High dielectric performance of tactic polynorbornene derivatives synthesized by ring-opening metathesis polymerization

Article abstract of DOI:10.1002/pola.26497

Functional polynorbornenes (PNBEs) containing pyrrolidine moiety and bis(trifluoromethyl)biphenyl side group were synthesized via ring-opening metathesis polymerization (ROMP), and the microstructure of polymer chain was characterized by NMR spectroscopy. Poly(N-3,5-bis(trifluoromethyl)biphenyl- norbornene-pyrrolidine) (PTNP) and poly(N-phenyl-norbornene-pyrrolidine) (PPNP) are supposed to have practically trans double bonds and adopt isotactic syn conformation, whereas poly(N-3,5-bis(trifluoromethyl)biphenyl-norbornene- dicarboximide) (PTNDI) has both trans and cis double bonds and atactic microstructure. PTNP, PTNDI, and PPNP have much different dielectric constants of 20, 7, and 3, respectively, which is attributed to both the polar 3,5-bis(trifluoromethyl)biphenyl group and the stereoregular chain structure. The existence of rigid pyrrolidine moiety has a positive contribution to form the tactic polymer chain during ROMP. Polymers are highly thermal stable up to ～300 °C. Having good dielectric properties and thermal stability, these functional PNBEs are expected as the potential dielectric material in thin film capacitors.

Full text of DOI:10.1002/pola.26497

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High Dielectric Performance of Tactic Polynorbornene Derivatives
Synthesized by Ring-Opening Metathesis Polymerization
Zewang You, Danyi Gao, Ouyue Jin, Xiaohua He, Meiran Xie
Department of Chemistry, East China Normal University, Shanghai 200241, China
Correspondence to: M. Xie (E-mail: mrxie@chem.ecnu.edu.cn)
Received 9 October 2012; accepted 20 November 2012; published online 26 December 2012
DOI: 10.1002/pola.26497
ABSTRACT: Functional polynorbornenes (PNBEs) containing
pyrrolidine moiety and bis(trifluoromethyl)biphenyl side group
were synthesized via ring-opening metathesis polymerization
(ROMP), and the microstructure of polymer chain was charac-
terized by NMR spectroscopy. Poly(N-3,5-bis(trifluoromethyl)bi-
phenyl-norbornene-pyrrolidine) (PTNP) and poly(N-phenyl-
norbornene-pyrrolidine) (PPNP) are supposed to have practi-
cally trans double bonds and adopt isotactic syn conformation,
is attributed to both the polar 3,5-bis(trifluoromethyl)biphenyl
group and the stereoregular chain structure. The existence of
rigid pyrrolidine moiety has a positive contribution to form the
tactic polymer chain during ROMP. Polymers are highly ther-
mal stable up to ꢀ300 ꢁC. Having good dielectric properties
and thermal stability, these functional PNBEs are expected as
C
V
the potential dielectric material in thin film capacitors.
2012
Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
whereas
poly(N-3,5-bis(trifluoromethyl)biphenyl-norbornene-
2013, 51, 1292–1301
dicarboximide) (PTNDI) has both trans and cis double bonds
and atactic microstructure. PTNP, PTNDI, and PPNP have much
different dielectric constants of 20, 7, and 3, respectively, which
KEYWORDS: dielectric properties; isotactic; microstructure; poly-
norbornene; ring-opening metathesis polymerization (ROMP)
INTRODUCTION High dielectric constant materials have been
more focused lately on novel polymers because of their pos-
sible application in high density film capacitors where
requiring the small volume and large energy storage density,
which has long been a scientifically challenging and industri-
ally important area.1 Ceramics, such as silicon oxide, silicon
nitride, and barium titanate, are typical high dielectric con-
stant materials, but the dielectric loss is large and the proc-
essing of materials is very expensive and complicated. Thin
film capacitors based on polymers, including polyethylene
terephthalate, polypropylene, polyester, and polycarbonate,2
have attracted a great deal of attention for energy storage
applications due to their desirable properties, such as light-
weight, low cost, and safety.3 However, these polymer film
capacitors generally suffer from either low energy density2,4
because of a low dielectric constant (2–3) or unacceptably
large energy loss5 that reduces storage capacity and causes
big problems in capacitor stability. One popular strategy6 to
solve these problems is to introduce ceramic fillers into poly-
mer and try to combine the advantages of both components.
For instance, polyvinylidene fluoride-based composite was
usually selected as the dielectric materials because of their
good dielectric properties with a relatively high dielectric
constant (ꢀ8), whereas the dielectric loss is high due to the
interface polarization2,7–10 and the dielectric dispersion is
large, which may bring problem for high frequency. In gen-
eral, thin film capacitors require a good film-forming and
high dielectric constant company with small dielectric loss
and dielectric dispersion, so using all-organic material for
high dielectric applications is reasonable.
Dielectric constant of polymer depends on the degree of
polarization itself. The stronger is the polarity of molecules,
the greater is the degree of polarization, and the dielectric
constant is likewise higher. Polymer has a higher dielectric
constant when the polar groups in the side position than
that in the main chain, and also the polar molecules with
asymmetric molecular structure have a higher dielectric con-
stant than that of symmetric ones. Thus, to get high dielec-
tric polymer, it is suitable by introducing functional groups
with a large dipole moment into polymer as the side groups.
