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

Abstract

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.