A novel perfluorocyclobutyl aryl ether-based graft copolymer via 2-methyl-1,4-bistrifluorovinyloxybenzene and styrene

Article abstract of DOI:10.1016/j.polymer.2010.08.055

A series of novel perfluorocyclobutyl aryl ether-containing graft copolymers with polystyrene side chains were synthesized by the combination of thermal step-growth [2π+2π] cycloaddition polymerization of aryl bistrifluorovinyl ether monomer and atom transfer radical polymerization (ATRP) of styrene. We first synthesized a new aryl bistrifluorovinyl ether monomer of 2-methyl-1,4-bistrifluorovinyloxybenzene in two steps using commercially available 2-methylhydroquinone as starting material and the corresponding perfluorocyclobutyl aryl ether-based homopolymer with methoxyl end groups was prepared through the homopolymerization of this monomer in diphenyl ether. Next, the pendant methyls of this fluoropolymer were mono-brominated by N-bromosuccinimide and benzoyl peroxide so as to be converted to ATRP initiation groups. The targeted poly(2-methyl-1,4-bistrifluorovinyloxybenzene)-g-polystyrene with relatively narrow molecular weight distributions (M_w/M_n≤1.38) was obtained by the combination of bulk ATRP of styrene at 110°C using CuBr/bpy as catalytic system and the grafting-from strategy. These fluorine-containing graft copolymers show excellent solubility in common organic solvents.

Full text of DOI:10.1016/j.polymer.2010.08.055

Polymer 51 (2010) 5198e5206
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Polymer
journal homepage: www.elsevier.com/locate/polymer
A novel perfluorocyclobutyl aryl ether-based graft copolymer via
2-methyl-1,4-bistrifluorovinyloxybenzene and styrene
,
b
a,
Hao Liu a, Sen Zhang a, Yongjun Li a, Dong Yang b , Jianhua Hu , Xiaoyu Huang
*
**
a Key Laboratory of Organofluorine Chemistry and Laboratory of Polymer Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road,
Shanghai 200032, PR China
b Key Laboratory of Molecular Engineering of Polymers (Ministry of Education), Laboratory of Advanced Materials and Department of Macromolecular Science, Fudan University,
220 Handan Road, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel perfluorocyclobutyl aryl ether-containing graft copolymers with polystyrene side chains
Received 21 June 2010
Received in revised form
13 August 2010
Accepted 27 August 2010
Available online 16 September 2010
were synthesized by the combination of thermal step-growth [2
p
þ 2
p] cycloaddition polymerization of
aryl bistrifluorovinyl ether monomer and atom transfer radical polymerization (ATRP) of styrene. We first
synthesized a new aryl bistrifluorovinyl ether monomer of 2-methyl-1,4-bistrifluorovinyloxybenzene in
two steps using commercially available 2-methylhydroquinone as starting material and the corre-
sponding perfluorocyclobutyl aryl ether-based homopolymer with methoxyl end groups was prepared
through the homopolymerization of this monomer in diphenyl ether. Next, the pendant methyls of this
fluoropolymer were mono-brominated by N-bromosuccinimide and benzoyl peroxide so as to be con-
verted to ATRP initiation groups. The targeted poly(2-methyl-1,4-bistrifluorovinyloxybenzene)-g-poly-
styrene with relatively narrow molecular weight distributions (Mw/Mn ꢀ 1.38) was obtained by the
combination of bulk ATRP of styrene at 110 ꢁC using CuBr/bpy as catalytic system and the grafting-from
strategy. These fluorine-containing graft copolymers show excellent solubility in common organic
solvents.
Keywords:
ATRP
Graft copolymers
Perfluorocyclobutyl aryl ether
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
In 1993, perfluorocyclobutyl (PFCB) aryl ether polymer, a rela-
tively new partially fluorinated polymer, was first obtained by Babb
Since the first example of fluoropolymer, polytetrafluoro-
ethylene (PTFE), was discovered by Dr. Plunkett of DuPont in 1938
[1], many different kinds of high-performance fluoropolymers have
been developed and applied in different fields because of their
excellent properties, such as high thermal and oxidative stability,
high chemical resistance, low surface energy, optical transparency
and high insulating ability [2], which originated from the incor-
poration of fluorocarbon functionality. However, the high crystal-
linity of fluoropolymers led to low solubility and processability so
that the extensive applications of fluoropolymers have been obvi-
ously limited [2]. Therefore, partially fluorinated polymers with
good solubility including polychlorotrifluoroethlene (PCTFE), Tel-
fon-AF, Cytop and various copolymers of PTFE have been synthe-
sized to meet the application needs [2].
et al. of Dow Chemical Co. [3,4]. This fluoropolymer was prepared
by the predominant head-to-head thermal [2 ] step-growth
þ 2
p
p
cyclopolymerization of aryl trifluorovinyl ethers (TFVE) at
temperature of 150e200 ꢁC in bulk or solution without any initiator
and catalyst. Many kinds of new thermoplastic and thermoset PFCB
aryl ether polymers have been synthesized by the thermal chain
extension of bis- and tri-functionalized TFVE monomers [5e9].
PFCB aryl ether-based polymers which have demonstrated entirely
amorphous not only have the common properties of fluoropolymer
such as high thermal/oxidative stability, high chemical resistance,
low dielectric constant, low moisture absorption and low surface
energy, but show many other advantages like optical transparency
and improved processability [10,11] due to the combination of
flexible thermally robust, aromatic ethers with fluorocarbon
linkage. Furthermore, the substitution groups of bis-or tri-phenol
block can be changed to afford many new PFCB aryl ether-based
polymers tailored for a variety of applications, such as optical
waveguide applications [10,12,13], proton exchange membrane
[14], hole-transporting material [15,16], curing additive [17] and
space durable materials [18,19].
