Synthesis and characterization of a novel fluorinated polyether glycol with fluorinated side chains via "living/controlled" cationic polymerization

Article abstract of DOI:10.1016/j.jfluchem.2015.04.007

A novel fluorinated polyether glycol with fluorinated side chains is synthesized via "living/controlled" cationic ring-opening polymerization of tetrahydrofuran and fluorine-containing epoxy compounds (FO). The effects of polymerization conditions on monomer conversion, number-average molecular weight (M_n), molecular weight distribution (M_w/M_n) are measured. Our investigations have shown that the use of a mixed solvent (dichloromethane/1,4-dioxane) can prevent intra- and intermolecular transfer reactions, due to more nucleophilic oxygen atom in 1,4-dioxane. Using BF₃·CH₃OH/CH₂OHCH₂OH as initiation system, polymers with predictable number-average molecular weight, narrow molecular weight distribution (1.03 < M_w/M_n < 1.08) were produced. On the basis of the reactivity ratio of FO/THF and monomer conversion, a mechanism of living/controlled polymerization has been proposed.

Full text of DOI:10.1016/j.jfluchem.2015.04.007

Accepted Manuscript
Title: Synthesis and characterization of a novel fluorinated
polyether glycol with fluorinated side chains via
“living/controlled” cationic polymerization
Author: Lingling Li Ying Li Xia Wang Yuanchun Qi Jiaojiao
Hu Zhou Fang Qingzhi Dong
PII:
S0022-1139(15)00103-7
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2015.04.007
FLUOR 8545
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
30-10-2014
9-4-2015
10-4-2015
Please cite this article as: L. Li, Y. Li, X. Wang, Y. Qi, J. Hu, Z. Fang, Q. Dong, Synthesis
and characterization of a novel fluorinated polyether glycol with fluorinated side chains
via “living/controlled” cationic polymerization, Journal of Fluorine Chemistry (2015),
http://dx.doi.org/10.1016/j.jfluchem.2015.04.007
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Highlights
Fluorinated glycol has been synthesized by the living/controlled polymerization.
The polymerization mechanism of fluorinated glycol was proposed.
1,4-dioxane was used as nucleophilic additive to attain living polymerization.
The BF3·CH3OH has been developed to prepare fluorinated polyether glycol.
The reactivity ratios of monomers were calculated according to Kelen-Tudos method.
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A novel fluorinated polyether glycol with fluorinated side chains was successfully
synthesized via “living/controlled” cationic polymerization. The reaction rate of
polymers increased linearly with the increase of monomer conversion. The obtained
polymer has predictable molecular weight, narrow molecular weight distribution.
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Synthesis and characterization of a novel fluorinated polyether glycol
with fluorinated side chains via “living/controlled” cationic
polymerization
Lingling Lia,b, Ying Lib, Xia Wangb*, Yuanchun Qia, Jiaojiao Hub, Zhou Fanga,
Qingzhi Donga*
a School of Materials Science and Engineering, East China University of Science and
Technology, Shanghai 200237, China.
b School of Materials Science and Engineering, University of Shanghai for Science
and Technology, Shanghai 200093, China.
To whom the correspondence should be addressed:
Professor. Xia Wang
School of Materials Science and Engineering, University of Shanghai for Science and
Technology
516 Jungong Road, Shanghai 200093, China
E-mail:liying@usst.edu.cn
Fax: +86-21-55270632. Phone: +86-21-55274069.
And
Professor. Qingzhi Dong
School of Materials Science and Engineering, East China University of Science and
Technology
130 Meilong Road, Shanghai, 200237,China
E-mail:qzhdong@ecust.edu.cn
Fax: +86-21-64251123. Phone: +86-21-64251123
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ABSTRACT
A novel fluorinated polyether glycol with fluorinated side chains is synthesized via
“living/controlled” cationic ring-opening polymerization of tetrahydrofuran and
fluorine-containing epoxy compounds (FO). The effects of polymerization conditions
on monomer conversion, number-average molecular weight (Mn), molecular weight
distribution (Mw/Mn) are measured. Our investigations have shown that the use of a
mixed solvent (dichloromethane/1,4-dioxane) can prevent intra- and intermolecular
transfer reactions, due to more nucleophilic oxygen atom in 1,4-dioxane. Using
BF3·CH3OH/CH2OHCH2OH as initiation system, polymers with predictable
number-average molecular weight, narrow molecular weight distribution (1.03 <
Mw/Mn < 1.08) were produced. On the basis of the reactivity ratio of FO/THF and
monomer conversion, a mechanism of living/controlled polymerization has been
proposed.