Of such functional groups are cyano, nitro, halogen, perfluor-
oalkyl, and so forth. Kobayashi11 reported that incorporation
of cyano into polyvinyl alcohol or copolymerization of vinyl
alcohol with acrylonitrile could improve the dielectric con-
stant and also the dielectric constant increased with the per-
centage of acrylonitrile. Yuan et al.2 compared the dielectric
constant of isotactic polypropylene to the copolymers of pro-
pylene and hydroxylated propylene and found that the
dielectric constant of copolymers was elevated from 2 to 5.
Obviously, those are not effective ways to enhance the
Additional Supporting Information may be found in the online version of this article.
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dielectric constant of polymers up to a desired high level.
Furthermore, the dielectric constant of polymers is related to
the microstructure of polymer chain, which is dependent on
the stereochemical configuration and arrangement of the
monomer units into the polymer chain when polymerization
especially ring-opening metathesis polymerization (ROMP)
happened. Polynorbornenes (PNBEs) are usually known as
low-dielectric materials12–15 owed to their symmetric struc-
ture, and they have been used in the microelectronics indus-
try.16 However, if the side groups in particular the polar
groups were introduced to PNBE, the dielectric constant of
polymer will greatly increase. Schrock and coworkers
reported that tactic polymers prepared by Mo carbene-cata-
lyzed ROMP of 2,3-bis(trifluoromethyl)norbornadiene exhibit
a much higher dielectric constant than the corresponding
atactic polymers prepared by using the catalytic system of
WCl6/SnMe4.17 High trans-tactic polymer has a higher dielec-
tric constant than that of half trans-polymer and high cis-
polymer, basically due to the dipolement cumulation of polar
trifluoromethyl (CF3) group on the tactic polymer chain.18
Solvents were distilled over drying agents under nitrogen
before use: dichloromethane (CH2Cl2), trichloromethane
(CHCl3), and 1,2-dichloroethane (DCE) from calcium hydride;
diethyl ether (Et2O) and tetrahydrofuran (THF) from
sodium/benzophenone.
Polymerization was carried out in Schlenk tube under dry
nitrogen atmosphere.
Characterization
1H (500 MHz), 13C (125 MHz), and 19F (500 MHz) NMR
spectra were recorded using tetramethylsilane as an internal
standard in CDCl3 on a Bruker DPX spectrometer. Melting
Point was determined by Micro melting point apparatus
(Yanoco). GC/MS measurements were performed with a Var-
ian Saturn 2100 GC/MS system with GC-3900 using a VF-5
MS, 30 m ꢂ 0.25 mm ꢂ 0.25 lm diffused silica capillary col-
umn. FTIR spectra were recorded on a Nicolet Nexus 670 in
the region of 4000 to 400 cmꢃ1 using KBr pellets. Gel per-
meation chromatography (GPC) was used to calculate rela-
tive molecular weight and molecular weight distribution
equipped with a Waters 1515 Isocratic HPLC pump, a Waters
2414 refractive index detector, and a set of Waters Styragel
columns (7.8 ꢂ 300 mm, 5 mm bead size; 103, 104, and 105
Å pore size). GPC measurements were carried out at 35 ꢁC
It is a more convenient way to get high dielectric materials
by designing a monomer with large dipole groups, and then
aggregated to produce a tactic polymer. As we all known,
there are two approaches to obtain a tactic polymer in
ROMP. One is that by using the catalyst with different ligands
to control the polymerization progress, and high trans/cis
whatever isotactic or syndiotactic microstructure19–24 is well
defined; the other one is to design a monomer tending to po-
lymerization regularly. A monomer carried with more rigid
structure, such as pyrrolidine moiety, is more likely to pro-
duce a tactic polymer during the ROMP process. Luh and co-
workers25–30 has paid more attention to polymerizing a rigid
norbornene monomer catalyzed by Grubbs catalyst to get
tactic polymer. In addition, the interaction, like p-p stacking
interaction,31–36 between the side groups of polymer is a
strong driving force to make the neighbor repeat units
arranged in the same direction.
using THF as the eluent with a flow rate of 1.0 mL minꢃ1
.
The system was calibrated with polystyrene standard. Differ-
ential scanning calorimeter (DSC) was performed on a
Netzsch 204F1 in nitrogen atmosphere. An indium standard
was used for temperature and enthalpy calibrations. All the
samples were first heated from 25 to 300 ꢁC and held at
this temperature for 3 min to eliminate the thermal history,
and then, they were cooled to room temperature and heated
again from 25 to 300 ꢁC at a heating or cooling rate of 10
ꢁC/min. Thermal gravimetric analysis (TGA) was performed
using a SDTA851e/SF/1100 TGA Instꢃru1ment under nitrogen
flow at a heating rate of 10 ꢁC min from 30 to 800 ꢁC.
Dielectric measurements were carried out by a Novocontrol
BDS40 dielectric spectrum analyzer over the frequency range
of 100 Hz to 1 MHz at room temperature, and a contacting
electrode method was used. The edge side (d) of the guarded
electrode is 0.3 mm. The capacitance (Cp) and the dissipation
factor (dielectric loss, loss tangent, or tan d) of the tested
films were recorded. The dielectric constant e can be calcu-
lated by eq 1:
It is rarely seen to increase the dielectric constant upon an
introduction of strong polar conjugated aromatic structure to
the chain of PNBE by now. In this article, we prepared func-
tional PNBEs containing the large aromatic group with polar
CF3 group and rigid pyrrolidine moiety via ROMP and inves-
tigated their unique dielectric and thermal properties.
