Aspects of the Synthesis of Poly(styrene-block-isobutylene-block-styrene) by TiCl₄-Co-initiated Cationic Polymerization in Open Conditions

The cationic polymerization of isobutylene and its block copolymerization with styrene using DiCumCl/TiCl4/2,6-lutidine initiating system has been studied in open conditions. It was shown that a higher concentration of proton trap is required in open conditions as compared to the glove box technique in order to have good control over molecular weight and polydispersity. Polyisobutylenes with M-n <= 50,000 g mol(-1) and low polydispersity (D <= 1.2) were prepared at [Lu] = 12 mM. The synthesis of poly(styrene-block-isobutylene-block-styrene) triblock copolymer (SIBS) in open conditions required the addition of proton trap into two steps, half at the beginning of the reaction and the second half together with styrene. Following this protocol, a series of triblock copolymers with different length of central polyisobutylene block (from M-n = 20,000 g mol(-1) to 50,000 g mol(-1)) and side polystyrene blocks (M-n = 4000 g mol(-1)-9000 g mol(-1)) with low polydispersity (D <= 1.25) were synthesized. High molecular SIBS (M-n > 50,000 g mol(-1)) with low polydispersity (D < 1.3) containing longer polystyrene blocks (M-n > 6000 g mol(-1)) demonstrated higher tensile strength (similar to 13.5 MPa).