Dispersion polymerization of aniline using hydroxypropylcellulose as stabilizer: role of rate of polymerization

Hydroxypropylcellulose (HPC) has been used as a steric stabilizer for prepa ring polyaniline dispersions using the route of oxidative dispersion polyme rization of aniline. Using strongly acidic conditions (1 mol l(-1) HCl), lo w temperature of about 2 degreesC and a concentration of aniline as low as 0.5%, ammonium peroxodisulfate at 1.25% and hydroxypropylcellulose concentr ations at 0.5-1 gdl(-1), unstable dispersions were obtained not only in wat er but also in aqueous alcohols (ethanol and methanol) up to at least 70vol % alcohol. in contrast, dispersions that remained stable for at least 72h w ere obtained when the alcohol concentration of the medium was as high as ab out 80vol%. Kinetic studies of the polymerization systems suggested that su ccess in the latter case was due to a lowering of the rate of polymerizatio n. Transmission electron microscopy studies showed that dispersion particle s prepared in 80vol% alcohol media are spherical in shape and their diamete r decreases with increasing stabilizer concentration. However, a change of morphology from spherical to aggregated needle-shaped was observed when the rate was increased by increasing the aniline concentration from 0.5% to 0. 75% gdl(-1) in the above recipe. The aggregated particles were found to be broken down to spherical nanoparticles when the as-prepared dispersions wer e sonicated for about 30min. The sonicated dispersion on drying showed the presence of fractal clusters of polyaniline particles in the dried film. Th e fractal dimension was determined to be 1.77 which agreed well with the th eoretical value determined by computer simulation based on a diffusion limi ted cluster-cluster aggregation model in three dimensions. (C) 2001 Society of Chemical Industry.