New highly fluorinated styrene-based materials with low surface energy prepared by ATRP

Article abstract of DOI:10.1021/ma034952b

2,3,5,6-Tetrafluoro-4-(2,2,3,3,3-pentafluoropropoxy)styrene (TF(F₅)S) and 2,3,5,6-tetrafluoro-4-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctaoxy)styr ene (TF(F₁₅)S) are prepared by nucleophilic substitution of 2,3,4,5,6-pentaflu

Full text of DOI:10.1021/ma034952b

788
Macromolecules 2004, 37, 788-794
New Highly Fluorinated Styrene-Based Materials with Low Surface
Energy Prepared by ATRP
Sa ch in Bor k a r ,†,‡ Ka tja J a n k ova ,† Hein z W. Siesler ,‡ a n d Sør en Hvilsted *,†
Danish Polymer Centre, Department of Chemical Engineering, Technical University of Denmark,
Building 423, DK-2800 Kgs. Lyngby, Denmark, and Department of Physical Chemistry, University of
Duisburg-Essen, Schu¨tzenbahn 70, D-45117 Essen, Germany
Received J uly 7, 2003; Revised Manuscript Received October 29, 2003
ABSTRACT: 2,3,5,6-Tetrafluoro-4-(2,2,3,3,3-pentafluoropropoxy)styrene (TF(F5)S) and 2,3,5,6-tetrafluoro-
4-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctaoxy)styrene (TF(F15)S) are prepared by nucleophilic
substitution of 2,3,4,5,6-pentafluorostyrene. The neat monomers are subjected to atom transfer radical
polymerization (ATRP) at 110 °C to high conversions in relatively short times, 10-120 min; TF(F5)S is
additionally polymerized at 70 and 90 °C. Block copolymers with styrene are prepared by the macroinitiator
approach. All polymers, in the number-average molecular weight range from 6000 to 35 000, have
polydispersity indexes between 1.08 and 1.37. The homopolymers show glass transitions from 16 to 62
°C depending on molecular weight, whereas the block copolymers exhibit phase separation mirrored in
two Tgs, which could be observed when the smallest block constitutes more than 10 mol %. The fluorinated
side chains of P(TF(F5)S) and P(TF(F15)S) enrich the surface of thin films, which results in an advancing
water contact angle of 117° and 122°, respectively. Both XPS analyses and contact angle measurements
strongly imply that the fluorinated parts of the block copolymers migrate to the surface and create low
surface energy films.
In tr od u ction
Furthermore, the 4-methoxy-substituted analogue,
2,3,5,6-tetrafluoro-4-methoxystyrene (TFMS), can be
polymerized in the same manner with controlled char-
acteristics.18,19 Moreover, both homo- and block copoly-
mers of TFMS could be demethylated and the corre-
sponding hydroxy sites derivatized with azobenzene side
chains in a Williamson ether synthesis. The potential
nucleophilic substitution in the para position of FS
prompted us to attempt the preparation of novel FS
monomers with 4-fluoroalkoxy side chains and subse-
quently investigate their polymerization potential with
a view to these novel materials’ self-assembly process
at surfaces. This paper therefore reports on the prepa-
ration of two novel, highly fluorinated styrene mono-
mers and how well-defined homo- as well as block
copolymers with styrene and FS can be prepared by
ATRP. Furthermore, we report on the preliminary
investigations of the surface characteristics of these new
polymers.
