Crosslinked poly(methyl methacrylate) with perfluorocyclobutyl aryl ether moiety as crosslinking unit: Thermally stable polymer with high glass transition temperature

Article abstract of DOI:10.1039/c9ra10166g

Crosslinked poly(methyl methacrylate) (PMMA) with high glass transition temperature (T_g) and thermal decomposition temperature was prepared by simple thermal crosslinking of PMMA-containing random copolymers bearing aryl trifluorovinyl ether (TFVE) moieties. A methacrylate monomer consisting of aryl TFVE moiety, 4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate (TFVOPMA), was first synthesized followed by radical copolymerization with methyl methacrylate (MMA) initiated by AIBN, providing the random copolymer containing aryl TFVE moieties, poly(4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate)-co-poly(methyl methacrylate) (PTFVOPMA-co-PMMA). Finally, crosslinked PMMA polymer with perfluorocyclobutyl (PFCB) aryl ether moieties as crosslinking units was obtained by [2π + 2π] cycloaddition reaction of aryl TFVE moieties in PTFVOPMA-co-PMMA copolymer. Thermal properties of both PTFVOPMA-co-PMMA and crosslinked PTFVOPMA-co-PMMA were examined by TGA and DSC. Compared to pure PMMA, T_g of PTFVOPMA-co-PMMA increased by 15.1 °C and no T_g was found in the DCS test of the crosslinked PTFVOPMA-co-PMMA. Thermal decomposition temperature (T_d,5%) of crosslinked PMMA was 47 °C higher than that of pure PMMA. Furthermore, the water absorption of crosslinked PMMA film greatly reduced in comparison with that of pure PMMA.

Full text of DOI:10.1039/c9ra10166g

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PAPER
Crosslinked poly(methyl methacrylate) with
perfluorocyclobutyl aryl ether moiety as
crosslinking unit: thermally stable polymer with
high glass transition temperature
Cite this: RSC Adv., 2020, 10, 1981
*
Yang Li and Hao Guo
Crosslinked poly(methyl methacrylate) (PMMA) with high glass transition temperature (Tg) and thermal
decomposition temperature was prepared by simple thermal crosslinking of PMMA-containing random
copolymers bearing aryl trifluorovinyl ether (TFVE) moieties. A methacrylate monomer consisting of aryl
TFVE moiety, 4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate (TFVOPMA), was first synthesized followed
by radical copolymerization with methyl methacrylate (MMA) initiated by AIBN, providing the random
copolymer containing aryl TFVE moieties, poly(4-((1,2,2-trifluorovinyl)oxy)phenyl methacrylate)-co-
poly(methyl methacrylate) (PTFVOPMA-co-PMMA). Finally, crosslinked PMMA polymer with
perfluorocyclobutyl (PFCB) aryl ether moieties as crosslinking units was obtained by [2p + 2p]
cycloaddition reaction of aryl TFVE moieties in PTFVOPMA-co-PMMA copolymer. Thermal properties of
both PTFVOPMA-co-PMMA and crosslinked PTFVOPMA-co-PMMA were examined by TGA and DSC.
Compared to pure PMMA, Tg of PTFVOPMA-co-PMMA increased by 15.1 ꢀC and no Tg was found in the
DCS test of the crosslinked PTFVOPMA-co-PMMA. Thermal decomposition temperature (Td,5%) of
crosslinked PMMA was 47 ꢀC higher than that of pure PMMA. Furthermore, the water absorption of
crosslinked PMMA film greatly reduced in comparison with that of pure PMMA.
Received 4th December 2019
Accepted 2nd January 2020
DOI: 10.1039/c9ra10166g
rsc.li/rsc-advances
with methacrylamide (MAAM) since hydrogen-bonding inter-
actions exist between these two monomer segments.16–19
Introduction
Fluoropolymers have attracted much curiosity in material
science due to their unique properties including thermal
stability, chemical resistance, ame retardancy, superior
electrical insulating ability, low dielectric constant and
refractive index, and unique surface property.20–22 To avoid
low processability of peruoropolymers, partially-uorinated
polymers like poly(vinylidene uoride) (PVDF),4,5 alternating
ethylene-tetrauoroethylene (ETFE)23 and alternating
ethylene-chlorotriuoroethylene (ECTFE) copolymers,24,25
have been prepared and exhibited improved processability.