EXPERIMENTAL
er ¼ Cpt=e0A
(1)
Materials
Norbornene-5,6-endo-dicarboxylic anhydride (NDA), lithium
aluminum hydride (LiAlH4), bis(tricyclohexylphosphine) ben-
zylidene ruthenium (IV) dichloride (Ru-I), tricyclohexylphos-
phine [1,3-bis (2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-
ylidene] benzylidene ruthenium dichloride (Ru-II), 4-amino-
30,50-bis(trifluoromethyl)biphenyl, and aniline were pur-
chased from Aldrich or Alfa Aesar and used as received. 4-
Dimethylaminopyridine (DMAP), ethyl acetate (EtOAc), anhy-
drous sodium acetate, acetic anhydride, and magnesium sul-
fate (MgSO4) were purchased from Shanghai Chemical
Reagents Co, and used as received without purification.
where t is the thickness of the film and e0, the permittivity
of the free space, is 8.85 ꢂ 10ꢃ12 F/m, A is the guarded elec-
trode area, A ¼ d2. Preparation of film samples: polymer was
dissolved in CHCl3 to a solution of 8–15 wt %, and then, the
solution was stirred for 12 h at room temperature, followed
by the sonication for extra 10 min. After that, the solution
was spin-coated on a pre-aluminumed substrate at spinning
speed of 1200–2500 rpm for 30 s, and dried in air over-
night, followed by continuous heat treatment in vacuum
for another 12 h to evaporate all the solvents. The thickness
of films was controlled by using different solution
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concentration and spinning speed, and tested by the Elcome-
ter (Veeco Dektak 6M). The typical thickness of the polymer
films was 3–10 lm, and then, a thin layer (500 Å) of Pt par-
ticle was sputtered on the exposure sides of the sample.
at the retention time of 7.9 min; EIMS: Calcd. for C23H19F6N:
423.4, Found: 423.5; IR (KBr): m ¼ 2969, 2883, 2836, 1602,
1532, 1459, 1374, 1271, 1198, 1167, 1107, and 1061 cmꢃ1
.
General Ring-Opening Metathesis Polymerization
Procedures
Preparation of Monomers
Typically, polymerization was carried out in a Schlenk tube
under dry nitrogen atmosphere for a preset time. After ter-
minating polymerization by addition of a small amount of
ethyl vinyl ether and stirring for 1 h, the solution was
poured into an excess of methanol. Polymer was dissolved in
CHCl3 or THF, and precipitated once again from methanol.
N-3,5-bis(trifluoromethyl)biphenyl-norbornene-
dicarboximide (TNDI)
A
solution of 4-amino-30,50-bis(trifluoromethyl)biphenyl
(4.88 g, 16 mmol) in 80 mL of DCE was added dropwise to
the stirred solution of NDA (3.15 g, 19.2 mmol) in 80 mL of
DCE for 1 h in an ice bath, DMAP (0.195 g, 1.6 mmol) was
then added at room temperature, and the mixture was fur-
ther refluxed for 20 h. The solution was washed by dilute
hydrochloric acid (5ꢂ 30 mL), followed by water, and dried
with anhydrous MgSO4. After filtration and removing the sol-
vent, a white needle crystal was obtained by recrystallization
twice from ethanol (6.13 g, 85% yield).
ꢁ
The obtained polymer was dried in a vacuum oven at 40 C
to a constant weight.
Polymerization of TNDI
Monomer TNDI (0.676 g, 1.5 mmol) and Ru-II (12.3 mg,
0.015 mmol) were stirred in 7.5 mL of CHCl3 at 50 ꢁC for
1 h. The number-average molecular weight (Mn) and polydis-
persity index (PDI ¼ Mw/Mn) of poly(N-3,5-bis(trifluorome-
mp 153 ꢁC; 1H NMR (500 MHz, CDCl3, d): 7.97 (s, 2H,
oAArHACF3), 7.87 (s, 1H, pAArHACF3), 7.65–7.64 (d, J ¼
8.35 Hz, 2H, mAArHANC¼¼O), 7.32–7.30 (d, 2H,
oAArHANC¼¼O), 6.29 (s, 2H, CHCH¼¼CHCH), 3.53 (s, 2H,
CHC¼¼O), 3.47 (s, 2H, CHCHC¼¼O), 1.82–1.80 and 1.65–1.63
(d, J ¼ 8.75 Hz, 2H, CHCH2CH); 13C NMR (125 MHz, CDCl3,
d): 176.6 (ArNC¼¼O), 142.4 (NCCH), 138.4 (NArACCH), 134.7
(CHCH¼¼CHCH), 132.5 (CAArCF3), 132.1 (CF3C), 127.9
(NCCHCH), 127.3 (NArACCH), 124.3 (CHCCF3), 122.2
(NCCH), 121.3 (ArCF3), 52.3 (CHCH2CH), 45.9 (CHC¼¼O), 45.6
(CHCHC¼¼O); 19F NMR (500 MHz, CDCl3, d): ꢃ62.85 (CF3);
ESI/MS: Calcd. for C23H15F6NO2: 451.3, Found: 451.1; IR
(KBr): m ¼ 2987, 2929, 2861, 1773, 1709, 1649, 1518, 1460,
thyl)biphenyl-norbornene-dicarboximide)
32,200 and 1.3, respectively.
