Interpenetrating polymer network composites of polypyrrole and poly(vinyl acetate)

Interpenetrating polymer network (IPN) composites of polypyrrole (PPy) and poly(vinyl acetate) (PVAc) were prepared by dipping FeCl3 impregnated PVAc films into solutions of pyrrole in water. PVAc becomes colored due to partial dehydroacetylation and also insoluble due to FeCl3 treatment. These properties do not change on leaching out FeCl3 from the films. However, differential scanning calorimetry shows that the T-g of PVAc remains unchanged in the FeCl3 treated films indicating that the dehydroacetylation did not proceed to significant extent. The FeCl3 impregnated films however swell rapidly with simultaneous leaching of FeCl3 when they are immersed in water. The extent of swelling decreases with decrease in temperature. Considerable swelling occurs even below the Tg Of the polymer. PPy forms inside the swollen films when the impregnated films are dipped into aqueous solutions of pyrrole instead of water. The DSC studies of the composite films reveal that the T-g of PVAc is increased to higher temperatures with increased incorporation of PPy indicating that there may be some mixing between PPy and PVAc. The percolation threshold for electrical conductivity occurs between 3.5 to 5 wt.% of PPy in the composites. The threshold values are found to be insensitive to the degree of swelling of the FeCl3 impregnated films. The low values of fp have been attributed to fractal growth of PPy phase in the water channels of the swollen films. This view is supported by the SEM images of the cryofracture surface of the composites which reveal the formation of PPy particles in the channels formed by water during swelling of the films. The effects of O-2, moisture and temperature on the conductivity of the films have also been studied. The present method is not universally applicable. Thus, with PMMA or polycarbonate used as the matrix polymers FeCl3 goes quickly into solution in water without swelling of the films and no composite is formed. (C) 1999 Elsevier Science S.A. All rights reserved.