Among partially-uorinated polymers, peruorocyclobutyl
(PFCB) aryl ether polymers26–31 are an intriguing class of u-
oropolymers, which not only retain the general outstanding
properties of uoropolymers originating from the low
polarity, strong electronegativity and small van der Waals
radius of uorine atom and strong C–F bond, but also
possess many other advantages such as improved process-
ability and optical transparency, structural versatility and
tunable properties. These PFCB aryl ether-based polymers
have been studied on the potential application in photonics,
polymer light-emitting diodes, proton exchange membrane
in fuel cell and atomic oxide resistance materials on space-
cra etc.32–40
Poly(methyl methacrylate) (PMMA) is a kind of transparent
polymeric material possessing diverse excellent properties such
as superior light transmittance, light weight, chemical stability,
weathering corrosion resistance, electrical insulation and good
processability, which make PMMA widely applied in many elds
including aerospace, building construction and optical instru-
ments.1–4 However, the glass transition temperature (Tg, 100 ꢀC)
and heat-deformation temperature of PMMA are relatively low
so as to limit its applications.5,6 In order to improve Tg and the
thermal stability of PMMA, investigators have explored various
methods,3,7–15 including the copolymerization of methyl meth-
acrylate (MMA) with comonomers bearing rigid or bulky groups
to overcome the miscibility puzzle, or the formation of a three-
dimensional network structure by the addition of crosslinking
agent. Wilkie et al. prepared MMA–DVB crosslinked polymers
using divinylbenzene (DVB) as crosslinking agents and the
degradation temperature (Td,5%
)
of resulting polymers
increased from 162 ꢀC to 294 ꢀC.12 Kuo et al. suggested an
approach to raise the Tg of PMMA through copolymerization
Department of Chemistry, Fudan University, 2005 Songhu Road, Shanghai 200438,
People's Republic of China. E-mail: hao_guo@fudan.edu.cn
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Inspired by the fact that PFCB aryl ether-based polymers
possess high heat resistance and optical transparency, Prof.
Huang of Shanghai Institute of Organic Chemistry et al.
prepared a series of PFCB-containing copolymers with high heat
resistance.41–43 The resulting polymethacrylate bearing sulfonyl
functionality exhibits excellent thermal stability (Td > 300 ꢀC)
and polyimide (PFCBBPPI) containing PFCB biphenyl ether
moieties shows excellent thermal stability and high trans-
parency. PFCB aryl ether polymers are most commonly
prepared through a thermal [2p + 2p] cycloaddition of aryl tri-
uorovinyl ethers (TFVE) at temperatures of between 150 ꢀC and
ꢀ
200 C without additional agent and no condensation byprod-
ucts are produced. Thus, TFVE group may act as a crosslinkable
group and the crosslinked region, peruorocyclobutyl (PFCB)
moieties, may give rise to better chemical resistance. Lee et al.
synthesized a novel uorinated aromatic polyether monomer
containing TFVE group and the resulting crosslinked polymers
aer thermal crosslinking showed higher Tg (239–271 ꢀC).44
All aforementioned discussions intrigued us to synthesize
methacrylate monomer containing TFVE group, which can be
copolymerized with MMA to provide polymethacrylate copolymers
containing TFVE groups so that the subsequent thermal cycload-
dition of TFVE groups can produce crosslinked polymethacrylate
copolymers with PFCB aryl ether moieties as the crosslinked
region. The resulting crosslinked polymethacrylate copolymers
may have higher thermal stability and good optical transparency
because of the below points: (1) PFCB aryl ether-based polymers
exhibit higher heat resistance and good transparency, (2) PFCB
aryl ether moieties with large volume may decrease the activity of
Scheme
1
Schematic illustration of preparation of transparent
crosslinked poly(methyl methacrylate) copolymers with PFCB aryl
ether as crosslinking unit.
remove the inhibitor, then washed with water, dried over CaCl2
and distilled twice in vacuo from CaH2 prior to use. 1,2-Dibro-
motetrauoroethane was prepared by condensing equimolar
ꢀ
amounts of Br2 and tetrauoroethylene at ꢁ195 C followed by
warming up to 22 C according to a previous report.1 4-methox-
ꢀ
ylphenol (Aldrich, 99%), caesium carbonate (Aldrich, 99%), boron
tribromide (BBr3, Alfa Aesar, 99%) and methacryloyl chloride (Alfa
Aesar, 97%) were used as received unless otherwise specied.
