Elastic behavior of poly(ethylene terephthalate) chains

Abstract

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 〈 R 2〉, the mean-square radius of gyration 〈 S 2〉, and the ratio of 〈 R 2〉/〈 S 2〉 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 〈 L 3 2 〉 / 〈 L 1 2 〉 increases with elongation ratio λ, however, some different behaviors are obtained for 〈 L 2 2 〉 / 〈 L 1 2 〉 . Here L 1 2 , L 2 2 and L 3 2 are the eigenvalues of the radius of gyration tensor S ( L 1 2 ⩽ L 2 2 ⩽ L 3 2 ) . 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 f U , and entropy contribution to force f S are also investigated. Both elastic force f and entropy contribution to force f S increases with λ, however, energy contribution to force f U and the ratio f U / f decreases with λ. The ratio of f U / 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.