In this paper, we describe the use of a temperature responsive polymer to reversibly assemble gold nanoparticles of various sizes. Temperature responsive, low critical solution temperature (LCST) pNIPAAm-co-pAArn polymers, with transition temperatures (T-c) of Si and 65 degrees C, were synthesized with a thiol modification, and grafted to the surface of 11 and 51 nm gold nanoparticles (AuNPs). The thermal-responsive behavior of the polymer allowed for the reversible aggregation of the nanoparticles, where at T < T-c the polymers were hydrophilic and extended between particles. In contrast, at T > T-c, the polymer shell undergoes a hydrophilic to hydrophobic phase transition and collapses, decreasing interparticle distances between particles, allowing aggregation to occur. The AuNP morphology and polymer conjugation were probed by TEM, FTIR, and H-1 NMR. The thermal response was probed by UV-vis and DLS. The structure of the assembled aggregates at T > T-c was studied via in situ small-angle X-ray scattering, which revealed interparticle distances defined by polymer conformation.