Keywords: fluorinated polyether glycol;“living/controlled” cationic polymerizations;
ring-opening polymerization; synthesis
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1. Introduction
It is well-known that polyurethane exhibits excellent mechanical properties,
thermal stability and microphase separation. Fluorinated polyurethanes, namely with
fluorocarbon chains in the polyurethane, not only maintain these excellent properties,
but also have very low surface energies [1,2], biocompatibility and biostability [3-7],
low water absorptivity, lubricity, and oxidative stability [8]. Therefore, they are
widely used as biomedical materials, anticorrosion coatings, aerospace materials, etc.
Recently, extensive works have been done on the synthesis and characterization
of fluorinated polyurethanes. Fluorinated chains have been incorporated into
polyurethanes via fluoro-containing diisocyanates [9], soft segments [10-11], hard
segments [12-14], or chain extenders [15-19]. Because of the higher cost and fewer
varieties of fluorinated dissocyanates, the synthetic route of fluorinated polyurethanes
with fluorinated dissocyanates was not often used. Owing to the lower molecular
weight and less fluorine content, the improvement of properties of fluorinated
polyurethanes synthesized by fluorinated chain extenders was not significant.
Currently, fluorinated polyurethanes are mostly synthesized using fluorinated
polyether glycols as a soft segment. However, the surface properties of fluorinated
polyurethane with fluorinated side chains are better than those with fluorinated groups
in the main chains. This is because the fluorocarbon side chains in the polyurethane
soft segments have less influence on the mechanical properties and cohesiveness of
polyurethanes. Also, because of the higher mobility and flexibility of fluorinated side
chains in the soft segments, fluorine groups are much easier to migrate to the surface
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and be enriched during molding. Therefore, the fluorinated polyurethane with lower
fluorine content possesses excellent performance.
However, fluorinated polyether glycol with fluorine in the side chain is one of
the most important components for further synthesis of fluorinated polyurethanes with
fluorinated pendent groups. Ge et al. [20,21] successfully synthesized fluorinated
polyether glycol by radical grafting of hexafluoropropylene (HFP) onto
polytetramethylene glycol (PTMG) in a high-pressure reactor. Fluorinated
polyurethanes with fluorine-containing pendent groups were then successfully
synthesized. XPS and contact angle data suggested that the surface of the fluorinated
polyurethanes was significantly enriched with fluorine groups.
In this work, we successfully synthesized a novel fluorinated polyether glycol
(FPO) with fluorinated side chains via “living/controlled” cationic ring-opening
polymerization. The advantage of the method is that the cationic active center is stable
during the course of the polymerization, suspending backbiting, reversible transfer
and intermolecular transfer reactions, and also, the structure and molecular weight of
FPO can be precisely controlled [22-29]. Here we report a “living/controlled” cationic
ring-opening polymerization leading to FPO with a controlled number-average
molecular weight and narrow molecular weight distribution. The effects of
polymerization conditions on monomer conversion, number-average molecular
weight (Mn), molecular weight distribution (Mw/Mn) were investigated. The possible
polymerization mechanism for the synthesis of FPO via “living/controlled” cationic
polymerization was proposed.
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2. Results and discussion
2.1. Copolymerization of fluorine-containing epoxy compounds (FO) and
tetrahydrofuran (THF)
Copolymers FO-THF were prepared using different ratios of the corresponding
monomers. The monomer reactivity ratio, the content of the reaction mixture and
copolymer were calculated according to Kelen-Tudos method [30] (Eq (1)). The
Kelen-Tudos parameters for FO and THF are listed in Table 1.
r
THF
r
THF



Eq (1)
η＝ rFO
+
ζ－



a
a
G
F
η＝
ζ＝
a+F
a+F
Where G=x(y-1)/y, F=x2/y, x=MFO/MTHF (mol/mol), y=dMFO/dMTHF (mol/mol), and
a=xminxman/(yminyman)0.5.