Fluoropolymers have a prominent position when
demanding chemical and physical properties are in
question. Among the particular fluoropolymer merits
are high thermal, chemical, aging and weather resis-
tance, oil and water repellency, excellent inertness, and
low flammability and refractive index. Recent, notable
applications are within such different topics as genera-
tion of low-energy surfaces,1-11 surface-modified mem-
branes,12 low permittivity or low dielectric constant,13
and low optical loss exploited in waveguide devices.14-16
The fluorinated block copolymers with well-defined
structures applied for generation of low-energy surfaces
are either polystyrene based and initially prepared by
living anionic polymerization3,4,6-8,10,11 or poly(butyl
methacrylate-co-perfluoroalkyl acrylate)9 synthesized by
atom transfer radical polymerization (ATRP). Low criti-
cal surface tensions have also been determined in
fluorinated poly(amide urethane) block copolymers with
fluorinated side chains prepared from diacid chlorides.1,2
In the styrene-based polymers the fluorination was
obtained by functionalization of polystyryllithium and
subsequent Williamson reactions,6,7 by deprotection of
poly(4-tert-butyldimethylsiloxyloxystyrene) followed by
Williamson reactions,7 or via oxidative hydroboration
of isoprene blocks succeeded by esterification with
perfluorinated acid chloride.3,4,6,11 On the other hand,
one example of a TEMPO-mediated controlled radical
polymerization of a fluorinated alkoxymethylstyrene
also exists.11
Exp er im en ta l Section
Ma ter ia ls. 1H,1H-Pentafluoropropane-1-ol and 1H,1H-pen-
tadecafluorooctane-1-ol (ABCR Chemicals, Germany) were
used as received. Styrene (St) and FS (Sigma-Aldrich) were
passed through a ready to use, disposable prepacked inhibitor
remover column, stored over CaH2, and vacuum-distilled before
use. Tetrahydrofuran was distilled prior to use from CaH2 over
sodium metal under dry nitrogen. Cu(I)Br, 1-phenylethyl
bromide (PhEBr), and bipyridine (bipy) (all from Sigma-
Aldrich) were used as received. All the reactions described
were carried out in an inert atmosphere.
We have recently demonstrated17 the fast, controlled
polymerization of 2,3,4,5,6-pentafluorostyrene (FS) by
use of ATRP. This technique also allows block copoly-
mers with other monomers, e.g., styrene, to be prepared.
Syn th esis of Mon om er s: 2,3,5,6-Tetr aflu or o-4-(2,2,3,3,3-
p en ta flu or op r op oxy)styr en e (TF (F 5)S). In a three-neck
round-bottom flask equipped with a magnetic stirrer, addition
funnel, and reflux condenser, a solution of 13.0 g (67 mmol) of
FS in 50 mL of dry THF was cooled to 0 °C. A solution of 12.7
g (74 mmol) of fluorinated sodium propane-1-olate in 100 mL
of THF was added slowly. Stirring was continued for 1 h and
then brought to reflux for 19 h. After cooling, the reaction
mixture was poured into 400 mL of ice water and extracted
† Technical University of Denmark.
‡ University of Duisburg-Essen.
* Corresponding author: e-mail sh@kt.dtu.dk.
10.1021/ma034952b CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/03/2004

Macromolecules, Vol. 37, No. 3, 2004
Highly Fluorinated Styrene-Based Materials 789
with diethyl ether. The organic layer was dried with sodium
sulfate, and the ether was evaporated. The residue was stored
over calcium hydride for 1 day and then distilled at 56 °C/1.3
1
mbar. Yield ) 17.5 g (80%). H NMR (CDCl3): δ ) 5.7 (d, 1H,
J ) 11.5 Hz, -CHdCH(1)), 6.05 (d, 1H, J ) 18.0 Hz, -CHd
CH(2)), 6.65 (dd, 1H, J ) 18.0 Hz and J ) 11.9 Hz, -CHd
CH2), 4.60 (t, 2H, J ) 12.3 Hz, -OCH2). 13C NMR (CDCl3): δ
) 147.0 (m), 142.8 (m), 138.6 (m), 134.8 (m), 122.7 (t), 121.3
(t), 116.1 (m), 112.5 (m), 69.5 (t). 19F NMR (C6F6): δ ) -155.12
(2Far), -141.26 (2Far), -121.73 (2F), -80.75 (3F).
2,3,5,6-Tetr a flu or o-4-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-p en ta -
d eca flu or oocta oxy)styr en e (TF (F 15)S). Following a similar
procedure by use of fluorinated sodium octane-1-olate, TF(F15)S
was synthesized in a yield of 85% and distilled at 94 °C/1.3
mbar. 1H NMR (CDCl3): δ ) 5.65 (d, 1H, J ) 11.5 Hz, -CHd
CH(1)), 6.05 (d, 1H, J ) 18.0 Hz, -CHdCH(2)), 6.60 (dd, 1H, J
) 18.0 Hz and J ) 11.8 Hz, -CHdCH2), 4.70 (t, 2H, J ) 12.3
Hz, -OCH2). 19F NMR (C6F6): δ ) - 155.15 (2Far), -141.36
(2Far), -123.33 (2F), -120.19 (2F), -119.77 (2F), -119.01 (4F),
-117.92 (2F), -78.25 (3F).
