Response of the mean‐square optical anistropy of chain molecules to the imposition of excluded volume

Abstract

The influence of the chain expansion produced by excluded volume on the mean‐square optical anisotropy has been studied in six types of polymers. The mean‐square optical anistropy for a specified configuration is calculated using the valence optical scheme. Realistic rotational isomeric state models are used for the configurational statistics of the unperturbed chains. Excluded volume is introduced by hard sphere interactions. Results obtained with chains of 100, 200, 300, and 400 bonds permit extrapolation to the behavior expected for much longer chains. The mean‐square optical anisotropy of polyethylene is insensitive to excluded volume. A similar conclusion was obtained several years ago in a study of chains confined to a tetrahedral lattice and weighted in a manner appropriate for the short‐range interactions in polyethylene.2 Different behavior is seen in poly(vinyl chloride), poly(vinyl bromide), polystyrene, poly(p‐chlorostyrene), and poly(p‐bromostyrene). The mean‐square optical anisotropy of these five vinyl polymers is sensitive to the imposition of excluded volume if the stereochemical composition is exclusively racemic. Much smaller effects are seen in meso chains and in chains with Bernoullian statistics and an equal probability for meso and racemic dyads.