Synthesis and structure-property comparisons of hydrogenated poly(oxanorbornene-imide)s and poly(norbornene-imide)s prepared by ring-opening metathesis polymerization

Article abstract of DOI:10.1002/pola.26171

Various structures of poly(norbornene-imide)s and poly(oxanorbornene-imide) s were synthesized and an optimal hydrogenation method was established. The thermal, thermomechanical, mechanical, and optical properties of thus prepared polymers were investigated, together with the structural characteristics shown by wide-angle X-ray scattering patterns. Poly(oxanorbornene-imide)s exhibit local nanostructure caused by intermolecular interactions between the imide and backbone oxygen moiety, which appears to prevent a significant decrease in T_g when compared with poly(norbornene-imide)s. Overall, hydrogenated poly(oxanorbornene-imide)s, obtained with more readily prepared exo-monomer, exhibit similar physical properties when compared with the corresponding hydrogenated poly(norbornene-imide)s. Copyright

Full text of DOI:10.1002/pola.26171

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Synthesis and Structure–Property Comparisons of Hydrogenated
Poly(oxanorbornene-imide)s and Poly(norbornene-imide)s Prepared by
Ring-Opening Metathesis Polymerization
Kyung-Hwan Yoon,1 Kyung Oh Kim,1 Chengqing Wang,2 Insook Park,3 Do Y. Yoon1
1Department of Chemistry, Seoul National University, Seoul 151-747, Korea
2Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
3Analysis and Evaluation Research Institute, Kolon Central Research Park, Yongin 446-797, Korea
Correspondence to: D. Y. Yoon (E-mail: dyyoon@snu.ac.kr)
Received 28 September 2011; accepted 10 May 2012; published online
DOI: 10.1002/pola.26171
KEYWORDS: high performance polymers; poly(norbornene imide); poly(oxanorbornene imide); ROMP; structure-property relations
INTRODUCTION Recently,
5-norbornene-2,3-dicarboximide
dride (ONDA) at very high yield, thereby eliminating the
need for thermal rearrangement of NDA.8 Moreover, the
ether moiety in the polymer backbone increases the polar,
hydrophilic character, rendering poly(7-oxa-5-norbornene-
exo,exo-2,3-dicarboximide)s (poly(ONDI)s) to exhibit some
attractive properties when compared with normal poly(NDI)s.
For example, Hillmyer et al. succeeded in preparing hydrogen-
ated poly(N-methyl-ONDI) in an aqueous solution, which
showed the glass transition temperature (Tg) as high as
170 C. And Grubbs et al. showed the possibility of applying
the poly(ONDI) films as ion permeable membranes due to
enhanced polarity.10(a) Such promising results were then fol-
lowed by further advances in poly(oxanorbornene)s including
block copolymerization, development of improved catalysts,
and water soluble polymers.10(b–j)
(NDI) monomers, synthesized from Diels–Alder reaction
between cyclopentadiene and maleic anhydride followed by
imidization with a primary amine, attracted significant inter-
est due to attractive thermomechanical properties of the
resulting polymers.1 Polynorbornenes synthesized by ring-
opening metathesis polymerization (ROMP) are known to
become more stable both chemically and thermally2(a–c) and
more optically transparent2(d) after hydrogenation of the
backbone double bonds. Hydrogenation is achievable either
by tosylhydrazine (TSH) degradation method or metal-based
catalyst method (Pd, Ru, Ir, or Os).3 The commercially avail-
able cycloolefin polymers are manufactured by ROMP and
subsequent hydrogenation based on high-pressure ruthe-
nium hydrogenation method.4 In general, hydrogenated poly
(NDI)s exhibit high thermal stability and high glass transition
temperature,1(a–f) together with excellent optical transpar-
ency and low birefringence in visible wavelength range due
to the incorporation of rigid imide moiety as side groups,1(g–
9
ꢀ
Despite such advances, there has been limited information on
the structures and properties of ‘‘hydrogenated’’ poly(ONDI)s as
compared with the corresponding hydrogenated poly(NDI)s.
