Upconversion nanoparticles (UCNPs) have gain increasing interest due to their unique optical properties. The growth of hyperbranched polymers from the surface of UCNPs was a part of the investigations conducted by Alireza Kavand during his PhD in the CMP team in collaboration with the UMR 7199 and UMR 7021 that have been recently reported in the journal Polymer Chemistry (doi: 10.1039/D0PY00452A). His results showed that the self-condensing vinyl RAFT polymerization was strongly affected due to the growing number of propagating chains, their immobilization on a surface, and specific mechanisms associated to surface-initiated RAFT polymerization. This work paves the way to the development to novel hybrid materials for bioimaging and theranostics.