Wessling methods

The efficiency of PPV may also be raised by introducing disorder into the polymer chains. The crystallinity of PPV may be lowered by employing a modified Wessling method utilizing a xanthate leaving group 63J. PPV produced by this method is believed to contain a mixture of cis- and rram-alkenc units. The efficiency of the material is 0.22% when employed in a single layer device with... 

As discussed in the previous edition, not all aryl bis-sulfonium salts will undergo efficient polymerization by the Wessling method, due to either the loss of aromaticity in forming the quinodimethane (e.g., 2,6-naphthalene) being too great, or the intermediate being too stable (e.g., 9,10-anthracene). It has been established that the polymerizability of a bis-sulfonium salt (and presumably of the other monomers) is determined by the enthalpy of formation of quinodimethane and so the accessibihty of a given PAV by these methods can now be predicted [22]. 

The most common synthetic routes for traditional PPVs are the Gilch, Witting condensation, and Wessling methods (Figure 11.12) [2]. For multifunctional and... 

Polyfpyridine vinylene) 55 may also be prepared by the Wessling route (Scheme 1 -19) [95]. Fully conjugated material may be obtained by thermal elimination of the sulfonium salt 61 or the halide 62. The method, however, does not... 

Poly(para-phenylenevinylene)s via Polymerization Methods The Wessling Procedure... 

Wessling, R. A. Method for Quantitatively Analyzing Substances Containing Elements Other Than Carbon, Hydrogen and Oxygen and Volatile Organic Compounds ... 

While the Wessling-Zimmermann route is a typical method of polymer synthesis, both PPVs and their corresponding oligomers can be synthesized by the extension of methods used for the synthesis of the easiest building block, stilbene 70 (scheme 13). Conceptionally, this is possible by (i) carbon-carbon double bond formation, for whieh synthetic organic chemistry provides a great number of methods [116], and (ii) by aryl-vinyl coupling [117] some examples of both methods are outlined in scheme 13. 

There are, however, some problems with this method. First, high molecular weight fractions are not soluble in the strongest solvent, A-methyl pyrroli-done, for emeraldine base. Second, Wessling has shown by membrane filtration and photon correlation spectroscopy that these transparent, clear blue liquids are in fact dispersions and not solutions. 

In this view the barriers between the (partly) crystalline metallic phases in the PAni primary particles also consist of PAni, and not of components of the insulating matrix. This is probably amorphous PAni, whereas the metallic phase consists of (partly) crystalline PAni. Assuming a crystallinity of 30%, this results in a barrier thickness of 1.6 run, giving a particle size of 9.6 nm, which approximates closely to the 10 nm estimated by other methods in earlier works by Wessling. Figure 11.115 shows the transport scenario. 

B, Wessling A Method of Preparing Compositions with Optimised Conductivity Behaviour. Summary of experimental results and various other articles. 

Poly(p-phenylene vinylene) (PPV) is a conjugated polymer, which becomes conductive by the addition of electron donors or acceptors [114, 115], Several methods have been reported for the synthesis of PPV [3, 4, 6], Direct chemical polymerization, which was used in the first attempt of synthesizing PPV, gave a product in the form of an insoluble powder that limited the use of the polymer in many applications [116], The most popular method for the preparation of PPV is base-induced polymerization of sul-fonium salt monomer in aqueous solution [114-118], In this method, PPV films are obtained from the precursor polymer after thermal elimination of the sulfonium groups. PPV has also been prepared electrochemically by reducing p-xylene-bis-(triphenylphosphonium). Two approaches are generally used for the synthesis of PPVs the Wessling... 

Combined methods are also used to monitor cathodic protection efficiency. In the intensive measurement described by Wessling et at. [68], both CIPS and DCVG are used. The worker walks the pipeline route and records the distance and the switch on and switch off potential changes vs. the portable reference electrode at small intervals. The measurements are supplemented with ON/OFF potential gradients in one or two directions perpendicular to the pipeline. The measured (real) values serve as the basis for calculating the insulation defects (% IR). Other techniques such as the intensive holiday detection method can be used to detect the coating defects in the pipelines. Implementation of the above methods has led to a considerable decrease in the number of breakdowns of underground pipelines. 

Denton, F.R., P.M. Lahti, and FE. Karasz. 1992. The effect of radical trapping upon formation of poly(a-tetrahydrothiophenio paraxylene) polyelectrolytes by the Wessling soluble precursor method. 7 Polym Sci A 30 2223. 

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