Table 1 Parameter of reactivity ratio
Entry
xa
yb
G
F
ζ
Η
1
2
3
4
5
6
7
8
3.00
2.00
1.50
1.00
0.67
0.50
0.40
0.30
3.00
2.00
1.50
1.00
0.90
0.67
0.67
0.50
2.00
1.00
0.50
0.00
-0.07
-0.24
-0.20
-0.30
3.00
2.00
1.50
1.00
0.50
0.37
0.24
0.18
0.47
0.78
0.72
0.63
0.61
0.38
0.24
0.00
0.47 -0.07
0.40 -0.26
0.29 -0.24
0.24 -0.40
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9
0.25
0.20
0.50
0.37
-0.25
-0.34
0.13
0.11
0.18 -0.34
0.16 -0.50
10
a Molar ratio of monomer feed; b Molar ratio in copolymer composition
Fig.1. Plots of ζ vs η
Fig.1 shows a plot of ζ versus η. The monomer reactivity ratio can be determined
by the slope and intercept of the straight line, rFO=0.7 and rTHF=0.4. It can be found
rTHF is smaller than rFO, indicating that THF is less reactive than FO in the present
polymerization reaction. Therefore, the FO concentration is one of the most important
parameters in controlling the degree of polymerization due to the high reactivity of
FO with its high reactivity ratio compared to THF. In order to effectively control the
concentration of monomer, FO was added dropwise into the reaction mixture
containing THF in the polymerization process. Fig.2 shows a plot of
Ln([THF]0/[THF]t) versus time for cationic ring-opening polymerization of FO-THF.
It can be seen that Ln ([THF]0/[THF]t) increases almost linearly with the reaction time.
The good linear relationship indicates that no reversible transfer and intermolecular
transfer reactions during the course of the polymerization.
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Fig.2. Ln([THF]0/[THF]t) versus duration for adding FO dropwise
Fig.3. Number-average molecular weight (Mn) against THF monomer conversion
Plots of number-average molecular weight (Mn) versus THF monomer conversion
are shown in Fig.3. It is clearly observed that molecular weights of the polymers
increase significantly with the monomer conversions. The good linear relationship
indicates that there might be polymer chains keeping active during the polymerization.
Moreover, the change of molecular weights is leveling off at the latter stage of the
polymerization. That is because the polymer chain propagation in the polymerization
gets weak when content of active sites is low, especially at the later stage of
polymerization with the decrease of the monomer concentration [31]. Owing to higher
reactivity of FO with its high reactivity ratio, FO monomer acts as an active center of
the chain propagation reaction, leading to the increase of the polymerization rate.
When fed FO dropwise into the reaction system, the concentration of the active center
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could be controlled. Moreover, production and consumption of the active center are in
equilibrium. These processes can decrease the rate of cationic polymerization and
reflect the nature of controlled/living cationic polymerization.
To further figure out the acting mechanism of FO during the polymerization, we
investigated the THF conversion before and after addition of FO into the reaction
mixture (Table 2).
Table 2 Effect of reaction time on THF conversion
Entry Reaction time (h) THF monomer conversion(%)
1
2
3
4
5
0a
1b
5.0
39.9
62.3
79.0
89.9
2 b
3 b
4 b
a There was no FO in reaction mixture;
b The reaction time when FO was added dropwise into the reaction system
As is seen in Table 2, the THF monomer conversion is only 5% when there is no
FO in the reaction mixture. However, the monomer conversions increase dramatically
with the increase of FO concentration, indicating that FO can induce THF
ring-opening polymerization, and play a crucial role in accelerating the growth of
FPO chain. Thus, according to the above experimental results, a possible mechanism
for the synthesis of FPO via cationic ring-opening polymerization of FO and THF
with BF3·Et2O and ethylene glycol (EG) as initiation system was proposed, as is
shown in Scheme 1. The complex of BF3·Et2O with Lewis acidity is used as
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co-initiator, in conjunction with initiator EG to create the cationic initiation, leading to
the formation of cationic active center with FO. Then the active center attacks the
oxygen atoms, resulting in ring-opening of THF and FO, cationic chain growth.
Because of the higher reactive, the concentration of FO associates with the growing
carbocation and thus affects the cationicity of the growing ends.