* Corresponding author. Tel.: þ86 21 55665280; fax: þ86 21 65640293.
** Corresponding author. Tel.: þ86 21 54925310; fax: þ86 21 64166128.
E-mail addresses: yangdong@fudan.edu.cn (D. Yang), xyhuang@mail.sioc.ac.cn
(X. Huang).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.08.055

H. Liu et al. / Polymer 51 (2010) 5198e5206
5199
Scheme 1. Synthesis of PMBTFVB-g-PS graft copolymer.
Until now, the majority of PFCB aryl ether-based polymer-
concerned researches focused on the homopolymerization and
random copolymerization of different TFVE monomers due to
very high polymerization temperature (>150 ꢁC) and unusual
polymerization of the macromonomers yielded the graft copoly-
mers with a broad chain-length distribution [26] and well-defined
graft copolymers with low molecular weights were obtained by the
living polymerization of the macromonomers [27]. The grafting-
onto approach of grafting the side chains onto the backbone by
a coupling reaction with a high coupling efficiency is suitable for
the synthesis of graft copolymers possessing short side chains
[28,29]. The grafting-from technology utilizes the pendant initia-
tion sites on the backbone introduced from the initiation-group-
containing monomer or by the post-modification of the backbone
to initiate the polymerization of another monomer to form the side
chains [30]. A variety of well-defined graft polymers have been
synthesized by living radical polymerization such as atom transfer
radical polymerization (ATRP) [31e33], modified ATRP [34,35],
single-electron-transfer living radical polymerization (SET-LRP)
[36,37], reversible addition fragmentation chain transfer (RAFT)
polymerization [38,39] via the grafting-from strategy. In particular,
the living nature of ATRP enabled it to form the side chains in
a well-defined way with controllable molecular weights and
polydispersities [30,40e42].
radical-mediated [2
p
þ 2
p
]
cyclopolymerization mechanism
[20], which apparently confined its development as an
emerging class of semi-fluorinated polymer. For enlarging its
application range, it is significant to combine the high perfor-
mance of PFCB aryl ether polymer with other commercial
polymers. Block and graft copolymers with a stable covalent-
bonded linkage between two different segments may be a good
choice. Recently, some groups have synthesized the block
copolymers containing PFCB aryl ether segment [21e24];
however, PFCB aryl ether-based graft polymer has never been
reported until now.
Generally, three strategies of grafting-through, grafting-onto
and grafting-from are employed for synthesizing the graft poly-
mers [25]. Graft polymers can be obtained by the homopolymeri-
zation or copolymerization of the macromonomers through the
grafting-through method. But, the conventional free radical

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H. Liu et al. / Polymer 51 (2010) 5198e5206
In this article, we reported a novel PFCB aryl ether-based graft
N2 purge with a heating rate of 10 ꢁC/min. The decomposition
temperature (Td) is defined as the temperature with 10% weight
loss.
polymer bearing polystyrene (PS) side chains. A new aryl bistri-
fluorovinyl ether monomer, 2-methyl-1,4-bistrifluorovinyloxy-
benzene (MBTVFB), was first homopolymerized at 200 ꢁC to provide
PFCB aryl ether-based backbone. The homopolymer was transformed
into ATRP macroinitiator via the mono-bromination of the pendant
methyls. The final graft copolymer, poly(2-methyl-1,4-bistri-
fluorovinyloxybenzene)-g-polystyrene(PMBTFVB-g-PS), was obtained
via ATRP graft copolymerization of styrene.
2.3. Synthesis of MBTFVB
2-Methylhydroquinone was used as starting material to
synthesize MBTVFB 1 monomer in two steps as shown in Scheme
1. To a 500 mL three-neck flask (flame-dried prior to use) fitted
with a N2 inlet and a Barrett trap topped with a reflux condenser,
2-methylhydroquinone (12.41 g, 0.10 mol), toluene (120 mL) and
DMSO (150 mL) were first added followed by deoxygenating
under N2 for 30 min. Next, KOH (12.44 g, 90%, 0.20 mol) was
added and the mixture was refluxed at 180 ꢁC to azeotropically
remove the water until no more water was collected in the trap.
The solution was then cooled to below 15 ꢁC and BrCF2CF2Br
(30 mL, 0.25 mol) was introduced dropwise within 1 h. The
mixture was warmed to room temperature for 12 h and heated to
35 ꢁC for another 8 h. The reaction was quenched by water and
the mixture was extracted with CH2Cl2. All organic layers were
collected and dried over MgSO4. 2-Methyl-1,4-bis(2-bromotetra-
fluoroethoxy)phenyl (19.76 g, 40.9%) as clear oil was obtained by
silica column chromatography. 1H NMR (300 MHz, CDCl3):
2. Experimental section
2.1. Materials
Styrene (St, Aldrich, 99%) was washed with 5% aqueous NaOH
solution to remove the inhibitor and then with water, dried over
MgSO4, and distilled twice from CaH2 under reduced pressure prior
to use. CuBr (Aldrich, 98%) was purified by stirring overnight over
CH3CO2H at room temperature, followed by washing the solid with
ethanol, diethyl ether, and acetone prior to drying in vacuo at 40 ꢁC
for 1 day. Granular zinc (Aldrich, 99.99%) was activated by washing
in 0.1 M HCl followed by drying in vacuo at 140 ꢁC for 10 h. Toluene
(Aldrich, 99%) was dried over CaH2 and distilled from sodium and
benzophenone under N2 prior to use. Anisole (Aldrich, 99%) and
diphenyl ether (Aldrich, 99%) were dried over CaH2 and distilled
under reduced pressure prior to use. N-Bromosuccinimide (NBS,
Aldrich, 99%) was recrystallized from water and dried in vacuo at
35 ꢁC for 1 day. Benzoyl peroxide (BPO, Alfa Aesar, 97%) was purified
by dissolving in acetone and precipitating in water followed by
drying in vacuo at room temperature for 1 day. BrCF2CF2Br was
prepared by condensing equimolar amounts of Br2 and tetra-
fluoroethylene at ꢂ195 ꢁC followed by warming up to 22 ꢁC [43].
