Synthesis of new photoresponsive polymers containing trifluoromethyl-substituted norbornadiene moieties

Article abstract of DOI:10.1021/ma0214207

Polymers containing trifluoromethyl (CF₃)-substituted donor-acceptor NBD moieties in the side chain or in the main chain were synthesized by substitution or addition of a CF₃-NBD-carboxylic acid derivative or by polycondensation of a

Full text of DOI:10.1021/ma0214207

1786
Macromolecules 2003, 36, 1786-1792
Synthesis of New Photoresponsive Polymers Containing
Trifluoromethyl-Substituted Norbornadiene Moieties
Ta k a bu m i Na ga i* a n d Miw a Sh im a d a
Daikin Environmental Laboratory, Ltd., 3 banchi, Miyukigaoka, Tsukuba, Ibaraki 305-0841, J apan
Yosh itom o On o a n d Ta d a tom i Nish ik u bo
Department of Applied Chemistry, Faculty of Engineering, Kanagawa University,
Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, J apan
Received September 3, 2002; Revised Manuscript Received J anuary 6, 2003
ABSTRACT: Polymers containing trifluoromethyl (CF3)-substituted donor-acceptor NBD moieties in the
side chain or in the main chain were synthesized by substitution or addition of a CF3-NBD-carboxylic
acid derivative or by polycondensation of a CF3-NBD-dicarboxylic acid derivative. The photoisomerization
of the NBD moieties in these polymers proceeded very smoothly to give the corresponding QC moieties.
Furthermore, the NBD moieties exhibited efficient fatigue resistance.
hafnium chloride-THF complex, 3-nitrobenzeneboronic acid,
tetrabutylammonium bromide (TBAB), and hexafluoro-2-bu-
tyne (HFB) were used without further purification.
In tr od u ction
Photochemical valence isomerization between nor-
bornadiene (NBD) and quadricyclane (QC) is of interest
as a solar energy conversion and storage system,1 since
photoenergy can be stored as strain energy (about 20
kcal/mol) in a QC molecule. Recently, this photochemical
reaction has also been investigated as an optical
waveguide utilizing photoinduced refractive index
changes2a-d or as a photochromic system potentially
applicable to data storage.2e
Taking these unique characteristics of NBD into
account, Nishikubo et al. have investigated the synthe-
sis and photochemical reaction of various photorespon-
sive polymers containing NBD moieties in the side
chain3-6 or in the main chain.7,8 However, the photore-
activity and fatigue resistance of these polymers were
insufficient for practical use as advanced materials. To
improve the photoreactivity of these polymers, they
recently synthesized polyesters containing donor-ac-
ceptor (D-A) NBD moieties and found these polyesters
had high photoreactivity and good durability for re-
peated cycles of interconversion.9 On the other hand,
Nagai et al. reported the synthesis of CF3-substituted
D-A-NBD derivatives. These compounds had large
absorption in a visible region and photoisomerized to
give the corresponding QC derivatives efficiently. Fur-
thermore, they exhibited efficient fatigue resistance.10
Therefore, we now report the synthesis of new photo-
responsive polymers containing CF3-substituted D-A-
NBD moieties, the photochemical reaction of the result-
ing polymers, and the durability of the NBD moieties
in the polymers.11
Ap p a r a tu s. Melting points were determined with a Yanaco
MP-500D hot-stage microscope and are not corrected. Infrared
spectra were obtained on a Perkin-Elmer 1600 FT-IR either
neat or in KBr pellets. Absorption was expressed as reciprocal
1
centimeters (cm-1). H NMR were recorded at 200 MHz on a
Varian Gemini-200 instrument and indicated in parts per
million (ppm) downfield from tetramethylsilane as the internal
standard (δ). 19F NMR spectra were measured at 188 MHz on
a Varian Gemini-200 instrument and indicated in parts per
million (ppm) upfield from CCl3F as the internal standard.
Low- and high-resolution mass spectral analyses were per-
formed under 70 eV electron-impact (EI) conditions on a Kratos
CONCEPT-1H double-focusing magnetic sector spectrometer.
Elemental analyses were made at Toray Research Center, Inc.,
Tokyo.
Ultraviolet (UV) spectra were recorded on a Hitachi model
U-3500 and model UV-2500PC. The molecular weights of the
polymers were estimated by gel permeation chromatography
(GPC) with the use of a Shimadzu model LC-10 equipped with
a refractive index detector using Shodex GPC KD 804 column
(eluent: DMF solution at flow rate of 1.0 mL/min, calibrated
using narrow molecular weight polystyrene as standards).
Syn th esis of 2-(Ben zofu r a n -2-yl)-7,7-d im eth yl-3-(5-ca r -
boxyth iop h en e-2-yl)-5,6-bis(tr iflu or om eth yl)-2,5-n or bor -
n a d ien e (NBD-Ca r boxylic Acid 1). 3-(Ben zofu r a n -2-yl)-
4,4-d im et h yl-1-(t h iop h en e-2-yl)-2-cyclop en t en ol (5). A
solution of 2-(benzofuran-2-yl)-4,4-dimethyl-2-cyclopentenone
(4, 13.26 g, 59 mmol) in THF (30 mL) was added dropwise at
-78 °C to a THF solution of lithium reagent obtained from
thiophene (5.7 mL) with n-BuLi (1.52 M, 46.7 mL). The
mixture was stirred for 30 min at this temperature, then
poured into ice-water, and extracted with ether. The ether
layer was washed with brine and dried over anhydrous MgSO4.
