Improving the dispersion of conductive graphitic fillers in functionalized polymer networks

Electrically-conductive polymers seem to be more promising substitutes of conventional inorganic conductive materials for many applications such as in biomedical engineering, microelectronic devices, thermoresponsive polymeric temperature sensors and others. Since most common polymers are non-conductive, it is necessary to add conductive fillers to confer this feature. The main problem, when conductive fillers are added to a polymer, is to ensure the completely homogenous dispersion in the polymer matrix. The unevenly dispersion of conductive fillers is due to the attractive forces between the (nano)aggregates and cannot be overlooked. These interactions became strong and involve the tendency of conductive fillers to assemble into bundles or ropes, thus adversely affecting the overall conductivity of the composite. According to literature, an important step before the dispersion of conductive fillers is their stabilization through functionalization (either covalent or non-covalent). In this research project, a non-covalent functionalization method is selected. Apart from use of ultrasonic treatment to promote exfoliation of fillers, it is necessary to maintain this exfoliation also in the matrix in order to ensure the best possible dispersion. On this account, the polymer matrix were functionalized with chemical groups “reactive” towards those present as pendant moieties along the polymer backbone. This procedure is based on the idea that appropriate pendant groups on the backbone create effective non-covalent interactions with the conductive fillers. The best candidate to perform this task appears to be the pyrene group being its high conjugate structure ensure π-π with the graphitic one of conductive fillers (e.g. carbon nanotubes). In this research project, we aimed at investigating the influence of different pendant groups (namely their intake and chemical structure) on the backbone in order to select the best candidate able to improve the dispersion of conductive fillers. Aliphatic polyketones (PK) and maleated ethylene/propylene rubbers (EPM-g-MA) are used as the polymer matrix in view of easy ways in which they can be modified. In terms of tangible products, nanocomposite blends between maleated ethylene/propylene rubbers grafted with furan, bismaleimide and pyrene modified polyketones have been prepared. All products were characterized in order to establish the successful of functionalization and the exact conversion degree. Later, the products were mixed with different amount of conductive fillers in order to establish the effect of different pendants group on the percolation threshold. The electrically-conductive behaviour of all products as well as their thermal properties were determined by means of DSC and TGA analyses. The combination of self-healing characteristics and electrically-conductive features, suggest possible application of the prepared nanocomposites in biomedical engineering and microelectronic fields