Synthesis and properties of cross-linkable high molecular weight fluorinated copolyimides

Article abstract of DOI:10.1002/pola.27007

A series of novel high molecular weight fluorinated co-polyimides (Co-PIs) containing styryl side chain based on 1,3-bis(2-trifluoromethyl-4-aminophenoxy)- 5-(2,3,4,5-tetrafluorophenoxy)benzene (6FTFPB) were successfully synthesized. The weight-average molecular weights (M_ws) and polydispersities of the co-polyimides were in the range 8.93-10.81 × 10⁴ and 1.33-1.82, respectively. The co-polyimide film showed excellent solubility in organic solvents, high tensile properties (tensile strength exceeded 91 MPa), excellent optical transparency (cutoff wavelength at 332-339 nm and light transparencies above 89% at a wavelength of 550 nm), and high thermal stability (5% thermal weight-loss temperature up to 510 °C). The casting and spinning films could be cross-linked by thermal curing. The cured films show better combination property (including excellent resistance to solvents) than that of co-polyimides. For instance, the glass transition temperature of Co-PI-1 (the molar weight ratio of 6FTFPB was 30%) increased from 217 to 271 °C, the tensile strength enhanced from 94 to 96 MPa, the 5% thermal weight-loss temperature improved from 514 to 525 °C. Moreover, after cured, Co-PI-1 film also has a coefficient of thermal expansion (CTE) value of 60.3 ppm °C ^-1, low root mean square surface roughness (R_q) at 4.130 nm and low dielectric constant of 2.60. 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 349-359 Novel cross-linkable high molecular weight fluorinated copolyimides are synthesized. The copolyimides exhibit excellent solubility, high tensile properties, and good optical transparency. The copolyimides can cross-link thoroughly after curing at 260 °C under a vacuum. The cured copolyimides have excellent chemical resistance and high thermal properties. The obtained cured films have a low dielectric constant and excellent surface planarity. Copyright

Full text of DOI:10.1002/pola.27007

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Synthesis and Properties of Cross-Linkable High Molecular Weight
Fluorinated Copolyimides
Hongyan Yao,1 Yunhe Zhang,1 Yu Liu,1,2 Kaiyuan You,1 Shanyou Liu,1
Baijun Liu,1 Shaowei Guan1
1Alan G. MacDiarmid Institute, Jilin University, Qianjin Street 2699, Changchun 130012, People’s Republic of China
2Institute of Metal Research Chinese Academy of Sciences, Wenhua Road 72, Shenyang 110016, People’s Republic of China
Correspondence to: S. Guan (E-mail: guansw@jlu.edu.cn)
Received 7 August 2013; accepted 30 October 2013; published online 17 November 2013
DOI: 10.1002/pola.27007
ABSTRACT: A series of novel high molecular weight fluorinated
co-polyimides (Co-PIs) containing styryl side chain based on
1,3-bis(2-trifluoromethyl-4-aminophenoxy)-5-(2,3,4,5-tetrafluoro-
phenoxy)benzene (6FTFPB) were successfully synthesized. The
weight-average molecular weights (Mws) and polydispersities
of the co-polyimides were in the range 8.93–10.81 3 104 and
1.33–1.82, respectively. The co-polyimide film showed excellent
solubility in organic solvents, high tensile properties (tensile
strength exceeded 91 MPa), excellent optical transparency (cut-
off wavelength at 332–339 nm and light transparencies above
89% at a wavelength of 550 nm), and high thermal stability
(5% thermal weight-loss temperature up to 510 ꢀC). The casting
and spinning films could be cross-linked by thermal curing.
The cured films show better combination property (including
excellent resistance to solvents) than that of co-polyimides. For
instance, the glass transition temperature of Co-PI-1 (the molar
weight ratio of 6FTFPB was 30%) increased from 217 to 271 ꢀC,
the tensile strength enhanced from 94 to 96 MPa, the 5% ther-
mal weight-loss temperature improved from 514 to 525 ꢀC.
Moreover, after cured, Co-PI-1 film also has a coefficient of
thermal expansion (CTE) value of 60.3 ppm ꢀC21, low root
mean square surface roughness (Rq) at 4.130 nm and low
C
V
dielectric constant of 2.60.
2013 Wiley Periodicals, Inc.
J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 349–359
KEYWORDS: crosslinking; fluoropolymers; polyimides; solubility;
transparency; refractive index
Compared to phenylethynyl, styryl can undergo cross-linking
reaction by both thermal heating and UV irradiation. Besides,
the thermal cross-linked reaction of styryl is readily accom-
plished by heating at a relative low temperature in the pres-
ence of a small amount of thermal initiator.9,10
INTRODUCTION As a kind of high-performance polymeric
materials, aromatic polyimide (PI) has exhibited remarkably
comprehensive characters, such as excellent thermal stabil-
ity, high mechanical strength, good electric and optical
properties.1–5 In the past several decades, fluorinated polyi-
mides with low moisture absorption, low refractive index,
and low dielectric constant while maintaining many of
advantages of polyimides have been prepared through
introducing fluorine to the structure of the macromolecules.
In addition, the incorporation of fluorine-containing sub-
stituents (ACF3) is also known to enhance the solubility
and optical transparency of polyimides.6–8 Consequently,
the fluorinated polyimides are of considerable interest for
optical and electronic applications in recent years.
