AbstractIt is investigated how binary blends of two asymmetric triblock terpolymers with the same type of monomers but different block sequences (ABC, BAC) and different block lengths lead to three new ABAC tetrablock terpolymer like morphologies. This study ascribes the formation of four microphases to a parallel chain orientation during the blend process. Because of the resultant spatial superposition, the B-blocks of both block copolymers can mix into each other as well as both C-blocks, whereas both A-blocks form independent microphases. The self-assembly of nine blends are studied. Their morphologies depend on the blending ratio and are monitored by transmission electron microscopy and small-angle X-ray scattering. Besides single morphologies, also coexisting morphologies are obtained, indicating that different superstructures are stable within finite compositional ranges of the blends. This work demonstrates that blending of triblock terpolymers with different block sequence is another interesting way in the huge area of morphological engineering by blending of block copolymers, leading to new and even complex, tailored nanostructures.