(PTNDI)
were
1H NMR (500 MHz, CDCl3, d): 7.96–7.87 (s, oAArHACF3
þ
pAArHACF3), 7.68–7.54 (d, mAArHANC¼¼O), 7.39 (d,
oAArHANC¼¼O), 5.89–5.69 (s, CH¼¼CH on polymer chain),
3.41–3.06 (s, CHC¼¼O þ CHCHC¼¼O), 1.84 and 1.53 (d,
CHCH2CH); 13C NMR (125 MHz, CDCl3, d): 175.4 (ArNC¼¼O),
142.1 (NCCH), 138.0 (NArACCH), 134.8 (CAArCF3), 132.7–
132.2 (CH¼¼CH on polymer chain), 129.5 (CF3C), 127.5
(NCCHCH), 127.0 (NArACCH), 124.6 (NCCH), 121.2
(CHCCF3), 119.0 (ArCF3), 49.0 (CHC¼¼O), 45.3 (CHCHC¼¼O),
40.65 (CHCH2CH).
1381, 1272, 1177, 1126, 1101, 1054 cmꢃ1
.
Polymerization of TNP
N-3,5-bis(trifluoromethyl)biphenyl-norbornene-
Monomer TNP (0.634 g, 1.5 mmol) and Ru-I (12.3 mg, 0.015
mmol) were stirred in 7.5 mL of CH2Cl2 at 30 ꢁC for 1 h.
The values of Mn and PDI of poly(N-3,5-bis(trifluoromethyl)-
biphenyl-norbornene-pyrrolidine) (PTNP) were 27,200 and
1.21, respectively.
pyrrolidine (TNP)
To a slurry of LiAlH4 (1.22 g, 32 mmol) in Et2O (40 mL),
TNDI (3.6 g, 8 mmol) in CH2Cl2 (40 mL) was added slowly
under nitrogen atmosphere at 0 ꢁC, and the mixture was
stirred at room temperature for 6 h. EtOAc (5 mL) was
added, and then water (2 mL) was carefully introduced. The
resulting suspension was filtered, and the residue was
washed with CH2Cl2 repeatedly. The organic phase was dried
with MgSO4 and the solvent was removed in vacuo to give
the crude product as a yellow color solid. After recrystalliza-
tion from ethanol for three times, the product was obtained
in a white flake (2.4 g, 72% yield).
1H NMR (500 MHz, CDCl3, d): 7.92 (m, oAArHACF3), 7.88 (m,
pAArHACF3), 7.43 (m, mAArHANCH2), 6.74–6.67 (m,
oAArHANCH2), 5.46 (d, CH¼¼CH on polymer chain), 3.27–
3.23 (m, ArNCH2), 2.92–2.72 (m, CHCHCH2N þ CHCH2N), 1.80
and 1.45 (d, CHCH2CH); 13C NMR (125 MHz, CDCl3, d): 157.2
(NCCH), 148.5 (NArACCH), 135.5 (CH¼¼CH on polymer chain),
127.8 (CF3C), 125.6 (NCCHCH), 124.6 (NArACCH), 122.7
(CAArCF3), 119.5 (CHCCF3), 126.7, 120.2, 115.8, 112.0
(ArCF3), 113.8 (NCCH), 49.9 (CHCH2N), 47.5–46.5 (CHCHCH2N),
45.0–44.7 (CHCH2N), and 37.5–35.7 (CHCH2CH).
mp 110 ꢁC; 1H NMR (500 MHz, CDCl3, d): 7.93 (s, 2H,
oAArHACF3), 7.70 (s, 1H, pAArHACF3), 7.48–7.47 (d, J ¼
8.65 Hz, 2H, mAArHANCH2), 6.55–6.53 (d, J ¼ 8.6 Hz, 2H,
oAArHANCH2), 6.19 (s, 2H, CHCH¼¼CHCH), 3.32–3.28 (m, J
¼ 17.9, 3.8 Hz, 4H, ArNCH2), 3.12–2.96 (m, 4H, CHCHCH2N
þ CHCH2N), 1.64–1.63 and 1.55–1.53 (d, J ¼ 8.6 Hz, 2H,
CHCH2CH); 13C NMR (125 MHz, CDCl3, d): 147.8 (NCCH),
143.4 (NArACCH), 135.8 (CHCH¼¼CHCH), 131.9 (CF3C), 127.8
(NCCHCH), 125.7 (NArACCH), 124.7 (CAArCF3), 122.5
(CHCCF3), 118.9 (ArCF3), 112.4 (NCCH), 52.1 (CHCH2N), 50.6
(CHCH2CH), 46.6 (CHCHCH2N), 45.5 (CHCH2N); 19F NMR
(500 MHz, CDCl3, d): ꢃ62.84 (CF3); GC: single peak observed
RESULTS AND DISCUSSION
Synthesis of Functional Monomers
Synthesis of norbornene-based monomers TNDI and TNP
was carried out by using the commercial chemicals in a
simple procedure as shown in Scheme 1.
