Densely grafted copolymers were synthesized using the "grafting from" approach via the combination of reversible addition-fragment chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). First, a novel functional monomer, 2,3-di(2-bromoisobutyryloxy)ethyl acrylate (DBPPA), with two initiating groups for ATRP was synthesized. It was then polymerized via RAFT polymerization to give macroinitiators for ATRP with controlled molecular weights and narrow molecular weight distributions. Last, ATRP of styrene was carried out using poly(DBPPA)s as macroinitiators to prepare comblike poly(DBPPA)-graft-polystyrenes carrying double branches in each repeating unit of backbone via "grafting from" approach. Furthermore, poly(DBPPA)-graft-[polystyrene-block-poly(t-BA)]s and their hydrolyzed products poly(DBPPA)-graft-[polystyrene-block-poly(acrylic acid)]s were also successfully prepared. (C) 2007 Wiley Periodicals, Inc.