Synthesis of fluorinated polymers and evaluation of wettability

Article abstract of DOI:10.3390/molecules21030358

Two kinds of fluorinated polymers were synthesized: an acrylate polymer having a fluorinated triethylene glycol as a pendant group (2a) and a fluoroalkyl acrylate polymer (2b). The contact angle of these fluorinated polymers against water, non-fluorinated alcohols and fluorinated alcohols were evaluated. As compared with the fluoroalkyl polymer (2b), fluoroethylene glycol polymer (2a) showed smaller contact angle against water and non-fluorinated alcohols. This supports the proposition that changing the alkyl chain into the ethylene glycol-type chain gave some interaction between etheric oxygen and water or non-fluorinated alcohols. In addition, fluoroalkyl acrylate polymer (2b) showed remarkably low values of critical surface tension.

Full text of DOI:10.3390/molecules21030358

molecules
Article
Synthesis of Fluorinated Polymers and Evaluation
of Wettability
Tamami Kimura 1,2, Maria Carmelita Kasuya 1, Kenichi Hatanaka 1 and Koji Matsuoka 2,
*
1
Institute of Industrial Science, The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan;
s12ds051@mail.saitama-u.ac.jp (T.K.); maria@iis.u-tokyo.ac.jp (M.C.K.); hatanaka@iis.u-tokyo.ac.jp (K.H.)
Graduate School of Science and Engineering, Saitama University, Sakura-ku, Saitama 338-8570, Japan
Correspondence: koji@fms.saitama-u.ac.jp; Tel.: +81-48-858-3099
2
*
Academic Editor: Derek J. McPhee
Received: 4 February 2016 ; Accepted: 8 March 2016 ; Published: 17 March 2016
Abstract: Two kinds of fluorinated polymers were synthesized: an acrylate polymer having
a fluorinated triethylene glycol as a pendant group (2a) and a fluoroalkyl acrylate polymer (2b).
The contact angle of these fluorinated polymers against water, non-fluorinated alcohols and
fluorinated alcohols were evaluated. As compared with the fluoroalkyl polymer (2b), fluoroethylene
glycol polymer (2a) showed smaller contact angle against water and non-fluorinated alcohols.
This supports the proposition that changing the alkyl chain into the ethylene glycol-type chain
gave some interaction between etheric oxygen and water or non-fluorinated alcohols. In addition,
fluoroalkyl acrylate polymer (2b) showed remarkably low values of critical surface tension.
Keywords: fluorous; fluorinated polymers; wettability; contact angle; critical surface tension
1. Introduction
The regulation of surface property is an important consideration in preparation of materials.
Polystyrene is used as hydrophobic materials for Petri dishes to support cell adherence [1]. The high
molecular weight poly(ethylene glycol) (PEG) is used to improve hydrophilicity. This results in strong
interactions between PEG and water, thus preventing protein adsorption [2].
Fluorinated polymers have attracted attention for the preparation of biomaterials due to their
unique properties such as thermal stability, chemical stability, flame retardancy, low dielectric constant,
low frictional property and unique surface property [3–9]. Among these properties, the unique surface
behavior of fluorinated compounds can prevent fouling of non-fluorinated compounds and can be
used as a biocompatible material which prevents protein adhesion [10]. In general, compatibility is
discussed in terms of hydrophilicity or lipophilicity. However, highly fluorinated compounds are
neither hydrophobic nor lipophobic, they are fluorophilic [11].
One of the means to evaluate compatibility between solid and liquid is by measuring the contact
angle. A small contact angle (<90˝) corresponds to high compatibility, while a large contact angle
(>90˝) corresponds to low compatibility [12]. Compatibility is predicted from the surface tension of
liquids and the critical surface tension of solids. A liquid can wet a solid if the surface tension is lower
than the critical surface tension. The critical surface tension according to Zisman’s approach gives
further surface information on the interaction between liquid and the solid surface [13–15]. In this
study, polymers with a fluorocarbon chain that is suitable for biomaterials were synthesized and the
contact angle was determined in order to evaluate compatibility. The critical surface tension was
calculated according to Zisman’s approach.
Molecules 2016, 21, 358; doi:10.3390/molecules21030358
www.mdpi.com/journal/molecules

