formaldehyde - Sciencemadness Dot Org

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FORMALDEHYDE
ingers studies of the polyoxymethylene diacetates and dimethyl ethers are
the basis for the modern interpretation of the chemistry of these polymers.
Although first discovered at an earlier date, the higher polyoxymethylene
dimethyl ethers, gamma-polyoxymethylene, and delt-a-polyoxymethylerie
were shown by Staudinger to be members of this group. The last is a
partially rearranged polyoxymethylene.
Polyoxymethylene Diacetates
Structure. Polyoxymethylene diacetates are obtained by the action
of acetic anhydride on paraformaldehyde and alpha-polyoxymethylenes.
Their chemical structure, as indicated below, is readily expressed by the
type formula,
CHi-COO-(CH3O)»'0C'CH8 or OH8-CO-0-CHa-0-CHa-0 ••• CHo-O-COCH,.
These derivatives are more stable than the glycols from which they are
obtained, and accordingly can be subjected in many instances to the standard
methods of chemical manipulation. Individual members of the series
containing up to approximately 20 formaldehyde units per molecule have
been isolated, and chemical structures have been determined by measurement
of molecular weight and analysis for formaldehyde and acetic acid 65 .
Molecular refraction figures are in agreement with the structure postulated
and do not support the theory that they may be molecular compounds of
polyoxymethylene and acetic anhydride, CH3C0 • 0 - OC - CH3 • nCE.$0.
X-ray studies of the diacetates show that they are chain molecules crystallized
in a molecular lattice and that they lie in parallel layers 70 . The molecular
lengths for pure diacetates can be accurately determined by the
same methods which have been employed by Miiller and Shearer 43 for fatty
acids. Due to their lack of solubility, the higher diacetates cannot be
isolated in a pure state. They decompose at or below their melting point
and gradually split up when heated in high-boiling solvents. That they are
higher members of the homologous series is demonstrated by their physical
and chemical properties and by chemical analysis.
Properties. The physical properties of some of the lower polyoxymethylene
diacetates, together with the results of molecular weight determination
and chemical analysis, are illustrated in Table 17, prepared
from the data of Staudinger and Luthy 66 - 71 . As will be seen, the physical
properties change progressively with increasing molecular weight just as
in the case of other homologous series of organic compounds. Solubility
in water, alcohol, ether, acetone, and other solvents continually drops off
with increase in the value of n m the type formula, while melting point,
density, viscosity, and refractive index increase. A high molecular weight
diacetate which could not be purified by recrystallization was found to