F2
C
O
O
HF2C
HO CH CH OH
BF3 OEt2 +
HF2C
2
2
2
F3B
O
H
CH2CH2
O
H
BF3
CF2H
F2C
O
CF2
CH2OCH2CF2CF2H
O
O
CH2CHOCH2CH2OCHCH2
CH2OCH2CF2CF2H
O
O
BF3OH
BF3OH
O
CH2CH2
O
BF3OH
BF3OH
HF2C
CF2
CF2H
FO and THF
F2C
O
O
CH2OCH2CF2CHF2
O
CH2CH2CH2CH2OCH2CHOCH2CH2OCHCH2OCH2CH2CH2CH2
CH2OCH2CF2CF2H
O
BF3OH
BF3OH
H2O
CH2OCH2CF2CHF2
OCH2CH-OCH2CH2O-CHCH2O CH2CH2CH2CH2O
OCH2CH2CH2CH2
n
H
H
m
n
m
Scheme 1. The reaction process of FPO
2.2 Influence of the Initiation system
The cationic copolymerization of FO and THF was carried out with
BF3·OEt2/EG and BF3·CH3OH/EG initiation systems, respectively. The effects of
different initiation systems on the polymerization rate, molecular weight and
molecular weight distribution were investigated.
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Fig.4. Ln([THF]0/[THF]t) against time for different initiation systems
Fig.4 shows Ln ([THF]0/[THF]t) versus reaction time. It can be clearly observed
that the reaction rate increases with increasing polymerization time. Using
BF3·OEt2/EG as the initiation system, the increase of reaction rate of THF is much
faster, and deviates from linearity (correlation coefficient of 0.82). However, there is
obvious change when BF3·CH3OH is used. The reaction rate increases steadily, which
is almost linearly with the reaction time (correlation coefficient of 0.97), indicating
that the BF3·CH3OH clearly has a significant effect on the controlling of the
polymerization rate. In order to figure out the initiation mechanism of BF3·CH3OH,
we further investigated the kinetics of cationic polymerization with BF3·CH3OH/EG
as the initiation system. The cationic polymerization of FO and THF was conducted at
various temperatures ranging from 33 to 39 °C.
Fig.5. Ln([THF]0/[THF]t) against time at various temperature
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Fig.6. Arrhenius plot of lnkp,app versus 1/T to determine apparent energy of activation
(Ea,app).
Fig.5 shows the Semi-log kinetic plots for various temperatures. The apparent rate
constants (Kapp) were obtained from the slope of the lines (0.1592, 0.2015 and
0.38043 mol·L-1·min-1, respectively). As a result, the apparent activation energy can
be obtained from the apparent rate constants Kapp according to the Arrhenius equation
lnk=lnA -ΔE/RT. Fig.6 shows a plot of lnKapp versus 1/T. The good fit to linearity
allows calculation of the activation energy from the slope of the straight line. The
value of activation energy obtained by the above methods is 90.6 KJ·mol-1. The high
and positive Ea can be explained by the formation of nucleophilic complex between
BF3 and CH3OH. The tightness of such complexes decreases the instantaneous
concentration of free Lewis acid, leading to the decrease in the ionization rate
constant, subsequently, in the concentration of active centers [32], and ultimately
results in the decrease of polymerization rate. Moreover, changing BF3·CH3OH
concentration has a significant effect on polymerization rate (Fig.7). As is expected,
the rate of polymerization increases with increasing concentration of BF3·CH3OH and
all plots are linear, which confirms the living nature of FO-THF polymerization under
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these conditions. Meanwhile, the monomer conversion steadily increases from 66.3%
to 97.5% (Fig.8).
Fig.7. Ln ([THF]0/[THF]t) against time for various BF3·CH3OH/EG molar ratios.
Fig.8. Conversion versus time for various BF3·CH3OH /EG molar ratios.
In addition, the effects of polymerization temperature and polymerization time
on molecular weight and molecular weight distribution were investigated. From Table
3, it can be seen that molecular weights markedly increase when the temperature
increases from 33 to 39 °C. Therefore, the copolymerization reaction could be
facilitated by increasing reaction temperature. However, the change of temperature
has slight influence on the molecular weight distribution of the obtained polymers.