Over the past decade, a great deal of effort has been concen-
trated on the introduction of cross-linkable structure to the
end of oligomers, internal groups, or pendant groups of mac-
romolecules. In recent years, phenylethynyl terminated imide
oligomers have been widely studied.11–17 However, to ensure
the cross-linkable groups terminated oligomers have sufficient
high cross-linking density, it is necessary to reduce the molec-
ular weight of oligomers. Therefore, some properties such as
mechanical strength and thermal properties should be sacri-
ficed. For example, Yang et al. synthesized a series of phenyle-
However, during the fabricated process of multilayer optoe-
lectronic device, the polymeric material must have good
resistance to organic solvents. In another word, the initial
material could be dissolved in organic solvents, but insoluble
after being films. For the purpose, the introduction of the
cross-linkable structure becomes necessary. Styryl and phe-
nylethynyl are both commonly used cross-linking groups.
thynyl terminated imide oligomers based on
a
new
endcapping agent. For these oligomers, the lower Mn oligom-
ers showed lower Tg values, lower curing onset temperatures
and stronger curing exothermal peaks. After thermal curing,
the oligomer with the lowest molecular weights possessed the
highest Tgs and worst mechanical properties which the tensile
C
V
2013 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
349

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1 Synthesis of the diamine monomer 1,3-bis (2-trifluoromethyl-4-aminophenoxy)-5-(2,3,4,5-tetrafluorophenoxy) benzene
(6FTFPB).
strength and elongation at break as low as 41.7 MPa and
6.2%, respectively.16 To balance the relationship between the
cross-linking density and molecular weight, some macromole-
cules containing cross-linkable group in the main chain have
been synthesized.18,19 But the cross-linked temperature of the
macromolecules is much higher than the terminated oligomer,
because the movement of cross-linkable internal groups is
more difficult. As a strategy to solve the problem above,
cross-linkable side chain copolymers have been extensively
studied.20–22 However, there are few studies on the polyimide
which contain the cross-linkable side chain in the literature.
purchased from Aldrich Chemical and used without further
purification. 1,4-Bis-(4-amino-2-trifluoromethylphenoxy)ben-
zene (6FAPB) was synthesized in our laboratory according to
the literature.7 N,N-Dimethylformamide (DMF), N,N-dimethyla-
cetamide (DMAc), and triethylamine were purified by distilla-
tion under reduced pressure over calcium hydride and stored
over 4 Å molecular sieves.
Measurements
Gel permeation chromatograms (GPC) were obtained on a
Waters 410 instrument with tetrahydrofuran (THF) as an
eluent at a flow rate of 1 mL min21 using polystyrene as a
standard. FTIR spectra were measured on a Nicolet Impact
410 Fourier-transform infrared spectrometer. Nuclear mag-
netic resonance (NMR) spectra were measured on a Bruker
AVANCE NMR spectrometer at a resonance frequency of 300
In our study, to introduce cross-linkable functionality into
the side chain of fluorinated PIs and to ensure a suitable cross-
linking density, a fluorinated diamine monomer 1,3-bis(2-tri-
fluoromethyl-4-aminophenoxy)-5-(2,3,4,5-tetrafluorophenoxy)-
benzene (6FTFPB) was designed and prepared via
a
1
MHz for H and 470 MHz for 19F. The chemical shifts relative
nucleophilic substitution between 5-bis(4-amino-2-trifluorome-
thylphenoxy)phenol and 2,3,4,5,6-pentafluorostyrene (as shown
in Scheme 1). A series of novel cross-linkable fluorinated co-
polyimides with styryl moieties in the side chain were prepared.
By varying the feed ratio of diamine monomers, polymer films
with different styryl content have been prepared. The solubility,
thermal, mechanical, and optical properties of the PIs were eval-
uated. It was characterized that PIs exhibited good solubility,
excellent mechanical properties, and high optical transparency.
Moreover, we investigated the thermal crosslinking of the co-
polyimides. After cured, the cross-linked PI films exhibited excel-
lent chemical resistant, high thermal and mechanical properties,
low dielectric constant, and excellent surface planarity.
to tetramethylsilane (TMS) for 1H NMR and CFCl3 for 19F
NMR as internal reference are reported on the ppm scale.
Differential scanning calorimetry (DSC) measurements were
performed on a Mettler Toledo DSC821e instrument at a
21
ꢀ
ꢀ
heating rate of 10 C min from 100 to 400 C under nitro-
gen. Thermo gravimetric analysis (TGA) on a Perkin Elmer
Pyris 1 thermal analyzer system was used to assess the ther-
mal stability of the polyimides. Before the analysis, the polyi-
mides were dried and kept in the TGA furnace at 100 ꢀC
under air for 30 min to remove water. The samples were
ꢀ
evaluated over a temperature range of 100–800 C at a heat-
ing rate of 10 ꢀC min21 under nitrogen. The coefficient of
thermal expansion (CTE) of the PI films was measured by a
thermal mechanical analysis (TMA) using a thermomechani-
cal analyzer TMA/SDTA841e (Mettler Toledo) at a heating
rate of 5 ꢀC min21. The CTE values were calculated as a
mean coefficient of linꢀear thermal expansion in the tempera-
ture range of 50–250 C after heating beyond Tg followed by
EXPERIMENTAL
Materials
Phloroglucinol, 4,40-(hexafluoroisopropylidene)diphthalic anhy-
dride (6FDA), and 2-chloro-5-nitrobenzotrfluoride were
350
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
cooling. The refractive indices of the polymer films were
obtained using a Gaertener L116B spectroscopic ellipsome-
ter. The dielectric constants of the polymer films (diameter
5 13 mm and thickness 5 0.5 mm, prepared by compres-
sion molding, and then coated with silver by a vacuum evap-
oration method) were obtained using an HP 4192A LF
impedance gain-phase analyzer with an HP-6047C. UV trans-
parencies were measured by a Shimadzu UV 2501-PC spec-
trophotometer. The mechanical tests in tension were
performed using a Shimadzu AG-I at a constant crosshead
speed of 10 mm min21. The photographs of the polyimide
films were taken by Canon EOS 600D. Atomic force micro-
scope (AFM) images were recorded with a Nanoscope IIIa
scanning probe microscope from Digital Instruments using
tapping mode under ambient conditions. The gel content of
the crosslinked samples was determined according to ASTM
D2765 method. Samples were extracted by Soxhlet’s appara-
tus in DMAc for 48 h. The residue after extraction was taken
as the gel component, and the gel content was calculated
according to the following eq (1).
refluxed with stirring. To the solution, a mixture of HCl (2
mL, 0.023 mol) and 40 mL of 50% aqueous ethanol was
then slowly added after which, the reaction mixture was fur-
ther refluxed for 5 h and 0.96 g NaOH was added. The hot
mixture was then filtered, and the filtrate was then distilled
to remove the solvent in vacuo. The crude product was puri-
fied by recrystallization from ethanol and deionized water to
ꢀ
give a brownish red solid. Yield: 84%. Mp: 176.8 C. IR (KBr,
cm21): 3430, 3353, and 3300 (NAH stretch), 1127 (CAF
stretch).
