Exploring the Rheological Properties of Entangled and Unentangled Crosslinked Polymer Nanocomposite Networks*

We explored the effect of entanglements and particle loading on viscoelastic properties of crosslinked polymer nanocomposite networks. The permanently cross-linked entangled and unentangled networks of poly (methyl acrylate) were synthesized in the presence of nanoparticles. The viscoelastic properties measured in a strain-controlled rheometer showed that with particles larger than the network mesh size, the reinforcement was independent on particle loading in entangled composite networks. The recovery to the initial modulus after deformation occurred fast in entangled networks suggesting that even with highly attractive particles, chain relaxations were unperturbed. In the permanent composite network where chains cannot relax, the reinforcement depended on particle loading and the localized particle aggregation of particles within a dense network. To further investigate the chain architecture effect on reinforcement mechanism of nanocomposite networks, new polymer loop-grafted nanoparticles were prepared and blended with long and short chain matrices. Interpenetrating network formation through loops and entanglements will be discussed.