4-Methoxytrifluorovinyloxybenzene was prepared according to
previous literature [44]. CH3CN (Aldrich, 99.8%), CCl4 (Aldrich,
99.5%), dimethyl sulfoxide (DMSO, Aldrich, 99.9%), KOH (Aldrich,
90%), 2,20-bipyridine (bpy, Aldrich, 99%) and 2-methylhy-
droquinone (Aldrich, 99%) were used as received.
d
(ppm): 2.24 (3H, CH3), 7.08, 7.13, 7.24 (3H, phenyl). HRMS:
C11H6O2Br2F8, calcd 479.8607, found 479.8604.
To a 250 mL three-neck flask (flame-dried prior to use) fitted
with a reflux condenser, zinc (11.44 g, 0.176 mmol) was first added
followed by three cycles of evacuating and backfilling with N2.
CH3CN (120 mL) was introduced via a gastight syringe and the
mixture was refluxed at 110 ꢁC. The above prepared intermediate,
2-methyl-1,4-bis(2-bromotetrafluoroethoxy)phenyl (24.19 g, 0.05 mmol)
was added dropwise within 1 h and the mixture was refluxed at 110 ꢁC
for 10 h. After cooling to room temperature, the suspending zinc
salt was removed by the filtration and the filtrate was washed with
water and dried over MgSO4. The crude product was purified by
silica column chromatography to afford 9.20 g (65.0%) of MBTFVB 1
as clear oil. FT-IR:
n
(cmꢂ1): 3045, 2968, 1833, 1600, 1496, 1422,
1315, 1279, 1179, 1157, 1009, 945, 874, 808, 767. 1H NMR (300 MHz,
2.2. Measurements
CDCl3):
d
(ppm): 2.33 (s, 3H, CH3), 6.93 (d, J ¼ 8.8 Hz, 1H, phenyl),
6.97 (s, 1H, phenyl), 7.01 (d, J ¼ 8.8 Hz, 1H, phenyl). 13C NMR
FT-IR spectra were recorded on a Nicolet AVATAR-360 FT-IR
spectrophotometer with a resolution of 4 cmꢂ1. All NMR analyses
were performed on a Bruker AM-300 spectrometer (300 MHz) in
(75 MHz, CDCl3): d (ppm): 15.7 (CH3), 114.3, 115.5, 119.0, 129.9
(phenyl), 132.8, 135.2, 143.9, 144.4, 146.5, 147,1, 149.3, 149.9 (OCF]
CF2), 150.3, 151.6 (phenyl). 19F NMR (282 MHz, CDCl3):
d (ppm):
CDCl3, TMS (1H NMR) and CDCl3
(
13C NMR) were used as internal
ꢂ120.3, ꢂ127.0, ꢂ134.3. EI-MS: m/z (%): 284 ([M]þ, 100.00), 187
(20.49), 159 (11.81), 140 (24.04), 119 (17.50), 109 (32.77), 90 (83.16),
77 (4.09), 51 (7.58). HRMS: C11H6O2F6: calcd 284.0272, found,
284.0268.
standards and CF3CO2H was used as external standard for 19F NMR.
EI-MS and HRMS were measured by an Agilent 5937N system and
a Waters Micromass GCT instrument, respectively. The bromine
content was determined by the titration with Hg(NO3)2. Relative
molecular weights and molecular weight distributions were
measured by conventional gel permeation chromatography (GPC)
system equipped with a Waters 1515 Isocratic HPLC pump, a Waters
2414 refractive index detector, and a set of Waters Styragel columns
2.4. Thermal homopolymerization of MBTFVB
PMBTFVB 2 homopolymer was prepared by the thermal step-
growth cyclo-addition polymerization of MBTFVB 1 monomer. To
a 50 mL Schlenk flask (flame-dried under vacuum prior to use)
sealed with a rubber septum, MBTFVB 1 (8.00 g, 28.16 mmol) and
diphenyl ether (16 mL) were first added under N2. The flask was
degassed by three cycles of freezingepumpingethawing followed
by immersing the flask into an oil bath thermostated at 200 ꢁC.
