1070-4272/01/7405-0860$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 5, 2001, pp. 860 !863. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 5,
2001, pp. 833!837.
Original Russian Text Copyright + 2001 by Elchueva, Aristova, Bortnikov, Tabachkov.
AND POLYMERIC MATERIALS
Synthesis of Single-Component Urethane Sealants
A. D. Elchueva, N. V. Aristova, I. V. Bortnikov, and A. A. Tabachkov
Kazan State Technological University, Kazan, Tatarstan, Russia
Received October 5, 2000; in final form, February 2001
Abstract-Single-component urethane sealing formulations with aldimines as cross-linking agents were
developed. The temperature dependence of the curing time of the sealants was examined. The influence of
the 3CH=N3/3NCO ratio and of fillers (industrial carbon and chalk) on their physicochemical properties was
Polyurethane elastomers are widely used in various
branches of industry. With progress of studies in the
field of development of single-component formula-
tions, their performance is improved and the applica-
tion field is expanded. The procedures used in indus-
try for curing of polyurethane sealants have significant
drawbacks. All sealants of this type are two-compo-
nent; they are not quite convenient in service and re-
quire performing certain manipulations directly before
use. Their curing is effected with diamines and gly-
cols. Curing of a single-component urethane sealant
based on an isocyanate-containing prepolymer results
in formation of defects (blisters, cavities) due to re-
lease of carbon dioxide on contact of isocyanate
groups with atmospheric moisture. The goal of this
work was to develop single-component urethane for-
mulations with aldimines as cross-linking agents.
Aldimines, when reacting with atmospheric moisture,
release active curing agents which react with isocya-
nate groups without releasing CO
, so that formation
of defects in the cured sealant can be avoided.
Urethane elastomers show considerable promise for
practice. Polyurethanes are prepared from compounds
containing highly reactive isocyanate groups. Their
transformations yield polymeric structures with di-
verse types of chemical bonds and allow preparation,
within the same class of polyurethanes, of materials of
widely varying properties.
An important factor determining the physicome-
chanical properties of polyurethanes, especially at
elevated temperatures, is the nature of cross-links in
the three-dimensional polymer network, depending on
the curing agent used.
Studies of the effect of diamines and water as
curing agents in single-component systems on the
properties of composites based on various diisocya-
nates showed  that strong intermolecular interaction
in polymers results in increased modulus of elasticity
and tensile strength. The rigid segments in the chain
(bulky aromatic diisocyanates and aromatic amines)
also enhance the cohesion strength. Flexible groups
(e.g., aliphatic amines) contribute to the elastic prop-
erties of the elastomers.
Thus, polyurethanes can be considered as block
copolymers  with flexible polyether or polyester
segments and rigid segments formed by urethane or
urea fragments. Flexible segments increase the elastic-
ity and relative elongation at break, whereas rigid
segments with enhanced intermolecular interactions
increase the hardness, tensile strength, melting point,
and glass transition point.
The structure of the three-dimensional polyurethane
network is determined by the synthesis conditions, in
particular, by the preparation procedure (single-stage
or two-stage). When the polymer is prepared by a
two-stage procedure via a prepolymer, formation of a
more regular network can be expected. Elastomers
prepared via prepolymer  exhibit higher cohesion
strength but lower values of the adhesion strength and
modulus of elasticity and are less elastic.
In a two-stage procedure for production of poly-
urethanes the prepolymers are usually highly viscous,
and special equipment is required for their mixing and
feeding to reaction vessels without air access. The
properties of the final product can largely depend on
the accuracy of temperature control and on the storage
time and stability of the prepolymer.
The advantage of the single-stage preparation of
polyurethanes is the stability of the reaction mixture.
With aromatic diamines, an additional advantage is