After evaporation of the solvent, the product was separated
by column chromatography (SiO2, hexane-EtOAc, 5:1) to give
5 (16.68 g, 91%) as a colorless viscous oil. 1H NMR (CDCl3): δ
1.22 (s, 3H), 1.32 (s, 3H), 2.33-2.49 (m, 2H), 2.73 (s, 1H), 6.37
(s, 1H), 6.52 (s, 1H), 6.90-6.92 (m, 2H), 7.09-7.28 (m, 3H),
7.36-7.45 (m, 2H). IR (KBr, cm-1): 3457, 2958, 1723, 1451,
1257, 751, 701. MS m/z 310 (M+). HRMS calcd for C19H18O2S
310.103; found 310.102.
Exp er im en ta l Section
Ma ter ia ls. Poly(glycidyl methacrylate) (PGMA),5a poly(2-
chloroethoxy vinyl ether) (PEVE),12 and 2-(benzofuran-2-yl)-
4,4-dimethyl-2-cyclopentenone10 were prepared according to
reported methods. 1,6-Hexanediol and trans-1,4-diaminocy-
clohexane were recrystallized from hexane. Poly(chlorometh-
ylstyrene) (3-/4- ) 3/2, Mw ) 55 000, PCMS), dimethylami-
nopropylethylcardodiimide hydrochloride (WSCD), (dimethyl-
amino)pyridine (DMAP), diphenylphosphoryl azide (DPPA),
2-(Ben zofu r a n -2-yl)-3-(th iop h en e-2-yl)-5,5-d im eth ylcy-
clop en ta d ien e (6). A solution of 2 (16.68 g, 53.7 mmol) and
p-TsOH‚H2O (0.93 g, 5.4 mmol) in toluene (400 mL) was
refluxed for 30 min. The mixture was poured into10% NaOH
solution and extracted with ether. The ether layer was washed
* To whom all correspondence should be addressed.
10.1021/ma0214207 CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/25/2003

Macromolecules, Vol. 36, No. 6, 2003
Photoresponsive Polymers 1787
with brine and dried over anhydrous MgSO4. After evaporation
of the solvent, the product was separated by column chroma-
tography (SiO2, hexane-EtOAc, 100:1) to give 6 (12.31 g, 78%)
as a slightly yellow viscous oil. 1H NMR (CDCl3): δ 1.34 (s,
6H), 6.38 (s, 1H), 6.41 (d, J ) 2.6 Hz, 1H), 6.83 (d, J ) 2.6 Hz,
1H), 6.99-7.07 (m, 2H), 7.12-7.30 (m, 3H), 7.42-7.49 (m, 2H).
IR (KBr, cm-1): 2961, 1450, 1256, 750, 699. MS m/z 292 (M+).
HRMS calcd for C19H16OS 292.092; found 292.092.
as a colorless viscous oil. 1H NMR (CDCl3): δ 1.13 (s, 3H), 1.21
(s, 3H), 2.31-2.57 (m, 4H), 3.02 (s, 1H), 6.93-7.00 (m, 2H),
7.27-7.34 (m, 1H). IR (KBr, cm-1): 3435, 2957, 1746, 1370,
1240, 1066, 996, 704. MS m/z 210 (M+). HRMS calcd for
C11H14O2S 210.071; found 210.071.
4,4-Dim eth yl-2-(th iop h en e-2-yl)-2-cyclop en ten e (10). A
solution of 9 (24.6 g, 117 mmol) and p-TsOH‚H2O (2.1 g, 12
mmol) in toluene (700 mL) was refluxed for 20 min. After
normal workup, the product was separated by column chro-
matography (SiO2, hexane-EtOAc, 10:1) to give 10 (20.15 g,
91%) as a colorless viscous oil. 1H NMR (CDCl3): δ 1.30 (s,
6H), 2.46 (s, 2H), 7.03-7.08 (m, 1H), 7.29-7.33 (m, 1H), 7.49
(s, 1H), 7.62-64 (m, 1H). IR (KBr, cm-1): 2959, 1694, 1409,
2-(Ben zofu r a n -2-yl)-3-(5-eth oxyca r bon ylth iop h en e-2-
yl)-5,5-d im eth ylcyclop en ta d ien e (7). Ethyl chloroformate
(4 mL, 42.1 mmol) was added dropwise at -78 °C to a THF
solution of lithium reagent obtained from 6 (12.31 g, 42.1
mmol) with n-BuLi (1.52 M, 36 mL, 54.7 mmol). The mixture
was stirred for 30 min at this temperature, then poured into
ice-water, and extracted with ether. The ether layer was
washed with brine and dried over anhydrous MgSO4. After
evaporation of the solvent, the product was separated by
column chromatography (SiO2, hexane-EtOAc, 20:1) to give
1249, 836, 731, 713. MS m/z 192 (M+). HRMS calcd for C11H12
-
OS 192.061; found 192.060.
4,4-Dim et h yl-1,2-b is(t h iop h en e-2-yl)-2-cyclop en t en ol
(11). A solution of 10 (20.15 g, 105 mmol) in THF (150 mL)
was added dropwise at -78 °C to a THF (200 mL) solution of
lithium reagent obtained from thiophene (12.6 mL, 157 mmol)
with n-BuLi (1.54 M, 102 mL, 157 mmol). The mixture was
stirred for 1.5 h at this temperature. After normal workup,
the product was separated by column chromatography (SiO2,
hexane-EtOAc, 10:1) to give 11 (25.18 g, 87%) as a colorless
viscous oil. 1H NMR (CDCl3): δ 1.19 (s, 3H), 1.28 (s, 3H), 2.40
(d, J ) 4.2 Hz, 2H), 2.54 (s, 1H), 6.13 (s, 1H), 6.84-6.94 (m,
4H), 7.10-7.16 (m, 1H), 7.19-7.25 (m, 1H). IR (KBr, cm-1):
3448, 2956, 1440, 1361, 1230, 1036, 832, 697. MS m/z 276 (M+).
