Synthesis and Characterization of Partially Fluorinated Polybenzoxazine Resins Utilizing Octafluorocyclopentene as a Versatile Building Block

Article abstract of DOI:10.1021/acs.macromol.5b01014

Two new fluorinated diamine-based benzoxazines using octafluorocyclopentene (OFCP) as a building block have been developed. Monomers were synthesized via two distinct synthetic procedures utilizing the facile nucleophilic addition-elimination reaction of

Full text of DOI:10.1021/acs.macromol.5b01014

Article
pubs.acs.org/Macromolecules
Synthesis and Characterization of Partially Fluorinated
Polybenzoxazine Resins Utilizing Octafluorocyclopentene as a
Versatile Building Block
Jingbo Wu,*,† Yang Xi,‡ Gregory T. McCandless,† Yinhuan Xie,† Remya Menon,† Yash Patel,†
Duck Joo Yang,† Scott T. Iacono,*,§ and Bruce M. Novak†
†Department of Chemistry and the Alan G. MacDiarmid NanoTech Institute and ‡Department of Materials Science and Engineering,
The University of Texas at Dallas, Richardson, Texas 75080, United States
§Department of Chemistry and Chemistry Research Center, United States Air Force Academy, Colorado Springs, Colorado 80840,
United States
S
* Supporting Information
ABSTRACT: Two new fluorinated diamine-based benzox-
azines using octafluorocyclopentene (OFCP) as a building
block have been developed. Monomers were synthesized via
two distinct synthetic procedures utilizing the facile
nucleophilic addition−elimination reaction of OFCP with
phenols amenable to a multigram scale-up. The structure
1
elucidation of both monomers was confirmed by H, 19F, and
13C NMR, ATR-FTIR, and high-resolution mass spectrometry.
Benzoxazine networks were prepared by a thermally mediated
ring-opening polymerization. ATR-FTIR analysis was utilized
to monitor the ring-opening reaction of the monomers. The
resulting two cured resins exhibit the combined excellent
properties of low dielectric constants (k = 3.2−2.6), excellent
thermal stability, and high char yields which are suitable for many applications such as flame-resistant materials as well as
aerospace and microelectronic industries.
aromatic diamine-based benzoxazines were reported.15 The
poor solubility of many aromatic diamines in the preferred
INTRODUCTION
■
Polybenzoxazines are a new class of high performance
solvents used for benzoxazine preparation and the formation of
thermosetting resins that have been developed as an attractive
an insoluble and stable triazine network resulted from the
alternative to traditional phenolic resins, epoxies, and even
condensation of aromatic diamines and paraformaldehyde
bismaleimide resins due to a combination of various out-
cause the difficulty in the preparation of aromatic diamine-
standing properties: high thermal stability, high glass transition
temperature, low moisture absorption, low dielectric constant,
based benzoxazines.12,16−19 Therefore, the development of a
facile approach for the preparation of aromatic diamine-based
low surface free energy, lack of byproduct release during
thermal curing, and high char yield.1−4 These outstanding
benzoxazine is strongly desired.
The incorporation of fluorinated structures into a polymeric
characteristics make polybenzoxazines suitable for a variety of
structure can enhance its performance on various properties
applications, such as composites, coatings, electronics, and
simultaneously.20−23 Previous studies have shown that the
introduction of fluorinated structures into polybenzoxazine can
effectively reduce the surface free energy and dielectric
constants and maintain all other properties.24−28 Various
fluorinated difunctional benzoxazines have been synthesized
from fluorinated bisphenols or diamines.2,14,24,25,27−30 How-
ever, both fluorinated biphenols and fluorinated diamines are
rare, limiting the molecule-design flexibility of fluorinated
benzoxazines. Many fluorinated aromatic diamines are difficult
adhesives.5−8
Monofunctional benzoxazine monomers are typically synthe-
sized using commercially available phenols, formaldehyde, and
primary amines as starting materials with or without solvent.9
Most difunctional benzoxazines are bisphenol-based benzox-
azines due to a wide variety of available phenolic feedstock.7,10
A small number of difunctional benzoxazines derived from
diamines, monophenols, and formaldehyde to give diamine-
based benzoxazines are also reported.11−14 The aromatic
diamine-based polybenzoxazines exhibited higher transition
temperatures (Tg’s), improved mechanical properties, and
better thermal stability than traditional bisphenol-based
polybenzoxazines.12,15 However, only a limited number of
Received: May 12, 2015
Revised: July 31, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
to synthesize and usually have to be prepared via multistep
procedures. Scale-up of highly fluorinated diamines cannot be
efficiently achieved using current fluorinated building blocks
and known synthetic methods.14 This encouraged us to look for
an inexpensive fluorinated building block for the synthesis of
novel fluorinated benzoxazine monomers with the prospects of
commercialization.
Scheme 1. Two Synthetic Pathways for the Preparation of
Benzoxazine Monomers
A commercially available perfluorocyclylic olefin, octafluor-
ocyclopentene (OFCP), exhibits unique chemistry due to the
presence of reactive vinyl fluorine atoms.31 Previous studies
have shown that the reactions of OFCP with phenolic
derivatives readily afford disubstituted perfluorocyclopentene
(PFCP) aryl ethers under very mild conditions in good to
excellent isolated yields via a nucleophilic addition−elimination
process.32 A variety of disubstituted PFCP aryl ethers were
synthesized for the potential application as electrical insulating
agents in the early 1990s.33 Although OFCP (AA type) and
monosubstituted PFCP aryl ethers (AB type) have been used as
monomers to prepare fluoropolymers,34,35 the more stable and
widely studied disubstituted PFCP aryl ethers have not been
used to prepare any fluorinated polymers.
In this study, a facile synthetic strategy to new fluorinated
diamine-based benzoxazine M1 was developed by the reaction
of reactive monofunctional benzoxazines with appropriate
linkers to afford difunctional benzoxazines (Scheme 1, method
1), which takes advantage of the unique nucleophilic addition−
elimination reaction of OFCP with phenols and avoids
potential difficulties in the preparation of both aromatic
diamine and its benzoxazine monomers when using the
commonly known methods. Further, we optimized reaction
conditions and successfully synthesized aromatic diamine 3 via
the reaction of OFCP with 4-aminophenol without the
protection of the amino group (Scheme 1, method 2). This
simple one-step process developed in this study will allow easy
scale-up in production. The fluorinated aromatic diamine 3 was
used to prepare benzoxazine M2 via a modified traditional one-
step process.15 The preparation and characterization of
aromatic diamine 3 and two novel benzoxazine monomers
M1 and M2 and the properties of the resulting polybenzoxazine
resins are presented.
