Effects of the elastic deformation on the average conformations of polymethylene chains

The average conformation properties, such as the a priori probability Pξη and the segmental orientation function 〈P2(ζ)〉 of polymethylene chains with chain length from N=13 to N=21 are investigated by enumeration calculation method based on the rotational-isomeric state (RIS) model. Here non-local interactions of L–J potential are also considered. In the process of tensile deformation, the a priori probability Pt increases with elongation ratio λ, meanwhile the a priori probability Pg+ (or Pg−) decreases with elongation ratio λ, and it leads the average energy per bond to decrease. The segmental orientation distribution function 〈P2(ζ)〉 of short deformed polymethylene chains may be expressed in the form of〈P2(ζ)〉/(λ2−λ−1)=a(λ2−λ−1)+bwhere a and b only depend on PM chain length. Many conformations will vanish in the process of deformation. We also investigate the probability density distribution function of gyration radius P(S). For a given chain length, the maximum of P(S) increase with λ, and the distributed region of P(S) becomes smaller for large λ. Some comparisons with Flory–Fisk function of P(S) are also made. Our calculations may provide some insights into the rubber-like elasticity.