HRMS calcd for C15H16OS2 276.064; found 276.063.
5,5-Dim e t h yl-2,3-b is(t h iop h e n e -2-yl)-cyclop e n t a d i-
en e (12). A solution of 11 (25.18 g, 91 mmol) and p-TsOH‚
H2O (1.6 g, 9.1 mmol) in toluene (600 mL) was refluxed for 20
min. After normal workup, the product was separated by
column chromatography (SiO2, hexane-EtOAc, 100:1) to give
12 (18.7 g, 79%) as a slightly yellow viscous oil. 1H NMR
(CDCl3): δ 1.30 (s, 6H), 6.40 (s, 2H), 6.78-6.81 (m, 2H), 6.92-
6.97 (m, 2H), 7.17-7.21 (m, 2H). IR (KBr, cm-1): 2961, 1462,
1430, 1233, 825, 695. MS m/z 258 (M+). HRMS calcd for
1
7 (12.78 g, 83%) as a yellow viscous oil. H NMR (CDCl3): δ
1.35 (s, 6H), 1.39 (t, J ) 7.1 Hz, 3H), 4.37 (q, J ) 7.1 Hz, 2H),
6.40 (s, 1H), 6.50 (d, J ) 2.7 Hz, 1H), 6.84 (d, J ) 2.7 Hz, 1H),
6.97 (d, J ) 3.8 Hz, 1H), 7.14-7.32 (m, 2H), 7.73 (d, J ) 3.8
Hz, 1H). IR (KBr, cm-1): 1702, 1450, 1288, 1256, 1098. MS
m/z 364 (M+). HRMS calcd for C22H20O3S 364.113; found
364.113.
2-(Ben zofu r a n -2-yl)-7,7-d im et h yl-3-(5-et h oxyca r b on -
ylth iop h en e-2-yl)-5,6-bis(tr iflu or om eth yl)-2,5-n or bor n a -
d ien e (8). 7 (12.78 g, 35 mmol) was placed in a stainless steel
tube with toluene (95 mL). To this tube, hexafluoro-2-butyne
(HFB, 5.67 g, 35 mmol) was introduced by a vacuum line. The
mixture was stirred at 80 °C for 15 h in the tube. After the
tube was cooled in an ice bath, it was opened and the mixture
was extracted with ether. After evaporation of the solvent, the
product was separated by column chromatography (SiO2,
hexane-EtOAc, 20:1) to give 8 (17.73 g, 96%) as yellow
needles; mp 99.2-99.7 °C. 1H NMR (CDCl3): δ 1.29 (s, 3H),
1.31 (s, 3H), 1.40 (t, J ) 7.1 Hz, 3H), 3.94 (m, 2H), 4.39 (q, J
) 7.1 Hz, 2H), 6.95 (bs, 1H), 7.20-7.40 (m, 2H), 7.46-7.64
(m, 3H), 7.79 (d, J ) 4.1 Hz, 2H). 19F NMR (CDCl3): δ -61.23
(q, 3F, J ) 6.7 Hz), -61.26 (q, 3F, J ) 6.7 Hz). IR (KBr, cm-1):
1703, 1452, 1299, 1272, 1179, 1145, 1102. Anal. Calcd for
C
15H14S2 258.054; found 258.053.
7,7-Dim eth yl-2,3-bis(th ioph en e-2-yl)-5,6-bis(tr iflu or om -
eth yl)-2,5-n or bor n a d ien e (13). 13 was synthesized in a
similar way from 12 (18.7 g, 72 mmol) with HFB (11.7 g, 72
mmol) in 99% yield (30.13 g) as yellow needles; mp 80.0-80.8
°C. 1H NMR (CDCl3): δ 1.27 (s, 3H), 1.35 (s, 3H), 3.75 (s, 2H),
7.02-7.33 (m, 6H). 19F NMR (CDCl3): δ -61.40 (s). IR
(KBr, cm-1): 1670, 1295, 1178, 1133, 700. Anal. Calcd for
C
26H20F6O3S: C, 59.31; H, 3.83. Found: C, 59.39; H, 3.82.
2-(B e n z o fu r a n -2-y l)-7,7-d i m e t h y l-3-(5-c a r b o x y -
t h iop h en e-2-yl)-5,6-b is(t r iflu or om et h yl)-2,5-n or b or n a -
d ien e (1). A 1 N NaOH solution (120 mL) was added to a THF
(120 mL) solution of 5 (17.4 g, 33 mmol) and stirred at 50 °C
for 48 h. After the mixture was acidified, it was extracted with
ether. The ether layer was washed with brine and dried over
anhydrous MgSO4. After evaporation of the solvent, the
product was recrystallized with EtOAc to give 1 (15.79 g, 96%)
as yellow needles; mp 162.4-163.0 °C. 1H NMR (CDCl3): δ
1.30 (s, 3H), 1.32 (s, 3H), 3.96 (s, 2H), 6.97 (s, 1H), 7.20-7.40
(m, 2H), 7.50-7.65 (m, 3H), 7.90 (d, J ) 4.1 Hz, 1H). 19F NMR
(CDCl3): δ -60.98 to -61.55 (m). IR (KBr, cm-1): 3379, 2989,
1679, 1395, 1348, 1294, 1213, 1156, 1134. Anal. Calcd for
C
19H14F6S2: C, 54.28; H, 3.36. Found: C, 54.42; H, 3.36.
7,7-Dim eth yl-2,3-bis(5-eth oxyca r bon ylth iop h en e-2-yl)-
5,6-bis(t r iflu or om et h yl)-2,5-n or b or n a d ien e (14). Ethyl
chloroformate (12.1 mL, 127 mmol) was added dropwise at -78
°C to a THF solution of lithium reagent obtained from 13
(25.39 g, 60 mmol) with n-BuLi (1.54 M, 86.3 mL, 133 mmol).
