Interpenetrating polymer network composites of polypyrrole and poly (methyl acrylate) or poly (styrene-co-butyl acrylate) with low percolation thresholds

Interpenetrating polymer network composites of polypyrrole (PPy) with poly (methyl acrylate) (PMA) and poly(styrene-co-butyl acrylate) (SBA) were prepared using FeCl3-impregnated matrix polymer films and dipping them into a solution of pyrrole in water using a pyrrole concentration of 67 mmol/dm3 and above. No polymerization occurs in solution outside the films. Polymerization occurs rapidly, about 90% of pyrrole being polymerized in the first hour inside the films. Slow polymerization continues after that, giving approximately 8 wt.% PPy incorporation in the films in 24 h. Not all of the matrix polymer can be extracted out of the composites by solvent extraction. This indicates that grafting of PPy is taking place on some of the molecules of the matrix polymers. FT-IR studies do not reveal any H bonding between the in PPy and the COO group in the matrix polymers. Differential scanning calorimetry reveals that PPy and SBA are immiscible while a 13 °C shift in Tg of PMA is noticed in the PPy /PMA composites which might be attributed to grafting of PPy into PMA. The percolation threshold (fc) occurs at 0.023 and 0.045 volume fractions of PPy for PPy/PMA and PPy/SBA composites, respectively, which are much lower than the theoretically predicted value of fc = 0.16 for conducting blends. The control experiment shows that FeCl3-impregnated films swell to a great extent on immersion in water due to the osmotic entry of the latter into the films. The water channels inside the films are believed to grow fractally to a dendritic structure. Pyrrole enters into these channels forming a dendritically grown PPy phase. This anisotropic growth is believed to be the cause behind the low fc. The conductivity of the films decreases when they are exposed to O2 atmosphere at room temperature. A 25% decrease occurs over 4–5 days, following which the rate of decrease slows down. In nitrogen the conductivity remains stable. In saturated water vapour atmosphere and in the absence of air, conductivity initially increases over 4–5 days by 60 and 20%, respectively, for PPy/PMA and PPy/SBA, and then remains stable. As regards the stability with temperature, the conductivity in air increases with temperature until about 80 °C and then some drop occurs up to the investigated temperature of 100 °C.