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2. Results and Discussion
2.1. Synthesis of Fluorinated Monomers
Two types of monomers were prepared: they are 1H,1H-perfluoro-3,6,9-trioxadecyl
acrylate (fluoroethylene glycol monomer) (1a) and 1H,1H-perfluorohexyl acrylate (fluoroalkyl
monomer) (1b). The monomers were prepared from 1H,1H-perfluoro-3,6,9-trioxadecan-1-ol or
1H,1H-perfluorohexane-1-ol with acryloyl chloride (Scheme 1).
Scheme 1. Preparation of fluoroethylene glycol polymer (2a) and fluoroalkyl polymer (2b).
2.2. Polymerization of Fluorinated Monomers
Radical polymerization of these monomers using AIBN was carried out to give the corresponding
fluorinated polymers. The tacticities of the polymers were confirmed from 1H-NMR. The molecular
weights of the polymers were calculated by light-scattering spectroscopy and the results are
summarized in Table 1. The molecular weight of fluoroalkyl polymer (2b) was unexpectedly greater
than that of the usually prepared polymer by radical polymerization. The fluoroalkyl polymer (2b
)
was determined to be aggregating. Since a higher than anticipated molecular weight was observed,
the fluoroalkyl polymer (2b) was hydrolyzed in order to prevent aggregation. After removal of
the fluoroalkyl chains from the polymer, the remaining polymer showed the anticipated degree of
polymerization.
Table 1. Molecular weight of fluoroethylene glycol polymer (2a) and fluoroalkyl polymer (2b).
Degree of Polymerization (n)
Molecular Weight 1 (Da)
Polymer
Yield (%)
Before Hydrolysis 1
After Hydrolysis 2
4.7 ˆ 105
1.2 ˆ 106
2a
2b
79.0
87.2
980
3200
850
1000
Calculated by static light scattering; 2 Calculated by size exclusion chromatography.
1
2.3. Contact Angle Measurements
Both polymers were dissolved in Novec
™ 7100 (Tokyo, Japan). A silicon wafer surface was
coated with polymers by solution casting method. Milli Q (water), pentan-1-ol, hexan-1-ol, heptan-1-ol,
1H,1H,5H-octafluoropentan-1-ol, 1H,1H-perfluorohexan-1-ol and 1H,1H,7H-dodecafluoroheptan-1-ol
were dropped on the silicon wafer covered with each polymer and the contact angle was measured.
Fluoroethylene glycol polymer (2a) exhibited a smaller contact angle against water and
non-fluorinated alcohols than fluoroalkyl polymer (2b) indicating that the fluoroethylene glycol
polymer (2a) is more hydrophilic and more alcoholphilic (Table 2). The contact angle values of
both fluorinated polymers against fluorinated alcohols were nearly 0˝. These results indicated that
both fluorinated polymers interacted more strongly with fluorinated alcohols than with water or
non-fluorinated alcohols.

