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) (SEA ) were prepared using FeCl3-impregnated matrix polymer Alms and dippin g them into a solution of pyrrole in water using a pyrrole concentrati on of 67 mmol/dm(3) and above. No polymerization occurs in solution ou tside the films. Polymerization occurs rapidly, about 90% of pyrrole b eing polymerized in the first hour inside the films. Slow polymerizati on continues after that, giving approximately 8 wt.% PPy incorporation in the Alms in 24 h. Not all of the matrix polymer can be extracted o ut of the composites by solvent extraction. This indicates that grafti ng of PPy is taking place on some of the molecules of the matrix polym ers. FT-IR studies do not reveal any H bonding between the > N-H group in PPy and the COO group in the matrix polymers. Differential scannin g calorimetry reveals that PPy and SEA are immiscible while a 13 degre es C shift in T-g of PMA is noticed in the PPy/PMA composites which mi ght be attributed to grafting of PPy into PMA. The percolation thresho ld (f(c)) occurs at 0.023 and 0.045 volume fractions of PPy for PPy/PM A and PPy/SBA composites, respectively, which are much lower than the theoretically predicted value of f(c) = 0.16 for conducting blends. Th e control experiment shows that FeCl3-impregnated films swell to a gre at 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 g row fractally to a dendritic structure. Pyrrole enters into these chan nels forming a dendritically grown PPy phase. This anisotropic growth is believed to be the cause behind the low f(c). The conductivity of t he films decreases when they are exposed to O-2 atmosphere at room tem perature. A 25% decrease occurs over 4-5 days, following which the rat e of decrease slows down. In nitrogen the conductivity remains stable. In saturated water vapour atmosphere and in the absence of air, condu ctivity initially increases over 4-5 days by 60 and 20%, respectively, for PPy/PMA and PPy/SBA, and then remains stable. As regards the stab ility with temperature, the conductivity in air increases with tempera ture until about 80 degrees C and then some drop occurs up to the inve stigated temperature of 100 degrees C.