This can be easily explained by the increasing rate constant of deactivation with
increasing temperature, and the rate constant of propagation remains nearly constant
[33]. Apparently, when reaction temperature is 39 °C, the number average molecular
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weight of FPO obtained by GPC is nearly identical to that of the theoretical value,
which suggests rapid initiation followed by slower propagation rates at higher
temperature [34].
Table 3 Effect of Reaction Temperature on Mn, Mw/Mn
Temperature (°C)
Mn(th) g/mol* Mn(GPC) g/mol Mw/Mn
33
37
39
2000
2000
2000
790
1620
1830
1.20
1.36
1.38
*Theoretical number average molecular weights were calculated according to Mn(th)
=
(mTHF+mFO)/nEG
Table 4 Influence of polymerization reaction time on Mn, Mw/Mn
polymerization time (h)
Mn(th) g/mol Mn(GPC) g/mol Mw/Mn
3
4
5
6
7
2000
2000
2000
2000
2000
1480
1610
1620
1820
1444
1.32
1.28
1.36
1.38
1.25
Table 4 shows the influence of reaction time on molecular weight and molecular
weight distribution. The results show that during the initial stage of reaction, the
molecular weights of FPO increase with increasing reaction time. However, with the
reaction time prolonged, the activity of the active center and monomer concentration
decrease, and also, the proportion of depolymerization increases, leading to the
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average molecular weights of the fluorinated glycol decrease. Based on the above
analysis, the optimum reaction condition to attain living polymerization of FPO with
BF3·CH3OH/EG is that reaction time is 6 h, reaction temperature is 39 °C.
According to the above experimental results, the copolymerization initiated by
EG/BF3·CH3OH initiation system was carried out at 39 °C for 6 h. Table 5 shows the
comparison between theoretical molecular weights and molecular weights obtained by
GPC.
Table 5 Number-average molecular weight (Mn(GPC)) and Mw/Mn vs theoretical
molecular weight (Mn(th)).
Entry
FPO1
FPO2
FPO3
FPO4
FPO5
M
n(th) g/mol
800
M
n(GPC) g/mol
910
Mw/Mn
1.05
1000
1080
1.03
1200
920
1.08
1500
1200
1.07
2000
1830
1.38
It can be seen that the molecular weights obtained by GPC have better correlation
with the calculated ones. And the quite interesting results are that the molecular
weights obtained by GPC are nearly identical to that of the theoretical value when
theoretical molecular weights are between 800 and 1500 g/mol, moreover, the
molecular weight distributions also stay narrow (1.05<Mw/Mn<1.07). This suggests
that low-molecular-weight copolymers of FO-THF with narrow molecular weight
distributions and controlled molecular weights can be obtained by EG/BF3·CH3OH
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initiation system, attaining living/controlled polymerization of FO-THF.
2.3 Effect of the nucleophilic reagent
The cationic polymerization with Brønsted acid/strong Lewis acid initiation
systems is usually not living and generated polymers of broad molecular weight
distributions and uncontrolled molecular weights. Such nonliving polymerizations can
be often converted into living processes by the addition of salts (ammonium and
phosphonium salts with various anions) or nucleophiles. Thus, we investigated the
effect of 1,4-dioxane (1,4-D) used as a nucleophilic additive on attaining well-defined
.
living polymerization of FO-THF with BF3 Et2O/EG as initiation system.
Table 6 Influence of nucleophilic reagent on Mn, Mw/Mn
VDCM /V1,4-D (ml)
M
n(GPC) g/mol
Mw/Mn
1.34
20/0.
15/5
10/10
5/15
1280
1500
1.11
1000
1.31
930
1.29
0/20
920
1.31
Table 6 shows the changing of molecular weight of FPO with the increase of
amount of 1,4-D in dichloromethane (DCM). Surprisingly, the increase in the 1,4-D
concentration from 0.00 to 5.00 vol gradually accelerates the increase of molecular
weight, and while the polymer molecular weight distribution become narrow
(Mw/Mn=1.1). However, when 1,4-D concentration increases continuously, the
molecular weights of FPO decrease, where the polymerization is drastically retarded
by the addition of the dioxane due to the interaction of the added ether with the
growing species [35]. Fig.9 shows the time - polymerization rate curves for the
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polymerization in the presence of 1,4-D (5 vol in DCM), the plots in the absence of
1,4-D are also depicted for comparison. It can be seen that the addition of a small
amount of 1,4-D has an significant effect on the polymerization rate. Comparing with
the polymerization rate in the absence of 1,4-D, the growth of polymerization rate
slows down and shows a good stability, reflecting the nature of living polymerization.
