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Experimental Section
General Procedures: 1H NMR spectra were recorded on VXR 300 NMR spectrometer
using the TMS/solvent signal as an internal reference. Chemical shift is reported in 
scale. The abbreviations s, d, t and m stand for singlet, doublet, triplet and multiplet
respectively. Infrared spectra were recorded on Nicolet Impact 400 FT-IR spectrometer.
Solid compounds were either recorded as thin KBr pellets or as chloroform solution in
CsBr cells. Viscosities were measured with an Ubbelohde viscometer in a constant
temperature bath. Thermo gravimetric analyses (TGA) were performed on a TGA-7
Perkin-Elmer instrument. About 5-10 mg samples were used and the heating scans were
done in air atmosphere at the rate of 20 oC min-1. DSC measurements were conducted
with a Perkin-Elmer Pyris 6 DSC. The calorimeter was calibrated using indium metal as
standard. About 2-5 mg samples were used with the heating rate of 10 °C min-1 under a
flow of nitrogen (20 mL min-1). The cooling data were collected by cooling the isotropic
melt obtained in the first heating of the polymer samples and the heating data were
collected during the second heating from room temperature. A polarizing light optical
microscope (Olympus B-12) equipped with a Linkam TP94 hot stage was used for visual
observation.
The samples were heated between a slide and cover slip, and the
photographs were taken with an Olympus DP-11 digital camera and the objectives used
were of either 20X or 50X magnification. The data were collected by cooling the
isotropic melt obtained after the first heating of the samples and the heating data were
collected during the second heating from room temperature.
The X-ray Diffraction
experiments were performed using a Rigaku Dmax 2500 diffractometer. The system
consists of a rotating anode generator and wide angle powder goniometer fitted with a
high temperature attachment. The generator was operated at 40 kV and 125 mA. The
sample holder was a copper block and a thin layer of sample was spread on the copper
plate. It was cooled/heated at the rate of 20 °C min-1 and when the sample temperature
reached a point within 20 °C of the required set temperature the cooling/heating rate was
automatically reduced to 2 °C min-1 to minimize the overshooting of the set temperature.
Materials: Dry NMP was purchased from Aldrich Chemical Co. and used without
further purification. The common organic solvents ethyl acetate, pet ether, chloroform,
dichloromethane, methanol and acetone were distilled prior to use. The AR grade of
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THF, chloroethyl formate, hydrazine hydrate and sodium azide were purchased from SD
Fine Ltd and used as such.
Synthesis: 4’-(Hydroxy-alkoxy)-biphenyl-4-carbonyl azide (Azide-3-8, n=3-8): The
hydroxy carboxylic acid (1 equiv) was dissolved in minimum amount of THF and cooled
to 0 C. To this was added triethyl amine (1 equiv) followed by chloroethyl formate (1
equiv) and the reaction mixture was stirred for 2 h at 0 C. Then was added saturated
solution of sodium azide in water (5 equiv) and continued stirring for further 1 h. The
reaction mixture was poured in water and the precipitated product was extracted with
dichloromethane. The organic layers were combined, washed with water, dried over
anhydrous sodium sulfate and concentrated at room temperature under reduced pressure
to get the hydroxy carbonyl azide as white solid (Yield: 76-89%). The carbonyl azides
were quite unstable in the solid state at room temperature.
However, they were
somewhat stable when dissolved in some common organic solvents like dichloromethane,
chloroform, ethyl acetate etc. Hence they were dissolved in dichloromethane and stored
in a refrigerator.
Azide-3: Yield: 89%; 1H NMR (CDCl3, , ppm): 2.08 (m, 2H), 3.89 (t, 2H, 1JHH = 5.50
Hz), 4.08 (t, 2H, 1JHH = 6.1 Hz), 6.99 (d, 2H, 1JHH = 8.54 Hz), 7.59 (dd, 4H, 1JHH = 8.54
and 8.54 Hz), 8.05 (d, 2H, 1JHH = 8.54 Hz). IR (CHCl3, cm-1): 3402, 3052, 2985, 2942,
2136, 1734, 1682, 1603, 1522, 1255, 1185, 744.
Azide-4: Yield: 83%; 1H NMR (CDCl3, , ppm): 1.8 (m, 2H), 1.94 (m, 2H), 3.75 (t, 2H,
1
JHH = 6.26 Hz), 4.07 (t, 2H, 1JHH = 6.26 Hz), 6.99 (d, 2H, 1JHH = 8.86 Hz), 7.6 (dd, 4H,
1
JHH = 8.86 and 8.55 Hz), 8.05 (d, 2H, 1JHH = 8.55 Hz). IR (CHCl3, cm-1): 3397, 3054,
2986, 2136, 1710, 1687, 1603, 1422, 1265, 1185, 895, 740.
Azide-5: Yield: 89%; 1H NMR (CDCl3, , ppm): 1.56 (m, 2H) 1.64 (m, 2H), 1.86 (m,
2H), 3.69 (t, 2H, 1JHH = 6.1 Hz), 4.02 (t, 2H, 1JHH = 6.71 Hz), 6.97 (d, 2H, 1JHH = 8.54
Hz), 7.6 (dd, 4H, 1JHH = 8.54 and 8.55 Hz), 8.05 (d, 2H, 1JHH = 8.55 Hz). IR (CHCl3, cm1
): 3410, 3054, 2985, 2942, 2136, 1727, 1686, 1603, 1524, 1265, 1185, 744.