F igu r e 1. 1H NMR spectrum of TF(F5)S (in CDCl3).
P olym er iza tion P r oced u r e. The polymerizations were
performed in a dry Schlenk tube keeping the initiator:CuBr:
bipy ratio at 1:1:3. In a typical homopolymerization experiment
the tube was charged with 3.500 g (10.80 mmol) of TF(F5)S,
0.126 g (0.68 mmol) of PhEBr, 0.097 g (0.68 mmol) of Cu(I)Br,
and 0.319 g (2.04 mmol) of bipy were added. In the case of
block copolymerization 1.0 g (0.159 mmol) of PTF(F5)S1 was
dissolved in 5 mL of xylene in a tube; 0.023 g of Cu(I)Br, 0.074
g of bipy, and 5.95 g (57 mmol) to 16.0 g (154 mmol) of St or
5.05 g (41.5 mmol) of FS were added. Oxygen was removed by
three freeze-pump-thaw cycles by applying vacuum and
backfilling with nitrogen. The tube with the polymerization
mixture was immersed into a silicon oil bath, preheated to 110
°C. After the desired time, the tube was removed from the bath
and cooled rapidly down to ambient temperature, and the
reaction mixture was diluted with THF. The polymers were
precipitated in methanol and dried under vacuum. The yields
were determined gravimetrically. These homopolymers were
further employed as macroinitiators for block copolymeriza-
tions with St and FS in xylene solution. The conversion of the
second monomer was determined gravimetrically, too.
Sch em e 1. Syn th esis of Novel F lu or in a ted Mon om er s
a n d P olym er s
from the integral peak intensities using a linear background.
The systematic error was on the order of 3-5%.
Th e con ta ct a n gle of water toward the air side of the
polymer films spin-coated on glass slides from 2 to 3% w/w
solutions in THF was measured using a contact angle meter
at 25 °C with an accuracy of (2°. The reported values are the
average of three measurements made at different positions of
a film.
1
Mea su r em en ts. H, 13C, a n d 19F NMR were recorded on
a Bruker 250 MHz spectrometer at room temperature using
chloroform-d as the solvent if not otherwise specified. Chemical
shifts for 1H and 13C NMR are reported in δ ppm downfield
from TMS, whereas for 19F NMR the values are stated
downfield from hexafluorobenzene.
Molecu la r w eigh ts were determined by size exclusion
chromatography (SEC) employing a Viscotek 200 instrument
equipped with a PLguard and two PLgel mixed D columns in
series from Polymer Laboratories using a RI detector. Mea-
surements were performed in THF at room temperature with
a 1 mL/min flow; molecular weights were calculated using PS
narrow molecular weight standards in the range 7 × 102-4 ×
105 employing the TriSEC software.
F TIR sp ectr a of the neat, powdered samples were recorded
on a Perkin-Elmer SpectrumOne FTIR spectrometer.
Th er m a l a n a lyses were performed with a differential
scanning calorimeter, DSC Q1000 from TA Instruments, in a
temperature range of -30 to 200 °C at a heating rate of 10 °C
min-1 under nitrogen. The glass transition temperature (Tg)
was determined automatically by the instrument from the
second heating trace and is reported as the midpoint of the
thermal transition.
Th er m a l d egr a d a tion was investigated by thermogravi-
metric analysis (TGA) performed with a TGA Q500 from TA
Instruments recording the total weight loss on approximately
10-12 mg samples from room temperature to 600 °C at a rate
5 °C min-1 in a nitrogen flow of 90 mL/min.
