We demonstrate a facile, yet efficient method for the functionalization of crosslinked polystyrene (PS) microspheres with biocompatible poly(vinylphosphonate)s via the combination of a UV grafting polymerization and a surface-initiated group transfer polymerization. Self-initiated photografting and photopolymerization of ethylene glycol dimethacrylate results in direct photografting of poly(ethylene glycol dimethacrylate) on the PS microspheres with dangling methacrylate functionalities, which are used to immobilize ytterbocene complexes to form the surface-bound rare-earth metal catalyst system. The surface-initiated GTP of dialkyl vinylphosphonates from the initiator system leads to the functionalization of PS microspheres with poly(vinylphosphonate) brushes. Polymerization kinetic investigation indicates that surface-initiated GTP leads to a constant and remarkably rapid weight gain of the microsphere (a microsphere weight increase of 600% within 3 min), owing to the highly living and efficient character of GTP. The surface-initiated GTP occurring inside the microsphere causes an accumulation of the tension between the polymer chains in the microsphere, which eventually induces fracture of the microsphere for longer polymerization time. (C) 2014 Wiley Periodicals, Inc.