1H NMR (300 MHz, DMSO-d6) d: 5.486 (s, 4H, NH2), 5.850–
5.881 (m, 3H), 6.795–6.833 (m, 2H), 6.887–6.929 (m, 4H),
9.627 (s, 1H, OH). 19F NMR (470 MHz, DMSO-d6) d: 260.703
(s, 6F). Mass spectrum: m/z 443.7.
Synthesis of 1,3-Bis(2-trifluoromethyl-4-aminophenoxy)-5-
(2,3,4,5-tetrafluorophenoxy)benzene (3)
3,5-Bis(4-amino-2-trifluoromethylphenoxy)phenol (1.31 g,
2.9 mmol), 2, 3, 4, 5, 6-pentafluorostyrene (0.6867 g, 3.5
mmol), calcium hydride (0.2482 g, 5.8 mmol), and cesium
fluoride (0.0448 g, 0.29 mmol) were added into a 25 mL
three-necked flask equipped with a mechanical stirrer, a
nitrogen inlet, and a water condenser (Scheme 1). Then,
DMAc (13 mL) was added into the flask under the nitrogen
atmosphere. The mixture was heated to 80 ꢀC with stirring
under nitrogen in the dark for 18 h. After cooled to room
temperature, it was poured into 150 mL deionized water,
washed with deionized water, extracted with ether, dried
with anhydrous MgSO4, and then filtrated. The solvent was
evaporated under vacuum, and the residue was then purified
by column chromatography (petroleum ether/ethyl acetate,
4/5) to afford the pure products. Yield: 68%. Mp: 145.8 ꢀC.
IR (KBr, cm21): 3485 and 3379 (NAH stretch), 1635 (CAC),
1127 (CAF stretch).
W2
Gel content5
3100%
(1)
W1
where W1 and W2 are the weights of the samples before and
after refluxed in DMAc for 48 h.
Monomer Synthesis
Synthesis of 3,5-Bis(4-nitro-2-trifluoromethylphenoxy)
phenol (1)
A mixture of phloroglucinol (12.61 g, 0.10 mol), 2-chloro-5-
nitrobenzotrfluoride (45.11 g, 0.20 mol), and K2CO3 (16.59
g, 0.12 mol) were dissolved in DMF (200 mL) and toluene
(40 mL) in a 500 mL three-necked round-bottomed flask
equipped with a mechanical stirrer, nitrogen inlet, thermom-
eter, Dean-Stark trap, and a reflux condenser (Scheme 1).
The apparatus was purged with nitrogen. The reaction mix-
1H NMR (300 MHz, DMSO-d6) d: 5.501 (s, 4H, NH2), 5.809–
5.848 (d, J 5 11.7 Hz, 1H), 5.942–5.956 (m, 1H), 6.027–
6.087 (d, J 5 18 Hz, 1H), 6.367 (s, 2H), 6.652–6.816 (m,
3H), 6.876 (s 2H), 6.917–6.946 (d, J 5 8.7 Hz, 2H). 19F NMR
(470 MHz, DMSO-d6) d: 260.818 (s, 6F), 2144.294 (2F, m),
2156.465 (2F, m). Mass spectrum: m/z 617.9. ELEM. ANAL
Calcd for C28H16F10N2O3: C 54.38, H 2.61, N 4.53; found: C
54.51, H 2.64, N 4.23.
ꢀ
ture was refluxed at 120 C for 5 h to ensure complete dehy-
dration. After removing toluene, the reaction mixture was
heated to 151 ꢀC and refluxed for 8 h under a nitrogen
atmosphere. After being poured into deionized water (2 L),
the precipitate was collected by filtration. The crude product
was washed with deionized water to give earthy yellow pow-
der. Yield: 89%. Mp (melting point): 169.4 ꢀC. IR (KBr,
cm21): 1530 and 1354 (ANO2 stretch), 3446 (OAH), 1143
(CAF stretch).
Polymer Synthesis
Synthesis of the Fluorinated Homo-PIs
1H NMR (300 MHz, DMSO-d6) d: 6.534–6.541 (d, J 5 2.1 Hz,
2H), 6.610–6.624 (m, 1H), 7.331–7.365 (d, J 5 10.2 Hz, 2H),
8.470–8.505 (m, 10.5 Hz, 4H), 10.489 (s, 1H, OH). Mass spec-
trum: m/z 501.9.
Homo-PI-1: A three-necked flask was charged with diamine
6FAPB (0.6425 g, 1.5 mmol) and 9 mL of DMAc. The solution
was stirred under a nitrogen atmosphere until diamine dis-
solved completely, and then 6FDA (0.6664 g, 1.5 mmol) was
added (Scheme 2). The reaction mixture was stirred at ambi-
ent temperature for 24 h under a nitrogen atmosphere to
form poly(amic acid) solution with 15 wt % solid content.
Chemical imidization was performed via the addition of 1.5 g
of triethylamine and 4.5 g of acetic anhydride into the PAA
solution at ambient temperature. The mixture was stirred at
Synthesis of 3,5-Bis (4-amino-2-
trifluoromethylphenoxy)phenol (2)
A total of 3,5-bis(4-nitro-2-trifluoromethylphenoxy)phenol
(28.90 g, 0.057 mol), Fe (38.51 g, 0.68 mol), and 50% aque-
ous ethanol (180 mL) were mixed in a 250 mL, three-
necked, round-bottomed flask equipped with a mechanical
stirrer and a reflux condenser (Scheme 1). The mixture was
ꢀ
60 C for 6 h to yield a polyimide solution. Then the solution
was poured into anhydrous ethanol to give a precipitate and
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
351

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2 Synthesis of the Co-PIs.
washed thoroughly with anhydrous ethanol. Finally, the
product was dried at 80 ꢀC in vacuo for 24 h. Yield: 91.6%.