Hillmyer et al. succeeded in hydrogenation of poly(N-methyl-
ONDI) with Crabtree’s catalyst ([Ir(COD)(PCy3)(py)]þPF6ꢁ), and
reported that the glass transition temperature was lowered by
h)
making them attractive candidates for potential applica-
tions as flexible substrates, bioactive materials, and gas sepa-
ration membranes.5
9
ꢀ
about 55 C after hydrogenation. However, they did not com-
pare the structures and properties of the poly(ONDI) samples
with those of poly(NDI) counterparts. Kang et al. prepared a se-
ries of polymer samples based on endo-5,6-bis(methoxymethyl)-
norbornene and exo-5,6-bis(methoxymethyl)-oxanorborne-
ne.11(a) Although they observed that polynorbornene derivatives
showed higher Tg values, by 25–40 ꢀC, than polyoxanorbornene
derivatives, the effect of exo- versus endo- stereoisomers was not
delineated. Cetinkaya et al. prepared a couple of poly(ONDI)s as
well as the corresponding poly(NDI)s, and reported that the Tg
values of poly(ONDI)s were 1–14 ꢀC lower than the correspond-
ing poly(NDI)s;11(b) however, they did not hydrogenate the
One disadvantage of using NDI monomers, however, is that
the starting Diels–Alder reaction product (Scheme 1) is pre-
dominantly 5-norbornene-endo,endo-2,3-dicarboxylic anhy-
dride (NDA) and the resultant endo-stereoisomer of NDI
exhibits considerably lower reactivity toward ROMP catalysts
than the exo-stereoisomer.6 Therefore, an additional step of
thermal rearrangement of NDA, before polymerization, has to
be carried out.7 In this regard, some research groups have
used furan instead of cyclopentadiene for the diene, because
the Diels–Alder reaction of furan and maleic anhydride
results in 7-oxa-5-norbornene-exo,exo-2,3-dicarboxylic anhy-
C
V
2012 Wiley Periodicals, Inc.
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RESULTS AND DISCUSSION
Monomers and polymers were successfully synthesized
according to the previously reported methods with minor
modifications. Molecular weights of resulting polymers were
determined with gel permeation chromatography (GPC)
against the polystyrene standards, and the results are
summarized in Table 1.
Various methods were investigated for hydrogenation of
polymers 1 and 6 (Scheme 1) as the representative case of
poly(NDI) and poly(ONDI), respectively. For the metal cata-
lyst-based hydrogenation method, we adopted the method
by Yoshida et al.2(a),3(c) The degree of hydrogenation was cal-
1
culated based on H NMR results (Fig. 1). Perfect hydrogena-
tion (over 99.9%) was achieved in toluene, xylene, chloro-
benzene, and tetrahydrofuran (THF) (Fig. 1). However, such
SCHEME 1 Synthesis of the hydrogenated poly(NDI)s and poly
(ONDI)s and designation of the synthesized polymer samples (1–6).
polymers. In a previous study of comparing polyoxanorbornene
derivatives with polynorbornene derivatives, Morita and his co-
workers hydrogenated a poly(oxanorbornene diester) with Ru/
C catalyst and compared the molecular weights, Tg, and refrac-
tive index with those of the corresponding poly(norbornene die-
ster).11(c) According to their results, the Tg value of poly(oxanor-
bornene diester) was lower by about 55 ꢀC than the
corresponding poly(norbornene diester).
Therefore, the polyoxanorbornene derivatives are generally
known to exhibit lower Tg values as compared with the poly-
norbornene counterparts, but there has been no detailed
comparison of structures and important properties such as
thermal, mechanical, and optical properties. In the present
study, we investigated an optimal hydrogenation method for
poly(ONDI)s and then compared the X-ray scattering pat-
terns, thermal, thermomechanical, and optical properties,
before and after hydrogenation, with those of the corre-
sponding poly(NDI)s.
TABLE 1 Molecular Weights of the Polymers before and after
Hydrogenationa
Before
Hydrogenation
After Hydrogenation
PDI Methodb
Polymer Mn
Mw
PDI Mn
Mw
1
512,000 644,000 1.26 563,000 742,000 1.32 [Ru]
2
3
4
5
6
a
426,000 479,000 1.12 318,000 372,000 1.17 TSH
389,000 488,000 1.25 486,000 607,000 1.25 TSH
375,000 459,000 1.22 174,000 264,000 1.52 [Ru]
345,000 492,000 1.42 109,000 200,000 1.83 [Ru]
95,000 176,000 1.86 84,000 135,000 1.61 TSH
Molecular weights were measured with GPC, equipped with Waters
2410 RI detector, against the polystyrene standards.
b
Hydrogenation methods are given in the last column. [Ru] stands for
FIGURE 1 1H NMR results of polymer 1 before (a) and after hy-
ruthenium catalyst hydrogenation in toluene or xylene, and TSH stands
for TSH decomposition method in DMF.
drogenation (b).
