Synthesis and properties of fluorinated thermoplastic polyurethane elastomer

Article abstract of DOI:10.1016/j.jfluchem.2009.09.018

A series of fluorinated thermoplastic polyurethane elastomers (FTPU) based on self-synthesized fluorinate polyether diol (PFGE) were prepared by two-step polymerization. For the purpose of improving the molecular weight and mechanical property of FTPU, polybutylene adipate (PBA) was used to be compounded with PFGE as the soft-segment of FTPU. Effects of the mass ratio of PFGE/PBA and the mass fraction of hard-segment on the mechanical property of FTPU were investigated. The structure and morphology of FTPU were characterized by FTIR, GPC, DMA, surface tension and AFM analysis.

Full text of DOI:10.1016/j.jfluchem.2009.09.018

Journal of Fluorine Chemistry 131 (2010) 36–41
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and properties of fluorinated thermoplastic polyurethane elastomer
Tao Liu, Lin Ye *
State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, 3# kehua north road, Chengdu, 610065, 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 fluorinated thermoplastic polyurethane elastomers (FTPU) based on self-synthesized
fluorinate polyether diol (PFGE) were prepared by two-step polymerization. For the purpose of
improving the molecular weight and mechanical property of FTPU, polybutylene adipate (PBA) was used
to be compounded with PFGE as the soft-segment of FTPU. Effects of the mass ratio of PFGE/PBA and the
mass fraction of hard-segment on the mechanical property of FTPU were investigated. The structure and
morphology of FTPU were characterized by FTIR, GPC, DMA, surface tension and AFM analysis.
ß 2009 Elsevier B.V. All rights reserved.
Received 15 July 2009
Received in revised form 18 September 2009
Accepted 25 September 2009
Available online 3 October 2009
Keywords:
Fluorinate polyether diol (PFGE)
Fluorinated thermoplastic polyurethane
elastomers (FTPU)
Mechanical property
Dynamical mechanical property
Surface property
Phase separation
1
. Introduction
By introducing fluorinated blocks into the molecular chains of
At present, FTPUs are mainly applied as biomedicine materials.
However, the low reaction activity of the fluorinated monomers
led to the low molecular weight and poor mechanical properties of
the resulting products, which restricted the wide applications of
FTPUs. The aim of this work was to synthesize FTPUs with
improved mechanical properties. The preparation and character-
istic properties were studied.
thermoplastic polyurethane elastomer (TPU), the fluorinated
thermoplastic polyurethane elastomers (FTPU) not only maintain
most of the outstanding properties of TPU, such as high strength,
high toughness and high damping properties, but also offer the
basic advantages of improved solvent and chemical resistance, a
lower surface tension, and low coefficient of friction, resulting in
the wide applications in the areas of coating, leather decoration,
textile and medicine [1–5].
2. Experimental
2.1. Materials
There are however only few examples of commercially
available fluorinated elastomers, such as the crosslinkable
copolymers of vinylidenfluoride or tetrafluoroethylene with few
suitable fluorinated comonomers like hexafluoropropene or
perfluorovinylethers, the fluorinated thermoplastic elastomer
recently developed by Daikin, where the soft phase is the
vinylidene fluoride–hexafluoropropene copolymer. The use of
short fluorinated chain extenders does not offer any advantage in
terms of the surface properties and elastomeric properties. No
more researches are found for other kinds of fluorinated
thermoplastic elastomers. The main reason is perhaps the very
limited availability of suitable fluorinated monomers or macro-
mers [6–9].
Diphenylmethylene diisocyanate (MDI) from Wanhua Polyur-
ethane Co. Ltd. (Yantai, China) was used as received; 1,4-
butanedilo (BDO), epichlorohydrin (ECH), and ethylene glycol
(
EG) all supplied by Bodi Chemical Co. Ltd. (Tianjin, China) were
used after been purified; polybutylene adipate (PBA) (Mn; 2000)
was purchased from Huada Chemical Engineering Co. Ltd. (Yantai,
China) and used after vacuum drying; tetrafluoropropanol (F–OH)
from Jiachen Chemical Co. Ltd. (Shanghai, China) was used as
received; boron trifluoride diethyl etherate (BF
purchased from Yangyuan Chemical Co. Ltd. (Changshu, China)
and used after purified by vacuum distillation.
3
ꢀEt
2
O) was
2.2. Synthesis of fluorinated polyether diol (PFGE)
Stoichiometric amounts of the ECH and NaOH were charged
*
Corresponding author. Tel.: +86 28 85408802; fax: +86 28 85402465.
into the 3-necked round bottom flask equipped with a mechanical
E-mail address: yelinwh@126.com (L. Ye).
stirrer, and the temperature was raised to 50 8C under high speed
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.09.018

