The kinetics of formation of the Form II mesophase from the melt has been investigated as a function of the concentration of ethylene chain defects in isotactic random butene-1/ethylene copolymers, using standard and fast scanning chip calorimetry. Presence of ethylene co-units in the butene-1 chain leads to a distinct reduction of the melt - Form II phase transformation rate which has been quantified by evaluation of the critical cooling rate to suppress ordering, and by isothermal analysis of half-times of Form II mesophase formation. For the first time, the temperature-dependence of the rate of Form II mesophase formation has been evaluated for butene-1/ethylene random copolymers and the butene-1 homopolymer. This study needs to be considered as a complementary addendum to former work about the Form II to Form I polymorphic transformation in isotactic random butene-1/ethylene copolymers. (C) 2013 Elsevier Ltd. All rights reserved.