Polystyrene (PSt)/polytetrahydrofuran (PTHF) A(2)B(2) miktoarm star copolymers were prepared by transformation of cationic ring-opening polymerization (CROP) to atom transfer radical polymerization (ATRP). The synthetic approach involves the synthesis of PTHF with two secondary bromine groups in the center of a macromolecular chain, (PTHF)(2)Br-2, by the CROP of THF with the symmetric tetrafunctional initiator ol,alpha,omega -dibromosebasionyl dichloride [ClCOCHBr(CH2)(6)CHBrCOCl] in conjunction with silver perchlorate; (PTHF)(2)Br-2 was used to initiate the polymerization of styrene to form (PSt)(2)(PTHF)(2) star copolymer. The copolymer obtained was characterized by gel permeation chromatography and H-1 NMR spectrum. The hydrolysis of (PTHF)(2)Br-2 was also investigated. (C) 2001 Elsevier Science Ltd. All rights reserved.