The living radical photocopolymerization of 2-(N,N-diethyldithiocarbamyl)ethyl methacrylate (DCEM) as inimer and stearyl methacrylate (STM) as comonomer was carried out under UV irradiation. According to this method, we synthesized hyperbranched polymers (HP) consisting of a STM sequence having a long alkyl side chain. The get permeation chromatography distribution of hyperbranched polymers had a unimodal pattern. The reactivity ratios (r(1) = 0.79 and r(2) = 0.81) were estimated by the Kelen-Tudos method (DCEM: [M](1) and STM: [M](2)). These values indicated that the two monomers showed almost equal reactivity toward propagating radical species. The radius of gyration (R-g) and the hydrodynamic radius (R-h) of copolymers were determined by static and dynamic light scattering (SLS and DLS), and the values of R-g/R-h changed from 0.79 to 1.59 with an increment of the feed amount of STM. These results indicated that the copolymer structures changed from hard spheres to loose branched molecules in solution. (c) 2008 Elsevier Inc. All rights reserved.