Spin diffusion in a triblock thermoplastic elastomer

Abstract

A triblock copolymer thermoplastic elastomer (SEBS) consisting of an ethylene–butylene random-copolymer rubbery domain flanked by rigid polystyrene short blocks has been analyzed using novel solid-state NMR techniques.13C NMR relaxation measurements suggest that at the T1(H) level (minimum observable phase size of about 18 nm) the material appears homogeneous, but at the T1ρ(H) level (minimum observable phase size of about 3 nm) the expected two distinct phases are noted. Two-dimensional WISE spectra (high-resolution 13C – broadline 1H) show the different mobility in the two phases. A broad component associated with the highly mobile rubbery phase indicates the presence of an interface. The mobile phase is selected using a dipolar filter pulse sequence and the magnetization is allowed to transfer to the rigid polystyrene phase during a period called "mixing time." From the growth of the polystyrene magnetization during the mixing period, the size of the dispersed polystyrene phase can be calculated to be 16 ± 2 nm.