RESULTS AND DISCUSSION
■
Preparation of M1 via a Nucleophilic Addition−
Elimination Reaction (Method 1). Reactions of OFCP
with phenols readily afford disubstituted PFCP aryl ether
products via a nucleophilic addition−elimination mechanism
using triethylamine as a base under very mild conditions in
good to excellent yields.35 To take advantage of this unique
chemistry, monofunctional phenols as a starting material react
with OFCP to form fluorinated difunctional molecules, which
can be used as a fluorinated monomer to prepare
fluoropolymers via a variety of standard polymerization
processes. In this methodology, OFCP acts both as a
fluorinated building block and as a linker. To implement this
methodology, a new fluorinated benzoxazine monomer M1 was
designed, which can be synthesized via the reaction of
benzoxazine-functionalized phenol 1 with OFCP using triethyl-
amine as a base (Scheme 1, method 1). According to previous
studies, the benzoxazine ring should remain intact under several
reaction conditions where triethylamine was used as a catalyst
or base.36−39 The stability of the benzoxazine ring under basic
conditions encouraged us to synthesize benzoxazine-function-
alized phenol 1 by following a published three-step procedure
(Scheme S1).40 Reaction of OFCP with benzoxazine-function-
alized phenol 1 (2.2 equiv) was carried out using triethylamine
as a base in DMF at 0 °C. Both the monosubstituted
intermediate and the disubstituted product M1 were formed
immediately after OFCP was added into the reaction mixture
monitored by TLC. In order to facilitate a complete
disubstituted conversion, the reaction mixture was slowly
heated to 50 °C. The final product M1 was obtained in a good
isolated yield. This simple process allows an easy multigram
scale-up. For practical applications, one advantage of method
one is that it is not necessary to remove the excess of
benzoxazine-functionalized phenol from the resulting monomer
M1 because thermally curing their mixture can still afford a
highly cross-linked copolymer.
Preparation of Aromatic Diamine 3 via a One-Step
Process (Step 1, Method 2). We successfully utilized the
chemistry of OFCP with benzoxazine-functionalized phenol to
prepare the novel fluorinated diamine-based benzoxazine M1;
however, the three-step synthetic procedure for the synthesis of
benzoxazine-functionalized phenol 1 (Scheme S2) and its
derivatives decreases the scope of molecular design flexibility
B
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
for benzoxazine resins due to the limited starting materials from
2-hydroxylbenzaldehyde or its derivatives.
We also investigated using the traditional method to
synthesize newly designed fluorinated difunctional benzoxazine
monomers from fluorinated aromatic diamines, monophenols,
and paraformaldehyde.24 To apply this traditional synthetic
route (Scheme 1, method 2), aromatic diamine 3 must be
prepared first. According to a previous report, the aromatic
diamine 3 was prepared by a two-step procedure (Scheme S2,
reported route). OFCP first reacted with 2 equiv of 4-
nitrophenol to give a dinitrobenzene intermediate; reduction
via hydrogenation of the nitro groups of this intermediate
afforded the desired aromatic diamine 3. The major drawback
of this method is the use of hydrogen, which is not the first
choice for industrial processes.14 This encourages us to develop
new approach to synthesize diamine 3 with high yields and ease
of scale-up and utilize it for the preparation of fluorinated
polymeric materials. As shown in Scheme S2 (ideal route), if
the desired aromatic diamine 3 can be prepared by directly
treating OFCP with 4-aminophenol without any protection of
the amino group under certain conditions, it would dramatically
simplify the synthetic process and reduce the large-scale
preparative costs. To our surprise, no study on the reaction
of 4-aminophenol with OFCP was reported in the literature.
However, after doing a literature research, we found a
previously published study on the reaction of 2-aminophenol
with OFCP (Scheme S3), which provided us a very good
starting point to study the reaction of 4-aminophenol with
OFCP.32 Encouraged by previous results, the reaction of OFCP
with 4-aminophenol (2 equiv) in the presence of K2CO3 (2
equiv) in MeCN was first studied at room temperature for 24 h.
The 19F NMR spectrum of the reaction mixture showed the
major product was a monosubstituted product, and a very small
amount of disubstituted diamine 3 was formed (Figure S1). By
substituting Cs2CO3 as the base, the reaction of OFCP with 4-
aminophenol (2.2 equiv) was carried out in the presence of
Cs2CO3 (3 equiv) in MeCN at 0−50 °C. Both the
monosubstituted intermediate and the disubstituted product
3 were formed in the first hour at 0 °C. Finally, the
monosubstituted intermediate completely converted into final
disubstituted product 3 after the reaction temperature was
slowly increased to 50 °C, affording aromatic PFCP diamine 3
in an 81% isolated yield. The characteristic resonances of
hydrogen atoms of the NH2 groups appear as a single peak at
3.58 ppm (Figure S2). The 19F NMR spectrum of diamine 3
(Figure 1) showed two characteristic resonances at around
−114 and −130 ppm corresponding to the fluorine atoms of
CF2−CF2−CF2 and CF2−CF2−CF2 on the PFCP ring in a
symmetrical fashion, and no resonance at −156 ppm
corresponding to the fluoroalkene (CCF) was shown,
indicating that the disubstituted monomers were successfully
formed. The resulting aromatic diamine 3 is soluble in common
organic solvents, such as dichloromethane, acetone, 1,4-
dioxane, DMF, and DMSO, which makes it a better candidate
for the preparation of diamine-based benzoxazine compared to
common aromatic diamines.
