2554 Notes
Macromolecules, Vol. 36, No. 7, 2003
1a). Fluorescence behavior of CPCY (curve 1 in Figure
1a) is very similar to that of BPADCY (curve 2 in Figure
1a), as expected. The emission of bulk CPCY and
BPADCY is very similar to that in solution. Fluores-
cence emission is usually detected for a concentration
in the range 10-5-10-9 M depending on the character-
istics of the fluorophores. In this concentration range,
both IC and PIC in THF solutions only show emission
around 295 and 302 nm (curves 5 and 6 in Figure 1a),
respectively. All of these model compounds exhibit the
emission typical of substituted benzene, and there is
essentially no emission observed around 400 nm. There-
fore, fluorescence emission from these species (mono-
mers, impurities, and intermediate cure products) can-
not account for the emission observed at 420 nm during
the cure reaction of BPADCY monomer.
The fluorescence spectra of TCT, the model for cure
product, is shown as curve 1 in Figure 1b. For TCT, the
broad emission around 420 nm as well as a peak near
290 nm is clearly shown. Even the possible presence of
small amount of unreacted CPCY cannot account for the
broad emission observed around 420 nm in TCT. The
soluble oligomer mixture has an emission at 295 nm and
another very strong one at 430 nm in the solid state
(curve 3 in Figure 1b). After dissolving in THF, the
emission peaks (curve 2 in Figure 1b) show up at 302
and 432 nm, which are similar to the emission from TCT
model compound. Cyanurate resin from BPADCY de-
velops an amber color after cure with increasing broad
UV absorption near 340 nm.6c When excited near 340
nm, little fluorescence is observed at 420 nm, indicating
that the side reaction responsible for the amber color is
not mainly responsible for the observed fluorescence
during cure.
F lu or escen ce Sp ectr oscop ic Ch a r a cter iza tion
d u r in g Tr im er iza tion of CP CY. Cumylphenoxy cy-
anate ester (monofunctional monomer, CPCY) has been
reported to undergo a quantitative cyclotrimerization
uncomplicated by side reactions.8 In the current study,
the formation of triazine rings has been confirmed by
FTIR spectroscopy. With increasing reaction time,
ambient fluorescence emission spectra during bulk
reaction of CPCY in argon at 200 °C emerges with a
maximum around 415 nm, which is also similar to that
of the model compounds, TCT and BPADCY oligomer.
Therefore, this result further supports that the emission
around 420 nm in polycyanate resins comes from
substituted triazine rings, which is the cross-linker in
the resin.
F igu r e 1. (a) Fluorescence emission spectra of monomers,
suspected impurities, and cure intermediates in THF (excited
at 265 nm: 1, CPCY, 1.84 × 10-5 M; 2, BPADCY, 9.60 × 10-6
M; 3, BPA, 2.76 × 10-6 M; 4, BPAC, 1.91 × 10-5 M; excited at
280 nm: 5, IC, 1.07 × 10-5 M; 6, PIC, 6.64 × 10-3g/mL). (b)
Fluorescence emission spectra of triazine model compound and
BPADCY oligomer in THF and solid state (excited at 280 nm;
1, TCT: 3.9 × 10-4 M; 2, oligomer: 2.8 × 10-5 g/mL; 3, solid
oligomer film).
The soluble BPADCY oligomer was prepared by heating
recrystallized BPADCY monomer at 200 °C for 60 min in
argon, since the reaction was stopped before the gelation. The
monofunctional monomer CPCY was melted between two
quartz plates for 3 min at 100 °C and trimerized in argon at
200 °C. All model compounds were dissolved in spectrophoto-
metric grade THF.
For fluorescence studies, a Perkin-Elmer LS50B lumines-
cence spectrophotometer was used at room temperature. A
Mattson Polaris 100 FTIR spectrometer was used for FTIR
measurement with samples mixed with KBr powder. NMR
spectra were collected in either CDCl3 or d6-acetone solution
with a Bruker AC-270 NMR or DMX-500 NMR spectrometer.
Resu lts a n d Discu ssion
Su m m a r y
F lu or escen ce Sp ectr oscop ic Ch a r a cter iza tion of
Mod el Com p ou n d s a n d Solu ble Oligom er . Fluores-
cence emission spectra in THF are shown in Figure 1a
for model compounds except the model cure product
TCT. The benzene ring usually exhibits fluorescence
emission around 275 nm.11 Therefore, BPA fluorescence
emission is typical of substituted benzene and similar
to that of phenol,12 with a emission maximum at 305
nm (curve 3 in Figure 1a). Fluorescence usually is weak
in molecules with an n-π* state as the lowest excited
singlet state such as cyanate ester moiety.13 Conse-
quently, the results show that BPA is about 500 times
more fluorescent than BPADCY, which has an emission
maximum at 295 nm (curve 2 in Figure 1a) when excited
at 265 nm.
To elucidate the origin of the spectral changes ob-
served in fluorescence emission during the cure reaction
of a bisphenol A dicyanate ester monomer, seven model
compounds representing monomers, impurities, cure
intermediates, and cure product have been investigated.
Fluorescence spectroscopic characterization indicate
that aryl cyanate esters, aryl carbamate, and aryl
iminocarbonate compounds exhibit a characteristic fluo-
rescence emission at around 300 nm from substituted
benzene rings. However, in the model cure product,
tricumylphenoxyl-s-triazine, the emission was observed
near 420 nm, which is similar to the fluorescence
observed during cure of cyanate ester monomer. The
soluble oligomer in the solid state and the trimer from
a monofunctional cyanate monomer also exhibit the
observed fluorescence emission near 420 nm. Therefore,
The emission peak of BPAC is between those of BPA
and BPADCY and appears at 301 nm (curve 4 in Figure
Xu, Youzhi Eugene