These results indicate that the addition of 1,4-D suppressed the formation of the
uncontrolled polymer and rendered the polymerization totally living.
Fig.9. Ln([THF]0/[THF]t) against time for different solvents. a. 20ml DCM, b. 5/15
v/v 1,4-D/DCM.
To examine the living polymerization of FPO with BF3·Et2O/EG as initiation
system further, the Mn and Mw/Mn values of the obtained polymers are plotted against
polymerization time in Fig.10, respectively. It can be seen that the values of Mn are
directly proportional to polymerization time. In particular, at the lower dioxane
concentrations, the increase of Mn is faster, and the molecular weight distributions
stay narrow (1.07 < Mw/Mn < 1.15) throughout the reaction compared to the absence
of 1,4-D (1.2 < Mw/Mn < 1.3), indicating that there are no reversible transfer and
intermolecular transfer reactions during the course of the polymerization. Several
theories have been advanced to describe the roles of 1,4-D in cationic polymerization:
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(1) the use of 1,4-D is necessary to prevent transfer reactions as it occurs in normal
polymerization in non-nucleophilic dipolar aprotic solvent, owing to the more
nucleophilic oxygen atom in 1,4-D; (2) the chains growth in 1,4-D is initially slowed
down, allowing for a high initiation rate to propagation rate ratio the production of
polymer with low molecular weight distribution [36].
Fig.10. Number-average molecular weight (Mn) and molecular weight distribution
(Mw/Mn) against time in DCM and in 5/15 v/v 1,4-D/DCM.
3. Conclusions
In summary, fluorinated glycol has been successfully synthesized by cationic
ring-open polymerization of FO and THF. On the basis of the reactivity ratios of
different monomers and THF monomer conversion, it is known that FO has high
reactivity due to its high reactivity ratio compared to that of THF. A possible
polymerization mechanism for FO and THF was proposed based on the results of the
Ln([THF]0/[THF]t) versus time and monomer conversion. The optimum reaction
condition to attain living polymerization of FPO with BF3·CH3OH is 6 h, and 39 °C,
and the polymers have narrow molecular weight distribution and controlled molecular
weights. The polymerization of FO-THF with the BF3·Et2O/EG initiation system in
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the presence of the suitable amount of 1,4-D afforded the living polymers with low
molecular weight distribution (Mw/Mn=1.1), the growth of polymerization rate and
molecular weight suggested that the 1,4-dioxane serves primarily as “suppressors” of
the uncontrolled polymerization, preventing reversible transfer and intermolecular
transfer reactions during the course of the polymerization, leading to attain
well-defined living polymerization of FO-THF with BF3·Et2O/EG as initiation
system.
4. Experimental
4.1. Materials
Dichloromethane (DCM) (Chemicals, Shanghai, China) was washed three times
with concentrated sulfuric acid to remove unsaturated impurities and then washed
several times with water, a 5% solution of NaHCO3, and again with distilled water.
After being dried for 24 h over CaCl2, the methylene chloride was distilled over CaH2
and kept in a vacuum ampoule over fresh CaH2. THF (Chemicals, Shanghai, China)
was kept for 48 h over KOH pellets to remove peroxide. After filtration, the THF was
heated over sodium for 12 h and then distilled. Ethylene glycol (EG) was distilled
twice. BF3·OEt2 (Chemicals, Shanghai, China), and BF3·CH3OH (Sigma, USA) was
used as supplied. The 1,4-dioxane (1,4-D) (Chemicals, Shanghai, China) was dried
over calcium hydride for 48
h
and then distilled before use. The
2,2,3,3-tetrafluoro-1-propanol (TFP) (Sigma, USA) and epichlorohydrin (ECH)
(Chemicals, Shanghai, China) were used as supplied.
