The semilocal structure (space scale: approximate to 50 Angstrom) of a styrene-butadiene-styrene triblock copolymer (SBS) was investigated by observing residual dipole-dipole interactions that govern the transverse relaxation of protons attached to the polymer. The molar masses were 10(4) and 5 x 10(4) g/mol for polystyrene (PS) and polybutadiene (PB), respectively. It is shown that, above the glass transition of PB, there exists a network structure; the comparison made with NMR properties of long PB chains, in the melt, suggests this structure is a network formed by entanglements. These chain coupling junctions are trapped by the presence of PS glassy domains where the interface plays the role of embedding points for PB block ends. The mean segmental spacing between chain coupling junctions was found to vary as c(-1) where c is the concentration of PB in heptane, a selective solvent of PB. A probability distribution function of end-to-end vectors joining two consecutive coupling junctions, along a PB chain, is proposed to analyze relaxation curves. The estimated lifetime of PB coupling junctions is 1 ms, at 220 degrees C, the temperature of the order-disorder transition that occurs in SBS. With regard to the PS properties, the glass transition process, as observed from NMR, spread over the range 50 to 130 degrees C; this result is in agreement with all earlier NMR studies reported about the PS glass transition.