T. Liu, L. Ye / Journal of Fluorine Chemistry 131 (2010) 36–41
37
Scheme 1. The reaction formula of PFGE.
stirring. F–OH was slowly added to the reaction system, and
followed by reacting at 50 8C for 2–3 h. Flurorinated glycidyl ether
FGE) was obtained after purified by vacuum distillation. There-
after, stoichiometric amounts of BF O and EG were charged
ꢀEt
2.4.6. AFM analysis
The images of FTPU were visualized on a Digital Instruments
Nanoscope IIIa AFM microscopy (USA) by tapping-mode. The
sample was dissolved in THF and coated on the mica substrate, and
then dried in vacuum at 60 8C for 12 h. It was measured in air at
(
3
2
into the 3-necked round bottom flask equipped with a mechanical
stirrer in nitrogen gas and cooled to 0 8C. FGE was slowly added to
the reaction system within 2–3 h, and maintained for 5 h. Then
fluorinated polyether diol was obtained after washed and distilled.
The reaction formula of synthesis of PFGE was shown in Scheme 1.
The molecular weight of PFGE ðMnÞ was 2089.
room temperature with a scanning area of 15
mm.
3. Results and discussion
The reaction formula of FTPU synthesized in this work was
shown in Scheme 2. The composition of FTPU was analyzed by
FTIR. As shown in Fig. 1, there was a strong N–H stretching
2.3. Synthesis of fluorinated thermoplastic polyurethane elastomer
ꢁ1
(FTPU)
vibration absorption peak at 3307.94 cm ; C 55 O stretching peak
ꢁ
ꢁ1
1
and N–H bending peak were observed at 1728.89 cm
and
was
ꢁ
1
Two-step procedure was adopted via bulk polymerization to
1531.11 cm
,
respectively; the peak at 1104.97 cm
prepare FTPU. The molar ratio of NCO/OH was 0.98. In the first step,
the synthesis of the –NCO end-capped prepolymer was conducted
by the bulk reaction of PFGE with MDI at 80 8C for 3 h. Then a
certain amount of BDO was added, and mixed homogenously. Then
the mixture was cast in a mold at 140 8C for 20 h.
assigned to the stretching vibration of C–O–C; and the absorptions
ꢁ1
ꢁ1
at 1226.72 cm
and 1299.76 cm
were attributed to the
stretching vibration of C–F. The diisocyanate (–N 55 C 55 O) band at
ꢁ
1
2250–2275 cm was absent in the spectra of the resulting FTPU,
indicating that this group was completely consumed in the
reaction [10].
2
2
.4. Measurements
3
.1. Relationship between the chemical structure and mechanical
.4.1. FTIR analysis
property of FTPU
The composition of the synthesized FTPU was analyzed with
Nicolet-560 Fourier-transform infrared spectrometer (FTIR) (USA).
The specimen was prepared by casting the polymer solution film
The mechanical property of FTPU is related with the chemical
bond, intermolecular force, and molecular weight of FTPU. It is
finally determined by the chemical structure of soft-segment and
hard-segment.
ꢁ1
on KBr discs. The scanning rate is 20 min , and the differentiate
ꢁ1
rate is 4 cm
.
PBA was adopted to be combined with PFGE as the soft-segment
of FTPU due to the low reaction activity of PFGE for the purpose of
improving the molecular weight and mechanical property of FTPU.
Effects of the mass ratio of PFGE/PBA and the mass fraction of hard-
segment on the mechanical property of FTPU were investigated.
2
.4.2. GPC analysis
The number ðMnÞ and weight ðMwÞ average molecular weights,
w n
and the index of the molecular weight distribution M =M of FTPU
were measured by gel permeation chromatography (GPC) on a
Waters 150-C instrument (USA) at 30 8C. Tetrahydrofuran (THF)
was used as an eluent (flow rate = 1 ml/min).
2.4.3. Tensile testing
The tensile properties of samples were measured with a 4302
material testing machine from Instron Co. (USA) according to
ISO527/1-1993 (E). The tensile speed and temperature were
2
00 mm/min and 23 8C, respectively.
2.4.4. DMA analysis
The dynamic mechanical analysis (DMA) was carried out using
a TA Instrument Q800 DMA (USA). All the samples were measured
with a single cantilever mode at a heating rate of 10 8C/min and a
3
frequency of 30 Hz. The sample size was 35 ꢂ 1 ꢂ 0.2 mm .
2.4.5. Contact angle
The contact angles of water and glycerol as testing liquids on
FTPU were measured by ErmaG-1 contact angle test apparatus
Japan) at room temperature by sessile drop method.
(
Scheme 2. The reaction formula of FTPU.

