The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (E m B n diblock copolymers and E m B n E m , B n E m B n triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature Γ°T c Γ in non-isothermal crystallization was determined. It is found that the E m B n diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, f E ; and the length, m, of the E block. Some block copolymers with extremely low T c ; which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike E m B n /B h blends, there is no obvious relationship between T c and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of x c =x ODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have x c =x ODT , 3; in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.