Figure 1. 19F NMR spectrum of the reaction mixture of OFCP and 4-
aminophenol.
give some insoluble polymeric byproduct due to the formation
of triazine networks.42 We modified this process by using an
excess of paraformaldehyde (3 equiv to the amine group,
instead of 2 equiv) to avoid the formation of the insoluble
polymeric byproduct because changing the stoichiometry of the
diamine and paraformaldehyde can mainly form soluble
oligomers instead of insoluble polymers with higher molecular
weights. The excess amount of paraformaldehyde can be easily
removed by washing the reaction mixture with water or heating
the reaction mixture at higher temperature to evaporate
formaldehyde. Previous studies have showed that concentration
was also an important factor in minimizing the formation of an
insoluble triazine network.14 Thus, the concentration of starting
materials was chosen to be approximately 10% (w/w). Because
of the good solubility of aromatic diamine 3 in various solvents,
one of the preferred solvents used for benzoxazine preparation,
1,4-dioxane, was used in our study. This modified process
proved to be successful because the heterogeneous reaction
solution turned into a clear homogeneous solution after heating
the reaction mixture at 90 °C after 1 h, which indicated that the
formation of polymeric byproducts was limited or the
decomposition of triazine networks was rapid and the
benzoxazine monomer M2 was obtained in good isolated
yields.
Characterization of Benzoxazines M1 and M2. The
structures of the benzoxazine monomers M1 and M2 were
1
confirmed by H, 19F, and 13C NMR spectroscopy. Figure 2
illustrates the 1H NMR spectra of M1 and M2. The
characteristic resonances of the oxazine ring assigned with the
Ar−CH2−N (b or 2) and N−CH2−O (a or 1) protons appear
as two singlet peaks at 4.55 and 5.27 ppm for monomer M1
and at 4.52 and 5.24 ppm for monomer M2. These results
indicate that the substitution on the phenyl ring of the phenol
moiety had minor influence on the oxazine ring. The aromatic
protons of two phenyl rings connected to a fluorinated five-
membered ring are clearly observed as doublets at 6.37 and
6.72 ppm for monomer M1 and 6.44 and 6.74 ppm for
monomer M2. The remaining aromatic protons of the phenol
rings have chemical shifts in the range of 6.88−7.28 ppm for
M1 and 6.78−6.97 ppm for M2. Figure S3 shows the 13C NMR
spectra of M1 and M2. The two singlets at 79.9 and 50.9 ppm
for M1 and 79.85 and 50.73 ppm for M2 are typical carbon
resonances of −N−CH2−O− and −N−CH2−Ph of the oxazine
Preparation of M2 via a Modified Traditional One-
Step Approach (Step 2, Method 2). Novel fluorinated
benzoxazine M2 was prepared by a modified traditional one-
step procedure via the reaction of aromatic PFCP diamine 3
with paraformaldehyde and 4-fluorophenol in 1,4-dioxane
(Scheme 1, method 2).15,41 Previous studies showed that
reactions of an aromatic diamine with paraformaldehyde could
C
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
1
Figure 2. H NMR spectra of M1 (top) and M2 (bottom).
Figure 3. 19F NMR spectra of M1 (top) and M2 (bottom).
ring, respectively. As shown in Figure 2, no phenolic hydrogen
peak was presented.
Figure 3 shows the 19F NMR spectra of M1 and M2 that give
further confirmation of the structures of the monomers and
provides evidence for the formation of disubstituted products.
The 19F NMR spectra of M1 and M2 both show two
characteristic resonances at approximately −114 and −130
ppm, which correspond to the fluorine atoms of CF2−CF2−
CF2 and CF2−CF2−CF2 on the PFCP ring in a symmetrical
fashion. There is no resonance at −156 ppm corresponding to
the fluorinated alkene (CCF) was shown, indicating the
disubstituted monomers were successfully formed. The 19F
NMR spectrum of M2 shows a singlet at −122 ppm
corresponding to the fluorine atom on the phenol ring.
The structures of M1 and M2 were further confirmed by
ATR-FTIR as shown in Figure 4. The absorption bands
assigned to the out-of-plane bending vibration of the C−H
located at 945 cm−1 (M1) and 955 cm−1 (M2) are due to the
characteristic mode of benzene ring with an attached oxazine
ring. The bands at 1227 cm−1 (M1) and 1221 cm−1 (M2)
correspond to the Ar−O−C asymmetric stretch in benzoxazine.
The bands at 1165 cm−1 (M1) and 1169 cm−1 (M2) and 853
cm−1 (M1) and 864 cm−1 (M2) are attributed to the
asymmetric and symmetric vibrations of C−N−C in the
oxazine rings. The CH2 wagging in the benzoxazine rings is
located at 1362 cm−1 for M1 and 1360 cm−1 for M2. The ATR-
FTIR further confirmed the inertness of the benzoxazine ring of
M1 during the nucleophilic addition−elimination reaction and
the formation of the benzoxazine ring of M2. The characteristic
Figure 4. ATR-FTIR spectra of fluorinated diamine-based benzox-
azines M1 (top) and M2 (bottom).
absorption peak of the para-disubstituted benzene ring
appeared at 827 cm−1 for M1, 829 cm−1 for M2, and 1506
cm−1 for both M1 and M2. The characteristic absorbance peaks
of the PFCP ring appeared at around 1682 cm−1 (CC), 1285
cm−1 (C−O), 1144 cm−1 (C−F), and 669 cm−1 (C−F), which
are clearly shown in both of the ATR-FTIR spectra of M1 and
M2.
D
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
The ATR-FTIR spectrum of M2 has a noticeably different
absorbance pattern in the range of 650−900 cm−1 due to the
trisubstituted benzene ring with an attached oxazine ring and a
fluorine atom. For M1, the characteristic absorption bands of
the ortho-disubstituted benzene with an attached oxazine ring
appeared at 1610, 1489, 1456, and 754 cm−1. The two
characteristic absorption bonds of the trisubstituted benzene
ring with an attached oxazine ring and a fluorine atom for M2
appeared at 818 and 1497 cm−1. These results are in agreement
with previous studies.15,32,41,43 Both ATR-FTIR spectra of M1
and M2 did not show the characteristic absorption peak of the
1
OH groups (Figure S9), which is consistent with H NMR
results.
In order to obtain its crystal structure, the monomer M2
were purified by flash column chromatography twice using a
mixture of hexane and ethyl acetate (95:5) as an elution. The
pure fractions were collected and allowed to slowly evaporate
to afforded X-ray quality crystalline solid. A crystalline fragment
(∼0.06 × 0.22 × 0.26 mm3) of M2 was chosen to study the
crystal structure. Figure 5 shows the single crystal structure of
Figure 6. DSC thermograms of the fluorinated PFCP-based
benzoxazine monomers M1 (bottom) and M2 (top).
at 277 °C. For monomer M2, the onset of the exothermic
process begins at 259 °C and reaches its maximum at 285 °C.