4-Methoxytrifluorovinyloxybenzene (2.87 g, 14.07 mmol) was
introduced via a gastight syringe after 4 h. The polymerization was
terminated by putting the flask into liquid N2 after another 6 h. THF
(15 mL) was added to dilute the solution followed by precipitating
into methanol. After repeated purification by dissolving in THF and
precipitating in methanol, PMBTFVB 2 homopolymer (4.53 g,
56.6%) as white powder was obtained after drying in vacuo over-
(HR3
(500e30,000),
HR4
(5000e600,000)
and
HR5
(50,000e4,000,000), 7.8 ꢃ 300 mm, particle size:
5
m
m). GPC
measurements were carried out at 35 ꢁC using tetrahydrofuran
(THF) as eluent with a flow rate of 1.0 mL/min. The system was
calibrated with linear polystyrene standards. Conversions of St
were determined by GC using an HP 6890 system with an SE-54
column and anisole was used as internal standard. Differential
scanning calorimetry (DSC) measurements were run on a TA Q200
system under N2 purge with a heating rate of 10 ꢁC/min. The glass
transition temperature (Tg) was recorded from the second heating
process after a quick cooling from 200 ꢁC and the value was
determined from the midpoint of Cp curve. Thermo-gravimetric
analysis (TGA) measurements were run on a TA Q500 system under
night. GPC: Mn ¼ 4600 g/mol, Mw/Mn ¼ 1.27. FT-IR:
n
(cmꢂ1): 3053,

H. Liu et al. / Polymer 51 (2010) 5198e5206
5201
Fig. 1. 1H NMR (A), 13C NMR (B), FT-IR (C), and EI-MS (D) spectra of MBTVFB 1.
2933, 1599, 1498, 1315,1267, 1203, 1120, 1009, 962, 925, 813, 743. 1H
NMR (300 MHz, CDCl3): (ppm): 2.06, 2.27 (3H, CH3), 3.77 (3H,
OCH3), 6.97, 7.10 (3H, phenyl). 13C MNR (75 MHz, CDCl3):
(ppm):
ATRP macroinitiator 3, CuBr and bpy were first added to a 25 mL
Schlenk flask (flame-dried under vacuum prior to use) sealed with
a rubber septum under N2. After three cycles of evacuating and
purging with N2, St was charged via a gastight syringe. The flask
was degassed by three cycles of freezingepumpingethawing fol-
lowed by immersing the flask into an oil bath preset at 110 ꢁC. The
polymerization was terminated by immersing the flask into liquid
N2 after certain time. The reaction mixture was diluted with THF
and passed through an alumina column to remove the residual
copper catalyst. The solution was concentrated and precipitated
into methanol. After repeated purification by dissolving in THF and
precipitating in methanol, PMBTFVB-g-PS 4 graft copolymer as
d
d
16.0 (CH3), 55.4 (OCH3), 105.7, 109.2, 112.7 (4C, PFCB), 116.5, 121.5,
131.0, 148.3 (phenyl). 19F NMR (282 MHz, CDCl3):
to ꢂ132.2 (6F, PFCB).
d
(ppm): ꢂ128.3
2.5. Mono-bromination of PMBTFVB
NBS and BPO were used to mono-brominate the pendant
methyls of PMBTFVB 2 homopolymer. In a typical procedure,
PMBTFVB 2 (Mn ¼ 4600 g/mol, Mw/Mn ¼ 1.27, 2.00 g, 7.04 mmol
CH3 group), NBS (1.2530 g, 7.04 mmol), and BPO (0.3415 g,
1.41 mmol) were first added to a 1000 mL three-neck flask (flame-
dried prior to use) fitted with a reflux condenser and the solution
was deoxygenated under N2. Next, CCl4 (400 mL) was introduced
via a gastight syringe and the solution was refluxed at 80 ꢁC for 1
day. After filtration, CCl4 was removed from the filtrate using
a rotary evaporator. The obtained solid was dissolved in 500 mL of
ethyl acetate and the resulting solution was washed with distilled
water (200 mL ꢃ 2) followed by drying over MgSO4. The solution
was concentrated and precipitated into methanol. After repeated
purification by dissolving in THF and precipitating in methanol,
1.0792 g of PMBTFVBeBr 3b macroinitiator as white powder was
obtained after drying in vacuo overnight. GPC: Mn ¼ 6200 g/mol,
white powder was obtained after drying in vacuo overnight. FT-IR:
(cmꢂ1): 3060, 3026, 2923, 2851, 1600, 1492, 1452, 1315, 1262, 1204,
1111, 1028, 961, 756, 698. 1H NMR (300 MHz, CDCl3):
(ppm): 1.43
n
d
(2H, CHCH2), 1.86 (1H, CHCH2), 2.04 (3H, CH2 connected to the aryl),
2.25 (3H, CH3), 3.73 (3H, OCH3), 4.41, 4.49 (1H, CHBr), 6.59, 7.09 (3H,
phenyl of the backbone; 5H, phenyl of PS side chain). 19F NMR
(282 MHz, CDCl3):
d
(ppm): ꢂ128.4 to ꢂ131.9 (6F, PFCB). ATRP
kinetics was investigated by using PMBTFVBeBr 3a macroinitiator
and anisole (Vanisole:VSt ¼ 1:20) was added as internal standard for
GC measurement.