Azide-6: Yield: 78%; 1H NMR (CDCl3, , ppm): 1.4-1.6 (m, 6H), 1.83 (m, 2H), 3.67 (t,
2H, 1JHH = 6.42 Hz), 4.0 (t, 2H, 1JHH = 6.23 Hz), 6.97 (d, 2H, 1JHH = 8.25 Hz), 7.6 (dd,
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4H, 1JHH = 8.55 and 7.94 Hz), 8.03 (d, 2H, 1JHH = 7.94 Hz). IR (CHCl3, cm-1): 3405,
3020, 2936, 2136, 1731, 1687, 1603, 1265, 747.
Azide-7: Yield: 89%; 1H NMR (CDCl3, , ppm): 1.4-1.6 (m, 8H), 1.80 (m, 2H), 3.66 (t,
2H, 1JHH = 6.71 Hz), 4.0 (t, 2H, 1JHH = 6.10 Hz), 6.98 (d, 2H, 1JHH = 8.54 Hz), 7.61 (dd,
4H, 1JHH = 8.54 and 8.54 Hz), 8.06 (d, 2H, 1JHH = 8.54 Hz). IR (CHCl3, cm-1): 3397,
3020, 2937, 2135, 1802, 1733, 1603, 1524, 1215, 769, 670.
Azide-8: Yield: 76%; 1H NMR (CDCl3, , ppm): 1.4-1.6 (m, 10H), 1.79 (m, 2H), 3.64 (t,
2H, 1JHH = 6.42 Hz), 3.99 (t, 2H, 1JHH = 6.11 Hz), 6.96 (d, 2H, 1JHH = 8.55 Hz)), 7.7 (dd,
4H, 1JHH = 8.25 and 7.94 Hz), 8.03 (d, 2H, 1JHH = 7.94 Hz). IR (CHCl3, cm-1): 3409,
3020, 2935, 2135, 1731, 1682, 1603, 1249, 1215, 1045, 761, 669.
Synthesis of Polyurethanes by Solution Polymerization: The -hydroxy carbonyl
azide monomers were dried thoroughly first under reduced pressure and then under dry
argon. To this was added minimum amount of anhydrous NMP and slowly heated at 110
C for 10 h. The reaction mixture was brought to room temperature and the NMP
solution was poured into excess of methanol (Some of the polymers were precipitated
from hot NMP solution). The precipitated solid was centrifuged, washed with methanol
and dried in the vacuum oven to get the polymer as brown solid. Yield: 54-75%
PU-3: Yield: 75%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.9 (m, 2H), 4.05 (t,
2H), 4.12 (t, 2H), 7.01 (d, 2H), 7.4 (m, 4H), 7.79 (d, 2H), 9.00 (s, 1H). IR (KBr, cm-1):
3323, 3039, 2951, 2925, 2861, 1703, 1663, 1598, 1537, 1499, 1469, 1423, 1399, 1327,
1230, 1176, 1114, 1061, 816, 766.
PU-4: Yield: 57%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.62 (m, 2H), 1.78 (m,
2H), 4.06 (t, 2H), 4.12 (t, 2H), 7.06 (d, 2H), 7.42 (m, 4H), 7.83 (d, 2H), 9.10 (s, 1H). IR
(KBr, cm-1): 3358, 3038, 2951, 2852, 1701, 1607, 1575, 1520, 1500, 1471, 1442, 1399,
1327, 1230, 1177, 1107, 1055, 968, 815, 770.
PU-5: Yield: 54%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.6 (m, 2H), 1.8 (m,
4H), 4.02 (t, 2H), 4.14 (t, 2H), 7.1 (d, 2H), 7.4 (m, 4H), 7.99 (d, 2H), 9.19 (s, 1H). IR
(KBr, cm-1): 3347, 3039, 2924, 2865, 1703, 1663, 1608, 1520, 1500, 1472, 1423, 1400,
1295, 1226, 1175, 1074, 1028, 816, 764.
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PU-6: Yield: 73%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.4 (m, 4H) 1.7-1.8 (m,
4H), 3.98 (t, 2H), 4.15 (t, 2H), 7.12 (d, 2H), 7.45 (m, 4H), 7.99 (d, 2H), 9.12 (s, 1H). IR
(KBr, cm-1): 3341, 3038, 2930, 2860, 1702, 1607, 1574, 1500, 1472, 1423, 1398, 1293,
1230, 1175, 1073, 1030, 817, 770.
PU-7: Yield: 55%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.4 (m, 6H) 1.7-1.8 (m,
4H), 3.99 (t, 2H), 4.11 (t, 2H), 7.1 (d, 2H), 7.5 (m, 4H), 7.97 (d, 2H), 9.14 (s, 1H). IR
(KBr, cm-1): 3313, 3038, 2925, 2854, 1697, 1603, 1522, 1500, 1470, 1423, 1398, 1239,
1176, 1111, 1075, 1030, 815, 769.
PU-8: Yield: 56%; 1H NMR at 80 C (TCE/DMSO-d6, , ppm): 1.4 (m, 4H), 1.6-1.8 (m,
8H), 3.98 (t, 2H), 4.15 (t, 2H), 7.2 (d, 2H), 7.70 (m, 4H), 7.96 (d, 2H), 9.28 (s, 1H). IR
(KBr, cm-1): 3350, 3040, 2930, 2851, 1708, 1677, 1596, 1524, 1501, 1472, 1294, 1237,
1175, 1082, 1039, 816, 759.
DSC traces of the polyurethanes (a) heating scan (b) cooling scan:
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