Synthesis and Rheological Properties of Polymer Loop-Grafted Nanoparticle Composites

Loop/linear blends have been previously studied in rheology. Topological constraints of the loops enable dynamic heterogeneities provided by the mixing between linear and loop chains. Here, we demonstrate that composites of loop-grafted particles exhibit gel-like mechanical response. A series of loop-grafted particles were prepared for this work. Linear poly(methyl methacrylate) chains grafted on silica nanoparticles were thiolated and then looped by radical mediated thiol-ene click reaction. Samples with different ratios of looped and linear chains were prepared and their molecular weights were measured in gel permeation chromatography. Hydrodynamic sizes of linear- and loop-grafted particles were found to be similar, indicating the absence of interparticle bridging during the reaction. After mixing the loopy particles with two different polymer matrices, we measured the rheological responses of these unique composites. The linear viscoelasticity of polymer loop-grafted nanoparticle composites is compared to that of bare and linear polymer-grafted nanoparticle composites. We measured strong gel-like behavior for loop-grafted composite system. Meanwhile, the loop sample exhibiting a significantly lower critical strain compared to the linear grafted and bare particle composites.