Sulfonium precursor polymer

These are the most widely used routes to PAVs. The first to be developed was the Wessling-Zimmerman route to PPV as shown in Scheme 6.1 [5]. Here the starting material is a p-xylenyl bis(sulfonium salt) 6, which on treatment with 1 equivalent of base generates a quinodimethane 7, which then polymerizes to produce the sulfonium precursor polymer 8. This is water soluble and can be used to make thin films that are thermally converted to the final films of PPV by heating at 220-250 °C under vacuum. Alternatively the sulfonium groups can be displaced by methanol to give the more stable methoxy-precursor 9, which requires a combination of heat and hydrochloric acid vapor for efficient conversion to 1. 

Conversion of the sulfonium precursor polymer 10 to PPV 1 is typically achieved by heating thin films to as high as 300 °C in high vacuum (10 mbar) for a period of several hours.The elimination conditions have a substantial influence on the properties of the thin film material particularly in device applications. Studies on the elimination process have shown a complex multistep mechanism but it is instructive to remember that the elimination products from a sulfonium chloride precursor polymer are HCl and thioethers. The size of the sulfonium group has been shown to influence both the intrachain and... 

Alkoxy Precursor Route. Sulfonium precursor polymers can be readily converted to methoxy-substituted polymers, which are soluble in organic solvents and which are much more stable than the sulfonium precursor. The alkoxy group can be removed by acid catalysis and/or heating to produce fully converted PPV derivatives [950, 968, 970]. 

The stability of the intermediate sulfonium precursor polymers in the solid state is relatively poor due to partial elimination and oxidation reactions, which turn them yellow colored and make them insoluble. Nevertheless, below 0°C, their solutions can be kept for several months. Han and Elsenbaumer [30] described a stabilization method, which consists of the addition of small amounts of a weak base (e.g., pyridine) to the aqueous or non-aqueous precursor solutions. High-quality freestanding films could be cast from pyridine-stabilized aqueous solutions of the polyelectrolyte and, after conversion to PPV and oxidative doping, the films exhibited conductivities 10 times higher than those derived from unstabilized precursors. 

The sulfonium precursor polymer can be converted to fully conjugated PPV either by treatment with excess base or by heating under vacuum or nitrogen. The tem-... 

Other methods that have been used for the conversion of sulfonium polymers to PPV include the use of strong acids [101] and microwave heating [102]. It is also possible to grow films of PPV from the sulfonium precursor polymer electrochemically. The formation of PPV is thought to arise from a local increase in the pH around the electrode due to hydrolysis reactions, leading to elimination of the precursor polymer [461. 

J. D. Stenger-Smith, T. Sauer, G. Wegner, and R. W. Lenz, Preparation, spectroscopic and cyclic voltammetric studies of poly( 1,4-naphthalene vinylene) prepared from a cycloalkylene sulfonium precursor polymer. Polymer 31 632 (1990). 

B, R, Hsieh, H. Antoniadis, M. A. A. Abkowitz, and M. Stolka, Charge transport properties of poIy(phen-ylene vinylene) and its sulfonium precursor polymer at different degrees of conversion, Polym. Prepr. 33 414(1992). 

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