PMMA main chain, which might increase the heat resistance of Measurements
resultant polymers, (3) three-dimensional network structure may
1H, 13C and 19F NMR spectra of intermediates were recorded on
limit the mobility and rotation ability of polymeric chain, which
benets heat resistance of resultant polymers. Herein, we report
the preparation of transparent crosslinked poly(methyl methac-
rylate) (PMMA) copolymers with high Tg and high Td via copoly-
merization of MMA with a methacrylate monomer containing
TFVE moiety, 4-((1,2,2-triuorovinyl)oxy)phenyl methacrylate
(TFVOPMA), followed by thermal crosslinking process as shown in
Scheme 1. These resultant PMMA-based copolymers containing
TFVE or PFCB aryl ether groups were investigated in detail by
NMR, FT-IR, differential scanning calorimetry (DSC) and ther-
mogravimetry analysis (TGA).
a JEOL resonance ECZ 400S spectrometer (400 MHz) in CDCl3.
Tetramethylsilane (TMS) and CDCl3 were used as internal
standards for 1H and 13C NMR, respectively; CF3CO2H was used
as an external standard for 19F NMR. FT-IR spectra were recor-
ded on a Nicolet AVATAR-360 FT-IR spectrophotometer with
a resolution of 4 cmꢁ1. Number-average molecular weights (Mn)
and molecular weight distributions (Mw/Mn) were obtained on
a conventional gel permeation chromatography (GPC) system
equipped with a Waters 515 Isocratic HPLC pump, a Waters
2414 refractive index detector, and a set of Waters Styragel
columns (HR3 (500–30 000), HR4 (5000–600 000) and HR5
(50 000–4 000 000), 7.8 ꢂ 300 mm, particle size: 5 mm). GPC
measurement was carried out at 35 ꢀC using tetrahydrofuran
(THF) as eluent with a ow rate of 1.0 mL minꢁ1. The system
was calibrated with linear polystyrene standards. Differential
scanning calorimetry (DSC) was performed on a TA Q200 DSC
instrument in N2 with a heating rate of 10 ꢀC minꢁ1. Ther-
mogravimetry analysis (TGA) was conducted on a TA Discovery
TGA 55 thermal analysis system in N2 with a heating rate of
10 ꢀC minꢁ1. UV/vis spectra were acquired on a Hitachi U-2910
spectrophotometer.
Experimental
Materials
Dimethylsulfoxide (DMSO, Alfa Aesar, 99%) was dried over CaH2
and distilled under reduced pressure prior to use. Triethylamine
(TEA, Alfa Aesar, 99%) was dried over KOH and distilled over
CaH2 under N2 prior to use. Granular zinc was activated by
ꢀ
washing in 0.1 N HCl followed by drying at 140 C in vacuo for
10 h. 2,20-Azobis(isobutyronitrile) (AIBN, Aldrich, 98%) was
recrystallized from anhydrous ethanol. Dichloromethane (DCM)
and acetonitrile was dried over CaH2 and distilled under N2 prior
to use. 2-Butanone was reuxed with KMnO4 and distilled under
Synthesis of 4-((1,2,2-triuorovinyl)oxy)phenyl methacrylate
CaCl2 and KMnO4 prior to use. Methyl methacrylate (MMA, 4-((1,2,2-Triuorovinyl)oxy)phenyl methacrylate (TFVOPMA)
Aldrich, 99%) was washed with 5% aqueous NaOH solution to was synthesized via four steps starting from 4-methoxylphenol
1982 | RSC Adv., 2020, 10, 1981–1988
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was washed with water and dried over MgSO4. The organic layer
was ltrated and evaporated under reduced pressure, and then
the residue was puried by ash column chromatography
(eluent: hexane) on silica gel to give 3.79 g (82%) of 4-(2-bromo-
1,1,2,2-tetrauoroethoxy)phenyl methacrylate as a colorless oil.
1H NMR (400 MHz, CDCl3): d (ppm): 7.12 (d, 2H, J ¼ 7.13 Hz,
C6H2H2), 7.06 (d, 2H, J ¼ 7.03 Hz, C6H2H2), 6.24 (s, 1H, J ¼
6.24 Hz, C]CHH), 5.66 (s, 1H, J ¼ 5.66 Hz, C]CHH), 1.94 (s, 3H,
J ¼ 2.05 Hz, CH3). 19F NMR (376 MHz, CDCl3): d (ppm): ꢁ70.02 (s,
2F), ꢁ88.01 (s, 2F). 13C NMR (101 MHz, CDCl3): d (ppm): 18.4,
122.7, 123.1, 127.7, 135.6, 145.9, 149.3, 165.6.
Scheme 2 Schematic illustration of synthesis of TFVOPMA monomer.