Homo-PI-2 was synthesized in an analogous procedure. ELEM.
ANAL Calcd for C47H18F16N2O7: C 54.99, H 1.77, N 2.73;
found: C 55.35, H 1.73, N 2.37.
syringe filter with a pore size of 0.22 lm and cast directly
onto clean glass plates with a programmed procedure (25
ꢀC, 6 h; 60 ꢀC, 6 h; 80 ꢀC, 6 h; 120 ꢀC, 6 h) in a vacuum
oven to remove the solvents. After dried thoroughly, tough
and flexible films of PIs were obtained (Fig. 7). The thick-
nesses of the films were in the range of ꢁ30 lm. To measure
the properties of cured films, the polyimide films were put
into a vacuum oven and treated at 260 ꢀC for 2 h to obtain
the cured films.
Synthesis of the Cross-linkable Fluorinated Co-PIs
A typical synthetic procedure for the preparation of cross-
linkable fluorinated co-polyimide (Co-PI-2) is as follows
(Scheme 2). To a solution of 6FTFPB (0.4638 g, 0.75 mmol)
and 6FAPB (0.3212 g, 0.75 mmol) in DMAc (10 mL), 6FDA
(0.6664 g, 1.5 mmol) was added. The mixture was stirred in
nitrogen at room temperature for 24 h to yield a viscous pol-
y(amic acid) (PAA) solution with 15 wt % solid content.
Chemical imidization was performed via the addition of 1.5 g
of triethylamine and 4.5 g of acetic anhydride into the PAA
solution at ambient temperature. The mixture was stirred at
60 ꢀC for 6 h to yield a polyimide solution. Then it was
poured into anhydrous ethanol to give a precipitate. Co-PI-2
was collected by filtration, washed thoroughly with anhydrous
ethanol, and dried at 80 ꢀC in vacuo for 24 h. Yield: 94.2%.
Other Co-PIs were synthesized in an analogous procedure.
Film Preparation for the Measurement of Refractive
Index
The polymer solutions were prepared in DMAc (1 g/10 mL).
The solutions were then filtered through a Teflon syringe fil-
ter with a pore size of 0.22 lm and spincoated onto a SiO2/Si
ꢀ
ꢀ
substrate with a programmed procedure (25 C, 6 h; 60 C, 6
ꢀ
ꢀ
h; 80 C, 6 h; 120 C, 6 h) under vacuum. Thermal curing of
the films was then performed by heating slowly to 260 ꢀC
and maintaining this temperature for 2 h in a vacuum oven.
RESULTS AND DISCUSSION
Synthesis and Characterizations of the Monomer
Film Preparation for the Measurement of Optical and
Mechanical Properties
Polyimides (0.5 g) were dissolved in DMAc (5 mL) overnight.
Afterwards, the solutions were then filtered through a Teflon
To improve chemical stabilities of the resulting materials,
many monomers have been designed to contain either ther-
mal or photochemical reactive groups that can undergo
intermolecular reactions under external stimuli to form
352
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Synthesis and Characterizations of the Polymer
Two Homo-PIs and a series of Co-PIs in Scheme 2 were pre-
pared via the conventional two-step method by reacting equi-
molar amounts of the diamines with 6FDA to form the poly
(amic-acid) at ambient temperature and sequential chemical
imidization by adding mixture of acetic anhydride and trie-
thylamine into PAA solution at ambient temperature followed
ꢀ
by heating at 60 C for 6 h to obtain polyimides. The molecu-
lar weights of PIs were determined by GPC and the results
are summarized in Table 1. The weight-average molecular
weights (Mws) and polydispersities were recorded in the
range of 8.93–10.81 3 104 and 1.33–1.82, respectively.
The chemical structures of the PIs were characterized with
FTIR and NMR spectroscopy. The typical FTIR spectrum of
Co-PI-1 is shown in Figure 6. All the PIs exhibited character-
istic absorption bands of the imide ring near 1788 and 1734
cm21 due to C@O asymmetric and symmetric stretching, and
1375 cm21 ascribing to CAN stretching. Furthermore, there
FIGURE 1 FTIR spectra of organic monomers. (a) 3,5-Bis(4-
nitro-2-trifluoromethylphenoxy)phenol. (b) 3,5-Bis(4-amino-2-
trifluoromethylphenoxy)phenol. (c) 1,3-Bis(2-trifluoromethyl-4-
aminophenoxy)-5-(2,3,4,5-tetrafluorophenoxy)benzene.
cross-linked polymer networks. A novel diamine monomer
with styryl side chain was designed and prepared as shown
in Scheme 1. Monomer 6FTFPB was prepared by a three-
stage synthetic procedure starting with nucleophilic substitu-
tion
reaction
of
phloroglucinol
and
2-chloro-5-
nitrobenzotrfluoride. Then the product of first step was
ꢀ
deoxygenized by Fe/HCl in ethanol/deionized water at 90 C.
Finally, as described similarly in the literature,9,10 the mono-
mer 6FTFPB was also synthesized through a nucleophilic
substitution reaction.
The structures of these monomers were confirmed by FTIR,
LC-MS, 1H NMR, and 19F NMR spectroscopy. Figure 1 shows
the FTIR spectra of monomers 1, 2, and 3. The nitro group
of 1 gave characteristic absorption bands at 1354 and 1530
cm21 (NO2 asymmetric and symmetric stretching). In addi-
tion, the hydroxyl of 1 exhibited characteristic absorption in
the region of 3307–3614 cm21 (OAH stretch). After reduc-
tion, the characteristic absorptions of the nitro group disap-
peared, and the amino group exhibited a pair of NAH
stretching bands in the region of 3304–3437 cm21. Finally,
after the second step of nucleophilic substitution reaction,
the vinyl group of monomer 3 gave absorption band at 927
1
cm21 (C@CAH out of plane vibrations). The H NMR and 19F
NMR spectra of 6FTFPB are shown in Figure 2. As shown in
Figure 2(a), the signals at 5.5 ppm were assigned to the pro-
tons in the amino groups of monomer 6FTFPB, while those
characteristic signals at 5.8–6.1 ppm were ascribed to the
protons on the vinyl group of the tetrafluorostyro units. To
confirm the structure of monomer 6FTFPB further, 19F NMR
measurement was also performed. The signals at 2156.53
and 2144.36 ppm corresponded to the aromatic fluorine
atoms, and the peak at 260.70 ppm was assigned to the flu-
orine atoms of ACF3. These results indicated that we had
successfully synthesized the 1,3-bis (2-trifluoromethyl-4-ami-
nophenoxy)-5-(2,3,4,5-tetrafluorophenoxy)benzene.