The mixture was stirred for 40 min at this temperature. After
normal workup, the product was separated by column chro-
matography (SiO2, hexane-EtOAc, 10:1) to give 14 (16.68 g,
49%) as yellow needles; mp 84.0-84.8 °C. 1H NMR (CDCl3):
δ 1.29 (s, 3H), 1.34 (s, 3H), 1.37 (t, J ) 7.1 Hz, 6H), 3.78 (s,
2H), 4.35 (q, J ) 7.1 Hz, 4H), 7.20 (d, J ) 4.0 Hz, 2H), 7.72 (d,
J ) 4.0 Hz, 2H). 19F NMR (CDCl3): δ-61.54 (s). IR (KBr, cm-1):
1708, 1454, 1297, 1252, 1172, 1135, 1096. Anal. Calcd for
C
24H16F6O3S: C, 57.83; H, 3.24. Found: C, 57.58; H, 3.30.
2-(Ben zofu r a n -2-yl)-7,7-d im et h yl-3-(t h iop h en e-2-yl)-
5,6-bis(tr iflu or om eth yl)-2,5-n or bor n a d ien e (16). 16 was
synthesized in a similar way from 6 with HFB in 91% yield
as yellow viscous. 1H NMR (CDCl3): δ 1.30 (s, 6H), 3.93 (s,
2H), 6.89 (s, 1H), 7.07-7.18 (m, 1H), 7.18-7.40 (m, 2H), 7.42-
7.62 (m, 4H). 19F NMR (CDCl3): δ -60.98 (q, 3F, J ) 8.9 Hz),
-61.34 (q, 3F, J ) 8.9 Hz). IR (KBr, cm-1): 1450, 1346, 1296,
1177, 1135. MS m/z 454 (M+). HRMS calcd for C23H16F6OS
454.083; found 454.082.
Syn th esis of 2,3-Bis(5-ca r boxyth iop h en e-2-yl)-7,7-d im -
eth yl-5,6-bis(tr iflu or om eth yl)-2,5-n or bor n a d ien e (NBD-
Ca r boxylic Acid 2). 4,4-Bim eth yl-1-(th iop h en e-2-yl)-2-
cyclop en ta n on e-1-ol (9). A solution of 3 (18.0 g, 143 mmol)
in THF (150 mL) was added dropwise at -78 °C to a THF
(350 mL) solution of lithium reagent obtained from thiophene
(25 mL, 314 mmol) with n-BuLi (1.54 M, 203 mL, 314 mmol).
The mixture was stirred for 1 h at this temperature. After
normal workup, the product was separated by column chro-
matography (SiO2, hexane-EtOAc, 5:1) to give 9 (24.6 g, 82%)
C
25H22F6O4S2: C, 53.19; H, 3.93. Found: C, 53.41; H, 4.02.
7,7-Bim eth yl-2,3-bis(5-ca r boxyth iop h en e-2-yl)-5,6-bis-
(tr iflu or om eth yl)-2,5-n or bor n a d ien e (2). A 1 N NaOH
solution (200 mL) was added to a THF (200 mL) solution of
14 (15.66 g, 27.7 mmol) and stirred at room temperature for
60 h. After normal workup, the product was recrystallized with
hexane-ether to give 2 (11.39 g, 80%) as yellow needles; mp
246 °C (decomposition). 1H NMR (CD3OD): δ 1.30 (s, 3H), 1.37
(s, 3H), 4.00 (s, 2H), 7.31 (d, J ) 3.9 Hz, 2H), 7.72 (d, J ) 3.9
Hz, 2H). 19F NMR (CD3OD): δ -60.78 (s). IR (KBr, cm-1):
2996, 1676, 1522, 1456, 1300, 1182, 1117. Anal. Calcd for
C
21H14F6O4S2: C, 49.61; H, 2.78. Found: C, 49.90; H, 3.06.
Bis(4-n itr op h en yl) Ester of 2 (15). A mixture of 2 (238.0
mg, 0.47 mmol), 4-nitrophenol (130.3 mg, 0.94 mmol), dim-
ethylaminopropylethylcardodiimide hydrochloride (WSCD, 180.0
mg, 0.94 mmol), and (dimethylamino)pyridine (DMAP, 12 mg)

1788 Nagai et al.
Macromolecules, Vol. 36, No. 6, 2003
in CH2Cl2 was stirred for 15 h at room temperature. After
evaporation of the solvent, the product was separated by
column chromatography (SiO2, hexane-EtOAc, 3:1) to give 15
(220 mg, 60%) as yellow needles; mp 205.1-206.0 °C. 1H NMR
(CDCl3): δ 1.34 (s, 3H), 1.40 (s, 3H), 3.86 (s, 2H), 7.33 (d, J )
4.0 Hz, 2H), 7.42 (d, J ) 9.2 Hz, 4H), 7.96 (d, J ) 4.0 Hz, 2H),
8.33 (d, J ) 9.2 Hz, 4H). 19F NMR (CDCl3): δ -61.54 (s). IR
(KBr, cm-1): 1732, 1529, 1350, 1298, 1232, 1205, 1064. Anal.
Calcd for C33H20F6N2O8S2: C, 52.80; H, 2.69; N, 3.37. Found:
C, 52.90; H, 2.84; N, 3.61.
Syn th esis of NBD P olym er s. Syn th esis of P -1. A mix-
ture of PCMS (305 mg, 2.0 mmol), potassium salt of 1 (1.072
g, 2.0 mmol), and TBAB (64.5 mg, 0.2 mmol) in DMF (14 mL)
was stirred at 60 °C for 72 h, and then the reaction mixture
was poured into water. The polymer obtained was reprecipi-
tated from CHCl3 into methanol and dried in vacuo at 70 °C.
