Head‐to‐head units in poly(propylene oxide) by ozonation

By extensive ozonation and lithium aluminum hydride reduction, poly(propylene oxide) can be converted to material containing dipropylene glycol. Since the diprimary, disecondary, and primary‐secondary isomers are readily separable by vapor‐phase chromatography, it has been possible to show that some (but not all) noncrystalline PPO samples contain many head‐to‐head, tail‐to‐tail monomer units. Correlation of the fraction of head‐to‐head units with the optical rotation of noncrystalline fractions from optically active monomer, indicates that there is one asymmetric center inverted for every unit inserted head‐to‐head. The earlier suggestion that the noncrystalline fraction was due to atactic stereochemistry is thus shown to be generally incorrect in favor of an explanation due to positional isomerization.