DimethylaluminumChloride-co-InitiatedQuasiliving Cationic (Co)Polymerization of Isobutylene and Styrene:Synthesis of Poly(styrene-block-isobutylene-block-styrene)

Abstract

The cationic polymerization of isobutylene with different methyl aluminum chlorides (Me_1.5AlCl_1.5 and Me₂AlCl) in conjunction with 1,4-bis(2-chloro-2-propyl)benzene (DiCumCl) as an initiator has been investigated. It was shown that both Me_1.5AlCl_1.5 and Me₂AlCl co-initiated quasiliving cationic polymerization of isobutylene, but the use of Me₂AlCl is preferable due to its much lower sensitivity to reaction conditions. In fact, the DiCumCl/Me₂AlCl initiating system induced the quasiliving cationic polymerization of isobutylene, yielding polyisobutylene with predicted by a monomer to initiator ratio molecular weight from M_n = 5,000 g mol^–1 to 50,000 g mol^–1 and low dispersity (Đ ≤ 1.15). A similar initiating system, TMPCl/Me₂AlCl, induced the quasiliving cationic polymerization of styrene only in the presence of 2,6-dimethylpyridine to afford well-defined polystyrenes with M_n ≤ 25,000 g mol^–1 and relatively low dispersity (Đ < 1.5). Triblock copolymers of isobutylene with styrene with high molecular weight (M_n = 72,000 g mol^–1; Đ = 1.25) displaying microphase-separated morphology and good mechanical properties (ultimate tensile strength of 13.2 MPa at about 900% elongation) were prepared with the DiCumCl/Me₂AlCl/Lu initiating system.