Resu lts a n d Discu ssion
Two new, highly fluorinated monomers, 2,3,5,6-
tetrafluoro-4-(2,2,3,3,3-pentafluoropropoxy)styrene
(TF(F5)S) and 2,3,5,6-tetrafluoro-4-(2,2,3,3,4,4,5,5,6,6,
7,7,8,8,8-pentadecafluorooctaoxy)styrene (TF(F15)S), have
been prepared by nucleophilic substitution of 2,3,4,5,6-
pentafluorostyrene with the sodium alcoholates of
the corresponding fluorinated alcohols, as shown in
Scheme 1.
The developed procedure, which is a modification of
a route20,21 to the 4-methoxy-substituted analogue,
TFMS, results in 80-85% yields of the vacuum-
distilled monomers that elude as pure compounds on
an OligoPore (optimized for small- and medium-sized
compounds) SEC column. The structures of both mono-
mers were confirmed by a combination of different
spectroscopic techniques. FTIR spectra show strong
bands at 1200 and 1103 cm-1 indicative of aliphatic
fluorocarbons. The 1H NMR spectrum of TF(F5)S in
Figure 1 confirms the presence of the three vinyl protons
and furthermore shows a strongly deshielded triplet at
4.6 ppm corresponding to two protons. The methoxy
protons of 2,3,5,6-tetrafluoro-4-methoxystyrene resonate
XP S a n a lysis was performed using a Sage 100 (SPECS,
Berlin, Germany) instrument with an Al KR X-ray source
operated at 300 W and a pressure of <10-7 Torr. The analysis
was carried out using a takeoff angle of 90° from the surface
plane. Atomic concentrations of each element were calculated

790 Borkar et al.
Macromolecules, Vol. 37, No. 3, 2004
Ta ble 1. Hom op olym er iza tion of TF (F 5)S, TF (F 15)S, a n d St by ATRP in Bu lk a n d Xylen e Solu tion
SEC
polymer
time (min)
Mn (targeta)
Mn (NMR)
Mn
PDI
yield (%)
Tg (°C)
PTF(F5)S1-Br
PTF(F5)S2-Br
PTF(F5)S3-Brb
PTF(F5)S4-Br
PTF(F15)S1-Br
PTF(F15)S2-Br
PS1-Br
10
20
20
23
120
60
5 000
20 000
20 000
36 000
50 000
10 000
5 000
6 700
15 300
6 300
18 400
16 900
25 400
1.30
1.09
1.08
1.20
86
77
58
69
74
70
77
84
34
60
56
62
26
16
81
87
28 500
9 700
135
420
4 000
9 700
1.26
1.18
PS2-Br
10 000
a
b
Assuming 100% conversion. In 30% xylene solution.
F igu r e 2. 19F NMR spectrum of TF(F5)S (in CDCl3-C6F6).
at 4.1 ppm.19 That is close to the position (4.0 ppm)
where the methyleneoxy protons of 1H,1H-pentafluo-
ropropane-1-ol emanate. Moreover, the triplet pattern
will result from the coupling with two neighbor fluorine
atoms. Also, the 13C NMR resonance at 69.5 ppm
(Experimental Section) is indicative of a methyleneoxy
carbon. The strongest evidence for the para substitution
of the fluorocarbon chain on the phenyl ring in TF(F5)S
is obtained from the 19F NMR spectrum depicted in
Figure 2. This spectrum demonstrates the presence of
four different types of fluorine atoms. Two types strongly
imply the symmetrical 4-substition on the phenyl ring
and the remaining two sets of fluorine atoms stem from
the side chain.
Similar observations were made for the other mono-
mer, TF(F15)S, where in fact the methyleneoxy protons
are further deshielded (4.7 ppm). Again, the 19F NMR
spectrum depicted in Figure 3 clearly supports the para
substitution on the phenyl ring. In addition, six different
kinds of fluorine resonances originating from the seven
groups of fluorine on the aliphatic fluorocarbon chain
are observed. The direction of the nucleophilic substitu-
tion exclusively in the para position of FS is likely
facilitated by a partial electron donation from the vinyl
group into the phenyl ring with the four electron-
withdrawing fluorine susbstituents. Moreover, the uni-
directional reaction is probably assisted by the fact that
the fluorine is a good leaving group in this strongly
activated nucleophilic substitution.
