formaldehyde - Sciencemadness Dot Org

FORMALDEHYDE POLYMERS 11
marily formed undergo further reaction with loss of combined water, and
paraformaldehyde is produced.
The primary reactions are undoubtedly poly-condensations of the type
which has been previously shown to occur in formaldehyde solution (pages
31-36), e.g.:
HOOHgOCHsOCHsOH 4- HOCH.OH-* HOCH20(CH20)£CH,OH 4- K20
HOCHaO'{CHaO)aCHaOH -j- HOCH2OH -» HOCH20(CH20)aCH2OH + H30, etc.
Conversion of the solid polymeric glycols to higher homologs may have
another mechanism. Staudinger 87 believes that monomelic formaldehyde,
formed by partial decomposition, undergoes a topochemical reaction -with
other polyoxymethylene glycol molecules as indicated below:
HOCHaO(CHiO)8CHaOH + CH20 -* HOCH20(CH30)4CH2OH
The conversion of lower polyoxymethylene glycols to paraformaldehyde
is demonstrated by the fact that the acetone-soluble polymers obtained
by cooling hot 80 per cent aqueous formaldehyde gradually lose water on
standing over phosphorus pentoxide, with a resulting increase in formaldehyde
content. At the same time the solubility of the polymeric mixture
falls off until it becomes completely insoluble in hot acetone, indicating the
disappearance of molecules containing 12 or less formaldehyde units 61 .
According to Staudinger 63 , the reactions responsible for this conversion are
catalyzed by the traces of formic acid usually present in crude polyoxymethylene
glycols. A purified hepta-polyoxymethylene glycol fraction
shows no change in formaldehyde content or acetone-solubility when
subjected to desiccation under the above conditions. It loses weight due
to volatilization, but does so at a slow though constant rate until completely
evaporated. In the case of crude polyoxymethylene glycol mixtures,
loss of weight by vaporization is at first rapid, but decreases constantly
on storage.
Alpha-Polyoxymethylene
Alpha-polyoxymethylene is a solid formaldehyde polymer normally containing
in the neighborhood of 99.7 to 99.9 per cent formaldehyde. It is
generally prepared by the action of acids and alkalies on formaldehyde
solutions. The term "trioxymethylene" was employed by Delepine and
other early investigators to designate this polymer.
Composition and Structure. According to Staudinger 82 , alpha-polyoxymethylene
is a mixture of polyoxymethylene glycols in which the n
value of the type formula, HO* (CH20)w*H, is not less than 100 and probably
much greater.
It is impossible to prove whether the small quantity of water (approxi-