The yield of polymer was 80%. The DF was 100 mol %,
estimated by the 1H NMR spectrum. 1H NMR (CDCl3): δ 0.98-
1.80 (m, 9H), 3.73-3.90 (m, 2H), 4.80-5.30 (m, 2H), 6.10-
6.62 (m, 2H), 6.70-7.25 (m, 5H), 7.25-7.57 (m, 3H), 7.57-
7.80 (m, 1H). IR (KBr, cm-1): 1713, 1453, 1296, 1268, 1179,
1136.
Syn th esis of P -2. A mixture of PCVE (91 mg, 0.85 mmol),
1 (426 mg, 0.85 mmol), K2CO3 (373 mg, 2.7 mmol), and TBAB
(276 mg, 0.85 mmol) was stirred in DMF (9 mL) at 80 °C for
72 h, and then the reaction mixture was poured into water.
The polymer obtained was reprecipitated from THF into
methanol and dried in vacuo at 70 °C. The yield of polymer
was 401 mg (82%). The DF was 91 mol %, estimated by the
1H NMR spectrum. 1H NMR (CDCl3): δ 0.95-2.05 (m, 9H),
3.40-3.95 (m, 4H), 4.20-4.55 (m, 2H), 6.77-6.98 (m, 1H),
6.98-7.33 (m, 2H), 7.33-7.63 (m, 3H), 7.63-7.70 (m, 1H). IR
(KBr, cm-1): 1712, 1453, 1296, 1268, 1178, 1136.
F igu r e 1. Apparatus for the examination of durability of NBD
polymer. The spectrophotometer, heater, and shutter were
controlled automatically by personal computer.
Syn th esis of P -5 fr om P olycon d en sa tion of 2 w ith 1,6-
Hexa n ed iol Usin g HfCl4(THF )2. In the presence of HfCl4-
(THF)2 (11 mg, 0.005 mmol), a mixed solution of 2 (45.2 mg,
0.09 mmol) and 1,6-hexanediol (10.5 mg, 0.09 mmol) in
o-xylene (1 mL) was refluxed for 48 h with removal of water
(4 Å molecular sieves). The reaction mixture was poured into
water, reprecipitated from THF into methanol, and dried in
vacuo at 70 °C. The yield of polymer was 42.8 mg (82%). The
number-average molecular weight of the polymer determined
1
from GPC was 39 300. H NMR (CDCl3): δ 1.28 (s, 3H), 1.34
(s, 3H), 1.30-1.65 (m, 4H), 1.65-1.92 (m, 4H), 3.78 (s, 2H),
4.17-4.42 (m, 4H), 7.15-7.25 (m, 2H), 7.65-7.75 (m, 2H). IR
(KBr, cm-1): 1718, 1458, 1297, 1244, 1178, 1137.
Syn th esis of P -5 fr om P olycon d en sa tion of 2 w ith 1,6-
Hexa n ed iol Usin g WSCD a s Con d en sa tion Rea gen t. A
mixed solution of 2 (31.0 mg, 0.06 mmol), 1,6-hexanediol (7.2
mg, 0.06 mmol), DMAP (1.8 mg, 0.015 mmol), and WSCD (28.1
mg, 0.15 mmol) in CH2Cl2 (1 mL) was stirred for 48 h at room
temperature. The reaction mixture was poured into deuterated
HCl. Then the polymer was washed with water, reprecipitated
from THF into methanol, and dried in vacuo at 70 °C. The
yield of polymer was 31.7 mg (88%). The number-average
molecular weight of the polymer determined from GPC was
18 300.
Typ ica l P r oced u r e for th e P h otoisom er iza tion of NBD
Moieties in th e P olym er s in Solu tion . A quartz cell was
charged with a solution of a NBD polymer in THF (5 × 10-5
mol/L), and then the solution was irradiated with a 500 W
xenon lamp (Ushio Electric Co., UXL-500D-O) with a thermal-
ray cut filter (Hoya; HA50), in which the energy of the incident
light (1.8-2.0 mW/cm2 (313 nm)) was monitored by an electric
photon counter (ORC model UV-M30). The conversion and the
photoisomerization rates from NBD moieties to QC moieties
were calculated by the disappearance of the maximum absorp-
tion of the NBD moieties, as measured by a UV spectropho-
tometer.
Exa m in a tion of th e Du r a bility of th e NBD Moieties
in th e P olym er . P r ep a r a tion of P olym er F ilm . A solution
of polymer (7.4 mg) in chloroform (1 mL) was degassed by three
consecutive freeze-pump-thaw cycles and cast on a quartz
plate. Then, the quartz plate-cast polymer was dried in vacuo
at 80 °C for 15 h. Furthermore, a solution of PMMA in
chloroform was cast on the film and dried in the same way as
above.
Exa m in a tion of th e Du r a bility. The experiment was
performed under an argon atmosphere by the apparatus
automatically, as shown in Figure 1. Initially, the polymer film
was irradiated with a 500 W xenon lamp until the absorbance
of the maximum absorption of the NBD moieties disappeared.
Then, the irradiated film was heated on a hot plate until the
absorbance of the NBD moieties was reversed (irradiated for
2 min and then heated at 80 °C for 20 min). The durability
was evaluated from the differences in the absorbance values
between the NBD moieties and the QC moieties at maximum
absorption of the NBD moieties on the first and nth cycles of
reactions.