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TABLE 2 Degree of Hydrogenation and Changes in Molecular Weights of 6 upon
Hydrogenation in DMF
Degree of
Hydrogenation
Methods
(%)a
Mn
Mw
PDI
Before hydrogenation
–
95,000 176,000 1.86
49,000 69,000 1.42
24,000 38,000 1.59
32,000 48,000 1.49
84,000 135,000 1.61
81,000 125,000 1.55
Hydrogenation by metal catalyst
Pd/C (5%)
76
RuHCl(CO)(PPh3)3 73
Grubbs first
55
100
100
Hydrogenation by TSH degradation TSH only
TSH þ TPA
a
Calculated by the ratio of the area of olefin peaks at 5.7 and 6.0 ppm in 1H NMR (400 MHz, CDCl3) to the
area of an aromatic peak at 7.3 ppm (Fig. 1).
a high degree of hydrogenation was not obtained in some
basic solvents: 6% of hydrogenation in pyridine, 53% in N,N-
dimethylformamide (DMF), 60% in N,N-dimethylacetamide
(DMAC), and 77% in N-methyl-2-pyrrolidinone (NMP).
weights against the polystyrene standards appeared to
increase after hydrogenation, probably due to possible cross-
linking during hydrogenation, fractionation during subse-
quent purification, or change in hydrodynamic volume after
hydrogenation.14
DMF solvent was chosen for the hydrogenation of 6, despite
the low hydrogenation result, due to its low solubility in
other aromatic solvents and THF. DMF is a better choice
than DMAC or NMP, due to its lower boiling point (153 ꢀC)
when compared with those of DMAC (164 ꢀC) and NMP
(202 ꢀC), because it is easier to completely remove solvents
with lower boiling points. We attempted hydrogenation of 6
with other metal catalysts such as 50 mg of Pd/C (5%) and
7.5 mg of Grubbs first generation catalyst (with 0.1 mL of
ethyl vinyl ether to prevent further polymerization) as well as
7.5 mg of RuHCl(CO)(PPh3)3.12 As summarized in Table 2,
even the highest degree of hydrogenation was still less than
80%. This low degree of hydrogenation of poly(ONDI) is prob-
ably due to the competing reaction, in which a transition metal
removes an allyl group from the neighboring oxygen or nitro-
gen atom,13(a,b) as shown by Cadot et al. with Grubbs
catalyst.13(c) Also, a ring-opening reaction of THF induced by
transition metals13(d) could take place in poly(ONDI) mole-
cules, resulting in unstable backbones; severe degradation in
molecular weights shown in Table 1 seems to be consistent
with this mechanism.
The thermal degradation temperatures (Td) were measured
with thermogravimetric analysis (TGA), and the Tg values
were determined for the polymers coated on glass fibers by
dynamic mechanical analysis (DMA) with a single-cantilever
clamp. In Table 3, it is seen that poly(ONDI)s are less ther-
mally stable than poly(NDI)s both before and after hydro-
genation. The average Td at 5 wt % loss of poly(NDI)s
ꢀ
increased from 409 to 421 C after hydrogenation, which is
consistent with previous studies.1,2 Although polymer 3
exhibited a slightly decreased Td after hydrogenation, such
an exceptional phenomenon is sometimes observed when
thermal degradation starts from side chains not from
backbones.15
The average Td at 5 wt % loss of poly(ONDI)s decreased
ꢀ
from 363 to 355 C after hydrogenation. The lower values of
Td of poly(ONDI)s when compared with poly(NDI)s is con-
sistent with the fact that the incorporation of ether linkage
decreases the thermal stability of polymers in general.16 The
unexpected decrease in Td upon hydrogenation is probably
due to the unstable nature of ether linkages susceptible to
change by either metal hydride (polymers 4 and 5) or p-tol-
uenesulfinic acid (polymer 6) during hydrogenation. As
shown in Table 1, MW values of poly(ONDI)s were signifi-
cantly decreased after hydrogenation. Either cleavage of car-
bon double bonds from the oxygen atom13(a–c) or ring-open-
ing reaction of ONDI molecule13(d) has induced chemical
degradation of backbones in polymers 4 and 5. This suggests
that parts of the polymer backbone do not maintain stable
cyclic structures any more and the opened rings could
induce a decrease in Td. Although p-toluenesulfinic acid did
not result in significant degradation in poly(NDI)s (polymers
2 and 3), its degradation potential seems more serious for
