On the unperturbed dimensions of cis‐1.4 polybutadiene

Contrary to the usual procedure which considers only the local conformations of minimum energy, the mean‐square end‐to‐end distance of cis ‐1.4 polybutadiene is recalculated taking into account the whole continuum of conformational states; elastic strain on the bond angles has been also allowed for, but only the values which minimize the conformational energy have been retained, for every set of rotation angles. Such a calculation has been carried out because in the polymer under consideration the broadness of the potential minima and the low energy barriers should lower the degree of accuracy of the results based on the equilibrium states calculations. As a matter of fact, the results show drastic differences with respect to those obtained by traditional procedures 6,7 , with analogous values of the potential energy parameters. Using different values of the zero‐strain angle, agreement with the experimental figures of r̄ /n at 20°C 1‐3 is obtained for positive values of the energy difference between the gauche and the trans state on the ‐ [CH 2 CH 2 ]‐ bonds. The corresponding calculated figures of d ln r̄ /dT are very close to zero; in this case, comparison with experiment is complicated by the disagreement between the oppositely signed results given by stresstemperature measurements 4,5 , on one hand, and by viscosity methods 2 , on the other hand.