FIGURE 2 (a) 1H NMR and (b) 19F NMR spectra of the 6FTFPB
in DMSO-d6.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
353

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 1 GPC Data and Monomer 6FTFPB Content of PIs
6FTFPB Content
(mol %)a
6FTFPB Content
from 1H NMRb
Mn (3104)
Mw (3104)
PDId (Mw/Mn)
c
c
Polymers (n/m)
Yield (%)
Homo-PI-1 (0/10)
Co-PI-1 (3/7)
0
0
91.6
93.4
94.2
89.7
88.2
5.76
7.73
5.47
5.13
6.99
10.04
10.31
8.93
1.74
1.33
1.63
1.82
1.55
30
50
70
100
32.5
50.7
70.6
100
Co-PI-2 (5/5)
Co-PI-3 (7/3)
9.34
Homo-PI-2 (10/0)
10.81
a
c
Feed molar ratio of 6FTFPB relative to the total diamines.
Mn, Mw values were determined by GPC in THF with PS as standard.
PDI values (Mw/Mn) were determined by GPC in THF with PS as
b
d
Feed molar ratio of 6FTFPB relative to the total diamines calculated by
the 1H NMR of PIs.
standard.
was not an amide carbonyl peak at 1650 cm21, thus indicat-
ing complete imidization during polycondensation. From the
1H NMR and 19F NMR (Fig. 3), the polymer structures were
found in good agreement with the designed structures. In the
1H NMR spectra, three resonances at 5.79, 6.04, and 6.67
ppm were observed and attributed to the protons on the vinyl
moiety of tetrafluorostyrol groups. No other aliphatic resonan-
ces could be found, indicating that the tetrafluorostyrol units
were introduced successfully into fluorinated polymers and
were stable to the polymerization and imidization conditions
used. Meanwhile, it was observed that these signals attributed
to the vinyl group of the tetrafluorostyrol units increased with
the increasing feed ratio of monomer 6FTFPB in the Co-PIs.
In addition, the protons 3 and 30 were in the same position of
the two kinds of diamines, but due to locating in the polymer
segment of different chemical environments, their chemical
shifts are different. The peak area of 3 and 30 was changed as
the proportion of the two kinds of diamines varied in the
polymerization. According to the 1H NMR, the actual content
of monomer 6FTFPB in the Co-PIs was equal to the ratio of
the peak area of 3 and the sum of the peak area of 3 and 30.
The value of the content of monomer 6FTFPB was calculated
and summarized in the Table 1. On detailed examination of
the 19F NMR spectra, it was observed that two little peaks
around at 260.8 and 263.0 ppm were attributed to F3, F30
and F4, F40 which belonged to the fluorine atoms of ACF3,
respectively. The two peaks at 2143.9 and 2155.9 ppm were
ascribed to the F1 and F2 of the tetrafluorostyrol units,
respectively. Compared to the signals of F3, F30 and F4, F40,
they increased proportionally with the increase of the feed
ratio of monomer 6FTFPB. All the characterizations show that
the series of polyimides were synthesized successfully.
Thermal Cross-linking and Thermal Properties of the
Polymers
Thermal properties of the PIs were evaluated by DSC, TGA,
and TMA. The thermal behavior data of all the PIs are sum-
marized in Table 3. DSC experiments were conducted at a
Solubility of the Polymers
The solubility of synthesized PIs was tested in various organic
solvent and the results are summarized in Table 2. The PIs
showed an excellent solubility in aprotic polar solvents such
as DMSO, DMAc, DMF, and NMP and were also soluble in less
polar solvents like THF, CHCl3, and acetone at room tempera-
ture. The solubility of polyimides is enhanced due to the
introduction of bulky pendant trifluoromethylphenyl group
and tetrafluorostyrol units which could inhibit close packing
and reduced the interchain interactions to enhance solubility.
FIGURE 3 (a) 1H and (b) 13C NMR spectra of the PIs in DMSO-d6.
354
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
TABLE 2 Solubility of the PIs in Organic Solvents
Solventa
Polymers
NMP
DMAc
DMF
DMSO
THF
CHCl3
Acetone
Ethanol
Homo-PI-1
Co-PI-1
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
2
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
2
2
2
2
Co-PI-2
Co-PI-3
Homo-PI-2
a
Qualitative solubility was determined with as 10 mg of polymer in 1 mL
of solvent.
11: soluble at room temperature; 2: insoluble on heating at 100 ꢀC.