3
8
T. Liu, L. Ye / Journal of Fluorine Chemistry 131 (2010) 36–41
Fig. 3. Mechanical property of FTPU as a function of mass ratio of PFGE/PBA.
Fig. 1. FTIR spectrum of FTPU.
product. The data of GPC results were listed in Table 1. With the
decrease of the mass ratio of PFGE/PBA and fluorine content, the
elution time of FTPU decreased and the molecular weight were
improved without much influence on molecular weight distribu-
tion.
The mechanical property of FTPU as a function of the mass ratio
of PFGE/PBA was shown in Fig. 3. It can be seen that the tensile
strength and elongation at break of FTPU increased with the
decrease of the ratio of PFGE/PBA. When the mass ratio of PFGE/
PBA was 50/50, the tensile strength of FTPU was improved from
6.61 MPa to 14.33 MPa, and the elongation at break of FTPU was
improved from 89.1% to 634.3%.
Mechanical property of FTPU with different mass fraction of
hard-segment was shown in Fig. 4. It can be seen that mass fraction
of hard-segment had much influence on the mechanical property
of FTPU. The sample with 30 wt% of hard-segment possessed
relatively high elongation at break and low tensile strength. As the
mass fraction of hard-segment increased, the tensile strength
increased and the elongation at break declined.
Fig. 2. GPC curves of FTPU.(1) PFGE/PBA (100/0); (2) PFGE/PBA (70/30); (3) PFGE/
PBA (50/50)
As can be seen from Fig. 2, the GPC curves of FTPU synthesized
with varying mass ratio of PFGE/PBA were single bell-shaped
without the distribution peak of small-molecular substance
indicating that PFGE and PBA were all consumed to get the final
3.2. Dynamic mechanical property of FTPU
Dynamical mechanical analysis provides information on
glass transition and the damping property of a polymer. The
Table 1
GPC result of FTPU.
4
4
FTPU
Mass fraction of
PFGE/PBA
Fluorine
Retention
Mn (ꢂ10 )
Mw (ꢂ10 )
Mw=Mn
content (%)
time (min)
1
2
3
100/0
70/30
50/50
23.9
16.6
11.9
13.27
12.60
12.14
0.62
1.07
1.48
1.53
2.87
4.17
2.5
2.7
2.8
Fig. 4. Mechanical properties of FTPU as a function of mass fraction of hard-segment.

