Nanogels have been widely prepared and characterized in recent years due to their unique advantages. Here, an effective, original, and facile method of emulsion-free photopolymerization at 532 nm without surfactant was developed to prepare nanogels based on poly(ethylene glycol) diacrylate (PEGDA). The 532 nm continuous laser with symmetrical energy distribution like a three-dimensional shape of a straw hat was used to control the reaction region. The self-emulsification of PEGDA in water was studied and PEGDA micelles were directly cross-linked by controlling the laser energy. The number of micelles par-ticipating in the microreaction region and the double bond crosslinking between micellar aggregates and inside micelles were reasonably regulated. The size of the nanogels could be effectively modulated by controlling reaction parameters including laser power, monomer concentration, initiator concentration, and reaction time. Finally, ultrasmall nanogels with around 30 nm in size were prepared by balancing double bond crosslinking between micellar aggregates and inside micelles. (c) 2020 Elsevier Inc. All rights reserved.