TNDI was prepared readily by the reaction of NDA with
4-amino-30,50-bis(trifluoromethyl)biphenyl in the presence of
catalyst DMAP in DCE at refluxed temperature, and the
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SCHEME 1 Synthesis of functional monomers and polymers.
reaction was monitored by thin layer chromatography analy-
sis. The crude product was purified by recrystallization from
ethanol to give a white needle crystal. TNDI was character-
ized by MS and NMR spectroscopy. 1H NMR spectrum [Fig.
1(A)] indicates that the presence of methylene group (proton
b) at 1.80–1.65 ppm and double bond (proton a) at 6.29
ppm on the norbornene ring, and the phenyl groups (pro-
tons e, f, g, and h) at 7.30–7.87 ppm. The molecular weight
of TNDI from MS analysis was in good accordance with the
calculated value, and the product has a high purity estimated
from the single peak of GC chromatogram. Also, the 19F NMR
spectrum of TNDI (Supporting Information Fig. S1A) shows
the resonance signal of CF3 group at ꢃ62.85 ppm. All of
these points assured that 3,5-bis(trifluoromethyl)biphenyl
group has been successfully connected to the norbornene
ring.
PNP was obtained from PNDI by the same procedure as that
of TNP. The 1H NMR spectrum of PNP (Supporting Informa-
tion Fig. S2B) indicates the new resonance signals of
TNP was obtained by reduction of TNDI with LiAlH4, and the
reaction was monitored by thin layer chromatography analy-
1
sis. H NMR spectrum [Fig. 1(C)] showed the new resonance
signals appeared at 3.32–3.28 ppm from two groups of
methylene (proton i) adjacent to the norbornene ring, meant
carbonyl group was completely reduced to methylene. GC/
MS also indicated that the product has a high purity and the
exact molecular weight. Additionally, IR spectrum showed
the disappearance of typical, characteristic C¼¼O stretch band
of TNDI at 1773 and 1709 cmꢃ1, confirming the transforma-
tion of carbonyl into methylene successfully. The 19F NMR
spectrum of TNP (Supporting Information Fig. S1B) showed
the resonance signal of CF3 group at ꢃ62.84 ppm, which fur-
ther confirmed the successful preparation of TNP.
PNDI was synthesized by two steps (Supporting Information
Scheme S1) in a similar procedure of literature.37 The 1H
NMR spectrum of PNDI (Supporting Information Fig. S2A)
showed the resonance signals of methylene (proton b) at
1.60–1.50 ppm, and double bond (proton a) at 6.14 ppm on
the norbornene ring. Moreover, the resonance signals of phe-
nyl (protons e, f, and g) at 7.22, 6.63, and 6.45 ppm can be
clearly observed, which correspond to the chemical structure
of PNDI. GC/MS also indicated that the product has a high
purity and the exact molecular weight.
FIGURE 1 1H NMR spectra of (A) TNDI, (B) PTNDI, (C) TNP,
and (D) PTNP.
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TABLE 1 Ring-Opening Metathesis Polymerization of
imide and pyrrolidine when carbonyl group transformed into
methylene group. The yield of PTNP increased as raising the
polymerization temperature from 30 to 50 ꢁC; however, PDI
is also broad under the similar conditions. What is more im-
portant, PTNP and PTNDI are completely soluble in common
organic solvents such as CHCl3, THF, and so forth, and this
feature favored the possibility of their application as thin
film. Similar with TNP, polymerization of monomer PNP was
carried out readily by Ru-I at 30 ꢁC for 1 h. Nevertheless,
poly(N-phenyl-norbornene-pyrrolidine) (PPNP) is only little
soluble in CHCl3 and THF, and this may be related to the
rigid phenyl rings in the side chain of polymer. When the po-
lymerization temperature raised to 50 ꢁC, polymer was
found to be insoluble in all the common solvents even in
decalin. A reduced ratio of monomer to catalyst from 100:1
to 50:1 was then used, and the corresponding polymer with
a lower molecular weight was soluble in THF and CHCl3. Of
course, the poor solubility of PPNP has a limitation to afford-
ing a high molecular weight polymer and its application to
the thin film capacitors.
Monomersa
b
T
t
Yield Mn
Run Monomera Cat. Sol.
(ꢁC) (h) (%)
(kDa) PDI
1
2
3
4
5
6
7
8
9
TNDI
TNDI
TNDI
TNDI
TNP
Ru-I CH2Cl2 30
Ru-I CHCl3 50
Ru-II CHCl3 50
Ru-II CHCl3 50
Ru-I CH2Cl2 30
Ru-I CHCl3 50
Ru-I CH2Cl2 30
Ru-I CHCl3 50
Ru-I CHCl3 50
1
6
1
2
1
1
1
1
1
–
–
–
36
80
90
81
93
85
95
95
10.9
32.2
37.7
27.2
35.1
17.0
–
1.22
1.30
1.51
1.21
1.48
1.35
–
TNP
PNP
PNP
PNPc
7.83
1.29
a
[M]0/[Cat]0 ¼ 100:1 (mol/mol), M ¼ monomer, Cat ¼ catalyst.
b
Determined by GPC in THF relative to monodispersed polystyrene
standards.
c
[M]0/[Cat]0 ¼ 50:1 (mol/mol).