T. Liu, L. Ye / Journal of Fluorine Chemistry 131 (2010) 36–41
39
Fig. 5. Damping factors of FTPU. (1) PFGE/PBA (100/0); (2) PFGE/PBA (70/30); (3) PFGE/PBA (50/50)
Table 2
DMA parameters of FTPU.
FTPU
2
Mass fraction of PFGE/PBA
Fluorine content (%)
T
gs (8C)
T
gh (8C)
Tan
d
max
tan
d
T > 0.3 (8C)
1
2
3
100/0
70/30
50/50
23.9
16.6
11.9
5.31
57.06
42.02
33.47
0.72
0.46
0.52
>ꢁ1.7
>ꢁ3.53
>8.9
ꢁ4.05
ꢁ22.86
d
p
dynamical mechanical properties of FTPU were shown in Fig. 5.
It can be seen that all the samples exhibited two loss peaks
corresponding to the glass transition temperature of soft-
segment and hard-segment, respectively, and the loss peak of
FTPU shifted towards high temperature with the increase of
fluorine content. Numerical DMA data of FTPU were listed in
Table 2. It can be seen that the sample prepared completely with
PFGE without PBA exhibited relatively high damping factor and
wide damping range.
liquid, respectively;
g
,
gs are polarity component and dispersion
s
component of solid, respectively.
Water and glycerin were selected as the test liquids and the
surface tension of FTPU can be obtained along with geometric-
mean equation. As listed in Table 3, with the increase of fluorine
content, the contact angle of water and glycerin on the surface of
FTPU increased, and the surface tension of FTPU decreased from
42.4 mN/m to 36.3 mN/m.
2
The –CF H unit with a relatively low surface energy moved onto
the surface of FTPU, which led to the decrease of the surface energy
of FTPU, as shown in Fig. 6.
3.3. Surface property of FTPU
The surface tension of solid (
g
s
) contains both polarity
3.4. Aggregation morphology of FTPU
p
d
component ðgs Þ and dispersion component ð
g
Þ [11,12].
s
p
d
(
1)
g
¼
g
þ
g It can be calculated with geometric-mean
s
The molecular chains of FTPU are composed of the soft-segment
originating from polyol, the hard-segment originating from
diisocyanate and the chain extender. Ideally, the two segments
are immiscible and phase separation occurred during the
formation of morphology.
s
s
equation: [13]
2)glVð1 þ cos
1
d
=2
p
l
p
1=2
d
l
(
u
Þ ¼ 2ðg g
Þ
þ 2ðg g
Þ
s
s
In the equation,
u is contact angle; glV is surface tension of
liquid; gdl
,
gl are polarity component and dispersion component of
p
Table 3
Surface properties of FTPU with varying fluorine content.
d
s
p
s
Mass fraction of PFGE/PBA
Fluorine content (%)
Contact angle (8)
g
(mN/m)
g
(mN/m)
g (mN/m)
Water
Glycerin
1
8
7
6
5
00/0
0/20
0/30
0/40
0/50
23.9
19.0
16.6
14.3
11.9
72.4
71.6
69.2
67.0
64.0
80.6
80.0
77.0
74.4
72.0
1.2
1.1
1.7
2.1
2.2
35.1
36.0
36.7
37.3
40.2
36.3
37.1
38.4
39.4
42.4
Fig. 6. Schematic illustration of fluorinated group of FTPU enriching at air–polymer interface.

4
0
T. Liu, L. Ye / Journal of Fluorine Chemistry 131 (2010) 36–41
Fig. 7. AFM images of micro-phase separation of FTPU (the observation domain: 20
m
m). (1) PFGE/PBA (100/0); (2) PFGE/PBA (70/30); (3) PFGE/PBA (50/50)
The multi-phase nature of FTPU has been strongly implied
from AFM analysis [14,15]. Fig. 7 presented the height image,
phase image and 3D image of FTPU. The scope of observation
respectively. All the samples of FTPU exhibited two loss peaks,
corresponding to the glass transition temperature of soft-segment
and hard-segment, respectively, and the loss peak of FTPU shifted
towards high temperature with the increase of fluorine content. It
can be seen that the sample prepared completely with 100% PFGE
exhibited relatively high damping factor and wide damping range.
With the increase of fluorine content, the surface tension of FTPU
decreased, while the extent of the phase separation increased, and
the soft and hard-segment exhibited continuous phase morphol-
ogy for the sample of FTPU with PFGE/PBA (100/0).
was 20
mm. A typical two-phase structure can be observed. The
comparatively bright part corresponded to the hard-segment of
FTPU, and the grey part corresponded to the soft-segment of
FTPU. In the 3D image, lots of parts of ‘‘wave trough’’
corresponding to the soft-segment and parts of ‘‘wave crest’’
corresponding to the hard-segment can be observed, which
indicated that there was a micro-phase separation in the
molecules of FTPU. Furthermore, it can also be seen that with
the increase of fluorine content, the degree of the phase
separation increased, and the soft and hard-segment exhibited
continuous phase morphology, respectively, for the sample of
FTPU with PFGE/PBA (100/0).
Acknowledgement
This work is supported by Natural Science Fund of China
(
10676024).
4
. Conclusions
References
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