F igu r e 3. 19F NMR spectrum of TF(F15)S (in CDCl3-C6F6).
monomers polymerize rapidly in bulk as seen from Table
1, and their ATRP is faster than the corresponding
ATRP of FS17 and TFMS.19 The obtained polydispersity
index (PDI) in all cases is below 1.3, which was also
observed in the cases of PFS (<1.2)17 and PTFMS.19
Generally, a PDI at this level is one of the benefits of a
“living”/controlled polymerization. For TF(F5)S even
PDIs lower than 1.1 were achieved in some instances.
The Mns of these novel polymers were determined by
SEC using PS standards; however, the Mn can addition-
1
ally be estimated by H NMR. The spectrum shown in
Figure 4 includes the basic structural components of
PTF(F5)S2-Br.
Principally, both the areas of the aromatic protons
(Ha) and the methyl protons (Hb) from the initiator and
the areas of either the main chain protons (Hp) or the
side chain protons (Hd) can be employed to calculate the
degree of polymerization. The results of Mn listed in
Table 1 show relatively good agreement between results
obtained by the two different methods. The polymeri-
zation of TF(F5)S in xylene solution also proceeds
rapidly and controlled, although to a lower conversion.
Consequently, the ATRP of TF(F5)S was also carried
out at both 90 and 70 °C, resulting in a lower rate of
polymerization, as listed in Table 2. The PDI observed
at these lower temperatures was slightly broader as the
reaction times were longer. This shows that the radical
termination is more efficiently suppressed also for these
monomers at the highest temperature when the polym-
erization rate is fastest. In principle, termination in any
radical polymerization is unavoidable; however, by
TF(F5)S and TF(F15)S were subjected to ATRP em-
ploying 1-phenylethyl bromide as the initiator with
Cu(I)Br and bipyridine as the catalyst system at 110
°C. All polymerizations reported here have been per-
formed with an initiator:Cu(I)Br:bipy ratio of 1:1:3. Both

Macromolecules, Vol. 37, No. 3, 2004
Highly Fluorinated Styrene-Based Materials 791
F igu r e 5. 1H NMR spectrum of PTF(F15)S2-Br (in 3:1 mixture
of C6F6 and CDCl3).
F igu r e 4. 1H NMR spectrum of PTF(F5)S2-Br (in CDCl3).
spectra could be recorded in a C6F6:CDCl3 mixture (3:1
v/v). The H NMR spectrum of PTF(F15)S2-Br shown in
Figure 5 includes the principal structural features that
were employed to calculate Mn,NMR (Table 1) in a
manner similar to the one described for PTF(F5)S2-Br.
1
Ta ble 2. ATRP a n d Con ven tion a l Ra d ica l P olym er iza tion
of TF (F 5)S a t Differ en t Tem p er a tu r es
SEC
temp
(°C)
time
(min)
yield
(%)
polymer
Mn
DPI
The relatively low PDI of PTF(F5)S produced by ATRP
most likely implies that the majority of the polymer
chains have retained the bromine end group functional-
ity, and therefore the homopolymer can be employed as
macroinitiator for the preparation of block copolymers
with styrene. The macroinitiator concept for synthesis
of highly fluorinated block polymers with PS has previ-
ously been demonstrated19 to be flexible; thus, with FS,
TFMS, and St the block sequences could be completely
interchanged. PTF(F5)S1-Br was employed as macro-
initiator for a set of block copolymers with St; in
addition, a single block copolymer with FS was pre-
pared. The inclusion of the block copolymer initiated
with PS2-Br complemented the set of PTF(F5)S-b-PS
polymers to a series with a PS content ranging from 51
to 89 mol %, as seen from Table 3. That the rate of
copolymerization of FS is much faster than that of St is
again clearly demonstrated since 55% of FS is polym-
erized by PTF(F5)S1-Br in 4.5 h, whereas only 5% of St
is converted at nearly the same conditions. Further-
more, the incorporation of 88 mol % of FS is accom-
plished in 4.5 h, whereas it lasted 17 h to achieve 89
mol % St block copolymer content under similar condi-
tions. It should be added that the block copolymer
PTF(F5)S4-Bra
PTF(F5)S5-Bra
PTF(F5)S6-Bra
PTF(F5)S7-Brb
110
90
70
23
75
180
30
69
65
47
86
25 400
23 900
30 000
145 900
1.20
1.28
1.37
1.60
70
a
b
Mn (target) 36 000. 0.1 wt % AiBN as the initiator.
