| Abstract: | 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. |
