STEREOCHEMICAL EQUILIBRIUM AND CONFIGURATIONAL STATISTICS IN POLYSTYRENE AND ITS OLIGOMERS

Mixtures of diastereoisomers of 2,4,6-triphenylheptane (TPH) have been epimerized in dimethyl sulfoxide (DMSO) containing t-BuOK. The mole fractions of isotactic, heterotactic, and syndiotactic isomers at equilibrium at 70° are 0.217, 0.499, and 0.284, respectively. These results, in conjunction with the ratio 0.48/0.52 previously reported for the meso and racemic 2,4-diphenylpentanes (DPP) at equilibrium at 25°, are interpreted according to the theory of stereochemical equilibrium. Proportions of various conformers in individual DPP and TPH isomers estimated from nmr coupling constants by Bovey and coworkers and by Pivcová and collaborators are interpreted similarly in terms of interactions associated with various conformations. The theory of equilibria between isomers and the associated theory of the conformer populations for each isomer provide a mutually consistent interpretation of the two kinds of results, the same arbitrary parameters (two in number) being used for both. Stereochemical equilibria and conformer populations calculated for polystyrene from the same parameters differ considerably from those for the oligomers. Deuterium exchange with the α-hydrogens in polystyrene has been demonstrated by base catalysis in d6-DMSO. © 1969, American Chemical Society. All rights reserved.