M2 has a higher initial and peak temperature for the thermal
polymerization of benzoxazine than that of M1, indicating that
the introduction of an electron-withdrawing fluorine atom to
the para position of the phenol moiety can enhance the thermal
stability of benzoxazine ring. Our result seems to be in
opposition to previous studies which show the introduction of
an electron-withdrawing chlorine atom on the para position of
the phenol moiety decreases the thermal stability of the
benzoxazine ring44 which indicated the complexity of the
influence of substituent effects on the thermal stability of the
benzoxazine ring, and more examples should be investigated to
make accurate conclusions.
Curing of Benzoxazines Monitored by ATR-FTIR.
Figure 7 shows the ATR-FTIR spectra of M1 and M2 after
cumulative curing at each thermal degree for 60 min. The
idealized structure for the fully cured polybenzoxazines is
shown in Scheme 2. For M1, after curing at 200 °C, the
absorption band of the ortho-disubstituted benzene with an
attached oxazine ring appeared at 1456 and 1489 cm−1, while
the Ar−O−C absorption at 1227 cm−1 and the oxazine
absorption at 945 cm−1 disappeared. A larger 1,2,3-
trisubstituted benzene absorption at 1618 cm−1 was formed.
For M2, after curing at 200 °C, the absorption band of the Ar−
O−C absorption at 1221 cm−1 and the oxazine absorption at
955 cm−1 were found to disappear. A larger 1,2,3-trisubstituted
benzene absorption at 1624 cm−1 appeared. For both M1 and
M2, the characteristic absorption peaks of the carbon−carbon
double bond on the fluorinated five-membered ring at 1682
cm−1 did not change, indicating that this double bond was not
involved in substantial side reactions during the thermal curing
process. Our curing studies showed that both monomers can be
effectively polymerized at much lower temperatures (approx-
imately 200 °C). The curing temperatures of two monomers
are much lower than their corresponding exothermic peaks
observed in this thermal study, which is consistent with
previous studies.24 The cured thermosetting resins from M1
and M2 were very brittle due to forming highly cross-linked
polymeric networks.
Figure 5. ORTEP representation of M2 crystal structure (as shown
50% probability and disorders).
M2, further confirming its structure. The two phenyl rings
connected to the molecule’s central fluorinated five-membered
ring via oxygen atoms deviate from orienting parallel to each
other by 13.9° and interact with each other by π−π stacking
(the distance between these phenyl rings is ∼3.7 Å, centroid-to-
centroid). With additional intermolecular and intramolecular
interactions such as CH/π interactions (Figure S4) and
fluorine−fluorine interactions (Figure S5), two M2 molecules
form a cuboid structure (Figure S6) and all M2 molecules
tightly pack together (Figure S7, see Supporting Information
for detail discussions).
Thermal Properties of the Benzoxazine Monomers via
DSC and TGA Studies. The thermally activated polymer-
ization behavior of novel diamine-based benzoxazine mono-
mers M1 and M2 were studied by DSC in nitrogen. The
nonisothermal polymerization thermograms are shown in
Figure 6, and according to previous studies, the exothermic
events are associated with the ring-opening polymerization of
benzoxazine.44,45 For monomer M1, the onset of the
exothermic process begins at 250 °C and reaches its maximum
E
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Figure 8. TGA thermograms of cured polymers P1 and P2.
DSC Studies on Uncured and Cured Benzoxazines
Monomers. To study the Tg of cured benzoxazine monomers,
DSC studies were performed by heating benzoxazine
monomers to 160 °C for two cycles, then heating the
monomers at 200 °C for 4 h to form their corresponding
polymers via a ring-opening polymerization, and finally heating
the cured polymer from 25 to 200 °C for several cycles to
measure their glass transition temperatures.
For uncured monomer M1, the DSC curve of the first
heating cycle shows an endothermic process taking place at
about 42 °C, likely a melting transition from the semicrystalline
monomer. After curing at 200 °C for 4 h at N2 atmosphere, the
DSC final heating cycle curve of the cured polymer exhibits a
broad Tg between 120 and 140 °C (Figure 9, top). For uncured
monomer M2, the DSC curve of the first heating cycle shows a
similar endothermic process taking place at about 65 °C. After
curing at 200 °C for 4 h at N2 atmosphere, the DSC curve of
the final heating cycle clearly shows a well-defined Tg at about
140 °C (Figure 9, bottom).
Figure 7. ATR-FTIR spectra of the resulting polymers after
cumulatively curing.
Scheme 2. Preparation of Polybenzoxazines P1 and P2
Dielectric Properties of the Cured Benzoxazine
Resins. Previous studies have shown that polybenzoxazines
are considered low dielectric constant polymeric materials,46
and the introduction of fluorinated structures into polymers can
effectively reduce their dielectric constants.12 In recent years,
the preparation of polybenzoxazines with low k has become an
area of interest. Typically, the dielectric constant of
polybenzoxazines is approximately 3.0−3.5 at 1 MHz,47 slightly
higher than the dielectric constant of typical low dielectric
constant materials (k < 3.0).27 The dependence of the dielectric
constants of the PFCP aryl ether polybenzoxazines on the
frequency of the applied field was studied at room temperature
with the frequency range of 1 kHz−1 MHz. In order to increase
the accuracy of measuring dielectric constants, the flat and thin
films of polybenzoxazines were prepared on a gold-coated glass
substrate. The thickness of thin film was measured by SEM
experiments as shown in Figure S8.
To obtain accurate dielectric results, the effect of top
electrode size on the Dk measurement accuracy was studied
(Figure S10).48 Dielectric results showed 400 μm was the most
suitable dimension in a wide range of frequency. The 400 μm
top electrode can yield stable dielectric response and provide
optimum dielectric properties with the least standard deviation
(Table S1). The top electrodes were deposited via e-beam
deposition and defined by shadow masks; the smaller
electrodes have larger standard error in size compared with
the larger electrodes due to the edge effect of the e-beam
deposition. The variation of the dielectric constant with
Thermal stability of polybenzoxazines P1 and P2 was
evaluated by thermogravimetric analysis (TGA) under a
nitrogen atmosphere. The weight loss curves are shown in
Figure 8. The values of 5% weight loss temperatures (Td5%) are
348 °C for P1 and 350 °C for P2. The char yields at 800 °C are
61% for P1 and 54% for P2. The resulting polybenzoxazines
exhibit high char yields and good thermal stability.