ATRP the termination is minimized by creating a
steady, low concentration of short-lived, active radical
chain ends.22
A polymerization of TF(F5)S was also performed with
the conventional radical initiator, AiBN at 70 °C. The
polymerization is fast and results in high conversion
(86%) in 30 min (Table 2). The polymer had a Mn of
approximately 146 000 with a relatively low PDI (1.6).
We are unable to offer an explanation so far for this
relatively low PDI; however, similarly low PDIs (∼1.6)
were also obtained for the other fluoropolymers, PFS17
and PTFMS,23 when prepared with AiBN in bulk.
Nevertheless, the PTF(F5)S obtained with AiBN cannot
be used for synthesis of block copolymers, one of the
goals of the investigation.
The ATRP of the other monomer, TF(F15)S, employing
the same initiator and catalyst system at 110 °C, results
in 74% yield in 2 h and 70% yield in 1 h when the target
molecular weights are 50 000 and 10 000, respectively,
as seen from Table 1. The homopolymers of TF(F15)S
were insoluble in common organic solvents with fluori-
nated solvents being the exception. Therefore, it was not
possible to perform a SEC analysis, while 1H NMR
1
composition was calculated from H NMR spectroscopy.
All the block copolymers were additionally subjected
to SEC analyses primarily in order to investigate the
PDIs. The SEC traces of the macroinitiator, PTF(F5)-
S1-Br, and the three block copolymers with increasing
Ta ble 3. P r ep a r a tion of Block Cop olym er s of P TF (F 5)S or P TF (F 15)S w ith St or F S by ATRP (1 g of Ma cr oin itia tor ,
P olym er iza tion Tem p er a tu r e 110 °C, In itia tor :Cu Br :bip y ) 1:1:3)
SEC
Mn
PS content
(mol %)
polymer
time (h)
(targeta)
xylene (mL)
convb (%)
Mn
PDI
Mn (NMR)
Tg (°C)
PTF(F5)S1-b-PS1
PTF(F5)S1-b-PS2
PTF(F5)S1-b-PS3
PTF(F5)S1-b-PFS
PS2-b-PTF(F5)S
PS1-b-PTF(F15)S
PS2-b-PTF(F15)S
4
8
17
4.5
9
25 000
50 000
100 000
50 000
67 000
50 000
9 500
3.3
5
5
5
5
8
55
48
69
63
10 800
12 400
14 800
34 700
19 900
6 800
1.20
1.23
1.37
1.34
1.30
1.30
1.24
70
80
89
88c
51
36
90
11 800
15 200
23 900
35 300
38 800
44 400
15 700
31; 75
30; 95
93
5
96
15
10
4
92; 53
72; 34
87
4
4
11 600
a
b
Assuming 100% conversion of the second monomer. Conversion of second monomer. c Content of PFS in mol %.

792 Borkar et al.
Ta ble 4. Con ta ct An gles a n d Gla ss Tr a n sition
Macromolecules, Vol. 37, No. 3, 2004
Tem p er a tu r es of Styr en e a n d P a r a -Su bstitu ted Styr en e
Hom op olym er s, P r ep a r ed by ATRP
contact angle (deg)
polymer
Mn (SEC) PDI Tg (°C) advancing receding
PS-Br
16 500
16 000
16 700
16 900
28 500c
1.11
1.18
1.25
1.08
100
98
94
56
26
95
108
115
117
122
80
97
101
105
104
PFS-Bra
PTFMS-Brb
PTF(F5)S3-Br
PTF(F15)S1-Br
a
Reference 17. b Reference 19. PTFMS ) poly(2,3,5,6-tetrafluoro-
4-methoxystyrene). c Mn by 1H NMR in C6F6-CDCl3.
PS content are overlayed in Figure 6. It is seen how the
SEC trace of each of the block copolymers is shifted to
a higher elution volume than that of the macroinitiator,
strongly implying the formation of a copolymer. More-
over, the block copolymers prepared separately gener-
ally retain the PDI from the macroinitiator. It is noted
that the Mn(SEC) values reported in Table 3 are only
indicative due to the normal problems with assessment
of Mn of copolymers by use of standard calibration.