NMP: N-methyl-2-pyrrolidone; DMAc: N,N-dimethylacetamide; DMF:
N,N-dimethylformamide; DMSO: dimethyl sulfoxide; THF: tetrahydrofu-
ran; CHCl3: chloroform.
heating rate of 10 ꢀC min21 in nitrogen. All the PIs’ DSC
heating scans exhibited only one distinct Tg in the range of
197–230 ꢀC. According to Fox equation, the Tg of a random
copolymer can be predicted based on the feed ratio of the
monomers using eq (2):22
The tetrafluorostyrol units in the fluorinated polymers can
undergo cross-linking reactions by both thermal heating and
UV irradiation. We investigated the thermal crosslinking of
the co-polyimides emphatically. The thermal crosslinking of
Co-PI-1 was studied by heating the polymer films at 260 ꢀC
for 1 h or 2 h in vacuum in the absence of any initiator. As
shown in Figure 5, an intense exothermic peak was regarded
as the reaction of the vinyl moiety for the uncross-linked
polymer. After thermal curing of the Co-PI-1, the Tg
increased from 217 to 271 ꢀC. But the Tgs of Co-PI-3 and
Homo-PI-2 were not observed in the DSC curve, possibly
because the cross-linking density of the two polyimides is
large enough to limit the molecular chain movement. The
characteristic absorption of the vinyl group near 928 cm21
out of plane vibrations of the vinyl group (CH2@CH) was
selected to monitor the reaction by FTIR spectroscopy. Fig-
ure 6 exhibits the comparisons of FTIR spectra of Co-PI-1
film before and after curing. The absorption peak near 928
cm21 disappeared totally after curing 260 ꢀC for 2 h. ASTM
D2765 method was experimentally used to detect the extent
of the cross-linking reaction. The cured films were extracted
in DMAc for 48 h using Soxhlet’s apparatus. And then the gel
contents of the polymers were calculated according to eq
1
Wt1 Wt2
¼
þ
(2)
Tg Tg1 Tg2
where Tg is the glass transition temperature of the copoly-
mer, Wt1 is the sum of the weight fractions of the repeat
units which contain 6FTFPB relative to the all repeat units,
Wt2 is the sum of the weight fractions of the repeat units
which contain 6FAPB relative to the all repeat units, Tg1 and
Tg2 are the glass transition temperatures of the Homo-PIs
derived from monomer 6FTFPB with 6FDA (Tg1 5 197 ꢀC)
ꢀ
and from 6FAPB with 6FDA (Tg2 5 230 C), respectively. Fig-
ure 4 displayed the measured Tg and the predicted trend
line according to the Fox equation. A good agreement of the
Tgs of the resulting copolymers with the values predicted by
the Fox equation was observed. Thus, it can be concluded
that the two diamine monomers have been randomly incor-
porated into the polymers.
TABLE 3 Mechanical Properties, Thermal Properties and Gel Content of PIs
Tensile
strength
(MPa)
Elongation
Young’s
CTE
Gel
contentd (%)
Polymers
at break (%)
Modulus (GPa)
T5%b (ꢀC)
(ppm ꢀC21 c
)
a
Tg (ꢀC)
Homo-PI-1
Co-PI-1
98
14.7
3.7
230
497
76.7
60.3
62.8
61.6
62.7
0
94 (96)
92 (97)
91 (96)
87 (92)
14.9 (12.5)
8.6 (6.4)
7.5 (6.7)
5.5 (3.2)
3.6 (3.9)
3.5 (4.0)
3.3 (3.8)
3.1 (3.7)
217 (271)
207 (283)
204 (–)
197 (–)
514 (525)
512 (530)
511 (530)
514 (535)
91.5
98.0
99.7
99.8
Co-PI-2
Co-PI-3
Homo-PI-2
c
The data in the parentheses were the data of the polyimides after cur-
ing at 260 ꢀC for 2 h under vacuum.
Coefficient of thermal expansion of cured PI films measured by TMA
in a temperature range of 50–250 ꢀC at a heating rate of 5 ꢀC min21 in
N2.
a
Glass transition temperature measured by DSC with a heating rate of
d
10 ꢀC min21 in nitrogen.
Gel content for cured samples.
b
Temperature at 5% weight-loss were recorded by TGA at a heating at
10 ꢀC min21 in nitrogen.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
355

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
The coefficients of thermal expansion (CTE) of the cured PI
21
ꢀ
films were determined to range from 60.3 to 76.7 ppm C
.
The CTE is dependent on both backbone chemistry and the
morphology and strongly influenced by molecular orienta-
tion. In general, polymers consisting of rigid backbone struc-
tures and causing
a higher degree of in-plane chain
orientation have shown relatively low CTE value.23–26 Com-
pared to Homo-PI-1, other PIs not only possess flexible
molecular structures, but also have cross-linkable styryl side
groups. The styryl groups underwent cross-linking reaction
and formed dense cross-linked structures when cured at
ꢀ
260 C. Lower CTE of the cross-linked PIs might attribute to
the cross-linked structures which limited the macromolecu-
lar chain segmental motion. The CTE of all of the PIs are
about 60 ppm ꢀC21, although the content of styryl side
groups increase from Co-PI-1 to Homo-PI-2. The phenomena
could be ascribed to that the crosslinking densities of these
PIs are high enough, when the content of styryl groups is
beyond 30%. It is consistent with the results of the gel con-
tent characterization. After been extracted by Soxhlet’s appa-
ratus in DMAc for 48 h, the gel component of cross-linked
PIs was more than 90%. The results also indicated that the
cross-linked PIs have excellent chemical resistance.
FIGURE 4 Correlation between Tg of PIs and the molar fraction
of the repeat unit containing 6FTFPB: (᭺) experimentally deter-
mined Tg values from DSC. The dotted line represents the cal-
culated values according to the Fox equation.
(1). The result indicated that the gel contents of the copoly-
mers were all more than 90%, confirming the formation of a
highly cross-linked network with good solvent resistance
and the cross-linking films was suitable for multi-layer
process.
Mechanical Properties of the Polymers
The mechanical properties of PI films are summarized in
Table 3. Before thermal cured, the PI films have tensile
strength of 87–98 MPa, tensile modulus of 3.1–3.7 GPa, and
elongation at breakage of 5.5–14.9%. By contrast, the
mechanical properties of polyimides which were cured at
260 ꢀC for 2 h were 92–99 MPa, 3.7–4.0 GPa, 3.2–14.5%,
respectively. Among them, Co-PI-1 offered the best mechani-
cal properties after crosslinking. These results indicate that
the incorporation of the tetrafluorostyrol group into the
structure of the polyimides retains the good tensile
properties.