F
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
are lower than that of normal nonfluorinated polybenzoxazines.
Further, due to the more fluorinated content of M2 compared
to M1, the dielectric constants of P2 are lower than that of P1.
Our results show the newly developed PFCP-based poly-
benzoxazines are suitable for low-k materials. Previous studies
showed the dielectric constant of a linear PFCP aryl ether
polymer possessing only a biphenyl backbone is about 4.8 at
room temperature.49 The decrease in dielectric constant may be
due to the fact that the PFCP-based polybenzoxazines contain a
higher number of aromatic rings and low polarization C−O
bonds than the biphenyl PFCP polymer in addition to the low
water absorption of polybenzoxazine materials.
CONCLUSION
■
In conclusion, fluorinated aromatic diamine-based benzoxazine
monomers M1 and M2 using octafluorocyclopentene as a key
fluorinated building block were successfully prepared via two
different synthetic routes. A new one-step synthetic strategy to
readily form M1 has been developed by taking advantage of the
nucleophilic addition−elimination reaction of OFCP with a
benzoxazine-functionalized phenol. To readily prepare more
fluorinated benzoxazine monomers, an optimized one-step
synthetic route to aromatic diamine 3 has been successfully
developed with high yields by directly reacting OFCP with 4-
aminophenol, which was used for the preparation of monomer
M2 via the traditional one-step process. The benzoxazine
groups were shown to readily undergo a thermally mediated
ring-opening polymerization at 200 °C without any catalyst and
formed cross-linked polymeric networks. The ATR-FTIR
spectra of cured polymers show the PFCP moiety is inert
during the ring-opening polymerization process. The thermal
and dielectric properties of cured polymers P1 and P2 were
studied. Dielectric constants of P1 and P2 are around 3.19 and
2.61 at 1 M Hz, respectively. The novel fluorinated
polybenzoxazines exhibit relatively lower dielectric constants
when compared to common BP-PFCP aryl ether polymers and
normal non-fluorinated polybenzoxazines.
Figure 9. DSC thermograms of uncured and cured benzoxazine
monomers M1 and M2.
frequency of the applied fields is shown in Figure 10. The
dielectric constants of thin films with 400 μm top electrodes
EXPERIMENTAL SECTION
■
Materials. 4-(2H-1,3-Benzoxazin-3(4H)-yl)-phenol (1) was syn-
thesized by following a published three-step procedure.40 Octafluor-
ocyclopentene (97%) was purchased from SynQuest Laboratories and
was used as received. Deuterated solvents were purchased from
Mallinckrodt Chemicals. All other chemicals and solvents were
purchased from Alfa Aesar or Acros Organics and were used as
received unless otherwise stated.
Measurements. 1H, 13C, and 19F NMR spectra were recorded on a
Bruker 500 MHz NMR spectrometer, and the chemical shifts were
measured in ppm (δ) with reference to the internal tetramethylsilane
(0 ppm), deuterated chloroform (77 ppm), and trichlorofluoro-
1
methane (0 ppm) for the H, 13C, and 19F NMR, respectively. ATR-
FTIR was recorded on a Shimadzu IR-Affinity 1 in an ATR module
with a germanium probe. Experiments were tested in the transmission
mode at a resolution of 4.0 measuring between 700 and 4000 cm−1 for
70−100 scans. Differential scanning calorimetry (DSC) analysis was
performed on a Mettler Toledo DSC 1 system under nitrogen at a
heating rate of 10 °C/min. The glass transition temperature (Tg) was
obtained from a second heating cycle using Star E version 10.0
software suite. The sample size varied from 2 to 5 mg. Thermal
gravimetric analysis (TGA) was performed on a Mettler-Toledo TGA/
DSC 1 LF instrument under nitrogen at a heating rate of 10 °C/min
up to 800 °C. The sample size was kept less than 10 mg in standard
aluminum pans. TGA graphs were reported in weight loss (%) as a
function of temperature (°C). High-resolution mass spectrometry
(HR-MS) was obtained at the Mass Spectrometry Laboratory,
Figure 10. Dielectric constant versus frequency of the cured PFCP
benzoxazine resins at room temperature.
were observed to vary from 3.43 to 3.19 for the self-curing
polymer P1 and from 2.81 to 2.61 for the self-curing polymer
P2. The dielectric constants of the cured polybenzoxazines are
fairly low, especially in high frequency range, which indicates
that these fluorinated polybenzoxazine systems can be used as
microelectronic packaging material. Fluorinated content lowers
the dielectric constant value by decreasing the polarizability and
the moisture absorption and by increasing free volume.27 The
dielectric constants of the novel fluorinated polybenzoxazines
G
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Department of Chemistry and Biochemistry, University of Texas at
Austin, 1 University Station A5300, Austin, TX 78712-0165. The
dielectric constants of the polymer film were investigated at room
temperature with a Casade Microtech Probe Station. The thickness of
the thin film and the diameter of the top circle electrode were
measured with a scanning electron microscope (SEM) (Zeiss: Supra
40).
X-ray Measurement. Under a liquid nitrogen cryostream (Oxford
Cryosystems), single crystal X-ray diffraction data were obtained using
a Bruker Kappa D8 Quest diffractometer. This diffractometer is
furnished with an Incoatec microfocus Mo Kα radiation source,
HELIOS multilayer optics, and a Photon 100 CMOS detector. Upon
completion of the low-temperature (T = 100 K) diffraction
experiment, the data were integrated and scaled with a Bruker
SAINT and SADABS (multiscan method), respectively. Evaluation of
hkl reflections for space group determination and data completion was
performed in Bruker XPREP. A starting model was generated with
SHELXT (intrinsic phasing method)50 with further refinement of the
structural model carried out in SHELXL2014.51
was dissolved in ethyl acetate, washed three times sequentially with 0.5
M aqueous NaOH and DI water, and then dried using MgSO4. The
solvent was removed by rotary evaporator, and the raw product was
purified by column chromatography (hexane:ethyl acetate, 10:1 v/v)
to afford the title compound as a viscous light yellow liquid (7.5 g,
1
83%). H NMR (500 MHz, CDCl3) δ: 6.94 (td, J = 8.6, 3.0 Hz, 2H),
6.86 (dd, J = 9.0, 4.7 Hz, 2H), 6.81 (dd, J = 8.3, 2.9 Hz, 2H), 6.77−
6.71 (m, 4H), 6.49−6.38 (m, 4H), 5.24 (s, 4H), 4.52 (s, 4H). 19F
NMR (471 MHz, CDCl3) δ: −114.66 (s), −122.18 (s), −130.06 (s).