Syn th esis of P -3. A mixture of PGMA (28 mg, 0.2 mmol),
1 (100 mg, 0.2 mmol), and TBAB (6.4 mg, 0.02 mmol) were
stirred in a mixture of DMF (1 mL) and 2-propanol (0.05 mL)
at 80 °C for 72 h, and then the reaction mixture was poured
into water. The polymer obtained was reprecipitated from THF
into n-hexane and dried in vacuo at 70 °C. The yield of polymer
1
was 82%. The DF was 100 mol %, estimated by the H NMR
spectrum. 1H NMR (CDCl3): δ 0.70-2.20 (m, 11H), 3.00-3.30
(m, 1H), 3.50-4.80 (m, 7H), 6.73-6.95 (m, 1H), 6.97-7.35 (m,
2H), 7.35-7.63 (m, 3H), 7.65-7.85 (m, 1H). IR (KBr, cm-1):
3436, 1715, 1453, 1296, 1263, 1179, 1136.
Syn th esis of P -4 fr om P olycon d en sa tion of 15 w ith 1,4-
Dia m in ocycloh exa n e. A mixture of 15 (32 mg, 0.04 mmol)
and 1,4-diaminocyclohexane (4.7 mg, 0.04 mmol) was stirred
in DMF (1.5 mL) at room temperature for 110 h, and then the
reaction mixture was poured into water. The polymer obtained
was reprecipitated from THF into H2O and dried in vacuo at
70 °C. The yield of polymer was 19.6 mg (81%). The number-
average molecular weight of polymer determined from GPC
was 17 800. 1H NMR (DMF-d6): δ 1.30 (s, 3H), 1.38 (s, 3H),
1.35-1.68 (m, 4H), 1.86-2.14 (m, 4H), 3.55-4.00 (m, 2H), 4.15
(s, 2H), 7.32-7.48 (m, 2H), 7.82-7.96 (m, 2H), 8.40-8.60 (m,
2H). IR (KBr, cm-1): 3307, 1630, 1540, 1455, 1296, 1178, 1138.
Syn th esis of P -4 fr om P olycon d en sa tion of 2 w ith 1,4-
Dia m in ocycloh exa n e u sin g DP P A a s Con d en sa tion Re-
a gen t. A mixture of 2 (44.8 mg, 0.09 mmol), 1,4-diaminocy-
clohexane (10.1 mg, 0.09 mmol), DPPA (48.3 mg, 0.18 mmol),
and triethylamine (35.6 mg, 0.35 mmol) was stirred in DMF
(1 mL) at room temperature for 48 h, and then the reaction
mixture was poured into water. The polymer obtained was
reprecipitated from DMF into H2O and dried in vacuo at 70
°C. The yield of polymer was 45.8 mg (88%). The number-
average molecular weight of polymer determined from GPC
was 42 700.
Syn th esis of P -4 fr om P olycon d en sa tion of 2 w ith 1,4-
Diam in ocycloh exan e Usin g 3-Nitr oben zen ebor on ic Acid.
In the presence of 3-nitrobenzeneboronic acid (1.5 mg, 0.009
mmol), a mixed solution of 2 (46.4 mg, 0.09 mmol) and 1,6-
hexanediol (10.4 mg, 0.09 mmol) in o-xylene (3 mL) was
refluxed for 48 h with removal of water (4 Å molecular sieves).
The reaction products were not soluble in DMF.

Macromolecules, Vol. 36, No. 6, 2003
Photoresponsive Polymers 1789
Sch em e 1. Syn th esis of NBD Der iva tives 1, 2, a n d 15
Sch em e 2
Resu lts a n d Discu ssion
substitutions into the 2,3-positions, the charge transfer
(C-T) donor site, of the NBD framework. NBD-car-
boxylic acid 1 was synthesized from the Diels-Alder
reaction of hexafluoro-2-butyne with cyclopentadiene
derivative 7 containing an ethoxycarbonyl group at the
5-position of the thiophene ring, followed by hydrolysis
using aqueous sodium hydroxide. The ethoxycarbonyl
group was introduced to the thiophene ring of 6 by the
Syn th esis of P olym er s Con ta in in g Tr iflu or om -
eth yl-Su bstitu ted Don or -Accep tor NBD Moieties.
NBD-carboxylic acid 1, NBD-dicarboxylic acid 2, and
bis(4-nitrophenyl) esters of 2 (15) were synthesized from
cyclopentanedione derivative 3 according to the reaction
sequences shown in Scheme 1. This NBD synthesis
strategy involves the facile introduction of a variety of

1790 Nagai et al.
Macromolecules, Vol. 36, No. 6, 2003
Sch em e 3
were added to the pendant group in the polymers. The
1H NMR spectrum of P -1 showed a signal of the CH2
protons of the benzyl ester at 4.75-5.40 ppm, although
no signal of the CH2 protons of the benzyl chloride at
1
4.10-4.55 ppm was detected. The H NMR spectrum of
P -2 showed a signal of the aromatic protons of the
thiophene ring at 7.43 and 7.66 ppm, although traces
of the signal of the aromatic protons of the thiophene
ring of 1 were found at 7.57 and 7.82 ppm. No traces of
signals of the CH2 protons of the glycidyl group at 2.65
1
and 2.85 ppm were detected in the H NMR spectrum
Ta ble 1. Syn th esis of P olya m id e Con ta in in g CF 3-NBD
of P -3. Furthermore, the CH protons (5.00-5.50 ppm)
from R cleavage of the epoxy ring were not detected. It
seems that â cleavage of the epoxy ring proceeded
selectively under the reaction conditions. These results
show that CF3-NBD moieties could be readily intro-
duced in the side chain of many polymers.