The occurred polymerization was confirmed by 1H NMR
spectra [Fig. 1(B,D) and Supporting Information Fig. S2C] on
the basis of the varied olefinic proton signals. The signal of
olefinic protons on the norbornene ring at about 6.19 ppm
is completely disappeared after ring opening, whereas the
new signal of olefinic protons on the backbone comes at
5.90–5.40 ppm, which points out polymerization is proc-
essed successfully. According to the previous assign-
ments,19,41 the trans/cis ratio of as-synthesized polymers can
be analyzed by integration of the 13C NMR signals related to
the vinyl group at 131–133 ppm in Figure 2(B,C), and the
results suggested that the most trans PTNP and PPNP
formed, whereas PTNDI seems to be that the quantitative
difference of trans to cis from Figure 2(A) is reduced, or the
content of cis PTNDI increased significantly. When getting
these highly trans polymers, the tacticity is supposed to be
determined by 13C NMR. When it comes to the tacticity of
endo-type substituted polymers, there are four possible
microstructures as it can be seen from Scheme 2 for the rep-
resentative case of PTNP. It would be two conformations
syn/anti, which means the orientation of side groups
attached to polymer chain in both isotactic and syndiotactic
styles.26 For the isotactic structures, syn conformation has a
plane of symmetry perpendicular to the polymeric backbone
and bisecting each monomeric unit. However, the two planes
of symmetry (r and r0) in two neighboring units are differ-
ent; therefore, two sets of 13C NMR signals would be antici-
pated. On the other hand, anti conformation has the center
of inversion (i) at the center of the carbon–carbon double
bond, it is expected that it would show only one set of 13C
NMR signals. For the syndiotactic structures, syn conforma-
tion has a C2 symmetry axis bisecting the C¼¼C double bond,
whereas the anti form has the C2 rotation axis perpendicular
to the polymeric backbone and orthogonal to the corre-
sponding C2 axis of the syn conformation. Each of the neigh-
boring monomeric units have the same environments, and
only one set of 13C NMR signals would be expected in both
syn and anti conformations.
proton h belong to methylene at 3.2–3.0 ppm, which means
carbonyl group has been reduced by LiAH4. GC/MS shows
that the molecular weight matched to the calculated value.
The structure was further confirmed by IR, which shows the
complete disappearance of bands corresponding to carbonyl
group (1714 cmꢃ1) in PNDI after the reaction. All of these
points affirmed the successful preparation of PNP with the
expected structure.
Preparation of Functional Polynorbornenes by Ring-
Opening Metathesis Polymerization
ROMP of monomers was conducted by using Ru-I or Ru-II
as the catalyst and produced the corresponding polymers in
an acceptable yield (Table 1). Catalyst Ru-I was the first
selection to initiate ROMP of TNDI on the basis of its charac-
ter to well control the polymerization process and the mo-
lecular weight of polymers. Unfortunately, PTNDI was not
formed by Ru-I under the mild conditions of 1 h and 30 ꢁC
likely because of the low reactivity of such endo-configura-
tion cyclic olefin of TNDI, and this was similar with that case
of polymerization of endo-PNDI by using Ru-I to achieve the
polymer PPNDI in a low yield.38 Raising temperature and
prolonging the reaction time, polymerization was really
occurred while the yield of PTNDI was only 36%. There
have been some reports on that the reactivity of exo isomers
of norbornene derivatives is higher than the endo ones due
to the steric interactions between the propagating ruthe-
nium-center and the endo-ring of an incoming monomer.38–40
Therefore, a more active catalyst Ru-II was chosen to
improve the polymerization behavior of endo-TNDI and to
give the corresponding polymer. As expected, polymerization
of endo-TNDI was well conducted by Ru-II with a good yield
at 50 ꢁC for 1 h. As the reaction time prolonged to 2 h, the
yield of polymer increased, and also the value of PDI became
wide in some extent.
Monomer TNP can be polymerized by Ru-I at 30 ꢁC, prob-
ably because of the difference of electronic effect between
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FIGURE 2 13C NMR spectra of (A) PTNDI, (B) PTNP, and (C) PPNP.
Specifically, in the endo-type substituted PNBE derivatives,
the signals of methylene carbon can provide undoubtedly
evidence. As shown in the 13C NMR spectra at 35–42 ppm,
there are two sets of peaks [Fig. 2(B)] for methylene carbon
(Cb) in PTNP, whereas the counterpart of Cb in PPNP
presents one set of signal [Fig. 2(C)]. The electron withdraw-
ing and donating side groups contribute to the difference of
the peaks of methylene carbon in PTNP and PPNP, which is
similar to that of literature.26 However, PTNDI shows a mul-
tiplicity of Cb peaks [Fig. 2(A)]. On the basis of the analysis,
it seems like that PTNP adopts isotactic stereochemistry
showing two sets of signals in methylene carbon, which have
practically trans double bond and the dipolar pendant
groups are coherently arranged in the syn conformation.
PPNP having one set of signals may be isotactic anti or syn-
diotactic syn and anti conformations. By contrast, PTNDI is
supposed to be atactic because of the multiple peaks of
methylene carbon, which is in accordance with trans and cis
isomers.
