1070-4272/04/7709-1544C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 9, 2004, pp. 1544!1546. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9,
2004, pp. 1555!1557.
Original Russian Text Copyright + 2004 by Bezbozhnaya, Zamashchikov, Lutsyk.
AND POLYMERIC MATERIALS
Synthesis of Urea!Formaldehyde Oligomers without a Solvent
T. V. Bezbozhnaya, V. V. Zamashchikov, and A. I. Lutsyk
Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine,
Received February 5, 2004
Abstract-A urea3formaldehyde oligomer comparing well with commercially avaliable KF-MT and KF-M
resins in the adhesive power was prepared from solid paraform and urea without a solvent.
Synthetic urea3formaldehyde oligomers (UFOs)
are widely used in wood-working industry as binders
and as a base for adhesives. However, UFOs tend to
self-cure during prolonged storage and transportation.
Furthermore, the modern industrial synthesis of UFOs
in multistep  and involves water as a solvent,
with its subsequent distillation.
In this study we examined the possibility of pre-
paring highly stable UFO without a solvent. The start-
ing compounds were paraform (F) and urea (U). The
products were tested as binders in production of chip
A flask equipped with a power-driven stirrer and
a thermometer was charged with urea [pure grade,
GOST (State Standard) 6691377] and paraform [TU
(Technical Specifications) 6-09-3208378] in a definite
molar ratio (the U : F ratio was varied from 1 : 1 to
1 : 6), after which solid sodium hydroxide (up to 2%
relative to the total weight of U and F) preliminarily
ground with a small amount of urea was added. The
mixture was heated with stirring at 333 K for 2.533h.
Within 5310 min after switching on the stirrer, the
mixture started to liquefy, and within 15320 min it
fully transformed into a viscous sticky liquid. Upon
further heating for 2.5 h, the products with U : F >
1 : 3 hardened, and those with U : F 1 : 3.25, 1 : 3.5,
1 : 4, and 1 : 6 remained liquid. At room temperature,
the oligomers with U : F 1 : 3.25 and 1 : 3.5 hardened
in several days, and that with U : F 1 : 4 remained a
stable viscous sticky liquid for at least 12 months.
The mixture starts to liquefy earlier with increasing
temperature, stirring intensity, degree of initial grind-
ing of urea grains, and amount of sodium hydroxide
added. In the absence of NaOH, the mixture does not
become liquid at 333 K over a period of 2.5 h. The
individual components (urea, paraform) separately
mixed with NaOH do not form liquid systems under
The liquefaction is not associated with accumula-
tion of water during the reaction. According to GLC
data (LKhM-8MD chromatograph, catharometer, sta-
tionary phase 5% TSEP on Polysorb, internal refer-
ence n-PrOH), the water content in the resin (initial
ratio U : F = 1 : 4) 3 h after the start of the reaction
did not exceed 4%. The change in the aggregation
state of the system is undoubtedly caused by the base-
catalyzed reaction of urea with paraform: during the
first 20 min, the formaldehyde concentration sharply
decreases (see figure) with accumulation of methylol
groups, and subsequent changes occur more smoothly
(the concentration of free formaldehyde in the resin
was determined according to GOST 14231388, and
the concentration of methylol groups, by iodometric
titration ). The main reaction of formation of meth-
ylol groups from formaldehyde is accompanied by
side Cannizzaro reaction. According to GLC data, the
methanol content in the oligomer sample with the
initial ratio U : F = 1 : 4 did not exceed 3%.
The solid products obtained at the initial molar
ratio U : F > 1 : 3 are virtually insoluble in water. The
oligomers obtained at a high initial content of formal-
dehyde are readily soluble in water, but at U : F =
1 : 6 dissolution in water is accompanied by the re-
lease of unchanged paraform.
As the oligomer with U : F = 1 : 4 showed high
stability, high solubility in water, and apparent adhe-
sive power, we chose this product for subsequent tests
as binder in chip board production.
This product has a high content of methylol groups
(up to 30%). The high degree of nitrogen functionali-