13C NMR (126 MHz, CDCl3) δ: 157.94 (s), 156.03 (s), 150.26 (d, J =
2.1 Hz), 148.89 (s), 145.12 (s), 121.48 (d, J = 6.5 Hz), 119.44 (s),
117.89 (d, J = 7.7 Hz), 117.53 (s), 115.04 (s), 114.86 (s), 113.06 (s),
112.87 (s), 79.85 (s), 50.73 (s). ATR-FTIR (cm−1): 677 (C−F), 710,
746, 781, 818 (trisubstituted benzene ring), 829 (para-substituted
benzene ring), 864, 926, 955, 980, 1005, 1113, 1132, 1150 (C−F),
1165, 1196, 1221 (Ar−O−C of benzoxazine ring), 1246, 1285 (C−O),
1331, 1360, 1431, 1497 (trisubstituted benzene ring), 1506 (para-
substituted benzene ring), 1682 (CC). HR-MS (CI) calculated
(found) for C33H22N2O4F8 662.1452 (662.1466).
Synthesis of Benzoxazine Monomer M1. To a 100 mL round-
bottom flask equipped with a magnetic stirrer were introduced 4-(2H-
1,3-benzoxazin-3(4H)-yl)-phenol (1) (3.83 g, 16.9 mmol), triethyl-
amine (2.3 mL, 16.9 mmol), and DMF (20 mL). The solution was
stirred at 0 °C for 30 min. Octafluorocyclopentene (1 mL, 7.45 mmol)
was then introduced with a syringe. The reaction mixture was allowed
to stir in an ice bath for 1 h and then was heated slowly to 50 °C for 3
h. Next, the reaction mixture was poured into DI water (100 mL), and
the product was extracted using dichloromethane. The organic layer
was sequentially washed with saturated NaHCO3 solution, 5 wt % HCl
solution, and brine and was dried using MgSO4. The solvent was
removed with a rotary evaporator, and the raw product was purified by
column chromatography (hexane:ethyl acetate, 10:1 v/v) to afford the
title compound as a viscous light yellow liquid (3.4 g, 73%). 1H NMR
(500 MHz, CDCl3) δ: 7.23 (t, J = 7.7 Hz, 2H), 7.08 (d, J = 7.5 Hz,
2H), 6.99 (t, J = 7.4 Hz, 2H), 6.91 (d, J = 8.2 Hz, 2H), 6.72 (d, J = 8.7
Hz, 4H), 6.37 (d, J = 8.7 Hz, 4H), 5.27 (s, 4H, O−CH2−N), 4.55 (s,
4H, Ar−CH2−N). 19F NMR (471 MHz, CDCl3) δ: −114.77 (s),
−130.09 (s). 13C NMR (126 MHz, CDCl3) δ: 154.26 (s), 148.74 (s),
145.25 (s), 128.22 (s), 126.83 (s), 121.02 (s), 120.55 (s), 119.46 (s),
117.38 (s), 116.88 (s), 79.89 (s, O−CH2−N), 50.88 (s, Ar−CH2−N).
ATR-FTIR (cm−1): 669 (C−F), 754, 827, 945, 980, 1003, 1033, 111,
1144 (C−F), 1169, 1196, 1227, 1252, 1285 (C−O), 1337, 1362, 1456,
1489, 1506, 1682. HR-MS (CI) calculated (found) for C33H24N2O4F6
626.1640 (626.1640).
Crystallographic data for M2 have been submitted to the
Cambridge Crystallographic Data Center with deposition number
CCDC 1063405. Copies can be obtained free of charge from CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK. Additional refinement and
elucidation details can be found in the Supporting Information.
Curing of Benzoxazine Monomers M1 and M2. The PFCP-
based benzoxazine monomer was thermally polymerized without an
initiator or catalyst under air atmosphere. Six 40 μL DSC aluminum
pans containing the monomer (7−12 mg) were put into a small air-
circulating oven. The samples were heated according to the following
schedule: 160 °C/1 h, 180 °C/1 h, 200 °C/2 h, 220 °C/1 h, 240 °C/
30 min, and 260 °C/30 min. At the end of each temperature stage, one
aluminum pan was taken out of the oven and cooled to room
temperature.
Preparation of the Film for the Measurement of k Value.
The parallel plate capacitors were fabricated on a gold-coated glass
slide (20 mm × 20 mm) by spin-coating a solution of the appropriate
monomer in THF (50 mg/mL) at 1500 rpm for 25 s. The slide was
placed into a plastic desiccator overnight under a vacuum to
completely remove the solvent and was heated at air atmosphere in
a small oven at 160 °C for 1 h and at 200 °C for 4 h. Finally, gold was
deposited via vacuum evaporation on the surface of the film as a top
electrode (diameter = 100, 200, or 400 μm). The thickness of the
polymer film on a glass substrate was measured using scanning
electron microscopy (SEM, Figure S8).
Synthesis of Aromatic Diamine 3. To a 500 mL round-bottom
flask equipped with a magnetic stirrer were introduced 4-aminophenol
(12.2 g 110 mmol), Cs2CO3 (37 g, 110 mmol), and acetonitrile (200
mL). The reaction mixture was stirred at 0 °C about 1 h, and then
octafluorocyclopentene (6 mL, 44.7 mmol) was added dropwise with a
syringe. The reaction mixture kept stirring at 0 °C for 3 h and then was
heated slowly to 50 °C until the monosubstituted intermediate was
consumed as monitored by TLC analysis. The solvent was removed
under vacuum, and the resulting residue was dissolved in ethyl acetate,
washed using saturated NaHCO3 solution and brine, and then dried
using MgSO4. The solvent was removed using a rotary evaporator, and
the crude product was purified by column chromatography
(hexane:ethyl acetate, 2:1 v/v) to afford the title compound as a
brown solid (14.3 g, 81%). 1H NMR (500 MHz, CDCl3) δ: 6.62 (d, J
= 8.9 Hz, 4H), 6.50 (d, J = 8.9 Hz, 4H), 3.58 (s, 4H). 19F NMR (471
MHz, CDCl3) δ: −113.99 (t, J = 4.3 Hz), −129.97−(−130.20) (m).