Dielectric Properties
The dielectric spectroscopy of a thin film was shown in
Figure 3. The thickness of film was about 3 lm. PTNP dis-
played an attractive dielectric constant of about 20 even at
frequency up to 1 MHz at room temperature, and this value
is significant higher than that of common polymer dielectrics,
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SCHEME 2 Possible conformations of isotactic and syndiotactic PTNP.
which is usually in the range of 2–6. Surprisingly, the dielec-
tric response of PTNDI is about 7, and it is only one-third of
that of PTNP. Also, the observed value of dielectric response
for PPNP is only 3 at frequencies of 100 Hz to 1 MHz.
The dielectric performance of polymers is closely related to
their chemical component and chain microstructure. The
stronger is polarity of side chain in polymer, the greater is
the degree of polarization, the higher is the dielectric con-
stant. PTNP has two CF3 substituents in each side chain,
which definitely increases the dipolement of the side chain
in a great content.18 Therefore, PTNP has a much more
higher dielectric constant about 20 than that of PPNP about
3. However, the existence of the polar group is not the only
reason for the high dielectric response. If the polar groups
were attached to the polymer chain irregularly, such as atac-
tic polymer, the dipolement would be cancelled out,17,18 as
depicted in the case of atactic PTNDI, its dielectric constant
decreased to about 7, although bearing two CF3 groups in
each TNDI unit. These results indicated that the dielectric
FIGURE 3 Dielectric constant of polymers versus frequency
from 100 Hz to 1 MHz.
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It can also be noted in Figure 3 that the dispersion of dielec-
tric constant is reasonable small. That is to say, the polymers
exhibited a relatively high dielectric constant in the low
frequency, and followed by a little reduction in the high fre-
quency. Such a slight dispersion may be a result of the
formation of large polar moieties42 and the strong electron-
withdrawing CF3 groups.
Figure 4 showed the dielectric loss of PTNP, PTNDI, and
PPNP. All these polymers exhibited a small dielectric loss in
the range of 0.01–0.05 at the frequencies of 100 Hz to 0.1
MHz. PPNP has the lowest dielectric loss of about 0.01 at
frequency below 0.1 MHz, and further down to 0.004 as the
frequency up to 0.1–1 MHz. PTNP has a more stable dielec-
tric loss of 0.045 without an obvious fluctuation in all the
frequency range. The dielectric loss of PTNDI is about 0.04
at the frequency of less than 0.1 MHz; however, it increases
sharply toward 0.1 near the frequency of 1 MHz. A low
dielectric loss is necessary for high performance devices as
it may result in higher efficiency and lower noise,42 which is
especially critical for high frequency applications. In general,
PTNP with high dielectric constant and relative low dielectric
loss is a suitable candidate for thin film capacitors.
FIGURE 4 Dielectric loss of polymers versus frequency from
100 Hz to 1 MHz.
response is determined not only by the polar group but also
by the chain microstructure of polymer. It has been reported
that metathesized polymers catalyzed by Ru-I easier to take
mainly trans conformation.24 The pyrrolidine moiety in the
side chain of PTNP is attributed to the stereochemistry26
and the dipolement. Because of the rigidity of pyrrolidine, all
rigid side groups aligned coherently in one orientation dur-
ing the ROMP process,28,29 which makes the most TNP units
arranged in the same direction, and tends to adopt the high
trans configuration and afford a syn conformation isotactic
polymer [Fig. 2(B)], resulting in a highly asymmetry of PTNP
chain and, hence, the high dielectric constant. On the other
hand, pyrrolidine is an electron-donating moiety, whereas
CF3 is an electron-withdrawing group, and the dipolement
will increase tremendously by this intramolecular asymmet-
ric structure and the large conjugated biphenyl group in
PTNP. By contrast, the dicarbonimide-based polymer PTNDI
has both trans and cis isomers, tending to be an atactic
polymer chain and the dipolement counteracted, and finally
lowered the dielectric response in a great extent.
To check if there is a thickness dependence of the dielectric
performance for polymer, the dielectric measurement of
polymers with various thicknesses has been carried out. The
results have been shown in Table 2. It is clearly demon-
strated that the dielectric constant of these polymers has no
obvious correlation to the sample thickness ranged from 3
to 10 lm. All of them just show a slight change of dielectric
constant when the sample thickness is altered. Specifically,
the values for PTNP are 20–21, PPNP has still relatively low
values of 3–3.2, and the dielectric constant of PTNDI remains
6–7.5. When it referred to the relationship between the
dielectric constant and polymerization degree of polymer,
the situation is no longer the same among these polymers.
The dielectric constant of PTNP has positive correlation to
the polymerization degree, and the values are 16–22 with
Furthermore, the presence of large aromatic group in PTNP
may be an important factor because they may interact with
the neighboring aryl pendant group. The existence of two ar-
omatic rings between the side groups of PTNP would intro-
duce strong p-p interactions.31,32 These p-p interactions
between the neighboring aromatic rings, especially with the
electron-withdrawing substituents,26 would be essential for
controlling the stereochemistry of polymerization during the
course of ROMP. These interactions induce the side chains of
polymer probably to take the homogeneous direction pre-
dominantly, and two CF3 groups in the side chain greatly
increase the dipolement of polymer, so the dielectric con-
stant of PTNP can reach a high level of 20. As a result, the
dielectric constant of isotactic PTNP is high and better than
those of atactic PTNDI and isotactic or syndiotactic PPNP.
Combined the high dielectric constant with the data of 13C
NMR spectrum, we believed that both the dipolar groups
and the tactic microstructure of polymer chain do play key
roles in the dielectric property of polymers.
