An oxyethylene/oxybutylene block copolymer with asymmetric volume fraction (E115B105) was blended with oxybutylene homopolymer (Bh) at different volume fractions of the block (φE) Crystallization behavior of the blends was studied and was compared with that of the blends from a symmetric block copolymer (E114B56). It was found that the crystallization temperature of E115B103/B28 blend is lower than that of the blends from symmetric block copolymer. For the blend with φE= 0.30 breakout crystallization with an Avrami exponent n≈ 3.0 is observed. At φE= 0.22 the blend exhibits a variable crystallization behavior: confined crystallization with n≈1.0 at lower crystallization temperatures but breakout crystallization at high crystallization temperatures. For the blend with φE= 0.14 and sphere morphology confined crystallization occurs at all crystallization temperatures studied. When compared with the blends from symmetric block copolymer

confined crystallization occurs more easily in the E115B103/B28 blends. The SAXS results agree with the isothermal crystallization kinetics. Deformation of the confined crystalline block is observed in the blend withφE=0.14 and mixed lamellar and cylinder morphologies in the blend withφE= 0.22.