poly(ONDI) (polymer 6). Other reactions such as coupling,
cyclization, addition of the p-toluene-sulfinate anion3(b) could
make thermal characteristics more complicated. Regardless,
the major outcome of the side reactions will be reflected in
For TSH degradation method, DMF acted as a better medium
when compared with other solvents, in contrast to the case
of metal catalyst method. To further investigate the benefit
of DMF, we applied the TSH method to highly soluble poly
(ONDI) (4) in xylene without tripropylamine (TPA) and
with TPA. Without TPA, the molecular weights decreased to
13% of the nonhydrogenated forms, whereas with TPA, the
molecular weights were reduced to 70%. However, when
DMF was used as the solvent, the molecular weights did not
decrease below 70% even without TPA. This is because the
basic nature of DMF acted as an acid-base buffer. Thus, we
applied both metal catalyst-based hydrogenation method and
TSH degradation method to each polymer. The results with
least degradation in molecular weight and highest
hydrogenation yield are provided in the ‘‘After hydrogena-
tion’’ column in Table 1. In some cases, the molecular
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TABLE 3 Thermal Properties of the Polymers Before and After Hydrogenation
Td at 5 wt % loss (ꢀC)a
Tg (ꢀC)b
Before
After
Before
After
Polymer
Hydrogenation
Hydrogenation
Hydrogenation
Hydrogenation
122
1
406
434
158
2
3
4
5
6
a
408
412
365
358
366
424
406
362
344
359
212
239
152
212
226
180
197
116
173
188
Td was measured at a heating rate of 10 ꢀC/min in TGA.
Tg was measured as the peak temperature in tan d (1 Hz) vs. temperature plot obtained at heating rate of
ꢀC/min in DMA.
b
2
the decreased Td values after hydrogenation of poly(ONDI)s,
consistent with experimental results.
preventing a significant decrease in Tg values of poly(ONDI)s
when compared with those of poly(NDI)s, but the details of
this structure are not understood at this moment. The results
of the intermolecular scattering peaks for other poly(NDI)s and
poly(ONDI)s are similar to those of 2 and 5, as shown in
Table 4.
In comparison, the Tg values of poly(ONDI)s are only slightly
lower than the corresponding poly(NDI)s for both nonhydro-
genated and hydrogenated polymers; the average Tg of poly
(NDI)s decreased from 203 to 164 ꢀC after hydrogenation,
whereas that of poly(ONDI)s decreased from 197 to 159 ꢀC.
This result is in agreement with the trend observed by of
Cetinkaya et al.11(b) for the nonhydrogenated polymers but is
quite different from the trend previously reported by Morita
et al.,11(c) who observed that the Tg value of a hydrogenated
poly(oxanorbornene diester) was lower by 55 ꢀC than the
corresponding hydrogenated poly(norbornene diester).
Therefore, the lack of significant decrease in Tg between poly
(NDI)s and poly(ONDI)s, as expected from the difference
between poly(norbornene diester) and poly(oxanorbornene
diester) may be due to the stronger intermolecular interac-
tions involving the imide moieties when compared with ester
moieties.
Refractive index values were measured with F20 thin-film
analyzer (Filmetrics) for polymer films spin-coated on silicon
wafer substrates. As shown in Table 4, refractive index val-
ues of polymers decreased slightly after hydrogenation,
which indicates that the chain packing density was reduced
somewhat, consistent with the observed decrease in Tg after
hydrogenation.
Further investigations of physical properties of hydrogenated
polymers were carried out with the polymer films prepared
by the conventional solution casting method with chloroform
or DMF as the solvent. As the results in Table 5 show, poly
(NDI) and poly(ONDI) films exhibit very close values of
tensile modulus, coefficient of thermal extension (CTE), and
optical transparency, but poly(ONDI)s absorb and transmit
slightly more water than poly(NDI)s due to increased
polarity.
To investigate the local structures related to intermolecular
interactions, we carried out wide-angle X-ray scattering
(WAXS) experiments down to very low angles of 2h ¼ 2ꢀ.