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Table 2. The contact angles of fluoroethylene glycol polymer (2a) and fluoroalkyl polymer (2b) against
different solvents.
1H,1H,5H-
Octafluoro-
1-pentanol
1H,1H-
Perfluoro-
1-hexanol
1H,1H,7H-
Dodecafluoro
-1-heptanol
Milli Q
1-Pentanol
1-Hexanol
1-Heptanol
101.4˝
126.7˝
57.4˝
69.1˝
58.3˝
78.3˝
61.1˝
82.5˝
Nearly 0˝
Nearly 0˝
Nearly 0˝
Nearly 0˝
Nearly 0˝
Nearly 0˝
2.4. Calculation of the Critical Surface Tension
The contact angles against ethylene glycol, propan-1-ol and glycerol were measured to calculate
the critical surface tension of each polymer. The calculated results indicated that the fluoroethylene
glycol polymer (2a) (18 mNm´1) has a higher critical surface tension than the fluoroalkyl polymer
(
2b) (7 mNm´1) as shown in Figure 1. The critical surface tension of fluoroalkyl polymer (2b) is
extremely low when compared with previous reports. The critical surface tension of fluoroethylene
glycol polymer (2a) is similar to polytetrafluoroethylene (PTFE) [16].
7
6
y = 1.5081x + 3.9597
5
4
fluoroethylene glycol polymer (2a)
3
y = 0.3602x + 2.5947
fluoroalkyl polymer (2b)
2
1
0
0
0.5
1
1.5
2
(γLp/γLd)1/2
Figure 1. Zisman plots for fluoroethylene glycol polymer (2a) and fluoroalkyl polymer (2b).
From the results of contact angle measurements, the fluoroethylene glycol polymer (2a) exhibited
higher compatibility than the fluoroalkyl polymer (2b) with each solvent. Both fluorinated polymers
exhibited fluorophilicity because significantly high compatibility was observed against only fluorinated
alcohols. The results obtained from the calculated critical surface tension of fluoroalkyl polymer (2b
indicated the large contact angle against water because of the remarkable low critical surface tension.
Based on these results, the fluoroalkyl polymer (2b) has potential application as a stain-resistant
biomaterial against the fouling such as hemoglobin adsorption [17].
)
Fluoroethylene glycol polymer (2a) has a similar critical surface tension to PTFE, which has been
widely used in various fields including biomaterial. Since PTFE is produced as a solid powder that
is insoluble, it is difficult to coat the material surface with PTFE. On the other hand, fluoroethylene
glycol polymer (2a) dissolves in fluorinated solvents such as Novec
be coated with the fluoroethylene glycol polymer (2a).
™ 7100. Hence, biomaterials may