13C NMR (126 MHz, CDCl3) δ: 147.17 (s), 143.49 (s), 118.35 (s),
115.46 (s).
Preparation of Diamine-Based Benzoxazine Monomer M2.
To a 100 mL two-necked flask was added aromatic diamine 3 (5.30 g,
13.6 mmol), paraformaldehyde (2.45 g, 81.0 mmol), and 1,4-dioxane
(40 mL). After the mixture was stirred for 30 min at room
temperature, 4-fluorophenol (3.0 g, 27 mmol) in dioxane (10 mL)
was added dropwise into the mixture. The reaction mixture was
maintained at 90 °C for 6 h, gradually becoming homogeneous and
turning brown. The solvent was removed under vacuum. The residue
Dielectric Constant Measurements. The dielectric constants of
the cured fluorinated benzoxazines P1 and P2 were measured by the
capacitance method at various frequencies, which has high-accuracy
measurements.52 The parallel plate capacitors were fabricated on gold-
coated glass slides by spin-coating a solution of the appropriate
monomer in THF. The resulting slides were cured via the optimized
curing profiles. Finally, gold was deposited via vacuum evaporation on
the surface of the film as a top electrode. The top electrodes with three
different sizes (100, 200, and 400 μm) were utilized in this study. The
thickness of the polymer film on a glass substrate was measured by
scanning electron microscopy (SEM). The capacity of polymer films
was measured with Cascade Microtech Probe Station. The dielectric
constant k of the corresponding film is calculated from the capacitance
from the equation
cd
k =
Sk′
where c is the observed capacitance, d is the thickness of the dielectric
film, S is the effective area of gold electrode, and k′ is vacuum
permittivity (8.854 × 10 −12 F m−1). The relationship of the dielectric
constants with frequency ranging from 103 to 106 Hz at room
temperature was studied. The margin of errors in the dielectric
constants at 1 MHz was determined by calculating the standard
deviation from multiple Dk measurements for each top electrode size.
H
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(22) Wu, J.; Liou, J.-H.; Shu, C. Y.; Patel, Y.; Menon, R.; Santucci, C.;
Iacono, S. T.; Smith, D. W., Jr.; Novak, B. M. React. Funct. Polym.
2015, 93 (0), 38−46.
(23) Dei, D. K.; Lund, B. R.; Wu, J.; Simon, D.; Ware, T.; Voit, W. E.;
MacFarlane, D.; Liff, S. M.; Smith, D. W. ACS Macro Lett. 2013, 2 (1),
35−39.
(24) Lin, C. H.; Chang, S. L.; Lee, H. H.; Chang, H. C.; Hwang, K.
Y.; Tu, A. P.; Su, W. C. J. Polym. Sci., Part A: Polym. Chem. 2008, 46
(15), 4970−4983.
(25) Velez-Herrera, P.; Doyama, K.; Abe, H.; Ishida, H. Macro-
molecules 2008, 41 (24), 9704−9714.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.5b01014.
1
Figures depicting H, 13C, and 19F NMR and ATR-IR
spectra, text describing crystallographic details and
alternate ORTEP views of monomer M2, table of
dielectric measurements, and figure of SEMs of polymer
films (PDF)
(26) Wang, C.-F.; Chiou, S.-F.; Ko, F.-H.; Chou, C.-T.; Lin, H.-C.;
Huang, C.-F.; Chang, F.-C. Macromol. Rapid Commun. 2006, 27 (5),
333−337.
AUTHOR INFORMATION
Corresponding Authors
*(J.W.) E-mail: wjbsioc2013@gmail.com.
*(S.T.I.) E-mail: scott.iacono@usafa.edu.
Notes
■
(27) Su, Y.-C.; Chang, F.-C. Polymer 2003, 44 (26), 7989−7996.
(28) Demir, K. D.; Kiskan, B.; Latthe, S. S.; Demirel, A. L.; Yagci, Y.
Polym. Chem. 2013, 4 (6), 2106−2114.
(29) Raza, A.; Si, Y.; Wang, X.; Ren, T.; Ding, B.; Yu, J.; Al-Deyab, S.
S. RSC Adv. 2012, 2 (33), 12804−12811.
(30) Gao, Y.; Huang, F.; Yuan, Q.; Zhou, Y.; Du, L. High Perform.
Polym. 2013, 25 (6), 677−684.
The authors declare no competing financial interest.
(31) Garg, S.; Twamley, B.; Zeng, Z.; Shreeve, J. n. M. Chem. - Eur. J.
2009, 15 (40), 10554−10562.
ACKNOWLEDGMENTS
■
The authors thank Alan G. MacDiarmid NanoTech Institute,
the NMR facility of chemistry department (NSF, Grant CHE-
1126177), and the University of Texas at Dallas for their
support.
(32) Bayliff, A. E.; Bryce, M. R.; Chambers, R. D. J. Chem. Soc., Perkin
Trans. 1 (1972-1999) 1987, 0, 763−767.
(33) Negele, M.; Bielefeldt, D.; Himmler, T.; Marhold, A.
Preparation of 1,2-bis(aryloxy)perfluorocycloalkenes and analogs as
electrical insulators. DE3817626A1, 1989.
(34) Campos, R.; Mansur, A. A.; Cook, C. H.; Batchelor, B.; Iacono,
S. T.; Smith, D. W., Jr. J. Fluorine Chem. 2014, 166 (0), 60−68.
(35) Cracowski, J. M.; Sharma, B.; Brown, D. K.; Christensen, K.;
Lund, B. R.; Smith, D. W. Macromolecules 2012, 45 (2), 766−771.
(36) Liu, X.; Gu, Y. Sci. China, Ser. B: Chem. 2001, 44 (5), 552−560.
