SPIN-DIFFUSION IN A TRIBLOCK THERMOPLASTIC ELASTOMER

A triblock copolymer thermoplastic elastomer (SEES) consisting of an ethylene-butylene random-copolymer rubbery domain flanked by rigid polystyrene short blocks has been analyzed using novel solid-state NMR techniques. C-13 NMR relaxation measurements suggest that at the T-1(H) level (minimum observable phase size of about 18 nm) the material appears homogeneous, but at the T-1p(H) level (minimum observable phase size of about 3 nm) the expected two distinct phases are noted. Two-dimensional WISE spectra (high-resolution C-13 - broadline H-1) 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.