Het effect van tegenionen op de eigenschappen van poly (p-fenyleen vinylenen) en hun precursorpolymeren

Abstract

The effects of counterions on the polyelectrolytes, poly(xylylene tetrahydrothiophene chloride) and poly(2,5-dimethoxy xylylene tetrahydrothiophene chloride), the conjugated polymer , poly(phenylene vinylene) and poly(2,5-dimethoxy phenylene vinylene) and the elimination reaction to these conjugated systems are discussed. First of all, we investigated the solution behaviour of the polyelectrolyte in presence of salts. The polyelectrolyte solution is titrated with different salt solutions and the solution behaviour of the polyelectrolyte is compared with the structural entropy value (ΔS0istr) of the anions. This ΔS0istr is a value for the structural entropy changes caused by the effects of anions on water, beyond the first hydrationshell of the anion. The precursor polymer does not precipitate when 50 ml NaH2P04-, Na2S04-, NaF-, NaI03-, NaHS04- or NaBr03-solution is added to the polyelectrolyte solution. For this anions the ΔS0istr-value is negative (water-structure making anions). The polymer precipitates if NaN02, NaCl, NaN03, NaBr, NaBF4, KCl04 or NaI is added. These anions have a positive AS0istr -value and are water-structure breaking anions. We have determined the critical salt concentration, CSC, for the latter anions and found that the precipitation of the polyelectrolyte occurs earlier for anions with more waterstructure breaking character. The effect of kations is also investigated, but they do not have any effect on the solution behaviour of the polyelectrolyte. The critical salt concentration is not influenced by the polymer concentration. The effect of the anions on the solution behaviour of the precursor polymers of PPV and PDMPV, stabilised with pyridine, is also investigated. The solubility of these precursor polymers in presence of salts is lower than that of the precursor polymer of PPV. The solubility decreases if the tetrahydrothiophene is substituted by pyridine. But the substitution of the methoxy-groups on the ring decreases the solubility considerable. Nevertheless there exists also a correlation between the critical salt concentration of stabilised polyelectrolyte solutions and the Δs0istr-value of the anion. When salt is added to the polyelectrolyte solution, also a gel is formed. This gel occurs only when the polymer-salt solution is in motion. It is however very difficult to find what causes this gel formation. The basic problem is the instability of the polymer. We found that the gel formation is independent of the type of salt and the polymer concentration. The speed of stirring, the salt concentration and the temperature do influence the gel formation.