The WAXS patterns of 2 and 5, both before and after hydro-
genation, are shown in Figure 2 as the representative exam-
ples of poly(NDI) and poly(ONDI), respectively. In contrast to
the result of a previous study that reported a highly crystal-
line structure for a fully hydrogenated polynorbornene,17
both poly(NDI)s and poly(ONDI)s remained fully amorphous
before and after hydrogenation.
The WAXS data in Figure 2 show a significant difference in
polymer microstructure between 2 and 5. While 2 exhibits a
typical amorphous halo around 2h ¼ 17ꢀ, regardless of hy-
drogenation, 5 exhibits a pronounced low-angle peak at 2h
of 6.0ꢀ (equivalent d-spacing 14.8 Å) before hydrogenation,
which shifts to 5.3ꢀ (equivalent d-spacing 16.6 Å) after hy-
drogenation. Therefore, increased polar interactions involving
the backbone oxygen atoms and the imide moieties seem to
lead to local ‘‘nanostructure’’ in an overall amorphous structure.
Presence of such a local nanostructure may be responsible for
FIGURE 2 WAXS intensity versus 2h (k ¼ 0.154 nm) obtained
for 2 and 5 before and after hydrogenation.
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TABLE 4 WAXS and Refractive Index Results of the Polymers Before and After Hydrogenation
Intermolecular Equivalent
˚
d-Spacing (A)
Refractive Index
After
Before
After
Before
Polymer
Hydrogenation
Hydrogenation
Hydrogenation
Hydrogenation
1
–
–
1.522
1.521
2
3
4
5
6
–
–
1.526
1.586
1.528
1.532
1.581
1.524
1.569
1.522
1.525
1.553
–
–
13.8
14.8
17.8
14.7
16.6
18.3
EXPERIMENTAL
Hz, respectively, and the temperature was raised from 50 to
300 C at a heating rate of 2 C/min.
ꢀ
ꢀ
General Method
Gas chromatography–mass spectrometry (GC–MS) was com-
prised of 6890GC and 5973MS (Agilent). Helium was eluted
at a flow rate of 2 mL/min through a HP-5 capillary column
with dimension of 0.25 mm ꢂ 0.25 lm ꢂ 30 m (Agilent).
WAXS measurements were performed with polymer powders
in a laboratory X-ray scattering instrument that utilizes pin-
hole-collimated Cu-Ka radiation, using three consecutive pin-
holes with diameters of 1000, 400, and 300 lm, decreasing
in diameter as the incident beam approaches the sample.
Data were obtained with Cu-Ka source with k ¼ 1.54 Å in
the Bragg angle (h) range of 2h ¼ 2–40ꢀ. The refractive
index was measured with F20 reflectometer (Filmetrics) on
thin films prepared by spin-coating 5 wt % polymer solu-
tions in cyclohexanꢀone onto a silicon wafer, followed by a
vacuum dry at 130 C for longer than 1 day.
ꢀ
Column oven temperature was held at 50 C for 1 min after
injection, then raised to 280 ꢀC at a heating rate of 10 ꢀC/
min. MS scanned m/z from 50 to 300. Nuclear magnetic res-
onance (NMR) spectrum was measured on Eclipse þ400
spectrometer (Jeol, Japan) at 400 MHz. Samples were pre-
pared in either CDCl3 or DMSO-d6. GPC was comprised of
CM4000 pump (Milton Roy) and 2410 refractive index detec-
tor (Waters, UK). DMF with 50-mM lithium bromide was
eluted at a flow rate of 0.8 mL/min through tandemly con-
nected MixedBed B and D columns (Agilent) maintained at
For measurement of freestanding film properties, polymer
films were prepared by a conventional solution casting
method in chloroform or DMF followed by a vacuum dry at
ꢀ
70 C. After an injection of 100 lL of 0.1 wt % sample solu-
ꢀ
130 C for longer than 1 day. For measuring tensile modulus,
tion, MWs of polymers were determined against polystyrene-
standard calibration curve. Thermograms of polymers were
obtained in TGA Q50 (TA instruments) at a heating rate of
films were fixed at a film tension clamp in DMA, and the ten-
sion force was applied at a rate of 5 N/min. Tensile modulus
values were determined by the inverse of the slope of the
stress versus strain curve in the linear elastic region. At the
same clamp, a static force of 0.1 N was applied to a fixed
film, and the temperature increased at a rate of 2 ꢀC/min.
