(371b) Molecular Dynamic Simulations of Polymer Crystallization at the Early Stage

The nucleus precursor structure in the induction period of the polymer melt crystallization has been observed in our simulation research. Molecular dynamics simulations are performed to study the crystallization process of poly(trimethylene terephthalate) (PTT). The thermal properties, such as glass transition temperature (Tg) and melting temperature (Tm), has been simulated successfully, and accurate to experimental value. According the potential energy analysis result, the torsional angle energy and van der Waals interaction affect the crystallization process in the induction period between Tg and Tm. We define the precursor structure by the polymer segments packing, and the fluctuation of the fraction of precursor has a periodic behavior at 400K. Moreover, the fraction quickly arises after longer thermal relaxation time at 350K and 450K. In addition to, the precursor's torsion angles of the segment O-CH2-CH2-CH2-O on the backbone of the chains tend to the crystal conformation such as trans-gauche-gauche-trans (t-g-g-t). Finally, we propose the mechanism of the nucleation that nuclear precursors are formed in the induction period, prior to the appearance of nuclei during the crystallization process.