Structure and Properties of Tapered Block Polymers of Styrene and Isoprene

TLDR: Tapered block polymers of styrene and isoprene were prepared by copolymerization of these two monomers, containing a trace amount of THF in the primary structure.

Abstract: Tapered block polymers of styrene and isoprene were prepared by copolymerization of these two monomers, containing a trace amount of THF. s-BuLi was used as an initiator, and benzene as the polymerization solvent. Analyses based on pyrolysis gas chromatography and 1H NMR indicated that a considerable amount of mixing of these two monomers took place in the block polymer chain, e.g., for TB-1 to TB-3. Such mixing in the primary structure is considered phenomenologically to give rise to the polystyrene-rich block chain and polyisoprene-rich block chain. The repulsive interaction between the two block chains is much weaker than that between the pure polystyrene and polyisoprene block chains, and this enhances the mixing of the polystyrene-rich chain and polyisoprene-rich chain, resulting in a microdomain structure consisting of the polystyrene-rich phase and polyisoprene-rich phase. Owing to this segmental mixing within each phase, the tapered polymer exhibits a lower critical temperature and the unique mechanical properties, in compared to ideal block polymers. The tapered block polymers have the unique solubilizing power of the corresponding homopolymers, arising from their microdomain structures.