Newly activated zinc (1.98 g, 0.035 mol) was added to a dried
three-neck round-bottom ask followed by evacuating and
backlling with N2 three times. Next, dry acetonitrile (40 mL) was
(Scheme 2). 1-Methoxy-4-(2-bromo-1,1,2,2-tetrauoroethyl)
benzene was rstly prepared by uoroalkylation reaction of 4-
methoxyphenol. To a 500 mL dried three-neck round-bottom
ask tted with a condenser and a constant pressure drop-
ping funnel, 4-methoxyphenol (20.00 g, 0.16 mol) and caesium
carbonate (33.60 g, 0.19 mol) were added followed by evacuating
and backlling with N2 three times. Next, DMSO (200 mL) was
added via a gastight syringe and the mixture was stirred for
30 min. 1,2-Dibromotetrauoroethane (22.60 mL, 0.19 mol) was
then dropped slowly, keeping the temperature below 35 ꢀC. The
resulting mixture was heated at 50 ꢀC for 5 h. Finally, 500 mL of
deionized water was added and the organic layer was separated
and extracted by dichloromethane, washed by water and brine
and then dried over magnesium sulfate (MgSO4). 1-Methoxy-4-
(2-bromo-1,1,2,2-tetrauoroethyl)benzene (40.69 g, 84%) was
obtained by silica column chromatography using hexane as
eluent. 1H NMR (400 MHz, CDCl3): d (ppm): 7.23 (d, 2H, J ¼
7.24 Hz, C6H2H2), 7.03 (d, 2H, J ¼ 7.02 Hz, C6H2H2), 3.82 (s, 3H, J
¼ 3.84 Hz, OCH3). 19F NMR (376 MHz, CDCl3): d (ppm): ꢁ68.2 (s,
2F), ꢁ86.6 (s, 2F). 13C NMR (101 MHz, CDCl3): d (ppm): 55.7,
114.6, 122.8, 142.0, 155.3. EI-MS (M+): 123 (100), 287 (1), 289 (1).
ꢀ
added and the oil temperature was lied to 90 C. 4-(2-Bromo-
1,1,2,2-tetrauoroethoxy)phenyl methacrylate (15.86 g, 29
mmol) was dropped slowly into the above mixture, keeping the
mixture boiling slightly. The mixture was reuxed for 10 h and
aer cooled to room temperature, the mixture was ltered. The
salt was washed by dichloromethane to extract the product. The
organic phase was collected and dried over MgSO4. Aer CH2Cl2
was evaporated, the crude product was puried by ash column
chromatography (eluent: hexane) to afford 4-((1,2,2-triuorovinyl)
oxy)phenyl methacrylate (TFVOPMA) as a colorless oil (3.98 g,
53%). 1H NMR (400 MHz, CDCl3): d (ppm): 7.23 (dd, 2H, J ¼
7.25 Hz, C6H2H2), 7.17 (dd, 2H, J ¼ 7.17 Hz, C6H2H2), 6.31 (s, 1H, J
¼ 6.35 Hz, C]CHH), 5.75 (s, 1H, J ¼ 5.78 Hz, C]CHH), 2.03 (s,
3H, J ¼ 2.05 Hz, CH3). 13C NMR (101 MHz, CDCl3): d (ppm): 18.1,
116.7, 123.2, 127.2, 135.6, 147.7, 165.6. 19F NMR (376 MHz,
CDCl3): d (ppm): ꢁ120.1 (dd, 1F), ꢁ126.9 (dd, 1F), ꢁ134.49 (dd,
1F). FT-IR (KBr): n (cmꢁ1): 2962, 2936, 2856, 1832, 1740, 1640,
1501, 1318, 1276, 1181, 1140, 947, 876, 812, 752.
In
a
pre-dried ask, 1-methoxy-4-(2-bromo-1,1,2,2-
Copolymerization of TFVOPMA and MMA
tetrauoroethyl)benzene (3.88 g, 13 mmol) was dissolved in
300 mL of anhydrous dichloromethane. The solution was
cooled to 0 ꢀC followed by adding dichloromethane solution of
BBr3 (25 mL, 25 mmol) dropwise within 30 min. The mixture
was slowly warmed up to room temperature and stirred at room
temperature for another 12 h. The resulting mixture was l-
trated and the residual salt was removed by washing with
dichloromethane and ltrating three times. The solvents were
removed by rotary evaporation, and the residue was subjected to
column chromatography (eluent: hexane) to afford 4-(2-bromo-
1,1,2,2-tetrauoroethoxy)phenol as a colorless liquid (3.15 g,
84% yield). 1H NMR (400 MHz, CDCl3): d (ppm): 7.10 (d, 2H, J ¼
7.11 Hz, C6H2H2), 6.86 (d, 2H, J ¼ 7.11 Hz, C6H2H2), 5.73 (s, 1H, J
¼ 3.84 Hz, OH). 19F NMR (376 MHz, CDCl3): d (ppm): ꢁ68.2 (s,
2F), ꢁ86.27 (s, 2F). 13C NMR (101 MHz, CDCl3): d (ppm): 116.3,
122.9, 142.0, 154.4. EI-MS (M+): 109 (100), 356 (2), 358 (2).