Moieties
b
b
reagents and conditions
yield (%) Mn × 10-4 Mw/Mn
15, DMF, rt, 4 days
81
88
gel
1.78
4.27
1.96
5.77
2, DPPA,a Et3N, DMF, rt, 2 days
2, 3-NO2C6H4B(OH)2 (0.1 equiv),
o-xylene, reflux, 2 days
Next, we synthesized polymers containing CF3-NBD
moieties in the main chain as shown in Schemes 3 and
4 and in Tables 1 and 2. Polyamide P -4 was synthesized
by polycondensation of the bis(4-nitrophenyl) ester 15,
obtained from NBD-dicarboxlic acid 2, with trans-1,4-
diaminocyclohexane as diamine.8,13 The yield and the
Mn of P -4 were 82% and 17 800, respectively. This
polyamide was also synthesized from 2 with diamine
using DPPA as condensation reagent; the yield and the
Mn were 88% and 42 900, respectively. On the other
hand, gel products were produced when polycondensa-
tion was carried out using 3-nitrobenzeneboronic acid
as the Lewis acid catalyst. These results suggest that
the procedure using a condensation reagent was suitable
for the synthesis of P -4. The polycondensation of 2 with
1,6-hexanediol as diol was carried out using hafnium
chloride as the Lewis acid catalyst14 to give polyester
P -5 with a small amount of gel products. The yield and
the Mn of P -5 were 82% and 39 300, respectively. This
polyester was also synthesized from 2 with diol using
WSCD as condensation reagent; the yield and the Mn
were 88% and 18 300, respectively.
a
b
Diphenylphosphoryl azide. Estimated by GPC based on
polystyrene standards (eluent: DMF).
Sch em e 4
Ta ble 2. Syn th esis of P olyester Con ta in in g CF 3-NBD
Moieties
reagents and
conditions
c
c
yield (%)
82
Mn × 10-4 Mw/Mn
2, HfCl4‚THF2 (0.2 equiv),
o-xylene, reflux, 2 days
3.93
2.33
2, WSCD,a DMAP,b CH2Cl2, 88
1.83
2.32
rt, 2 days
15, DMF, rt, 7 days
no reaction
a
Dimethylaminopropylethylcarbodiimide hydrochloride. b (Dim-
ethylamino)pyridine. c Estimated by GPC based on polystyrene
standards (eluent: DMF).
On the other hand, polycondensation of 15 with diol
did not proceed, although polycondensation of 15 with
diamine proceeded smoothly, because the nucleophilicity
of diamine to 15 was higher than that of diol. These
results suggest that the procedure using a Lewis acid
catalyst was suitable for the synthesis of P -5. IR and
NMR spectra confirmed the structure of the new poly-
mers.
reaction of ethyl chloroformate with a lithium reagent
prepared from 6. NBD-dicarboxylic acid 2 was synthe-
sized from NBD derivative 13 containing two thienyl
groups at the 2,3-positions of the NBD framework by
the introduction of a carboxyl group in the same way
as 1. Bis(4-nitrophenyl) ester 15 was obtained from 2
by esterification with 4-nitrophenol using carbodiimide
derivatives as condensation reagent. The structure of
the resulting NBD derivatives was confirmed by el-
emental analysis, MS, IR, and NMR spectra.
Polymers containing CF3-NBD moieties in the side
chain were synthesized according to Scheme 2. The
substitution reaction of potassium salt of 1 with PCMS3
proceeded using TBAB as PTC catalyst in DMF at 80
°C for 48 h to give P -1 in 80% yield. The substitution
reaction of potassium salt of 1 with poly(2-chloroethyl
vinyl ether)4 also proceeded using TBAB in DMF at 90
°C for 72 h to give P -2 in 83% yield. The addition
reaction of 1 with poly(glycidyl methacrylate)5 proceeded
using TBAB in DMF-2-propanol (20:1) at 80 °C for 48
h to give P -3 in 82% yields. The polymers obtained by
the above reaction conditions did not contain any gel
P h otoisom er iza tion of NBD P olym er s. As shown
in Table 3 and Figure 2, these polymers had a large
absorption band in the visible region and the absorption
edge reached 500 nm, because they had a charge-
transfer absorption band ascribed to charge-transfer
interaction between the donor olefin and acceptor olefin
parts of the molecule. As shown in Table 3, the CF3-
NBD moieties in the polymer had a longer wavelength
absorption band than the parent CF3-NBD derivatives,
16 and 13, which had no carbonyl group in the aryl
group. This means that carbonyl seems to act mainly
by extending the conjugation of the aryl group and that
its electron-withdrawing effect does not compensate for
its conjugative effect.
The photoisomerization of the NBD moieties in the
polymer in THF solution (5 × 10-5 mol/L) was carried
out by irradiation with a 500 W xenon lamp. Changes
in the UV spectra of P -1 and P -5 in THF solution are
shown in Figure 2. The maximum absorption of the
NBD moieties decreased very rapidly, and the NBD
1
products. It was estimated from the H NMR spectral
data of the reaction mixture of P -1, P -2, and P -3 that
100, 93, and 100% NBD carboxylic acid, respectively,

Macromolecules, Vol. 36, No. 6, 2003
Photoresponsive Polymers 1791
F igu r e 2. Change of UV spectra of NBD polymers in the THF solution upon irradiation with a Xe lamp (1.80-2.00 mW/cm2 at
310 nm): (a) P -1; (b) P -5.
F igu r e 3. Photoisomerization of NBD moieties of NBD polymers in THF solution upon irradiation with a xenon lamp (1.80-
2.00 mW/cm2 at 310 nm): (a) P -1; (b) P -5.
