Synthesis of methyl methacrylate, styrene, and isobutylene multiblock copolymers using atom transfer and cationic polymerization

Abstract

ABCBA-type pentablock copolymers of methyl methacrylate, styrene, and isobutylene (IB) were prepared by the cationic polymerization of IB in the presence of the α,ω-dichloro-PS-b-PMMA-b-PS triblock copolymer [where PS is polystyrene and PMMA is poly(methyl methacrylate)] as a macroinitiator in conjunction with diethylaluminum 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 °C, significantly affected the IB content in the resulting copolymers; a higher content was obtained at −78 °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 °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 (Tg), 104.5 °C, was observed for the aforementioned triblock copolymer, and the pentablock copolymer containing 61.3 mol % IB showed two well-defined Tg's: −73.0 °C for PIB and 95.6 °C for the PS–PMMA blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3823–3830, 2005