In a pre-dried ask, 4-(2-bromo-1,1,2,2-tetrauoroethoxy)
phenol (3.70 g, 13 mmol) and triethylamine (1.49 mL, 0.015
mol) were dissolved in 300 mL of 2-butanone. The solution was
cooled to 0 ꢀC followed by adding the solution of methacryl
chloride (1.48 mL, 15 mmol) in 10 mL of 2-butanone dropwise.
The mixture was warmed up to room temperature and stirred for
another 1 h. The salt was removed by ltration and the ltrate
AIBN (17.8 mg, 0.108 mmol) was rstly added to a 25 mL Schlenk
ask (ame-dried under vacuum prior to use) sealed with
a rubber septum for degassing. Next, TFVOPMA (1.28 g, 5 mmol),
MMA (0.50 g, 5 mmol) and 2-butanone (3.4 mL) were introduced
via a gastight syringe. The solution was degassed by three cycles
of freezing–pumping–thawing followed by immersing the ask
ꢀ
into an oil bath preset at 60 C to start the polymerization. The
polymerization was terminated by putting the ask into liquid
nitrogen aer 3 h. Aer repeated purication by dissolving in 2-
butanone and precipitating in ethanol three times, 1.39 g (78%)
of white powder, poly(4-((1,2,2-triuorovinyl)oxy)phenyl methac-
rylate)-co-poly(methyl methacrylate) (PTFVOPMA-co-PMMA), was
obtained aer drying in vacuo at 30 ꢀC. GPC: Mn ¼ 50 900 g
molꢁ1, Mw/Mn ¼ 1.84. 1H NMR (400 MHz, CDCl3): d (ppm): 0.84,
1.02, 1.18 (3H, CH3), 1.85–2.04 (4H, CH2), 3.58 (3H, OCH3), 7.11
(4H, C4H2H2). 19F NMR (376 MHz, CDCl3): d (ppm): ꢁ119.2 (m,
1F), ꢁ126.1 (m, 1F), ꢁ134.0 (m, 1F). FT-IR (KBr): n (cmꢁ1): 2998,
2947, 2845, 1834, 1731, 1499, 1299, 1138, 984, 838, 812, 751.
Crosslinking of PTFVOPMA-co-PMMA
PTFVOPMA-co-PMMA copolymer was dissolved in ethyl acetate
and the solution was then spin-cast onto the freshly cleaned
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glass substrate followed by heat treatment at 30 ꢀC for 30 min, methacrylate monomer, 4-((1,2,2-triuorovinyl)oxy)phenyl
40 ꢀC for 30 min and 65 ꢀC for 1 h. The obtained thin lm was methacrylate (TFVOPMA).
placed into a beaker and then the beaker was placed into a tube
The chemical structure of TFVOPMA monomer was charac-
furnace, followed by evacuating and backlling with N2 three terized by FT-IR, 1H NMR and 19F NMR. The characteristic
times. The temperatuꢁre1 of tube furnace was raised to 100 ꢀC peaks of double bond are found to be located at 5.75 (‘b’) and
with a rate of 5 ꢀC min . Aer keeping at 100 ꢀC for 30 min, the 6.31 (‘c’) ppm in 1H NMR spectrum of TFVOPMA (Fig. 1A). The
temperature was raised to 150 ꢀC with a rate of 5 ꢀC minꢁ1. Aer proton resonance signal of methyl linked to the double bond
keeping at 150 ꢀC for 30 min, the temperature was raised to appears at 2.03 ppm (‘a’), while the resonance signals at 7.17
180 ꢀC with a rate of 5 ꢀC minꢁ1. Aer reacting at 180 ꢀC for 10 h, (‘d’) and 7.23 ppm (‘e’) belong to phenyl protons. In 19F NMR
the furnace was cooled and crosslinked PTFVOPMA-co-PMMA spectrum of TFVOPMA (Fig. 1B), characteristic peaks of –OCF]
copolymer lm was obtained. FT-IR (KBr): n (cmꢁ1): 2998, 2950, CF2 group appear at ꢁ120.3, ꢁ127.8 and ꢁ135.3 ppm, respec-
1732, 1501, 1488, 1452, 1276, 1199, 1150, 969, 842, 807, 752.
tively. And the appearance of the peak at 1832 cmꢁ1 in FT-IR
spectrum of TFVOPMA (Fig. 2A) further conrms the presence
of –OCF]CF2 group. The sharp peak located at 1740 cmꢁ1 was
attributed to stretching vibration of carbonyl, while the peak at
1640 cmꢁ1 belongs to the stretching vibration of double bond.