3. Results and discussion
Mw/Mn ¼ 1.14. EA: Br%: 16.28%. 1H NMR (300 MHz, CDCl3):
d (ppm):
3.1. Synthesis of MBTFVB aryl bistrifluorovinyl ether monomer
1.99, 2.18 (3H, CH3), 3.68 (3H, OCH3), 4.17, 4.34 (2H, CH2Br), 6.86,
7.04, 7.16 (3H, phenyl). 13C MNR (75 MHz, CDCl3):
d (ppm): 15.3
MBTVFB 1 aryl bistrifluorovinyl ether monomer was synthe-
sized according to standard procedures of the fluoroalkylation with
BrCF2CF2Br and Zn-mediated elimination in two steps with a total
yield of 26.6% using commercially available 2-methylhydroquinone
as starting material [18,20,45]. The chemical structure of this
monomer was examined by FT-IR, EI-MS, HRMS, 1H NMR, 19F NMR
and 13C NMR. 1H NMR spectrum of MBTFVB 1 is shown in Fig. 1A
and the typical resonance signal of the methyl appeared at
2.33 ppm. A series of peaks around 7.00 ppm belonged to 3 protons
(CH3), 24.6 (CH2Br), 54.7 (OCH3), 105.0, 107.8, 111.7 (4C, PFCB), 116.5,
118.7, 120.8, 129.3, 148.1 (phenyl). 19F NMR (282 MHz, CDCl3):
d
(ppm): ꢂ127.1 to ꢂ132.7 (6F, PFCB).
2.6. ATRP graft copolymerization of St
ATRP bulk graft copolymerization of St was performed by using
PMBTFVBeBr 3 as macroinitiator and CuBr/bpy as catalytic system.

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H. Liu et al. / Polymer 51 (2010) 5198e5206
Fig. 3. FT-IR spectra of PMBTFVB 2 (A) and PMBTFVB-g-PS 4 (B).
Fig. 2. 19F NMR spectra of MBTVFB 1 (A) and PMBTFVB 2 (B).
with 4-methoxytrifluorovinyloxybenzene. The disappearance of
the signals of the trifluorovinyl was also illustrated by 13C NMR
spectrum after thermal homopolymerization (Fig. 4B) in compar-
ison with that of the monomer (Fig. 1B). Instead, new peaks origi-
nated from 4 carbons of PFCB linkage were found to be located in
the area ranging from 106.5 ppm to 112.7 ppm. Another new peak
at 55.4 ppm was attributed to the carbon of terminal methoxyl.
The relative molecular weight of PMBTFVB 2 (Mn ¼ 4600 g/mol)
was obtained by GPC measurement calibrated with linear poly-
styrene standards and 1H NMR was employed to determine the
‘absolute’ molecular weight of the homopolymer. The molecular
weight of PMBTFVB 2 (Mn,NMR) can be evaluated according to Eq. (1)
(Sa and Sb are the area of peak ‘a’ at 3.77 ppm and peaks ‘b’ at 2.06
and 2.27 ppm in Fig. 4A, respectively; 284 and 204 are the molec-
of the benzene ring. The singlet at 6.97 ppm is attributed to 1
proton adjacent to the methyl. Another 2 doublets at 6.93 and
7.01 ppm originated from other 2 protons of benzene ring. The
peaks ranging from 132.8 ppm to 149.9 ppm in 13C NMR spectrum
of MBTFVB 1 (Fig. 1B) corresponded to 2 carbons of the tri-
fluorovinyl [18,46]. The signal of the methyl located at 15.7 ppm
and the peaks at 114.3, 115.5, 119.0, 129.9, 150.3 and 151.6 ppm
belonged to 6 carbons of the benzene ring [18,46]. In addition, three
typical muitiplets at ꢂ120.3, ꢂ127.0 and ꢂ134.3 ppm [18,46] in 19F
NMR spectrum (Fig. 2A) showed the existence of the trifluorovinyl.
Fig. 1C shows FT-IR spectrum of MBTVFB 1 and the typical peak of
the trifluorovinyl was found to be located at 1833 cmꢂ1. The signals
of the benzene ring and the ether bond appeared at 1600, 1496, 808
and 1179 cmꢂ1, respectively. EI-MS spectrum of MBTFVB 1 is shown
in Fig. 1D and the peak of m/z 284 corresponded to the molecular
ion peak of MBTFVB 1. Moreover, HRMS provided the formula of
C11H6O2F6 and the found mass was 284.0268, which is almost equal
to the calculated mass of 284.0272. Therefore, all these evidences
confirmed the successful synthesis of bistrifluorovinyl-containing
monomer 1.
ular weights of MBTFVB
1 monomer and 4-methoxytri-
fluorovinyloxybenzene). The value of Sb/Sa is 15.5 and the molecular
weight is calculated to be 9200 g/mol. This result indicates that
every PMBTFVB 2 chain possesses 31.0 (¼15.5 ꢃ 2) repeating units.
Mn;NMR ¼ 284 ꢃ ð2Sb=SbÞ þ 204 ꢃ 2
(1)
Thus, all the above results verified the structure of PMBTFVB 2
homopolymer. In addition, this homopolymer can dissolve in most
3.2. Preparation of PMBTFVB homopolymer
PMBTFVB 2 homopolymer was obtained via thermal [2
p
þ 2
p]
step-growth cycloaddition polymerization of bifunctional MBTFVB
1 monomer in diphenyl ether at 200 ꢁC and both ends of the
homopolymer were capped by mono-functional 4-methoxytri-
fluorovinyloxybenzene. FT-IR, 1H NMR, 13C NMR and 19F NMR were
employed to characterize this homopolymer. FT-IR spectrum after
thermal homopolymerization (Fig. 3A) showed the complete
disappearance of the typical signal of the trifluorovinyl at
1833 cmꢂ1 and a new sharp peak of PFCB linkage appeared at
962 cmꢂ1 in Fig. 3A compared to that of the monomer (Fig.1C), thus
indicating the existence of PFCB linkage in the homopolymer.