The thermal stability (Td, temperature at 5% weight-loss) of
PIs was investigated by TGA at a heating rate of 10 ꢀC
min21 under nitrogen. The Tds of uncured Co-PIs were
recorded in the range of 511–514 ꢀC. Compared to uncured
PIs, the cured Co-PIs have higher Tds which were in the
range of 525–534 ꢀC. This reason is that the Co-PIsꢀ have
undergone cross-linking reaction for treatment at 260 C for
2 h. The TGA data indicated that these cured Co-PIs had
high thermal stability.
FIGURE 5 DSC curves of Co-PI-1 (a) before curing; (b) after cur-
ing at 260 ꢀC for 1 h under vacuum; and (c) after curing at 260
ꢀC for 2 h under vacuum.
FIGURE 6 FTIR spectra of Co-PI-1 (a) before curing; (b) after
curing at 260 ꢀC for 1 h under vacuum; and (c) after curing at
260 ꢀC for 2 h under vacuum.
356
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 7 Photographs of the PIs (ꢁ30-lm thick). [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
Optical and Dielectric Properties of the Polymers
All the PIs could be processed into transparent and flexible
films by casting from the DMAC polymer solutions and the
photographs of these films are shown in Figure 7. The corre-
sponding UV–vis spectra of the PIs films (ꢁ30-lm thick) are
shown in Figure 8. The cut-off wavelength values and the
percentages transmittance at 400 nm and 550 nm from
these spectra are listed in Table 4. All the PIs had k0 about
332–339 nm, and exhibited high optical transparency about
90% at a wavelength of 550 nm. These results indicated that
the PI films are light-colored films. Because of the highly
conjugated aromatic structures and intermolecular charge-
transfer complex (CTC) formation of PI, most polyimides
have strong absorption in the UV and visible area. However,
our polyimide materials with the bulky and electron-
withdrawing ACF3 groups in their diamine moieties pos-
sessed light color. It could be explained by the decreased
CTC formation of polymer chains through higher steric hin-
drance and lower inductive effect. Moreover, the influence of
ACF3 groups on the film transparency was the weakening
intermolecular dispersion forces due to low polarizability of
the CAF bond.27 The color of the PI films decreased in the
order: Homo-PI-2 > Co-PI-3 > Co-PI-2 > Co-PI-1 > Homo-
PI-1 (Fig. 7), which is relevant to the transmittance order at
400 nm wavelength. The regularity is also consistent with
the side groups and fluorine content in the PIs. Besides, we
also investigated the relationship between transparency of
FIGURE 8 Transmittance UV–visible spectra of PIs films (a) PIs
films (ꢁ30-lm thick), (b) Co-PI-1 films with different thickness:
(19–41 lm).
the films and their thickness. The corresponding UV–vis
spectra of these PI films with different thickness are shown
in Figure 8(b). According the data from this figure, the
dependence of the cutoff wavelength, transmittance at 400
nm, and the thickness of films could be summarized as
TABLE 4 Optical and Dielectric Properties of PIs
Refractive index
na1,310 nm nb 1,550 nm
Dielectric
constantc
Transmittance
at 400 nm (%)
Transmittance
at 550 nm (%)
Film
d
Polymers
ko (nm)
thickness (lm)
Homo-PI-1
Co-PI-1
1.5332
1.5319
1.5311
1.5311
1.5307
1.5310
1.5295
1.5287
1.5288
1.5284
2.62
2.60
2.78
2.67
2.74
339
338
334
335
332
54
60
62
63
65
89
89
90
90
90
29
30
30
29
31
Co-PI-2
Co-PI-3
Homo-PI-2
a
d
Refractive indices of polyimides at 1,310 nm: n1,310nm
Refractive indices of polyimides at 1,550 nm: n1,550nm
Dielectric constant of cured PI films at 1 MHz.
.
Cut-off wavelength defined as the point at which the transmittance
becomes less than 1%.
b
c
.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
357

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 11 AFM images of the Co-PI-1 films coated on silicon
wafer substrates: (a) height images of uncured film; (b) height
images of cured film. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
decreased regularly with 6FTFPB content increasing, due to
the fluorine content of 6FTFPB was higher than 6FAPB.
FIGURE 9 Cutoff wavelength and transmittance at 400 nm of
Co-PI-1 films with different thickness: (19–41 lm).
The dielectric constants for the cured PI films were eval-
uated by capacitance method and were listed in Table 4. All
the cured PIs showed low E values in the range of 2.60–2.78
due to the existence of bulky CF3 groups in the main chain,
which brought about less efficient chain packing and an
increased free volume.
presented in Figure 9. With the increase of the thickness of
PI films, the cutoff wavelength increases from 321 to 346
nm and transmittance at 400 nm decreases from 71 to 53%.
The results indicated that the transparency of films is
dependent on their thickness heavily.
Morphology Analyses of the Films
The height AFM images of uncured and cured Co-PI-1 films
are summarized in Figure 11. The root mean square surface
roughness (Rq) for the films is 1.940 nm and 4.130 nm,
respectively. It indicated that the cured films with excellent
surface planarity could be obtained. Above all, the Co-PIs are
expected to be applicable polymeric materials for optoelec-
tronic devices.29
The refractive indices were measured using spectroscopic
ellipsometer. These results are summarized in Table 4. All
the PIs showed very low refractive indices in the range of
1.5307–1.5332 at 1310 nm and 1.5284–1.5310 at 1550 nm,
respectively. As the refractive indices could change with the
free volume (packing density), polarizability of the material,
temperature, and humidity,28 it seems easy to explain that
the very low refractive index of the co-polyimides are attrib-
uted to the smaller electronic polarizability and large free
volume of the CAF compared to CAH bond. In addition, the
variation of refractive index at 633 nm with 6FTFPB content
is shown in Figure 10. As expected, the refractive indices
CONCLUSIONS
A series of novel high molecular weight cross-linkable fluori-
nated co-polyimides were successfully synthesized using
newly designed 1, 3-bis(2-trifluoromethyl-4-aminophenoxy)-
5-(2,3,4,5-tetrafluorophenoxy)benzene with 6FAPB and
6FDA. The co-polyimides showed excellent solubility in com-
mon organic solvents, high tensile properties, excellent opti-
cal transparency, and high thermal stability. The co-
polyimides could be cross-linked thermally, yielding materi-
als with outstanding chemical resistance. The cross-linking
density of the copolymers was readily controlled by adjust-
ing the feed ratio of 6FTFPB to 6FAPB. After curing, the glass
transition temperature of co-polyimides obviously increased
except Co-PI-3 and Homo-PI-2 whose Tgs could not be
observed owing to their high cross-linking density. All the
tensile strength, Young’s Modulus, and the 5% thermal
weight-loss temperature of the co-polyimides were
enhanced. Furthermore, despite the root mean square sur-
face roughness changed slightly, the cross-linked films still
possessed excellent surface planarity. In addition, the cross-
linked PI films show low dielectric constant ranging 2.60–
2.78. These attracting properties make our Co-PIs potential
matrixes for constructing optoelectronic devices. The next
work of the application for fabricating the optical waveguide
is under way in our group.
