AbstractThe effect of polymorphism of isotactic polybutene‐1 (iPB‐1) on the peel behavior of the specific peel system low‐density polyethylene/polybutene‐1 (LDPE/iPB‐1) was investigated using wide‐angle X‐ray scattering, calorimetry, and the T‐peel test. Melt‐crystallization of iPB‐1, initially, yields tetragonal form II crystals which transform as a function of time to trigonal form I crystals. The kinetics of transformation at ambient temperature follows an exponential function, and is completed after about 50–75 h. The presence of LDPE in the peel system does not affect the transformation kinetics. The structure of the crystalline phase of iPB‐1 controls the peel force which decreases by about 25% during the crystal–crystal transformation in a blend with 20m% iPB‐1. The reduction of the peel force depends linearly on the mass fraction of iPB‐1 crystals in the peel system which further evidences the correlation between the crystal–crystal transformation of iPB‐1 and the peel‐characteristics of LDPE/iPB‐1 blends. Isothermal reorganization of crystals of LDPE is excluded as reason for the change of the peel‐performance of LDPE/iPB‐1 blends, since it is 5 to 10 times faster than the decrease of the peel force, and crystal–crystal transformation of iPB‐1, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008