(37) Agag, T.; Arza, C. R.; Maurer, F. H. J.; Ishida, H. J. Polym. Sci.,
Part A: Polym. Chem. 2011, 49 (20), 4335−4342.
REFERENCES
■
(1) Ghosh, N. N.; Kiskan, B.; Yagci, Y. Prog. Polym. Sci. 2007, 32
(11), 1344−1391.
(2) Qu, L.; Xin, Z. Langmuir 2011, 27 (13), 8365−8370.
(3) Yagci, Y.; Kiskan, B.; Ghosh, N. N. J. Polym. Sci., Part A: Polym.
Chem. 2009, 47 (21), 5565−5576.
(4) Ishida, H.; Allen, D. J. J. Polym. Sci., Part B: Polym. Phys. 1996, 34
(6), 1019−1030.
(38) Kiskan, B.; Yagci, Y.; Ishida, H. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46 (2), 414−420.
(5) Kiskan, B.; Ghosh, N. N.; Yagci, Y. Polym. Int. 2011, 60 (2), 167−
177.
(39) Koz, B.; Kiskan, B.; Yagci, Y. Polym. Bull. (Heidelberg, Ger.)
2011, 66 (2), 165−174.
(6) Wang, C.-F.; Su, Y.-C.; Kuo, S.-W.; Huang, C.-F.; Sheen, Y.-C.;
Chang, F.-C. Angew. Chem., Int. Ed. 2006, 45 (14), 2248−2251.
(7) Sawaryn, C.; Landfester, K.; Taden, A. Macromolecules 2010, 43
(21), 8933−8941.
(8) Li, X.; Xia, Y.; Xu, W.; Ran, Q.; Gu, Y. Polym. Chem. 2012, 3 (6),
1629−1633.
(9) Ning, X.; Ishida, H. J. Polym. Sci., Part B: Polym. Phys. 1994, 32
(5), 921−927.
(10) Wang, J.; Wu, M.-q.; Liu, W.-b.; Yang, S.-w.; Bai, J.-w.; Ding, Q.-
q.; Li, Y. Eur. Polym. J. 2010, 46 (5), 1024−1031.
(11) Chang, S. L.; Lin, C. H. J. Polym. Sci., Part A: Polym. Chem.
2010, 48 (11), 2430−2437.
(12) Lin, C. H.; Chang, S. L.; Hsieh, C. W.; Lee, H. H. Polymer 2008,
49 (5), 1220−1229.
(13) Zhu, K.; Lund, B.; Stern, R.; Budy, S. M.; Smith, D. W.; Iacono,
S. T. J. Polym. Sci., Part A: Polym. Chem. 2014, 52 (4), 552−560.
(14) Velez-Herrera, P.; Ishida, H. J. Fluorine Chem. 2009, 130 (6),
573−580.
(15) Agag, T.; Jin, L.; Ishida, H. Polymer 2009, 50 (25), 5940−5944.
(16) Shen, S. B.; Ishida, H. J. Appl. Polym. Sci. 1996, 61 (9), 1595−
1605.
(40) Andreu, R.; Reina, J. A.; Ronda, J. C. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46 (10), 3353−3366.
(41) Huang, R.; Carson, S. O.; Silva, J.; Agag, T.; Ishida, H.; Maia, J.
M. Polymer 2013, 54 (7), 1880−1886.
(42) García, J. M.; Jones, G. O.; Virwani, K.; McCloskey, B. D.;
Boday, D. J.; ter Huurne, G. M.; Horn, H. W.; Coady, D. J.; Bintaleb,
A. M.; Alabdulrahman, A. M. S.; Alsewailem, F.; Almegren, H. A. A.;
Hedrick, J. L. Science 2014, 344 (6185), 732−735.
(43) Wang, J.; He, X.-Y.; Liu, J.-T.; Liu, W.-B.; Yang, L. Macromol.
Chem. Phys. 2013, 214 (5), 617−628.
(44) Deng, Y.; Zhang, Q.; Zhou, Q.; Zhang, C.; Zhu, R.; Gu, Y. Phys.
Chem. Chem. Phys. 2014, 16 (34), 18341−18348.
(45) Andreu, R.; Reina, J. A.; Ronda, J. C. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46 (10), 3353−3366.
(46) Ishida, H. In Handbook of Benzoxazine Resins; Agag, H. I., Ed.;
Elsevier: Amsterdam, 2011; Chapter 1, pp 3−81.
(47) Manuspiya, H.; Ishida, H. In Handbook of Benzoxazine Resins;
Agag, H. I., Ed.; Elsevier: Amsterdam, 2011; Chapter 36, pp 621−639.
(48) Han, G.; Ryu, J.; Yoon, W.-H.; Choi, J.-J.; Hahn, B.-D.; Kim, J.-
W.; Park, D.-S.; Priya, S. Mater. Lett. 2011, 65 (14), 2193−2196.
(49) Sharma, B.; Verma, R.; Baur, C.; Bykova, J.; Mabry, J. M.; Smith,
D. W. J. Mater. Chem. C 2013, 1 (43), 7222−7227.
(50) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71,
3−8.
(17) Takeichi, T.; Kano, T.; Agag, T. Polymer 2005, 46 (26), 12172−
12180.
(18) Men, W.; Lu, Z. J. Appl. Polym. Sci. 2007, 106 (4), 2769−2774.
(19) Gao, B.; Wang, J.; An, F.; Liu, Q. Polymer 2008, 49 (5), 1230−
1238.
(51) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71,
3−8.
(52) Yuan, C.; Jin, K.; Li, K.; Diao, S.; Tong, J.; Fang, Q. Adv. Mater.
2013, 25 (35), 4875−4878.
́ ́
(20) Soules, A.; Pozos Vazquez, C.; Ameduri, B.; Joly-Duhamel, C.;
Essahli, M.; Boutevin, B. J. Polym. Sci., Part A: Polym. Chem. 2008, 46
(10), 3214−3228.
(21) Wu, J.; Iacono, S. T.; McCandless, G. T.; Smith, D. W.; Novak,
B. M. Chem. Commun. (Cambridge, U. K.) 2015, 51, 9220−9222.
I
DOI: 10.1021/acs.macromol.5b01014
Macromolecules XXXX, XXX, XXX−XXX