A random copolymer of propylene with small amounts of 1-butene comonomer, synthesized with a Ziegler-Natta catalyst, was fractionated by temperature rising elution fractionation (TREF) to systemically investigate the fraction samples' molecular microstructure, as well as their relationship to the melting and crystallization behavior. First, TREF was employed to fractionate the sample, and then crystallization analysis fractionation (Crystaf) was used to check the effect of the TREF experiment. In the characterization of the molecular microstructure, carbon-13 NMR spectroscopy (C-13 NMR) and gel permeation chromatography (GPC) experiments gave the following results: the fraction samples have relatively uniform molecular microstructure; with an increase in elution temperature, the I-butene content in the fraction samples decreases, but the molecular weight (M-n) and number average sequence length of propylene ((n) over bar (P)) increase. In the study on melting and crystallization behavior, differential scanning calorimetry (DSC) experimental results show that the melting temperature increasingly decreases with an increase in 1-butene content; however, dependence of the melting temperature on molecular weight becomes weaker and weaker with an increase in the number average molecular weight in the range of number average molecular weight below 1.82 X 10(5) g/mol. (c) 2005 Wiley Periodicals, Inc.