Thermomechanical behavior of hydrogen-bond based supramolecular poly(ε-caprolactone)-silica nanocomposites

Supramolecular polymer nanocomposites represent an attractive alternative to traditional polymers for advanced materials that exhibit stimuli-responsive and self-healing properties. Here, we investigate the effects of specific hydrogen bonding interactions between surface functionalized silica nanoparticles and ureidopyrimidinone (UPy) based hydrogen bonded supramolecular poly(ε-caprolactone) in a supramolecular polymer nanocomposite. The effect of varying levels of nanoparticle UPy surface functionalization is considered. In addition to the anticipated improvements in Young's modulus (∼50%) and storage modulus (∼2×) with silica loading, increases in strain at breaking point (∼25%) with silica loading were observed and attributed to particle-matrix hydrogen bonding. However, increasing the extent of UPy surface functionality at a constant nanoparticle loading level led to a marked decrease in storage modulus relative to nanocomposites prepared with as-received silica nanoparticles. TEM investigation of these nanocomposites show an increase in nanoparticle aggregation. Nanoparticle aggregation provides both an explanation for the observed storage modulus reduction and evidence of particle-particle interactions. These results give interesting insight into the competing effects of specific supramolecular interactions in supramolecular polymer nanocomposite materials.