4.2. Synthesis of the fluorine-containing epoxy compound
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Fluorine-containing epoxy compounds (FO) were prepared from
2,2,3,3-tetrafluoro-1-propanol (TFP) and epichlorohydrin (ECH) using a liquid alkali
solution as catalyst. First, excess ECH and cyclohexane (as water-carrying agent)
were heated. When the temperature was raised to 80 oC, an aqueous solution of 40 %
NaOH and TFP were fed dropwise in 2 h. The reaction mixture was kept for another 3
h at 80 °C.
The composition of the FO was analyzed with FTIR and 1H NMR spectrum (Fig.11
and Fig.12). As is shown in Fig.11, the strong C-F stretching vibration absorption
peaks appears at 1203 and 1128 cm-1. The stretching vibration peak of C-O-C is at
1102 cm-1, and the stretching vibration absorption of the three-ring structure is at 1409
cm-1. The -CH2- stretching vibration absorption peaks are occurred at 3019 and 2933
1
cm-1. The H NMR spectrum is shown in Fig.12. It can be seen that the peaks at
5.76-6.06 ppm are assigned to the proton in -CF2H. The peaks at 3.74-3.95 ppm are
attributed to -CH2 in -OCH2CF2-. The peaks appears at 3.34-3.43 ppm are assigned to
the protons of -OCH2-, the peaks at 2.49-3.12 ppm are relative to the CH2, CH in the
epoxy group, respectively.
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Fig.11. FTIR spectrum of FO
Fig.12. 1H NMR spectrum of FO
4.3. Synthesis of the fluorinated glycol with fluorine-containing side chain
The polymerization reactions were conducted under nitrogen at 0 °C in a glass
flask. Cationic copolymerization of FO with THF was performed by slowly adding
FO to the reaction mixture containing bulk THF, EG and BF3·OEt2. After 6 h, distilled
water was added and stirred for 5 min to quench the reaction. Then reaction solution
was washed with distilled water 3-4 times to neutrality. After vacuum dehydration for
2-3 h, a colorless, transparent and sticky fluorinated glycol was collected.
1
The structure of FPO was determined by H and 13C NMR spectra (Fig.13 and
1
Fig.14). H NMR (in CDCl3, δppm): The peaks at 5.74-6.01 ppm are relative to the
fluoromethenyl protons (-CHF2). The peaks at 3.71-3.87 ppm are assigned to the
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-OCH2CF2. The peak assigned to the -OCH- protons is at 3.45 ppm, and the peaks at
1.51-1.69 ppm are assigned to the -CH2CH2CH2- protons of THF. It can be seen
further from the 13C NMR spectrum of fluorinated glycol (Fig.14) that the peaks at
105-120 ppm corresponding to the carbons of -CH2CF2CF2H observed [29]. The peak
centered at 76.5 ppm is assigned to the carbons of O-CH (CH2-)-CH2-, the peak at
73.7 ppm is attributed to the carbons of -CH2CF2CF2H. Two peaks at 58.1 ppm and
27.3 ppm are assigned to the carbons of -OCH2CH2CH2CH2O-. The peak at 69.2 ppm
is attributed to the carbons of -CH-CH2-O-. The peak at 61.5 ppm is assigned to the
carbons of -CH2CH2CH2CH2OH [21], therefore, it can be confirmed that the end
group in FPO is -CH2CH2CH2CH2OH.
Fig.13. 1H NMR spectrum of FPO
Fig.14. 13C NMR spectrum of FPO
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4.4. Characterization
The FO structures were analyzed with Fourier-transform infrared spectrometer
1
(FTIR) using KBr discs from 4000 to 400 cm-1 with 8 replicates. The H and 13C
NMR spectra were obtained on a Bruker AC 300 spectrometer operating at 500 MHz.
1
Chemical shifts for H and 13C spectra were referenced using internal solvent
resonances and are reported relative to tetramethylsilane.
The gel permeation chromatography (GPC) measurements were performed with
tetrahydrofuran as the eluent at a flow rate of 1.0 ml/min at room temperature. The
measurement was carried out at ambient temperature. The system was calibrated with
polystyrene standards.
The monomer conversion was measured using a gas chromatography (GC)
system equipped with programmed temperature and TCD detector. The detector
temperature was 250 °C, and the injection temperature was 300 °C.
Acknowledgement
This project was supported by Natural Science Foundation of China
（NO.3212310008）
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