Difunctional anionic initiator based on 1.3-diisopropenylbenzene. 5. Effect of polar additives and initiator seeding on the synthesis of poly(styrene-b-butadiene-b-styrene) copolymer

The initiation of butadiene and styrene polymerization by a pure hydrocarbon soluble difunctional organolithium, 1,3-bis(1-lithio-1,3,3‘-trimethylbutyl)benzene, has been studied in a hydrocarbon solvent. The initiation occurs in such a way that part of the diadduct remains unreacted. When a second monomer feed along with tetrahydrofuran (THF) is added to the living chains, the residual diadduct is activated to the point where novel chains are formed. Weakly polar additives such as lithium alkoxides and aromatic ether can prevent part of the initiator from being inactive, although these additives are not effective enough to initiate the controlled synthesis of poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers. The seeding of the initiator which consists of butadiene oligomerization in the presence of anisole and tBuOLi in cyclohexane, has proved to be very efficient in providing SBS containing 85% 1,4-microstructure polybutadiene (PBD) and with high mechanical properties, e.g., ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%.