The effective barrier to reorientation is calculated for a chain which may occupy two equivalent energy states, 180° apart for the case where the chain is allowed to twist during the reorientation process. Results are obtained for (I) a ``parabola‐antiparabola'' and (II) a cosine form for the intermolecular energy. The results for (I) and (II) are similar, but differ both in form and magnitude from that obtained earlier using a cusplike barrier. Both (I) and (II) lead to the conclusion that a chain will behave as a rigid rod up to a critical chain length, and then exhibit twisting for all lengths exceeding this critical value.
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