The insolubility of PTF(F15)S necessitated the block
copolymer route starting from the PS-Br macroinitia-
tor. Two different block copolymers with 36 and 90 mol
% PS content were synthesized in xylene solution. The
introduction of the PS block in the block copolymers
rendered solubility in THF and CDCl3 to these block
copolymers. The SEC analyses of the PS-b-PTF(F15)S
polymers reveal a relatively narrow PDI (Table 3), and
the observed shift in elution volume also signals the
formation of block copolymers. However, the Mn by SEC
of these block copolymers is very different from the
theoretically predicted, whereas the NMR values are
much closer to the theoretical values.
F igu r e 6. SEC overlays of PTF(F5)S1-Br (s, Mn 6300, PDI
1.30) and its block copolymers, PTF(F5)S1-b-PS1 (- -, Mn
*
10 800, PDI 1.20), PTF(F5)S1-b-PS2 (- ‚ -, Mn 12 400, PDI
1.23), and PTF(F5)S1-b-PS3 (- - -, Mn 14 800, PDI 1.37) as a
function of increasing PS content.
Th er m a l P r op er ties. The glass transition temper-
atures (Tg) of all these novel polymers were determined
by DSC. Tg of PTF(F5)S is in the range 34-62 °C (Table
1) depending on Mn. PTF(F5)S1-Br (Mn ∼ 6700) has the
lowest Tg whereas the remaining PTF(F5)S polymers
seem to approach a maximum Tg of approximately 62
°C. PTF(F15)S has even lower Tg (16-26 °C) also with a
Mn dependence. We have previously observed a Tg
dependence of Mn for PFS with a maximum value (∼102
°C) similar to that of PS.17 This strongly suggests that
the introduction of alkoxy side chains in the para
position of the fluorinated phenyl rings of the polymers
results in a plasticizing effect with a corresponding
decrease of the Tg. Furthermore, the length of the
substituting alkoxy group seems to govern the level of
Tg inasmuch as the longest alkoxy groups decreases Tg
mostly. Substantial support for this claim is provided
in Table 4 where Tgs of polymers of nearly the same
Mn but with different and increasing alkoxy group
length are compared.
The Tgs of the block copolymers listed in Table 3 show
some interesting phenomena. First, copolymers with the
fluorinated alkoxy side chains and PS demonstrate
phase separation with two-phase morphology as re-
flected in two Tgs when the molar composition is not
too different. Figure 7 shows a representative DSC trace
of a PTF(F5)S-b-PS polymer. It is also intriguing that
the length of a particular block reflects the Tg typical
of that block length. For example, in PTF(F5)S1-b-PS1
and PTF(F5)S1-b-PS2 the Tg assigned to the PTF(F5)S
block is very close to the one observed in the macroini-
tiator. On the other hand, in PS2-b-PTF(F5)S where the
PTF(F5)S block is larger the Tg of this is recorded to 53
F igu r e 7. DSC trace of PS2-b-PTF(F5)S with a heating rate
of 10 °C/min.
°C. However, when one of the blocks becomes too short
typically around 10 mol % with the Mn discussed here,
only the Tg of the largest block is detected. Similar
observations emerge in the case of the PS1-b-PTF(F15)S
polymer where a Tg of 34 °C has been assigned to the
PTF(F15)S block, and a Tg of 72 °C is attributed to the
PS block. However, in the second block copolymer where
the PS block constitutes 90 mol % only a Tg ∼ 87 °C
from that block is observed.
Finally, the thermal stability of the novel homopoly-
mers was investigated and compared to those of PS,
PFS, and PTFMS. Figure 8 shows the weight loss of
PTF(F5)S and PTF(F15)S in a N2 atmosphere as a
function of temperature. It is seen that both polymers
have almost the same thermal stability and that the
stability of both is inferior to the stabilities of both PFS17
and PTFMS;19 the fluoroalkoxy side groups are appar-
ently more thermally labile than the methoxy group.