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3. Experimental Section
3.1. Preparation
3.1.1. 1H,1H-Perfluoro-3,6,9-trioxadecyl Acrylate (1a)
Fluorinated ethylene glycol monomer (1a) was synthesized from 1H,1H-perfluoro-3,6,9-
trioxadecan-1-ol (2.0 g, 5.0 mmol) in anhydrous acetonit˝rile (9.8 mL) with triethylamine (841.9
µL,
6.0 mmol) and acryloyl chloride (444.0 µL, 5.5 mmol) at 0 C. The mixture was stirred for 2 h at room
temperature. After the complete reaction, water was added and extraction was carried out with ethyl
acetate. The reaction mixture was washed with saturated sodium hydrogen carbonate, water and
brine, dried over anhydrous magnesium sulfate, and concentrated in vacuo. The product was purified
by column chromatography (1:20 ethyl acetate-hexane) to afford 1H,1H-perfluoro-3,6,9-trioxadecyl
1
acrylate (1a), 39.8%, as a fluorinated ethylene glycol monomer. H-NMR (CDCl3, 600 MHz):
δ 4.53 (t,
J = 18.66 Hz, 2H), 5.96 (d, J = 10.44 Hz, 1H), 6.15 (dd, J = 10.44, 17.58 Hz, 1H), 6.49 (d, J = 17.58 Hz, 1H);
13C-NMR (CD3OD, 150 MHz): δ 61.31, 61.53, 61.75, 126.57, 133.13, 164.17.
3.1.2. 1H,1H-Perfluorohexyl Acrylate (1b)
Fluoroalkyl monomer (1b) was synthesized from 1H,1H-perfluorohexan-1-ol (1.9 mL, 10.3 mmol)
in anhydrous tetrahydrofuran (20.0 mL) with triethylamine (4.3 mL, 30.9 mmol) and acryloyl chloride
˝
(2.5 mL, 30.9 mmol) at 0 C. The mixture was stirred overnight at room temperature and water
was added to the mixture. Extraction was carried out with dichloromethane and the organic layer
was washed with saturated sodium hydrogen carbonate, water and brine, dried over anhydrous
magnesium sulfate, and concentrated in vacuo. The residual mixture was purified by distillation under
reduced pressure at 35 ˝C to yield pure 1H,1H-perfluorohexyl acrylate (1b), 68.0%, as a fluoroalkyl
1
monomer. H-NMR (CDCl3, 600 MHz):
δ 4.67 (t, J = 26.94 Hz, 2H), 6.00 (d, J = 10.50 Hz, 1H), 6.19 (dd,
J = 10.44, 17.58 Hz, 1H), 6.53 (d, J = 17.58 Hz, 1H); 13C-NMR (CD3OD, 150 MHz):
δ 59.39, 59.56, 59.75,
126.57, 133.34, 164.31.
3.1.3. Polymerization of 1a and 1b
The fluorinated ethylene glycol (1a) and fluoroalkyl (1b) monomers were polymerized
overnight at 70 ˝C using 1-azobisisobutyronitrile (AIBN) as a free radical initiator in anhydrous
N,N-dimethylformamide (DMF) (321.1 L). The reaction mixtures were dissolved in Novec 7100
and the products were purified by reprecipitation using methanol.
Both fluorinated polymers dissolved in Novec 7100 and their molecular weights were
calculated by static light scattering spectroscopy, respectively. Fluorinated ethylene glycol polymer
2a) (50 mg) and fluoroalkyl polymer (2b) (50 mg) in Novec 7100 (1.0 mL) were hydrolyzed
α,α
µ
™
™
(
™
overnight at room temperature in the presence of aqueous sodium methoxide (22.7 mg, 0.42 mmol),
respectively. The molecular weight of each polymer was estimated by size exclusion chromatography
after hydrolysis.
Fluoroethylene glycol polymer (2a); 1H-NMR (CDCl3, 600 MHz):
δ 1.73–1.88 (br, 1H), 2.04–2.19 (br, 1H),
2.47–2.64 (br, 1H), 4.37–4.59 (br, 2H).
Fluoroalkyl polymer (2b); 1H-NMR (CDCl3, 600 MHz):
δ 1.41–2.00 (br, 1H), 2.00–2.30 (br, 1H), 2.30–2.75
(br, 1H), 4.40–4.80 (br, 2H).
3.2. Evaluation of Contact Angle
Contact angles of the fluorinated ethylene glycol polymer (2a) and fluoroalkyl polymer (2b) were
measured. First, the silicon wafer was cleaned by ultrasonication for 10 min in hexane followed by,
ethanol and finally, in chloroform at room temperature. The films were prepared by solution casting
method 5 w% of each solution was prepared. Each solvent (Milli Q, pentan-1-ol, hexan-1-ol, heptan-1-ol,

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1H,1H,5H-octafluoropentan-1-ol, 1H,1H-perfluorohexan-1-ol, 1H,1H,7H-dodecafluoroheptan-1-ol,
ethylene glycol, propan-1-ol and glycerol) (5 L) was dropped on each polymer and the contact
µ
angles were directly measured using a microscope. Each reported value was obtained from at least
five different measurements and average values were calculated.
4. Conclusions
Two fluorinated polymers were synthesized and their contact angles were evaluated against water,
non-fluorinated alcohols and fluorinated alcohols. Polymer (2a) having pendant-type fluoroethylene
glycol chains showed smaller contact angles than those of the fluoroalkyl polymer (2b) against water
and non-fluorinated alcohols.
Author Contributions: T.K., M.C.K., K.H. and K.M. conceived and designed the experiments; T.K. performed the
experiments and analyzed the data; T.K., M.C.K., K.H. and K.M. contributed preparation of the paper; T.K. mainly
wrote the paper. This study is a PhD work of T.K. under the supervision of K.H. and K.M.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
The following abbreviations are used in this manuscript:
PEG
poly(ethylene glycol)
PTFE
AIBN
DMF
polytetrafluoroethylene
α,α -Azobisisobutyronitrile
N,N-Dimethylformamide
1
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2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
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