Moreover, the representative signals of the trifluorovinyl in 19F
NMR spectrum disappeared after thermal homopolymerization
(Fig. 2B) and new multiplets in the range between ꢂ128.3 ppm and
ꢂ132.2 ppm appeared instead, which also demonstrated the pres-
ence of PFCB functionality. The singlets at 2.06 and 2.27 ppm in 1H
NMR spectrum after thermal homopolymerization (Fig. 4A)
belonged to 3 protons of the methyl and the broad peaks at 6.97
and 7.10 ppm were attributed to 3 protons of the benzene ring. The
signal of 3 protons of terminal methoxyl clearly appeared at
3.77 ppm as a singlet, which confirmed the effective end-capping
Fig. 4. 1H NMR (A) and 13C NMR (B) spectra of PMBTFVB 2 in CDCl3.

H. Liu et al. / Polymer 51 (2010) 5198e5206
5203
Table 1
Preparation of PMBTFVBeBr 3 macroinitiator.a
c
c
d
e
f
Sample NBS
(equiv)
0.7
1.0
Br%b (%) Mn,GPC
Mw/Mn
Mn,NMR
(kDa)
NATRP
DATRP (%)
(kDa)
3a
3b
12.34
16.28
5.7
6.2
1.18
1.14
10.4
10.8
16.2
22.3
52.3
71.9
a
Reaction temperature: 80 ꢁC; reaction time: 24 h; feeding ratio: [methyl]:
[BPO] ¼ 1:0.2.
b
c
d
e
f
Determined by the titration with Hg(NO3)2.
Measured by GPC in THF at 35 ꢁC.
Determined by 1H NMR.
The number of ATRP initiation group per chain.
Grafting density of ATRP initiation group.
common organic solvents including THF, CH2Cl2, chloroform,
hexane, cyclohexane, toluene, acetone, ethyl acetate and DMF;
however, it can’t dissolve in water and methanol.
3.3. Transformation of PMBTFVB into Br-containing ATRP
macroinitiator
Mono-bromination of the pendant methyls of PMBTFVB 2
homopolymer was conducted in CCl4 by reacting with NBS and BPO
so that the homopolymer was converted to PMBTFVBeBr 3 mac-
roinitiator. Two different feeding ratios of NBS to the methyls have
been used to adjust the degree of bromination and it was found that
adding more NBS led to the raising of the bromine content as listed
in Table 1. After the reaction with NBS and BPO, the bromine
contents of both samples increased from 0% to 12.34% for 3a and
16.28% for 3b (Table 1), respectively, this obviously indicating the
presence of Br-containing ATRP initiation sites in both samples
[47,48]. The molecular weights of both samples after the reaction
with NBS and BPO (Mn,GPC in Table 1) were higher than that of
PMBTFVB 2 homopolymer (Mn,GPC ¼ 4600 g/mol), which also evi-
denced the occurrence of the bromination reaction.
Fig. 6. GPC traces of PMBTFVBeBr 3 and PMBTFVB-g-PS 4 in THF.
that the polymeric architecture was kept during the reaction. Fig. 6
shows a unimodal and symmetrical GPC curve for PMBTFVBeBr 3a,
which also verified that the architecture of polymer chain was not
altered during the bromination [49]. These results also confirmed the
successful mono-bromination of PMBTFVB 2 homopolymer without
affecting the polymeric backbone.
The number of CH2Br ATRP initiation group (NATRP) can be
estimated via the data of Br% (Table 1) according to the following
equation set, (‘x’ and ‘y’ are the numbers of repeating unit with
CH2Br and CH3 group as shown in Scheme 1; 204 and 80 are the
molecular weights of 4-methoxytrifluorovinyloxybenzene and
bromine atom; 363 and 284 are the molecular weights of repeating
unit with CH2Br and CH3 group; 31.0 is the number of repeating
unit of PMBTFVB 2 homopolymer). The values of NATRP for
PMBTFVBeBr 3a and 3b are calculated to be 16.2 and 22.3,
respectively. Thus, the grafting densities of CH2Br ATRP initiation
group (DATRP) are 52.3% ¼ 16.2/31.0 and 71.9% ¼ 22.3/31.0 for 3a and
3b macroinitiators as listed in Table 1, respectively.
1H NMR spectrum after the reaction (Fig. 5A) shows the appear-
ance of two new peaks at 4.17 and 4.34 ppm, which corresponded to 2
protons of newly formed CH2Br group. A new peak attributed to the
carbon of CH2Br group also appeared at 24.6 ppm in 13C NMR spec-
trum after the reaction (Fig. 5B). In addition, the remaining of the
original signals of PMBTFVB 2 homopolymer in 1H NMR (Fig. 5A), 13
C
NMR (Fig. 5B) and 19F NMR spectra after the reaction demonstrated
The molecular weights of PMBTFVBeBr
3 macroinitiators
(Mn,NMR) were determined by 1H NMR according to Eq. (4), in
which Sa, Sb and Sc are the area of peak ‘a’ at 3.68 ppm, peaks ‘b’
at 1.99 and 2.18 ppm and peaks ‘c’ at 4.17 and 4.34 ppm in Fig. 5A,
respectively. The values are 10.400 g/mol for PMBTFVBeBr 3a
and 10,800 g/mol for PMBTFVBeBr 3b as listed in Table 1,
respectively.
Mn;NMR ¼ 363 ꢃ ð3Sc=SaÞ þ 284 ꢃ ð2Sb=SaÞ þ 204 ꢃ 2
(4)
Therefore, we can conclude that bromine-containing ATRP
initiation sites have been successfully introduced into the main
chain without affecting the polymeric architecture, and 16.2 and
Fig. 5. 1H NMR (A) and 13C NMR (B) spectra of PMBTFVBeBr 3 in CDCl3.

