Dielectric behavior was examined for solutions of a styrene-isoprene-styrene (SIIS) triblock and SI diblock copolymers in an I-selective solvent, n-tetradecane (C14). The SI copolymer had noninverted type-A dipoles in the I block while the SIIS copolymer, a head-to-head coupled dimer of SI, had once-inverted dipoles in the I block. At a low temperature (5 degrees C) where the S blocks formed glassy, spherical microdomains, the I blocks of SIIS had either the bridge or loop configurations. The loop fraction phi(1) in these I blocks was estimated from the dielectric losses of the SIIS and SI solutions at low frequencies. The phi(1) was found to increase (from 0.6 to 0.8) with decreasing SIIS concentration (from 50 to 20 wt %). This increase of phi(1) was attributed to stretching and destabilization of the bridge configuration on dilution. The equilibrium elasticities of the bridge and dangling loop, estimated from the phi(1) values and rheological data of the concentrated SIIS/C14 solutions, were comparable in magnitude. This significant elasticity of the dangling loops reflected the strong osmotic constraint on the I block conformation in the concentrated I/C14 matrix phase.