TABLE 2 Dielectric Constant of Polymer Versus Molecular
Weight and Thickness of Film
b
Polymer
na
Mn (kDa)
PDI
dc (lm)
ed
PTNDI-1
PTNDI-2
PTNDI-3
PTNP-1
PTNP-2
PTNP-3
PPNP-1
PPNP-2
PPNP-3
a
84
51
31
83
64
30
81
57
37
37.7
23.0
14.0
35.0
27.2
12.7
17.0
12.0
7.83
1.51
1.28
1.16
1.48
1.21
1.12
1.35
1.22
1.29
3
7.5
3–10
6–7.5
7
3
3
22
3–10
20–21
16
3
3
3.5
3–10
3
3–3.2
2.6
The polymerization degree.
b
Determined by GPC in THF relative to monodispersed polystyrene
standards.
c
The thickness of polymer films.
d
The dielectric values of polymer films.
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FIGURE 6 TGA curves of polymers.
FIGURE 5 DSC traces of polymers.
dine-containing PTNP and PPNP, because the presence of CF3
moieties inhibits packing of the phenyl ring and decreases
the temperature to attain the relaxation process, so the Tg of
PTNP was lower than that of PPNP.
different polymerization degree ranging from 30 to 83. The
values for PPNP have also a slightly increase from 2.6 to 3.5
with increased polymerization degree of 37–81. However,
there is a little change of dielectric constant (7–7.5) existed
in the case of PTNDI, and its variation is below 1 with vari-
ous polymerization degree of 31–84. Therefore, the impres-
sive dielectric response we have observed should be the
intrinsic behavior of PTNP, and it is contributed by the colla-
borated tactic microstructure of polymer and the dipolement
of side groups. The different microstructures of PTNP and
PTNDI introduce such discrepancy in their dielectric con-
stants. As for PPNP, there is still an enhancement of dielec-
tric constant with the increased polymerization degree.
Because of the low dipole of phenyl group in PPNP, the val-
ues are changed in a relative low range.
The thermal properties of polymers were affected by the
chain structure and the side substitutions and evaluated by
TGA (Fig. 6). The decomposition temperatures (Tds) of PTNP
and PTNDI at 5% weight loss are 315 and 365 ꢁC, respec-
tively, whereas that the counterpart of PPNP is just 250 ꢁC,
suggesting the thermal stability of PTNP and PTNDI is much
better than that of PPNP with analogous structure, and that
is because of the two CF3 groups in the side chain of PTNP
and PTNDI.38 PPNP presents the lower Td value at 10%
weight loss of polymer although Tds are all above 350 ꢁC,
which indicates that all these functional PNBEs are of rela-
tively high thermal stability. PTNDI displayed the highest val-
ues of Td and Tg among these polymers because of the dicar-
bonimide-based structure and CF3 substitutions on the
pendant phenyl ring. Having the excellent thermal stability
and high Tg make the functional PNBEs more likely to fabri-
cate the thin film capacitors.
Thermal Properties
The DSC technique is invited to obtain the glass transition
temperature (Tg), in order to erase any previous thermal his-
tory, two steps were performed. First, ꢁthe polymers weꢁre
ꢁ
heated to 300 C and then cooled to 25 C at a rate of 10 C
minꢃ1. Second, they were heated once more to 300 ꢁC and
ꢁ
CONCLUSIONS
cooled to 25 C with the same heating and cooling rate. Dur-
ing the second heating cycle, we obtained the values. From
the curves (Fig. 5), Tgs for PTNP, PPNP, and PTNDI were
observed at 161, 181, and 244 ꢁC, respectively (Table 3). Tg
is depended on the trans content of polymer, and decreased
as the higher trans existed. The lower Tg of PTNP compared
with PTNDI is probably because of the higher content of
trans double bond, which indicates a fairly typical manifesta-
tion of variation in chain microstructure.17 As for the pyrroli-
Novel dielectric functional PNBEs with different side groups
and dipolement were synthesized by ROMP using Grubbs
catalyst under the mild reaction conditions, and the micro-
structure of polymer chain was characterized by NMR spec-
troscopy. Isotactic PTNP with large dipolement group 3,5-
bis(trifluoromethyl)biphenyl and pyrrolidine moiety pos-
sesses a high dielectric constant of 20, whereas isotactic or
syndiotactic PPNP with phenyl group and pyrrolidine moiety
has a dielectric constant of only 3. By comparison of the
dielectric constant about 7 of atactic PTNDI with 3,5-bis(tri-
fluoromethyl)biphenyl group and imide moiety, we believe
that the pyrrolidine moiety is an essential element to control
the stereoregularity of polymers. The thermal properties of
polymers were also investigated. Having high dielectric prop-
erties and thermal stability, PTNP is expected to be a good
potential dielectric material in the thin film capacitor.
TABLE 3 Thermal Properties of Polymers
Polymer
Td5% (ꢁC)
Td10% (ꢁC)
Tg (ꢁC)
PTNP
PPNP
PTNDI
315
250
365
380
355
408
161
181
244
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ACKNOWLEDGMENTS
The authors thank the National Natural Science Foundation of
China (No. 50973030 and No. 21074036) and Large Instru-
ments Open Foundation of East China Normal University for fi-
nancial supports of this work.
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