The absorption at 812 cmꢁ1 indicates para-substitution of
benzene ring. All these results conrm the successful synthesis
of TFVOPMA, the methacrylate monomer with TFVE moiety.
Water absorption of crosslinked PMMA-based copolymer
The water uptake experiments were carried out as follows:
sample lms (PMMA and crosslinked PTFVOPMA-co-PMMA)
were dried in vacuo at 55 ꢀC for 24 h and a constant weight
(ꢃ0.0001 g) can be obtained for the lm (about 0.5 g). The lms
were immersed in ultra-pure water at 25 ꢀC. At certain interval,
the lms were then taken out of water and the water absorbed
on the surface was wiped off by a cleaning cloth. The weight of
the lms was weighed immediately.
Preparation and crosslinking of PTFVOPMA-co-PMMA
copolymer
Compared to living/controlled polymerization, conventional
free radical polymerization allows achieving higher molecular
weights and the related industrial technology is mature.
Therefore, free radical copolymerization of MMA and TFVOPMA
was conducted in 2-butanone at 60 ꢀC using AIBN as initiator to
provide the corresponding random copolymer, poly(4-((1,2,2-
triuorovinyl)oxy)phenyl methacrylate)-co-poly(methyl methac-
rylate) (PTFVOPMA-co-PMMA).
Results and discussion
Synthesis of TFVOPMA monomer
TFVOPMA, a methacrylate monomer containing aryl TFVE
moiety, was synthesized via four steps using 4-methoxylphenol
and 1,2-dibromotetrauoroethane as starting materials. Firstly,
hydroxyl of 4-methoxylphenol was transformed into –OCF2-
CF2Br group via the uoroalkylation with BrCF2CF2Br. Subse-
quent demethylation of resultaning compound by BBr3
provided 4-(2-bromo-1,1,2,2-tetrauoroethoxy)phenol, which
was treated with methacryloyl chloride to obtain 4-(2-bromo-
1,1,2,2-tetrauoroethoxy)phenyl methacrylate. Finally, –OCF2-
CF2Br moiety of the methacrylate was converted to –OCF]CF2
functionality by Zn-mediated elimination to give the target
The resulting copolymer was characterized by GPC, FT-IR, 1H
NMR and 19F NMR. GPC retention curve of PTFVOPMA-co-
PMMA shows a unimodal elution peak with a relatively broad
molecular weight distribution of 1.84 and the molecular weight
Fig. 1 1H (A) and 19F (B) NMR spectra of TFVOPMA in CDCl3.
1984 | RSC Adv., 2020, 10, 1981–1988
Fig. 2 FT-IR spectra of TFVOPMA (A) and PTFVOPMA-co-PMMA (B).
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Preparation and properties of crosslinked PMMA-based
copolymer
Triuorovinyl ether groups (–OCF]CF2) can form per-
uorocyclobutane units via [2p + 2p] cycloaddition reaction at
high temperature, thus we rstly monitored this cross-linking
reaction by DSC. As we can see from Fig. 5, Tg of PTFVOPMA-
co-PMMA was ꢀabout 137.6 ꢀC in round 1, higher than that of
PMMA (122.5 C). We supposed that the introduction of rigid
benzene ring with large volume makes rotational hindrance of
polymeric chain difficult, which leads to higher Tg of
PTFVOPMA-co-PMMA. Interestingly, Tg of PTFVOPMA-co-PMMA
increased with the scan times and the values of Tg reached
169.7 ꢀC in the sixth scan. The phenomenon demonstrated that
[2p + 2p] cycloaddition reaction of triuorovinyl ether groups in
PTFVOPMA-co-PMMA copolymer occured at higher temperature
during the DSC measurement and the formed PFCB cross-
linking unit further limited the mobility of polymer chains,
endowing the polymer with higher Tg.