5204
H. Liu et al. / Polymer 51 (2010) 5198e5206
Table 2
Synthesis of PMBTFVB-g-PS 4 graft copolymer.a
d
e
f
g
Sample Time (h) Mn,GPCd (KDa) Mw/Mn
NSt
nSt
Mn,NMR (kDa)
4ab
4bb
4cb
4db
4ec
4fc
1.5
3
5
7
1.5
3
22.0
28.8
41.3
64.9
31.7
47.6
67.5
98.6
1.29
1.22
1.23
1.23
1.33
1.38
1.28
1.34
247.9 15.3
367.7 22.7
453.6 28.0
831.1 51.3
278.8 12.5
533.0 23.9
36.2
48.6
57.6
96.8
39.8
66.2
4gc
4hc
5
7
967.8 43.4 111.5
1179.7 52.9 133.5
a
Polymerization temperature: 110 ꢁC; feeding ratio: [St]:[CH2Br group]:[-
CuBr]:[bpy] ¼ 400:1:1:2.
b
Initiated by PMBTFVBeBr 3a.
c
Initiated by PMBTFVBeBr 3b.
d
Measured by GPC in THF at 35 ꢁC.
e
Total number of St repeating unit obtained from 1H NMR.
f
The number of St repeating unit per PS side chain obtained from 1H NMR.
g
Determined by 1H NMR.
22.3 CH2Br groups are involved in PMBTFVBeBr 3a and 3b mac-
roinitiators, respectively.
Fig. 7. 1H (A) and 19F (B) NMR spectra of PMBTFVB-g-PS 4 in CDCl3.
3.4. Synthesis of PMBTFVB-g-PS graft copolymer
ATRP of St was initiated by PMBTFVBeBr 3 macroinitiator at
110 ꢁC using CuBr/bpy as catalytic system to yield PMBTFVB-g-PS 4
graft copolymers via the grafting-from strategy and the results are
summarized in Table 2. It was found that the molecular weights of
the obtained graft copolymers were all much higher than those of
the macroinitiators, which indicated ATRP of St was performed. The
molecular weights of graft copolymers also increased with the
extending of polymerization time, which accorded with the char-
acteristic of ATRP [31]. In this case, the intermolecular coupling
reactions were suppressed by the combination of a high feeding
ratio of St to CH2Br initiation group (400:1) and a relatively low
conversion of St (<15%) according to previous reports [47e55]. All
graft copolymers showed unimodal and symmetrical GPC curves
(Fig. 6) with relatively narrow molecular weight distributions (Mw/
Mn ꢀ 1.38), which confirmed that intermolecular coupling reac-
tions could be neglected [52].
Fig. 3B shows FT-IR spectrum of PMBTFVB-g-PS 4 graft copol-
ymer and the typical signal of perfluorocyclobutyl unit located at
961 cmꢂ1. The bands at 3026, 1600, 1492 and 1452 cmꢂ1 originated
from the benzene ring of PMBTFVB backbone and PS side chains. In
particular, two sharp peaks at 756 and 698 cmꢂ1 witnessed the
existence of mono-substituted benzene ring in PS side chains. All
characteristic 1H NMR signals of the corresponding protons of
PMBTFVB backbone and PS side chains appeared in 1H NMR spec-
trum after graft copolymerization (Fig. 7A). The strong peaks at 1.43
and 1.86 ppm were attributed to 2 protons of CH2 group and 1
proton of CH group of PS side chains, respectively. Fig. 7A also
shows the disappearance of the signals of 2 protons of CH2Br
initiation group connected to the benzene ring which appeared at
4.17 and 4.34 ppm in Fig. 5A, thus indicating the complete
involvement of every pendant ATRP initiation group in graft poly-
merization of St. Furthermore, two minor peaks corresponding to
CHBr end group of PS side chain were found to be located at 4.41
and 4.49 ppm, which demonstrated ATRP mechanism of graft
copolymerization of St [56]. The signal of 3 protons of terminal
methoxyl of the backbone remained at 3.73 ppm after copolymer-
ization. The presence of PFCB linkage in PMBTFVB-g-PS 4 graft
copolymer was also verified by a series of peaks between ꢂ128.4
and ꢂ131.9 ppm in 19F NMR spectrum after copolymerization
(Fig. 7B). Therefore, all these evidences confirmed the structure of
PMBTFVB-g-PS 4 graft copolymer.
Since the molecular weight of the graft copolymer measured by
GPC is much lower than the ‘real’ value [57], we used 1H NMR to
determine the molecular weight of PMBTFVB-g-PS 4 graft copol-
ymer (Mn,NMR) instead of GPC. The total number of St repeating unit
(NSt), the molecular weight of the graft copolymer (Mn,NMR) and the
number of St repeating unit per PS side chain (nSt) were calculated
according to Eq. (5) (Sd and Sa are the area of peak ‘d’ at 1.43 ppm
and peak ‘a’ at 3.73 ppm in Fig. 7A, respectively), Eq. (6) (Mn,3 is the
molecular weight of PMBTFVBeBr 3 macroinitiator as listed in
Table 1 and 104 is the molecular weight of St) and Eq. (7) (NATRP is
the number of grafted ATRP initiation group per chain as listed in
Table 1), respectively. The molecular weights obtained from 1H
NMR (Table 2) are actually much higher than those measured by
GPC.
