formaldehyde - Sciencemadness Dot Org

FORMALDEHYDE POLYMERS 67
ylene.* It must be remembered, however, tbat this classification is more
or less arbitrary and is made only for purposes of convenience. The three
groups merge into one another and absolute dividing lines cannot be drawn
between them.
In general, the polyoxymethylene glycols have the appearance of colorless
powders possessing the characteristic odor of formaldehyde. Their
properties, such as melting point, solubility, chemical reactivity, etc, vary
with their molecular weight. As the degree of polymerisation) indicated
by n in the type formula, HO(CH20)^H, increases, their formaldehyde
content approaches 100 per cent and the physical and chemical properties
approach those of eu-polyoxymethylene, (CH20)B.
Eu-polyoxymethylene is derived from anhydrous liquid formaldehyde
and apparently does not contain combined water. However, since even a
trace of water would be sufficient to hydrate the large molecules involved,
it is possible that it may be a polyoxymethylene glycol of extremely high
molecular weight. Conversely, it is also possible that some of the higher
polyoxymethylene glycols may be true polyoxymethylenes contaminated
with a trace of adsorbed water.
Lower Polyoxymethylene Glycols
When aqueous formaldehyde solutions containing from approximately
30 to 80 per cent formaldehyde are brought to room temperature or below,
a precipitate consisting principally of the lower polyoxymethylene glycols
is obtained. The point at which precipitation takes place is dependent on
the concentration of the formaldehyde solution and the rate of cooling.
As previously pointed out (pages 31-34), the lower members of this group
are normally present in aqueous formaldehyde solutions. On standing,
the products first precipitated undergo condensation, and polyoxymethylene
glycols having a higher degree of polymerization are formed.
The lower polyoxymethylene glycols are colorless so3ids melting in the
range 80 to 120°C. They differ from paraformaldehyde and other higher
homologs in being soluble in acetone and ether, dissolving with little or no
decomposition. They dissolve rapidly in warm water with hydrolysis and
depoiymerization to form formaldehyde solution. They are insoluble in
petroleum ether.
A number of the lower polyoxymethylene glycols have been isolated by
Staudinger 58 in a fair degree of chemical purity. In the case of the lowest
homologs, this was accomplished by adding acetone to concentrated water
solutions of formaldehyde, drying the resultant mixture with anhydrous
* The so-called beta-polyoxymethylene is_ apparently an alpha-polyoxyruethyletie
containing a small percentage of sulfuric acid.