Next, we conducted thermal crosslinking process of
PTFVOPMA-co-PMMA copolymer. Firstly, thin lm of
PTFVOPMA-co-PMMA was obtained by dissolving PTFVOPMA-
co-PMMA into ethyl acetate and spin-casting the solution onto
the freshly cleaned glass substrate followed by heat treatment at
30 ꢀC for 30 min, 40 ꢀC for 30 min and 65 ꢀC for 1 h. Then, this
lm was performed in a tube furnace under N2 at 180 ꢀC for
10 h, affording a transparent lm with a pale yellow color. From
FT-IR spectrum of PTFVOPMA-co-PMMA aer thermal cross-
linking (Fig. 6C), the peak at 1836 cmꢁ1 corresponding to TFVE
group disappeared and a new peak at 969 cmꢁ1 corresponding
to PFCB ring was found, which indicated the formation of PFCB
aryl ether moieties in the copolymer by thermal cycloaddition of
aryl TFVE groups. Other typical characteristic peaks can also be
seen in FT-IR spectrum aer crosslinking (Fig. 6C).
Fig. 3 GPC curve of PTFVOPMA-co-PMMA in THF.
of PTFVOPMA-co-PMMA is about 50 900 g molꢁ1 (Fig. 3). In the
FT-IR spectrum of PTFVOPMA-co-PMMA (Fig. 2B), the typical
signal of double bond at 1640 cmꢁ1 disappeared aer poly-
merization and the signal of TFVE was located at 1834 cmꢁ1
,
which indicated that TFVE group was not affected during the
copolymerization of TFVOPMA and MMA. Other typical signals
such as 1731 (C]O, symmetric stretch), 1499 (phenyl ring,
stretch), 812 and 838 (Ar–H deformation) are visible and the
stretching vibration of –CH3 (2998 cmꢁ1) and –CH2 (2947 and
2845 cmꢁ1) become stronger, which also illustrate the prepa-
ration of PTFVOPMA-co-PMMA copolymer. Fig. 4A shows 1H
NMR spectrum of PTFVOPMA-co-PMMA copolymer, which also
showed the disappearance of proton resonance signal of double
bond. The peaks of polymethacrylate backbone appeared at
1.85–2.04 ppm (‘b’) and 0.84, 1.02, 1.18 ppm (‘a’), corresponding
to the protons of methylene and methyl in –CH2CCH3 moiety.
The peak at 3.58 ppm (‘c’) is attributed to 3 protons of methoxy
group, while the peaks at 7.11 ppm (‘d’) belongs to the protons
of phenyl. Therefore, the composition of this copolymer
(NTFVOPMA/NMMA) was about 1 : 1.93, which was calculated
according to the equation (NTFVOPMA/NMMA ¼ 3Sd/4Sc, Sc and Sd
are the integration area of peak ‘c’ at 3.58 ppm and peak ‘d’ at
7.11 ppm in Fig. 3A). Moreover, the existence of TFVE group
appeared at ꢁ119.2, ꢁ126.1 and ꢁ134.0 ppm in 19F NMR
spectrum (Fig. 4B) further conrmed the preservation of TFVE
groups in PTFVOPMA-co-PMMA copolymer.
As it can be seen from Fig. 5, no Tg was found on the DSC
curve of crosslinked PTFVOPMA-co-PMMA below 250 ꢀC, that is,
All the above evidence veried that TFVE group did not affect
the radical copolymerization of TFVOPMA and MMA and the
PMMA-based copolymer containing TFVE aryl ether moieties
has been successfully prepared.
Fig. 4 1H (A) and 19F (B) spectra of PTFVOPMA-co-PMMA copolymer Fig. 5 DSC curves (in N2) of PMMA, PTFVOPMA-co-PMMA and
in CDCl3.
crosslinked PTFVOPMA-co-PMMA with a heating rate of 10 ꢀC minꢁ1
.
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Fig.
8
UV/vis spectra of PTFVOPMA-co-PMMA and crosslinked
Fig. 6 FT-IR spectra of PMMA (A), PTFVOPMA-co-PMMA (B) and
crosslinked PTFVOPMA-co-PMMA (C).
PTFVOPMA-co-PMMA films.
ether moieties as crosslinked units shows higher thermal
stability compared to PMMA and PTFVOPMA-co-PMMA. This
can be explained that the formation of PFCB ring aer thermal
treatment decreases the activities of PMMA main chain because
of its large volume, and three-dimensional network structure
limits the mobility and rotation ability of polymer chain, which
may improve the thermal stability of the resultant PMMA-based
copolymer.