ꢀ
ꢀ
10 C/min from 30 to 500 C under nitrogen flow. For meas-
uring Tg values, polymer samples coated on glass fibers were
held at a single cantilever clamp in a DMA 2890 (TA instru-
ments). Amplitude and frequency were set at 30 lm and 1
TABLE 5 Various Film Properties of Hydrogenated Polymersa
Water
Tensile
Modulus
(GPa)
Light
Absorption
(wt % in
1 day)
Water-Vapor
Transmission
Rate (g/m2/day)
CTE
(ppm/K)b
Transmittance
at 550 nm (%)c
Polymer
1
2
3
4
5
a
1.6
1.8
1.8
1.8
1.8
72
52
36
83
57
88
79
70
91
81
0.46
0.28
1.25
0.50
0.67
73
39
52
130
51
Film of 6 was too brittle to handle for measurements.
Estimated in the temperature range of 40–120 ꢀC.
b
c
Light transmittance was normalized to the thickness of 50 lm.
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CTE was determined by the sample length increase against
temperature. The light transmittances of the films at 550 nm
were measured in UV–vis spectrometer (V-530 spectrometer,
JASCO). Water absorption was calculated by the weight
increase afteꢀr dipping the films in water reservoir main-
tained at 30 C for 24 h. Water vapor transmission rate was
determined with a homemade equipment described in the
report by Park et al.18
ONDIs are unstable at high temperature due to the retro-
Diels–Alder reaction.19 The chemical structures were con-
firmed with H NMR and GC–MS. The total yield was around
1
70%.
1H NMR (400 MHz, CDCl3): N-Propyl-ONDI: d 6.50 (t, 2H),
5.26 (t, 2H), 3.45 (t, 2H), 2.83 (s, 2H), 1.58 (m, 2H), 0.88 (t,
3H). N-Cyclohexyl-ONDI: d 6.49 (t, 2H), 5.24 (t, 2H), 3.90 (m,
1H), 2.76 (s, 2H), 1.81–2.13 (m, 4H), 1.25–1.53 (m, 6H). N-
Phenyl-ONDI: d 7.44–7.25 (m, 5H), 6.48 (t, 2H), 5.25 (t, 2H),
2.84 (t, 2H).
Materials
endo-NDA, n-propyl amine, cyclohexyl amine, aniline, and
ethyl vinyl ether were purchased from TCI, Japan. Grubbs
first generation catalyst, Grubbs third generation catalyst
(dichloro[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]
(benzylidene)bis(3-bromopyridine)ruthenium(II)), carbonyl-
chlorohydrido-tris(triphenylphosphine)ruthenium(II) (RuHCl
(CO)(PPh3)3), p-toluenesulfonyl hydrazide, Pd/C, and lithium
bromide were purchased from Aldrich. Acetic anhydride, so-
dium acetate anhydrous, sodium carbonate, TPA, ethyl ace-
tate, dichloromethane, chloroform, toluene, xylene, pyridine,
chlorobenzene, THF, DMF, DMAC, and NMP were purchased
from Samchun Chemical, Korea.
13C NMR (400 MHz, CDCl3): N-Propyl-ONDI: d 176.5, 136.6,
81.0, 47.4, 40.6, 21.0, 11.2. N-Cyclohexyl-ONDI: d 176.5,
136.6, 81.1, 52.2, 52.0, 47.1, 28.8, 25.9, 25.1. N-Phenyl-ONDI:
d 175.5, 136.8, 131.8, 129.2, 128.9, 126.6, 81.5, 47.6.
Polymerization
ROMP was performed in a round-bottomed flask filled with
nitrogen gas.20 Each monomer was dissolved in chloroform at
concentration of 10 wt %, and the molar ratio of monomer to
the Grubbs third generation catalyst was fixed at 1000 to 1.
After stirring at 45 ꢀC for 3 h, the catalysts were removed
from the polymer solutions by addition of 0.1 mL of ethyl
vinyl ether and stirring overnight. After a short silica column
filtration, polymers were precipitaꢀted into methanol, filtered,
and dried in a vacuum oven at 60 C for more than 12 h.
