J. Budhathoki-Uprety, B.M. Novak / Polymer 51 (2010) 2140e2146
2141
2
. Experimental
1.24 (17H, br), 0.87(3H, eCH3, J ¼ 6.9, t). 13C NMR, 100 MHz (CDCl
3
,
d
ppm): 156.63, 143.10, 140.49, 137.08, 126.69, 124.11, 40.46, 32.15,
2.1. General
30.39, 29.91, 29.89, 29.85, 29.60, 27.19, 22.92 and 14.35.
The chemicals were purchased from Aldrich (SigmaeAldrich,
2.2.2. Preparation of carbodiimides, 2aec
Milwaukee, WI) and Fisher Scientific, Fair Lawn, NJ and used as
received unless stated otherwise. 6-nitropiperonal was received
from Tokyo Chemical Industry, Japan. The solvents, tetrahydrofuran
The substituted urea derivatives (compounds 1aec) were
dehydrated to the corresponding carbodiimides using known
procedures [25] with slight modifications. In a typical procedure,
dibromotriphenyl phosphorane (1.3 equivalents) was suspended in
(
THF) dichloromethane and chloroform were distilled prior to use.
1
13
ꢀ
H and C NMR data were recorded on a Varian or Mercury
5 mL dichloromethane at 0 C under nitrogen atmosphere and
1
3
1
00 MHz or 400 MHz spectrometers (300 or 400 MHz for H, 75 or
triethyl amine (2.5 equivalents) was added drop wise. The mixture
was stirred at low temperature in an ice bath for 10 min and then
urea derivative (1a, 1b or 1c, 1e3 g scale, 1.0 equivalent) was added
in four equal portions at an interval of 10 min. The reaction mixture
was allowed to warm to room temperature and stirred overnight
under inert atmosphere. The solvent was removed by rotavapora-
tion and the carbodiimide was extracted from the solid by pentane.
The crude carbodiimide monomer sample was purified by column
chromatography on silica gel using ethyl acetate and hexane (1:1)
mixture to provide colorless oils in all cases.
00 MHz for 13C NMR) at room temperature. The chemical shift
values were reported relative to TMS (
¼ 0.00 ppm) as an internal
standard. IR spectra were obtained from JASCO FT/IR-410. Wave
d
ꢁ1
numbers in cm are reported for characteristic peaks. Melting
points of the compounds were recorded using a Mel-Temp appa-
ratus. Mass spectra were obtained at the NCSU Department of
Chemistry Mass Spectrometry Facility using electrospray ionization
(
ESI) on an Agilent Technologies 6210 LC-TOF mass spectrometer.
Specific optical rotation was recorded on a JASCO P-1010 polarim-
eter. Thermo Gravimetric Analysis (TGA) was performed on Hi-Res
TGA 2950 Thermogravimetric Analyzer under nitrogen atmosphere
0
2.2.2.1. Compound 2a; N-hexyl-N -pyridin-3-ylcarbodiimide; yield:
ꢀ
ꢀ
ꢀ
1
from 25 C to 600 C at a heating rate of 10 C per minute. All the
manipulations for polymerizations were done inside an MBraun
UNIlab drybox under nitrogen atmosphere.
70%, colorless oil. H NMR, 300 MHz (CDCl
3
,
d
ppm): 8.40 (AreH,
J ¼ 2.4 Hz, 1H, d), 8.32 (AreH, J ¼ 3.6 Hz, 1H, dd), 7.38e7.34 (AreH,
1H, m), 7.23e7.18 (AreH, 1H, m), 3.44 (2H, J ¼ 6.9 Hz, t), 1.74e1.64
(
2H, m), 1.44e1.37 (2H, m), 1.33e1.28 (6H, m), 0.88(3H, eCH3,
13
2
2
.2. Synthesis of monomers
J ¼ 6.9, t). C NMR, 100 MHz (CDCl
3
, d ppm): 145.55, 145.44, 138.30,
ꢁ
1
1
30.35, 124.03, 46.71, 31.25, 26.42, 22.51 and 13.98. IR(cm ): 2146
.2.1. Preparation of urea derivatives, 1 aec
(carbodiimide). HRMS [Mþ1] m/z: 204.15.
The urea compounds 1a, 1b and 1c were prepared from
0
commercially available amino pyridine derivatives; 3-amino-
pyridine or 3-(methyl amino)pyridine; and alkyl isocyanates; n-
hexylisocyanate or n-dodecylisocyanate. In a typical procedure, the
aminopyridine derivative (1.0 equivalent) was dissolved in
2.2.2.2. Compound 2b; N-hexyl-N -(pyridin-3-ylmethyl)carbodii-
1
3
mide; yield: 72%, colorless oil. H NMR, 300 MHz (CDCl , d ppm):
8.56e8.52 (AreH, 2H, m), 7.66e7.63 (AreH, 1H, m), 7.30e7.26
(AreH, 1H, m), 4.38 (ArCH2-, 2H, s), 3.16 (2H, J ¼ 6.9 Hz, t),
ꢀ
13
dichloromethane. The solution was cooled to 0 C and an alkyl
1.49e1.45 (2H, m), 1.28e1.24 (6H, m), 0.87(3H, eCH3, J ¼ 6.9, t).
