Polymer Grafted Nanoparticle Composites with Enhanced Thermal and Mechanical Properties.

The distribution of filler particles within a polymer matrix nanocomposite has a profound influence on the properties and processability of the material. While filler aggregation and percolation can significantly enhance particular functionalities such as thermal and electrical conductivity, the formation of larger filler clusters and networks can also impair mechanical properties like strength and toughness and can also increase the difficulty of processing. Here, a strategy is presented for the preparation of functional composites that enhance thermal conductivity over polymer alone, without negatively affecting mechanical performance or processability. Thermal cross-linking of self-suspended polymer grafted nanoparticles is used to prepare highly filled (>50 vol %) macroscopic nanocomposites with homogeneously dispersed, non-percolating alumina particles in an organic matrix. The initial composites use low glass transition temperature polymer grafts and thus are flexible and easily shaped by thermoforming methods. However, after thermal aging, the resulting materials display high stiffness (>10 GPa) and enhanced thermal conductivity (>100% increase) and also possess mechanical strength similar to commodity plastics. Moreover, the covalent bonding between matrix and filler allows for the significant elevation of thermal conductivity despite the extensive interfacial area in the nanocomposite. The thermal aging of polymer grafted nanoparticles is therefore a promising method for producing easily processable, mechanically sturdy, and macroscopic nanocomposites with improved thermal conductivity.