Macromolecules 2002, 35, 877-882
877
Spectroscopic Characterization of Model Urea, Urethane Compound,
and Diamine Extender for Polyurethane-Urea
Sh i-Kw u n Wa n g a n d Ch on g Sook P a ik Su n g*
Polymer Program, Department of Chemistry, Institute of Materials Science, University of Connecticut,
9
7 North Eagleville Road, Storrs, Connecticut 06269-3136
Received J uly 24, 2001; Revised Manuscript Received November 19, 2001
ABSTRACT: During the reaction injecting molding process of polyurethane-urea (PUU) based on 4,4′-
methylenebisphenyl diisocyanate (MDI), urethane as well as urea linkages are produced when a highly
fluorescent aromatic diamine is used as a chain extender. To explore intrinsic fluorescence as a cure
characterization technique, model urethane and urea compounds with similar chemical structures to
MDI-based PUU were synthesized. Their fluorescence behavior were compared with that of diethyltolu-
enediamine (DETDA), which is often employed as a chain extender. The emission maxima for DETDA in
polypropylene oxide (PPO) polyol occurred at 336 nm, while the urea (diphenylurea) and the urethane
(ethyl N-phenylcarbamate) model compounds showed emission maxima at 301 and 303 nm, respectively.
The relative quantum yield for DETDA was determined to be 57 times greater than the urea compound,
while the urethane compound possessed a relative quantum yield 11 times greater than the urea
compound. The viscosity effect increased DETDA fluorescence intensity greater than the observed
fluorescence intensity decrease associated with a temperature increase of 55 °C. DETDA was found to be
an effective collisional quencher for the urea and the urethane model compounds. The urea compound
does not appear to quench the urethane compound’s fluorescence significantly. Study of FT-IR spectra of
model urea, urethane compounds, and DETDA provided characteristic peaks for each compound: 1727
-
1
-1
-1
cm for urethane, 1647 cm for urea, and 1623.7 cm for DETDA, which were also proportional to
their concentration in PPO. NIR spectra of model compounds and DETDA indicate characteristic peaks
for the urea, the urethane compounds, and DETDA. However, the urea peak absorbance was difficult to
use for quantitative analysis, while the urethane and DETDA peaks could be readily applied for such
analysis.
In tr od u ction
as by the changes in viscosity and temperature during
cure.
Hoyle and Kim investigated the emission spectra of
Recently, our laboratory has been involved in devel-
oping intrinsic fluorescence, phosphorescence, and UV-
vis spectroscopic techniques for the characterization of
8
model urethane or amine compounds to follow the
photolysis mechanism of MDI-based polyurethanes in
solution. They assigned the fluorescence peak at 301(
2 and 335( 2 nm to urethane and aromatic amine,
respectively, in dimethylformamide. Nevertheless, there
is little information published on the effects of their
interactions on the fluorescence emission spectra.
In this study, we report on the fluorescence behavior
of three model compounds representing the urea and
the urethane compounds as well as DETDA. Possible
interactions between the three model compounds and
their effects on the fluorescence characteristics were
investigated in addition to the effect of changes in
viscosity or temperature during cure. FT-IR and N IR
studies are also reported in an attempt to identify the
characteristic peaks for these three model compounds
and to evaluate whether such peaks can be used for
quantitative analyses.
1
cure in several polymers and composites such as epoxy,
2
3
4
polyimide, bis(maleimide), polyurethane, vinyl poly-
5
6
mers, and polycyanurate.
In polyurethanes based on nonfluorescent 4,4′-p-
methylenebisphenyl diisocyanante (MDI), fluorescence
intensity at the emission maxima of 314 nm was found
to increase about 87 times when MDI was converted to
diurethane, following reaction with 1-butanol or hy-
droxy-terminated poly(propylene oxide).4b The rate con-
stants and the activation energies for the model reaction
(
MDI with 1-butanol) and polyurethane formation (MDI
with hydroxy terminated polyol) were obtained from the
fluorescence results, which were correlated to the extent
of reaction determined by IR.
In polyurethane-ureas (PUU) which are often the
polymers made by reaction injection molding (RIM), the
chain extender is usually a highly fluorescent aromatic
diamine such as diethyltoluenediamine (DETDA), with
Exp er im en ta l Section
7
MDI and polyol as the other components. Thus, during
cure to form PUU, urethane linkage is formed from the
MDI-polyol reaction, while urea linkage is formed from
the MDI-DEDTA reaction. To explore intrinsic fluo-
rescence for cure characterization in PUU, we first
needed to characterize the fluorescence behavior of the
three fluorophores present in PUU: the urethane
derivative of MDI, the urea derivative of MDI, and
DETDA, individually. Furthermore, the fluorescence
intensities of these fluorophores may be influenced by
the interaction with each other (e.g., quenching) as well
Mod el Com p ou n d s. Diethyltoluenediamine (DETDA) with
a 80/20 isomer ratio as shown in Scheme 1 was received from
Ethyl Corp. and was purged with argon before storage in a
refrigerator. For the model compound representing mono-
urethane, ethyl N-phenylcarbamate was synthesized from the
reaction of excess ethanol with phenyl isocyanate from Aldrich
Chemical Co. by refluxing in ethanol at 70 °C in an oil bath
for 16 h under an argon gas purge. After removing unreacted
ethanol and phenyl isocyanate via vacuum distillation at 10
mmHg, the products were dissolved in cyclohexane at 50 °C,
followed by recrystallization upon slow cooling. The urea model
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0.1021/ma011316+ CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/04/2002