Ta ble 3. Absor p tion Sp ectr a l Da ta of P olym er s
Ta ble 4. F ir st-Or d er Ra te Con sta n ts of
P h otoisom er iza tion of NBD P olym er sa
Con ta in in g CF 3-NBD Moieties in THF
compound
λmax (nm)a
λedge (nm)a,b
λ
iso (nm)a
kobsd (s-1) in
kobsd (s-1) in
polymer
THF solutionb
polymer
THF solutionb
16
273, 389
282, 407
282, 407
282, 407
364
480
505
505
505
470
503
505
P -1
P -2
P -3
13
P -4
P -5
271
271
271
P -1
P -2
P -3
0.65
0.63
0.83
P -4
P -5
c
0.64
Irradiated by 500 W Xe lamp. 5 × 10-5 mol/L. c P -4 solved
a
b
288, 379
285, 385
288
285
in THF not completely.
a
b
5 × 10-5 mol dm-3 solution in THF. ꢀ ) 10.
the NBD moieties to take suitable conformations for
photoisomerization. Furthermore, the photoisomeriza-
tion rate of the NBD moieties in P -5 was almost the
same as that of the NBD moieties in P -1 and P -2,
although P -5 contained the NBD moieties in the main
chain and the structure of the NBD moieties was not
the same as that of P -1 and P -2. It seems that the
photoisomerization rate of the NBD moieties in these
polymers (P -1, P -2, and P -5) was the same irrespective
of the structure of NBD molecules in this irradiation
condition, since these two NBD moieties have a large
absorption band in the visible region and the wave-
length of the absorption edge of these NBD moieties was
almost the same, although the reactivity of the photoi-
somerization of these NBD moieties was affected by the
structure of NBD moieties.
Exa m in a tion of th e Du r a bility of th e NBD Moi-
eties in th e P olym er . We also examined the durability
of the CF3-NBD moieties in the polymer for repeated
cycles of interconversion. Recently, Nagai et al. reported
that CF3-NBD derivatives had efficient fatigue resis-
tance.10 As shown in Figure 4, the CF3-NBD moieties
in P -3 possessed good fatigue resistance, and the
degradation of the NBD moieties was 55% after 1000
cycles. It is apparent that the NBD polymers containing
CF3-D-A NBD moieties are more durable than other
NBD polymers as the introduction of the CF3 groups
moieties isomerized quantitatively to the corresponding
QC moieties after 6 and 8 s of irradiation, respectively.
In addition, isosbestic points at 235 and 272 nm in P -1
or 241 and 288 nm in P -5 were observed. These results
mean that the photoisomerization of the NBD moieties
in these polymers to the QC moieties occurred selec-
tively without any side reactions.
As shown in Figure 3, the NBD moieties in these
polymers in THF solution isomerized very fast, and the
observed rate of the photoisomerization of the NBD
moieties obeyed first-order kinetics. As shown in Table
4, the photoisomerization rate of P -3 was slightly higher
than that of P -1 and P -2. These results suggest that
the photoisomerization rate of the NBD moieties was
affected by the structure of the main chain of the
polymers. It has been reported that the photoisomer-
ization rate of NBD derivatives was affected by the
polarity of the solvent and was higher in a more polar
solvent.15 Furthermore, it has also been reported that
the photoisomerization rate of the NBD moieties in a
polymer was affected by the structure of the polymer
chain.4c Photoisomerization of the NBD moieties in P -3
proceeded more effectively, because P -3 contains a hy-
droxy group which gives the NBD moieties a polar
environment and, further, has flexibility which allowed

1792 Nagai et al.
Macromolecules, Vol. 36, No. 6, 2003
Education, Science, Sports and Culture, which is grate-
fully acknowledged.
Refer en ces a n d Notes
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F igu r e 4. Durability of P -3.
and the donor substituents into the NBD framework
suppresses the formation of byproducts caused by the
polymerization of the NBD and QC moieties, since the
large steric effect of the CF3 groups and the donor
substituents shield the CdC bond of NBD moieties and
the strained QC moieties which contained the cyclopro-
pane and cyclobutane rings. It has been reported that
the CF3 group was rigid and spherical and showed as
large a steric effect as that of the sec-butyl group.16
Furthermore, the physical and chemical stability of the
CF3 groups possibly gives the NBD and QC moieties
durability. It is known that fluorine imparts to mol-
ecules increased oxidative and thermal stability because
the C-F bond is stronger than the C-H, C-C, or C-N
bond.
(6) Iizawa, T.; Sueyoshi, T.; Hijikata, C.; Nishikubo, T. J . Polym.
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However, these data show that the durability of the
CF3-NBD moieties in the polymer was slightly lower
than that of the CF3-NBD derivatives that were ex-
amined in PMMA solid film doped with NBD (5 wt %).10
It was reported that the durability of fulgide derivatives
decreased in PMMA solid film, which was highly doped
with fulgide derivatives in comparison with that in a
dilute solution.17 It seems that a side reaction that
produced polymerization of the NBD and QC molecules
occurred readily in polymer film highly doped with
NBD. Therefore, the monomer might show better du-
rability than the CF3-NBD moieties in the polymer that
contained NBD moieties in high concentration.
Con clu sion
(11) The preparation of the polymers containing CF3-substituted
D-A-NBD moieties was reported as
a communication.
From all these results, the following conclusions can
be drawn. (1) Polymers containing CF3-NBD moieties
in the side chain or in the main chain were synthesized
by substitution or addition of CF3-NBD-carboxylic acid
derivative or by polycondensation of CF3-NBD-dicar-
boxylic acid derivative, respectively. (2) These polymers
had a large absorption band in the visible region, and
NBD moieties in these polymers isomerized very fast.
(3) The CF3-NBD moieties in these polymers showed
efficient resistivity to repeated cycles of interconversion.
Nagai, T.; Shimada, M.; Nishikubo, T. Chem. Lett. 2001, 1308.
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Ack n ow led gm en t. This work was partly supported
by High-Tech Research Project from the Ministry of
MA0214207