The time-resolved dynamic light scattering has been employed to investigate gelation of divinylbenzene (DVB; branched chains) and vitrification of styrene (St; linear chains) during radical polymerization in bulk. The intensity correlation function (ICF) was obtained every 30s during polymerization process. The DVB system exhibited a power law behavior in ICF characteristic of gelation threshold, which was followed by vitrification. In the case of St, two relaxation modes appeared before vitrification, which were assigned to be the cooperative and the slow relaxation modes. (c) 2005 Elsevier Ltd. All rights reserved.