C
isocyanate (1.3 equivalents) diluted in dichloromethane was added
to the reaction mixture drop wise via addition funnel. The reaction
mixture was allowed to warm to room temperature and then
refluxed overnight. Solvent was removed and the resulting urea
3
NMR, 100 MHz (CDCl , d ppm): 149.10, 140.41, 135.58, 135.30,
ꢁ
1
123.64, 48.14, 46.67, 31.46, 31.32, 26.54, 22.69 and 14.17. IR (cm ):
2127 (carbodiimide). HRMS [Mþ1] m/z: 218.16.
ꢀ
0
derivatives were purified by recrystallization from ethanol at 0 C.
2.2.2.3. Compound
2c;
N-dodecyl-N -pyridin-3-ylcarbodiimide;
1
The reactions were performed in 1e6 g scales.
yield: 84%, colorless oil. H NMR, 400 MHz (CDCl
.40e8.39 (AreH, 1H, m), 8.32 (AreH, J ¼ 3.2 Hz, 1H, dd), 7.37e7.34
(AreH, 1H, m), 7.22e7.18 (AreH, 1H, m), 3.44 (2H, J ¼ 6.8 Hz, t),
3
, d ppm):
8
2
.2.1.1. Compound 1a; 1-hexyl-3-(pyridin-3-yl) urea; yield: 96%,
ꢀ
1
13
white solid, mp: 92 C. H NMR, 300 MHz (CDCl
3
,
d
ppm): 8.30
1.72e1.65 (2H, m), 1.31e1.25 (17H, m), 0.87(3H, eCH3, J ¼ 6.8, t).
NMR, 100 MHz (CDCl ppm): 145.34, 145.26, 138.09, 134.08,
130.13, 123.81, 46.71, 31.92, 31.29, 29.63, 29.55, 29.49, 29.35, 29.06,
C
(
(
(
AreH, J ¼ 2.4 Hz, 1H, d), 8.19 (AreH, J ¼ 3.3 Hz, 1H, dd), 8.04e8.00
3
, d
AreH, 1H, m), 7.80 (CONH, 1H, s), 7.22e7.18 (AreH, 1H, m), 5.46
CONH, J ¼ 5.4 Hz, 1H, t), 3.26e3.19 (2H, m), 1.50e1.43 (2H, m),
ꢁ1
26.76, 22.70 and 14.13. IR (cm ): 2140 (carbodiimide). HRMS
13
1
.31e1.25 (6H, m), 0.85(3H, -CH3, J ¼ 6.9, t). C NMR, 100 MHz
[Mþ1] m/z: 288.24.
(
3
CDCl , d ppm): 156.66,143.05,140.56,136.93,126.55,123.95, 40.30,
31.57, 30.17, 26.68, 22.65 and 14.10.
2.3. Synthesis of polymers, 3aec
2
9
8
.2.1.2. Compound 1b; 1-hexyl-3-(pyridin-3-ylmethyl) urea; yield:
ꢀ
1
9%, white solid, mp: 93 C. H NMR, 300 MHz (CDCl
3
,
d
ppm):
All the mentioned polymers Poly 3a, 3b and 3c were synthe-
.49e8.47 (AreH, 2H, m), 7.66e7.62 (AreH, 1H, m), 7.25e7.21
sized inside an inert atmosphere dry box. In a typical procedure, the
monomer sample (0.50e2.0 g in scale) was mixed with catalyst (I)
[22]; with a monomer to catalyst ratio 100:1 or 200:1. The poly-
merizations were performed at room temperature and without any
solvent. The reaction mixture transformed into a dark red viscous
liquid and solidified within 48 h. The reaction mixture was allowed
to remain at room temperature inside the dry box for 7 days for any
secondary monomer diffusion. The resulting light orange solid was
dissolved in chloroform and precipitated in methanol to remove
the catalyst and unreacted monomer. The light yellow solid thus
obtained was washed with several volumes of methanol and then
dried under vacuum overnight.
(
(
1
AreH, 1H, m), 5.05 (CONH, 1H, br), 4.70 (CONH, 1H, br), 4.36
ArCH2-, 2H, J ¼ 6.0 Hz, d), 3.17e3.11 (2H, m), 1.48e1.44 (2H, m),
13
.29e1.26 (6H, m), 0.87(3H, eCH
3
, J ¼ 6.9, t). C NMR, 100 MHz
(
3
CDCl , d ppm): 159.19, 148.61, 148.31, 135.72, 135.13, 123.56, 41.50,
4
0.42, 31.63, 30.33, 26.68, 22.67 and 14.12.
2.2.1.3. Compound 1c; 1-dodecyl-3-(pyridin-3-yl) urea; yield: 98%,
ꢀ
1
3
white solid, mp: 92 C. H NMR, 300 MHz (CDCl , d ppm): 8.30
(
(
(
AreH, J ¼ 2.4 Hz, 1H, d), 8.19 (AreH, J ¼ 3.3 Hz, 1H, dd), 8.05e8.01
AreH, 1H, m), 7.78 (CONH, 1H, s), 7.22e7.18 (AreH, 1H, m), 5.45
CONH, J ¼ 5.1 Hz, 1H, t), 3.23 (2H, J ¼ 6.9 Hz, dd), 1.51e1.47 (2H, m),