FIGURE 10 Variation of refractive index at 633 nm with 6FTFPB
content; (a) before curing; (b) after curing at 260 ꢀC for 2 h
under vacuum.
358
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
13 Y. F. Liu, Z. Wang, H. L. Yang, L. X. Gao, G. Li, M. X. Ding,
J. Polym. Sci. Part A: Polym. Chem. 2008, 46, 4227–4235.
ACKNOWLEDGMENT
The authors would like to thank the China Natural Science
Foundation (Grant nos. 51173062 and 51203172) for finan-
cial support of this work.
14 H. J. Sun, H. T. Huo, H. Nie, S. Y. Yang, L. Fan, Eur. Polym.
J. 2009, 45, 1169–1178.
15 Y. Yang, L. Fan, M. Ji, S. Y. Yang, Eur. Polym. J. 2010, 146,
2145–2155.
16 Y. Yang, L. Fan, X. M. Qu, M. Ji, S. Y. Yang, Polymer 2011,
52, 138–148.
REFERENCES AND NOTES
17 Y. H. Zhang, P. Luo, H. Y. Yao, S. W. Guan, React. Funct.
Polym. 2012, 72, 621–626.
1 D. A. Tomalia, A. M. Naylor, W. A. Goddard III, Angew.
Chem. Int. Ed., 1990, 29, 138–175.
18 M. E. Rezac, E. T. Sorensen, H. W. Beckham, J. Membr. Sci.
1997, 136, 249–259.
2 D. Wilson, H. D. Stenzenberger, P. M. Hergenrother, Polyi-
mides; Chapman and Hall: New York, 1990.
19 Y. C. Xiao, T. S. Chung, H. M. Guan, M. D. Guiver, J.
Membr. Sci. 2007, 302, 254–264.
3 M. K. Ghosh, K. L. Mittal, Polyimides: Fundamentals and
Applications; Marcel Dekker: New York, 1996, pp 697–884.
20 X. Y. Ma, Z. H. Lv, D. Wang, S. W. Guan, C. H. Chen, G. B.
Wang, D. M. Zhang, Z. H. Jiang, J. Photochem. Photobiol. A
2007, 188, 43–50.
4 B. V. Kotov, B. M. Rumyantsev, V. I. Berendyaev, E. V.
Lunina, B. P. Bespalov, E. L. Frankevich, M. M. Triebel, Synth.
Met., 2001, 121, 1553–1554.
21 Z. H. Jiang, X. Y. Ma, C. H. Chen, X. F. Li, S. W. Guan, D.
Wang, Chinese Patent, Z. L., 10011381. X., 2004.
5 Y. R. Wang, S. G. Xu, T. Chen, H. W. Guo, Q. Y. Liu, B. X. Ye,
Z. Zhang, Z. Q. He, S. K. Cao, Polym. Chem., 2010, 1, 1048–
1055.
22 G. H. Li, J. Y. Wang, G. P. Yu, X. G. Jian, L. H. Wang, M. S.
Zhao, Polymer 2010, 51, 1524–1529.
6 K. Xie, J. G. Liu, H. W. Zhou, S. Y. Zhang, M. H. He, S. Y.
Yang, Polymer, 2001, 42, 7267–7274.
23 T. Takeichi, M. Zuo, M. Hasegawa, J. Polym. Sci. Part B:
Polym. Phys. 2001, 39, 3011–3019.
7 K. Xie, S. Y. Zhang, J. G. Liu, M. H. He, S. Y. Yang, J. Polym.
Sci., Part A: Polym. Chem. 2001, 39, 2581–2590.
24 Y. Terui, S. Matsuda, S. Ando, J. Polym. Sci. Part B: Polym.
Phys. 2005, 43, 2109.
8 S. H. Hsiao, C. P. Yang, C. K. Lin, J. Polym. Res. 1995, 2,
25 J. Ishii, A. Takata, Y. Oami, R. Yokota, L. Vladimirov, M.
Hasegawa, Eur. Polym. J. 2010., 46, 681.
1–12.
9 Y. H. Qi, J. F. Ding, M. Day, J. Jiang, C. L. Callender, Chem.
Mater. 2005, 17, 676–682.
26 M. Hasegawa, Y. Sakamoto, Y. Tanaka, Y. Kobayashi, Eur.
Polym. J. 2010, 46, 1510.
10 Y. H. Qi, J. F. Ding, M. Day, J. Jiang, C. L. Callender,
Polymer 2006, 47, 8263–8271
27 S. Ando, T. Matsuura, S. Sasaki. Polym. J. 1997, 29, 69–76.
28 J. W. Kang, J. P. Kim, J. S. Lee, J. J. Kim, J. Lightwave.
Technol., 2005, 23, 364–373.
11 M. E. Wright, D. A. Schorzman, A. M. Berman, Macromole-
cules 2002, 35, 6550–6556.
12 X. H. Rao, H. W. Zhou, G. D. Dang, C. H. Chen, Z. W. Wu,
Polymer 2006, 47, 6091–6098.
29 T. Matsuura, S. Ando, S. Sasaki, F. Yamamoto, Macromole-
cules 1994, 27, 6665–6670.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 349–359
359