A series of well-defined block copolymers composed of di(ethylene glycol) methyl ether methacrylate (188 g/mol) and oligo(ethylene glycol) methyl ether methacrylate (300 g/mol), PMEO(2)MA-b-(PMEO(2)MA-stat-POEGMA(300)), were successfully synthesized at room temperature via a two-step atom transfer radical polymerization (ATRP) process using 1,1,4,7,10,10-hexamethyl triethylene tetramine (HMTETA) as the ligand. The ratio of MEO(2)MA/OEGMA(300) in the second block controls the thermal behaviors of these copolymers. When the ratio of MEO(2)MA/OEGMA(300) is 80/20, only one thermal transition was observed. However, two thermal transitions were observed for MEO2MA/OEGMA300 ratios of 70/30 and 0/100. We believed that the first transition was associated with the formation of micelles and the second transition corresponded to the formation of larger aggregates consisting of several preformed micelles. This hypothesis was confirmed by light scattering, where the hydrodynamic radius (R-h) of the aggregates of 70/30 and 0/100 systems increased from 48 to 95 nm and 88 to 147 nm with a corresponding increase in the R-g/R-h from 0.76 to 1.1 and 0.68 to 1.0 respectively. TEM analyses confirmed the formation of spherical particles, where the sizes of these particles increased with increasing temperatures. (C) 2012 Elsevier Ltd. All rights reserved.