Cinética da polimerização química do pirrol em água utilizando 1-Bromododecano como co-dopante

Abstract

A very important class of polymers has been studied, the so-called intrinsic conducting polymers, in which conduction of the electric current happens without the incorporation of conductive charges. The polymer synthesized in this work, polypyrrole (PPy), belongs to this class and has several applications, such as electrodes, electrochromic devices, LEDs, solar cells, among others. Two methods are mostly used for the PPy synthesis: electrochemical polymerization and oxidative polymerization. A few substances can be used in the synthesis, as the oxidizing agent, which in addition to initiating the polymerization chain also acts as a dopant. Also, a co-dopant or surfactant may further be used to improve the morphology of the polymer. Therefore, the aim of this work was to evaluate the kinetics of the pyrrole (Py) chemical polymerization in water using ferric chloride as oxidant and ionic liquid 1-bromododecane as co-dopant. The polymerization reactions were carried out in a jacketed batch reactor, with a magnetic stirrer to maintain a constant rotation. The PPy samples were removed from the reaction medium over time, filtered and oven dried at 40 °C. The conversion profiles (gravimetric) were plotted and the kinetic parameters were determined. A few operating parameters were varied: agitation velocity (200 and 300 rpm), total volume (0.05 and 0.5 L), Py concentration (0.730, 0.085, 0.043 mol/L), FeCl3.6H2O concentration (1.47, 0.2, 0.1, 2.0, 0.05 mol/L), temperature (5 and 20 °C), and, finally, the addition of the ionic liquid (LI). In this study, it was observed that, although the ionic liquid 1-bromododecane decreases the conversion in the experiments, in the literature there are some advantages of its use, such as increase in thermal stability and electrical conductivity of the formed polymer, besides of improving the particles morphology. It was also found that a smaller rotation was more efficient in the polymerization reaction, as well as the volume variation practically did not affect the conversion. Increasing the concentration of both Py and FeCl3.6H2O reagents increased the conversion of Py to PPy. In relation to the kinetic data of polymerization reaction using the integral and differential methods, the values of R2 were always higher than 0.8 and good fittings were verified for reaction orders of Pi smaller than those of FeCl3.6H2O. The same response was found for the linear regression model, a result consistent to the literature (α = 1 for Pi and β = 2 for FeCl3.6H2O). The obtained results demonstrate the great effect that both reagents possess on the polymerization reaction rate in aqueous media. Finally, a smaller activation energy was found to the reactions containing LI, using the temperatures of 5 °C and 20 °C.