NSt ¼ 3 ꢃ ðSd=SaÞ
(5)
(6)
(7)
Mn;NMR ¼ Mn;3 þ 104 ꢃ NSt
nSt ¼ NSt=NATRP
PMBTFVBeBr 3a macroinitiator was employed to study the
kinetics of bulk ATRP of St and the conversions of St were measured
by GC as summarized in Table 3. The molecular weights increased
with the raising of the conversions of St and the graft copolymers
showed unimodal and symmetrical GPC curves in Fig. 6 with
narrow molecular weight distributions (Mw/Mn ꢀ 1.23), which also
matched the characteristics of ATRP. The semilogarithmic plot of Ln
Table 3
Kinetics studies of ATRP of St initiated by PMBTFVBeBr 3a.a
c
Sample
Time (h)
Conv.b (%)
Mnc (kDa)
Mw/Mn
4i
4j
4k
4m
1.5
3.0
5.0
7.0
2.33
7.15
10.03
12.31
11.4
24.8
31.9
36.7
1.21
1.23
1.23
1.20
a
Polymerization temperature: 110 ꢁC; feeding ratio: [St]:[CH2Br group]:[-
CuBr]:[bpy] ¼ 400:1:1:2; VSt:Vanisole ¼ 20:1.
b
Determined by GC using anisole as internal standard.
Measured by GPC in THF at 35 ꢁC.
c

H. Liu et al. / Polymer 51 (2010) 5198e5206
5205
Fig. 8. Kinetic plots for bulk ATRP of styrene initiated by PMBTFVBeBr 3a at 110 ꢁC,
[St]:[CH2Br group]:[CuBr]:[bpy] ¼ 400:1:1:2.
([M]0/[M]) vs. time is depicted in Fig. 8 on the basis of the data of
conversions of St, which shows the conversion of St increases with
the time and a linear dependence of ln([M]0/[M]) on the time when
the feeding ratio of St to CH2Br initiation group is 400:1. It is
obvious that the apparent polymerization rate is first-order with
respect to the concentration of St, illustrating a constant number of
propagating species during the graft copolymerization of St. This
phenomenon accorded with the characteristic of ATRP [31,32].
Thus, we can conclude that a series of PMBTFVB-g-PS 4 graft
copolymers consisting of a PFCB aryl ether-based backbone pos-
sessing 31 repeating units and PS (15e53 repeating units per chain)
side chains were successfully synthesized by the well-controlled
ATRP of St initiated by PMBTFVBeBr 3 macroinitiator.
Fig. 10. TG (A) and DTG (B) curves (in N2) of PMBTFVB 2, PMBTFVBeBr 3a, and
PMBTFVB-g-PS 4c with a heating rate of 10 ꢁC/min.
3.5. Properties of graft copolymer
to that of PS homopolymer [58]. ThelowerTg at 85.8 ꢁC was attributed to
PMBTFVB backbone, which was much higher than those of PMBTFVB 2
homopolymer (Tg ¼ 52.5 ꢁC) and PMBTFVBeBr 3a macroinitiator
(Tg ¼ 63.6 ꢁC) as shown in Fig. 9; this can be explained that the free
rotation of PMBTFVB backbone was confined by PS branches. The
presence of two different Tgs also indicated a bulk microphase separation
exist in PMBTFVB-g-PS 4 graft copolymer [59,60].
Thermal stability of the polymers was measured by TGA and the
typical TG (thermogravimetry) and DTG (derivative thermo-
gravimetry) curves are shown in Fig.10. The pyrolysis of PMBTFVB 2
homopolymer and PMBTFVBeBr 3a macroinitiator processed in
a one-stage decomposition pattern and Td of PMBTFVB 2 and
PMBTFVBeBr 3a is recorded at 431 ꢁC and 364 ꢁC respectively.
However, the thermolysis of PMBTFVB-g-PS 4c graft copolymer
shows a two-step degradation process around about 221 ꢁC and
425 ꢁC, which corresponded to the weight loss of PS branches and
PMBTFVB backbone, respectively.
Solubility tests were performed for PMBTFVB-g-PS 4 graft
copolymers with different molecular weights in common solvents.
These copolymers are soluble in most organic solvents such as THF,
CH2Cl2, chloroform, acetone, ethyl acetate, toluene and DMF;
however, it is insoluble in water and methanol.
Fig. 9 shows DSC thermogram of PMBTFVB-g-PS 4c graft copolymer
and twoTgs appeared at 100.9 ꢁC and 85.8 ꢁC, respectively. The higher Tg
at 100.9 ꢁC apparentlycorresponded to PS side chains, which was similar
4. Conclusions
In summary, a novel perfluorocyclobutyl aryl ether-based graft
copolymer with relatively narrow molecular weight distributions
(Mw/Mn ꢀ 1.38) was synthesized by the sequential thermal step-
growth cycloaddition polymerization of 2-methyl-1,4-bistri-
fluorovinyloxybenzene and ATRP of styrene. The pendant methyls
on the perfluorocyclobutyl aryl ether-based backbone were con-
verted to ATRP initiation groups by NBS and BPO without affecting
the main chain. The targeted graft copolymers were obtained by
Fig. 9. Third heating DSC scans (in N2) of PMBTFVB 2, PMBTFVBeBr 3a, and PMBTFVB-
g-PS 4c with a heating rate of 10 ꢁC/min.

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H. Liu et al. / Polymer 51 (2010) 5198e5206
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