Elastic behavior of poly(ethylene terephthalate) chains

The Monte Carlo (MC) method based on the rotational-isomeric-state (RIS) model is adopted in studying the elastic behavior of poly(ethylene terephthalate) (PET) chains in this paper. The mean-square end-to-end distance 〈R2〉, the mean-square radius of gyration 〈S2〉, and the ratio of 〈R2〉/〈S2〉 all increase with elongation ratio λ. The interior conformations are also investigated through calculating the a priori probability of rotational state in the process of tensile elongation. The radius of gyration tensor S is introduced here in order to measure the shape of PET chains, and image increases with elongation ratio λ, however, some different behaviors are obtained for image. Here image, image and image are the eigenvalues of the radius of gyration tensor image. The average energy per repeat unit 〈U〉 and the average free energy per repeat unit 〈A〉 are also calculated, and we find that the average energy decreases with elongation ratio λ, however, the average free energy per repeat unit increases with elongation ratio λ. Elastic force f, energy contribution to force fU, and entropy contribution to force fS are also investigated. Both elastic force f and entropy contribution to force fS increases with λ, however, energy contribution to force fU and the ratio fU/f decreases with λ. The ratio of fU/f is less than zero and almost independent of chain length. The results of these microscopic calculations may explain some macroscopic phenomena of rubber elasticity.