ABSTRACTBinary blends of a semicrystalline polymer, poly (butylene terephthalate), PBT, with an amorphous polymer, polyarylate, PAr, were studied for a wide range of compositions. SMall angle x-ray scattering, thermal and mechanical analyses were conducted to determine the location of the uncrystallizable PAr relative to the crystal lamellae of PBT, for blends crystallized by heating from the quenched state. Comparison of experimental and calculated long periods indicates that interlamellar PAr placement becomes less probable as the PAr composition increases. When PBT crystallizes in these blends, Most PAr is rejected from the regions near the crystal surfaces when PAr fraction exceeds about 0.40.