The light transmittance of PTFVOPMA-co-PMMA and cross-
linked PTFVOPMA-co-PMMA lms were investigated by UV/vis
spectroscopy. As shown in Fig. 8, the transmittance of
PTFVOPMA-co-PMMA lm are 74% at 500 nm and 80% at
600 nm, and the transmittance of the crosslinked lm
decreased to 62.5% at 600 nm.
the resultant crosslinked polymer is in glass state below 250 ꢀC,
which demonstrated that the formed network with PFCB aryl
ether moieties as crosslinking segment largely improved the
heat resistance of the obtained PMMA-based copolymer.
Thermal degradation of PTFVOPMA-co-PMMA before and aer
crosslinking was investigated by TGA as shown in Fig. 7. The 5%
weight loss temperatures (Td,5%) for PMMA, PTFVOPMA-co-
PMMA and crosslinked PTFVOPMA-co-PMMA are 254 ꢀC, 250 ꢀC
and 301 ꢀC, respectively; while the 10% weight loss tempera-
tures (Td,10%) are 269 ꢀC, 276 ꢀC and 326 ꢀC, respectively.
PTFVOPMA-co-PMMA containing TFVE groups shows lower
thermal degradation temperature at rst stage before Td,6%
ꢀ
(257.6 C) as compared to that of PMMA, which may be attrib-
uted to the polarity and soness of TFVE group. However,
PTFVOPMA-co-PMMA containing TFVE groups shows higher Td
at late stage (aer Td,6% ¼ 257.6 ꢀC), which may be attributed to
the formation of enough PFCB rings at higher temperature. As
we can see, crosslinked PTFVOPMA-co-PMMA with PFCB aryl
Among the unique properties of uorinated polymers, low
water absorption is a typical one. The moisture resistance was
evaluated by measuring the weight change of PMMA and
crosslinked PTFVOPMA-co-PMMA lms aer immersing into
pure water for a certain time (Fig. 9). It is noted that the water
Fig.
7 TGA curves (in N2) of PMMA, PTFVOPMA-co-PMMA and Fig. 9 Water absorption rate of PMMA and crosslinked PTFVOPMA-
crosslinked PTFVOPMA-co-PMMA with a heating rate of 10 ꢀC minꢁ1
.
co-PMMA films.
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absorption of crosslinked PTFVOPMA-co-PMMA lm greatly 13 R. Chauhan and V. J. Choudhary, Appl. Polym. Sci., 2009, 112,
decreased in comparison with pure PMMA (0.03% vs. 1.73% 1088.
aer 8 h). Furthermore, the water absorption of crosslinked 14 L. Lou, Y. Koike and Y. Okamoto, Polymer, 2011, 52, 3560–
PTFVOPMA-co-PMMA lm retained below 0.06%, while that of 3564.
PMMA increased with the immersing time. The decreasing 15 F. Atabaki, A. Abdolmaleki and A. Barati, Colloid Polym. Sci.,
water absorption could be due to the highly hydrophobic nature
of aryl PFCB moieties.
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16 S. W. Kuo and H. T. Tsai, Macromolecules, 2009, 42, 4701–
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17 S. Dong, Q. Wang, Y. Wei and Z. J. Zhang, Appl. Polym. Sci.,
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Conclusions
In summary, a methacrylate monomer containing aryl TFVE 18 L. T. Yang and D. H. Sun, J. Appl. Polym. Sci., 2006, 100, 918–
group, TFVOPMA, was synthesized and copolymerized with 922.
MMA to provide the copolymer containing aryl TFVE groups, 19 F. Atabaki, A. Shokrolahi and Z. Pahnavar, J. Appl. Polym. Sci.,
PTFVOPMA-co-PMMA, which was treated at 180 ꢀC to give
2018, 135, 46603.
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of crosslinked network PTFVOPMA-co-PMMA copolymer is high
and they are thermally stable with less water absorption.
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21 D. A. Babb, R. V. Snelgrove, D. W. Smith and S. F. Mudrich,
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Conflicts of interest
There are no conicts to declare.
24 M. O. Abdel-Hamed, Polym. Adv. Technol., 2018, 29, 658–667.
25 M. Guerre, M. Uchiyama, G. Lopez, B. Ameduri, K. Satoh,
M. Kamigaito and V. Ladmiral, Polym. Chem., 2018, 9, 352–
361.
Acknowledgements
The authors thank nancial supports from Shanghai Science
and Technology Committee (18DZ1201607) and International
Science
&
Technology Cooperation Program of China 26 D. A. Babb, R. V. Snelgrove, D. W. Smith and S. F. Mudrich,
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