Monomer Synthesis
Monomers were synthesized according to the previously
reported methods with minor modifications.1 For prepara-
tion of both NDI and ONDI monomers, n-propylamine, cyclo-
hexylamine, and aniline were chosen as primary amines. To
prepare NDI, after thermal isomerization of endo-NDA at 185
ꢀC for 4 h, the resulting exo-NDA was purified by recrystalli-
zation in ethyl acetate twice. To the 0.5 M solution of exo-
NDA in acetonitrile, 1.1 mol equivalent amount of amine was
added dropwise, followed by stirring forꢀ1 additional h. Solu-
tions were then heated to reflux at 100 C for 4 h after addi-
tion of sodium acetate anhydride (0.1 equiv of exo-NDA) and
acetic anhydride (2 equiv of exo-NDA), and then precipitated
into water. After filtration, NDI monomers were further puri-
fied by a silica column separation with an eluent of chloro-
form/ethyl acetate (3/1). The chemical structures were con-
firmed with 1H NMR and GC–MS. The total product yield
was around 20%.
13C NMR (400 MHz, CDCl3 or DMSO-d6): poly(N-propyl-NDI):
d 178.4, 133.6, 132.1, 51.0, 46.0, 42.1, 40.2, 21.1, 11.3.
poly(N-cyclohexyl-NDI): d 178.2, 133.9, 51.7, 45.5, 42.6, 28.8,
25.9, 25.1. poly(N-phenyl-NDI): d 177.1, 132.3, 131.9, 129.2,
128.8, 126.4, 51.8, 45.9, 43.0. poly(N-propyl-ONDI): d 176.4,
133.6, 81.3, 52.4, 40.4, 21.1, 11.3. poly(N-cyclohexyl-ONDI): d
176.5, 133.6, 81.2, 52.2, 40.1, 28.9, 25.9, 25.0. poly(N-phenyl-
ONDI): d 176.5, 133.8, 131.8, 129.3, 128.8, 126.6, 80.5, 41.6.
Hydrogenation
For homogeneous ruthenium catalyst method, 2 g of polymer
and 4 mg of RuHCl(CO)(PPh3)3 were dissolved in 40 mL of
toluene in a stainless steel autoclave (volume 120 mL). Under
hydrogen pressure of 100 bar, the solution was stirred vigo-
rously at 165 ꢀC for 4 h. After cooling to room temperature,
the solution was precipitated into methanol, filtered, and
dried. For TSH method, 2 g of polymer and 2.2 equimolar
amount of TSH (calculated against the theoretical amount of
double bonds) were dissolved in 40 mL of DMF in a round-
bottomed flask equiꢀpped with a reflux condenser. The solution
was stirred at 135 C for 4 h, cooled down to the room tem-
perature, precipitated into methanol, filtered, and dried.
1H NMR (400 MHz, CDCl3): N-Propyl-NDI: d 6.30 (s, 2H),
3.44 (t, 2H), 3.26 (t, 2H), 2.68 (d, 2H), 1.48–1.62 (m, 4H),
0.86 (t, 3H). N-Cyclohexyl-NDI: d 6.28 (s, 2H), 3.95 (m, 1H),
3.25 (d, 2H), 2.60 (d, 2H), 2.13 (m, 2H), 1.79–1.84 (m, 2H),
1.33–1.60 (m, 8H). N-Phenyl-NDI: d 7.44–7.25 (m, 5H), 6.34
(t, 2H), 3.40 (t, 2H), 2.84 (t, 2H), 1.47–1.60 (m, 2H).
13C NMR (400 MHz, CDCl3): N-Propyl-NDI: d 178.2 137.9,
52.3, 47.9, 45.8, 42.8, 40.4, 21.2, 11.5. N-Cyclohexyl-NDI: d
178.3, 137.9, 51.7, 47.5, 45.5, 42.6, 28.8, 25.9, 25.1. N-Phe-
nyl-NDI: d 177.1, 138.1, 131.9, 129.2, 128.8, 126.4, 48.0,
45.9, 43.0.
13C NMR (400 MHz, CDCl3 or DMSO-d6): poly(N-propyl-NDI):
d 179.3, 51.6, 44.3, 43.8, 42.3, 40.0, 34.3, 33.9, 21.1, 11.4.
Poly(N-cyclohexyl-NDI): d 179.2, 51.7, 45.5, 42.6, 34.2, 33.8,
28.8, 25.9, 25.1. Poly(N-phenyl-NDI): d 179.1, 131.9, 129.3,
128.9, 126.5, 51.7, 45.9, 43.0, 34.3, 33.8. Poly(N-propyl-
ONDI): d 176.4, 81.5, 52.4, 40.4, 31.3, 21.1, 11.3. Poly(N-
cyclohexyl-ONDI): d 176.4, 81.1, 52.2, 40.2, 31.2, 28.9, 25.9,
25.0. Poly(N-phenyl-ONDI): d 176.5, 131.9, 129.4, 128.8,
126.5, 80.5, 41.6, 31.4.
