Further computer simulation studies of the orientational behaviour of poly(ethylene terephthalate) chains

The energy parameter governing the glycol gauche conformation of the Willia ms-Flory rotational-isometric-state (RIS) model of poly(ethylene terephthal ate) (PET) is varied to give values of (< r(2)>/M)(infinity) and % gauche-g lycol conformers that agree with experiment for bulk PET. Such agreement is not given by the original Williams-Flory model. The RIS Metropolis Monte-C arlo (RMMC) model developed by Molecular Simulations Incorporated (MSI) can also be modified, through values of the effective relative permittivity, t o match the same experimental quantities. The orientational behaviours of t he glycol segments, terephthaloyl segments and the repeat units with respec t to the chain end-to-end vector are investigated by calculating the Legend re polynomials < P-2(xi(gly))>, < P-2(xi(ter))> and < P-2(xi(rep))>, respec tively, as functions of end-to-end chain extension, r/r(max), for selected RIS and RMMC parameters. The calculations show that the more flexible glyco l segments orientate more readily than the terephthaloyl segments and the r epeat units show orientations between these two extremes. The various model s of segmental orientation presented in this paper will enable more realist ic interpretation of the experimental stress-optical behaviour of PET in bu lk. In this context, the Langevin model based on freely-jointed chains is s een to be completely inadequate for describing changes in segmental orienta tion with chain extension.