ABCBA-type pentablock copolymers of methyl methacrylate, styrene, and isobutylene (M) were prepared by the cationic polymerization of IB in the presence of the alpha,omega-dichIoro-PS-b-PMMA-b-PS triblock copolymer [where PS is polystyrene and PMMA is poly(methyl methaerylate)] as a macroinitiator in conjunction with diethyl-aluminum chloride (Et2AlCl) as a coinitiator. The macroinitiator was prepared by a two-step copper-based atom transfer radical polymerization (ATRP). The reaction temperature, -78 or -25 degrees C, significantly affected the IB content in the resulting copolymers; a higher content was obtained at -78 degrees C. The formation of the PIB-b-PS-b-PMMA-b-PS-b-PIB copolymers (where PIB is polyisobutylene), prepared at -25 (20.3 mol % IB) or -78 degrees C (61.3 mol % IB; rubbery material), with relatively narrow molecular weight distributions provided direct evidence of the presence of labile chlorine atoms at both ends of the macroinitiator capable of initiation of cationic polymerization of IB. One glass-transition temperature (T-g), 104.5 degrees C, was observed for the aforementioned triblock copolymer, and the pentablock copolymer containing 61.3 mol % IB showed two well-defined T-g's: -73.0 degrees C for PIB and 95.6 degrees C for the PS-PMMA blocks. (c) 2005 Wiley Periodicals, Inc.