For ONDI, maleic anhydride was first converted to ONDA
through the Diels–Alder reactionꢀwith furan in dichlorome-
thane (4 M concentration) at 30 C for 24 h. The remaining
procedures are identical to those used for NDI, except for
the reflux temperature of 70 ꢀC instead of 100 ꢀC, because
6
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5 For electronic applications, see 4(g) and 4(h). For bioactive
materials, see (a) Maynard, H. D.; Okada, S. Y.; Grubbs, R. H.
Macromolecules 2000, 33, 6239–6248; (b) Ilker, M. F.; Schule, H.;
Coughlin, E. B. Macromolecules 2004, 37, 694–700. For gas trans-
portation, see (c) Contreras, A. P.; Tlenkopatchev, M. A.; Lopez--
Gonzalez, M. D.; Riande, E. Macromolecules 2002, 35,
4677–4684; (d) Tlenkopatchev, M. A.; Vargas, J.; Lopez-Gonzalez,
M. D.; Riande, E. Macromolecules 2003, 36, 8483–8488.
CONCLUSIONS
In summary, we polymerized various structures of poly
(NDI)s and poly(ONDI)s and established an optimal hydro-
genation method. The thermal decomposition temperature (5
wt % loss) of poly(ONDI)s is decreased by 65 ꢀC to about
ꢀ
350 C when compared with poly(NDI)s. The glass transition
temperatures are only slightly lower (<10 ꢀC) for poly(ON-
DI)s. The WAXS patterns show the presence of localized
nanostructure for poly(ONDI)s in an overall amorphous
structure, probably due to favorable interactions between
the imide and backbone oxygen moiety. Hydrogenated poly
(ONDI)s have similar mechanical and optical properties
when compared with the corresponding hydrogenated poly
(NDI)s, but they have slightly larger water absorption and
permeability due to increased polarity. Therefore, the advant-
age in preparing exo-monomers for polymerization makes
poly(ONDI)s more attractive candidates than poly(NDI)s for
practical applications such as flexible substrate films and
separation membranes, for example.
6 (a) Rule, J. D.; Moore, J. S. Macromolecules 2002, 35,
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Fontaine, L. Macromol. Chem. Phys. 2004, 205, 824–833.
7 Castner, K. F.; Calderon, N. J. Mol. Catal. 1982, 15, 47–59.
8 (a) Woodward, R. B.; Baer, H. J. Am. Chem. Soc. 1948, 70,
1161–1166; (b) Anet, F. A. L. Tetrahedron Lett. 1962, 25, 1219–1222;
(c) Lee, M. W.; Herndon, W. C. J. Org. Chem. 1978, 43, 518.
9 Hillmyer, M. A.; Lepetit, C.; McGrath, D. V.; Novak, B. M.;
Grubbs, R. H. Macromolecules 1992, 25, 3345–3350;
10 (a) Grubbs, R. H.; Novak, B. M., California Institute of Tech-
nology. U.S. Patent 4,945,135, 1990; (b) Weck, M.; Schwab, P.;
Grubbs, R. H. Macromolecules 1996, 29, 1789–1793; (c) Lynn,
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ACKNOWLEDGMENTS
The authors gratefully acknowledge the assistance of Dong-hee
Lee and Jeongyeol Moon, Heon-Sung Chae, and Choong-Seok
Kang in Kolon Central Research Institute. The authors thank
Hye-Young Jang in Ajou University and Wen-Li Wu in NIST for
advice and helpful discussions. This work was supported by
the Chemistry and Molecular Engineering Program of the Brain
Korea 21 Project and Midterm Strategy Project of Korean gov-
ernment.
11 (a) Kang, H. A.; Bronstein, H. E.; Swager, T. M. Macromole-
cules 2008, 41, 5540–5547; (b) Cetinkaya, S.; Ozker, T.; Bayram,
R. Appl. Catal. A 2011, 393, 24–28; (c) Morita, T.; Hiraike, H.;
Toyoshima, K.; Higuchi, I., Sekisui Chemical Co., Ltd. Jpn Pat-
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