The conformational analysis of high-density poly(ethylene) (HDPE) during the melting and crystallization processes has been performed by the aid of the time-reserved Fourier transform infrared spectroscopy and multivariate analysis technique. Upon heating, the conformational transition of HDPE takes place, gradually, due to the restraint of crystal lattice, and various conformational transformations can be discerned clearly. However, during the cooling process, HDPE crystallizes very quickly and only one major conformational transition occurs in the crystallization process. The comparison of conformational changes during the melting and crystallization processes exhibits that although the polymer crystallization is the reverse process of polymer melting, there still exist some obvious differences in the conformational transformation between them. (c) 2006 Wiley Periodicals, Inc.