Activation energy of crystallization of aromatic copolyester with bulky side group
Fukada Akihiko; Inabe Katsuyuki
Abstract:The activation energy for the crystallization of an aromatic copolyester with bulky side group was obtained by using a differential scanning calorimeter (DSC). The results of non-isothermal crystallization experiments indicate that there are two crystallization processes; the fast process and the slow process. The crystallization during cooling is controlled by diffusion. The activation energy for the slow process is quite large because of difficulty in diffusion of a molecule due to the rigid rod structure. On the other hand, the isothermal crystallization takes place by nucleation and growth. The activation energy based on kinetic data was 645 kJ mol-1. The value is somewhat larger than those of flexible polymers because of the large energy barrier in molecular movement due to the rigid backbone and bulky side groups. The equilibrium melting temperature and heat of fusion were determined, and the equilibrium entropy change of 0.63 J mol-1 K-1 was calculated from the thermodynamical relationship, DSf = DHf/Tm. Compared to the literature values for flexible polymers such as polyethylene (9.88 J mol-1 K-1) and polypropylene (15.1 J mol-1 K-1), the obtained value is rather small. This is because the transition from nematic melt to crystals induces less entropy change than that from isotropic melt to crystals. Key Words:aromatic copolyster, activation energy, crystallization, thermotropic, liquid crystal