements show that the rods are packed into the same structure as the poly(p-phenylene vinylene) homopolymer. The rods are again perpendicular to the surface. When only two PV units are present, no nano-scale organization is observed and glassy solids were obtained instead. This latter observation shows that in order to obtain ordered nanostructures, a rod containing two PV units is not sufficient. 

Hide et al. [606] fabricated a diode with the structure Au/P(DCNT)/MEH-P(PV)/Au [P(DCNT)=poly(3,4-dicyanothiophene)>lEH-P(PV)=poly(2-methoxy-5-(2 -ethyl-hexyloxy)-l,4-phenylene-vinylene)], and found rectification ratios > 10 and photodiode behavior with a DC sensitivity at -3 V reverse bias of 4 X lO AAV, translating to a quantum yield of 0.1 %. Fig. 23-7 shows I-V characteristics of this device. In another contribution [985] Hide et al. studied diodes fabricated from blends of MEH-P(PV) and poly(2,6-(4-phenylquinoline)). In devices with the structure ITO/CP-blend/Al, EL quantum efficiencies of ca. 0.08% were seen, said to be greater than those for ITO/MEH-P(PV)/Al devices by a factor of 20. 

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