In fact, the thermal stability of PTF(F5)S and PTF(F15)S
is even lower than that of PS; thus, the beneficial
fluorination on the phenyl ring,17 which was also partly
experienced in the case of PTFMS,19 is unable to
compensate for the thermal lability of the fluoroalkoxy
groups.
Su r fa ce P r op er ties. Preliminary investigations of
the novel materials’ surface properties were conducted
by determination of the contact angles of a water drop
on spin-coated surfaces. The results are listed in Table

Macromolecules, Vol. 37, No. 3, 2004
Highly Fluorinated Styrene-Based Materials 793
Ta ble 5. Resu lts of XP S An a lysis a n d Con ta ct An gle Mea su r em en ts Usin g Wa ter Dr op lets on F ilm Su r fa ces of th e
F lu or in a ted P olym er s
elements (%, XPS)
contact angle (deg)
advancing receding
117 105
polymer
PS (mol%)
F
C
O
F/C × 100
F/C × 100 theor
PTF(F5)S1
0
51
70
80
89
100
0
46.2
43.4
37.7
39.3
31.3
48.3
50.0
57.7
55.4
63.3
5.5
6.6
4.6
5.3
5.4
96
87
65
71
49
130
74
PS2-b-PTF(F5)S
PTF(F5)S1-b-PS1
PTF(F5)S1-b-PS2
PTF(F5)S1-b-PS3
PS
113
111
109
105
95
102
104
100
99
54
35
19
80
PTF(F15)S
PS1-b-PTF(F15)S
PS2-b-PTF(F15)S
57.0
54.7
36.7
40.1
42.7
61.4
3.0
2.6
1.9
142
128
60
188
101
34
122
119
111
104
103
102
36
90
F igu r e 8. TGA curves of PS, PFS, PTFMS, PTF(F5)S, and
PTF(F15)S in a N2 atmosphere with a heating rate of 5 °C/
min.
F igu r e 9. F/C ratio determined by XPS at the surface as a
functionof % PTF(F15)S (9) or PTF(F5)S (0) in block copoly-
mers.
4 where a gradual increase in the advancing contact
angle when going from PS over PFS and PTFMS to
PFT(F5)S and PFT(F15)S is seen. However, already the
fluorination of the phenyl ring increases the hydropho-
bicity of the material surface as argued from the
increase in contact angle. A further raise in hydropho-
bicity is gained when the fluorinated phenyl ring is
added methoxy groups (PTFMS), whereas the substitu-
tion of methoxy groups with the fluorinated propoxy
groups (PFT(F5)S) only slightly increases the contact
angle from 115° to 117°. This observation is somehow
surprising since the surface tension of CH3 groups (30
dyn/cm)2 is much higher than that of CF3 groups (15
dyn/cm). When even longer fluorooctaoxy groups exist
on the phenyl ring (PFT(F15)S), an advancing water
contact angle of 122° is found. Such a very large contact
angle has previously been detected for surfaces of
fluorinated alkyl side-chain ionenes5 and was explained
by excellent alignment of the CF3 groups on the surface.
In comparison, poly(tetrafluoroethylene) under the same
conditions shows a contact angle of 115°.5 The length
of the fluorinated side chain thus seems to be critical
for the packing and alignment of the CF3 groups in order
to fully exploit a material’s potential for creating low-
energy surfaces. A fluorinated octyl side chain on PFS
is sufficient to achieve the lowest possible surface energy
whereas a fluorinated propyl side chain appears to be
too short. Further support for this claim is provided by
XPS analysis of the films reported in Table 5. In the
case of PTF(F5)S 46% fluorine was detected on the
surface whereas the surface of PTF(F15)S is further
enriched in fluorine (57%). It should be added that the
analysis seems to underestimate the fluorine content
as evident from a comparison of the determined F/C
ratio with the calculated, theoretical F/C ratio.
Thin films of the block copolymers of PTF(F5)S and
PTF(F15)S with PS were likewise investigated by XPS
and subjected to contact angle measurements. Interest-
ingly, all block copolymers show relative high fluorine
content at the surfaces as seen from Table 5. Even the
copolymers with the lowest content (∼10 mol %) of the
fluorinated block reveal fluorine contents of 31-37%.
This strongly suggests that the fluorinated blocks orient
toward the surfaces. As a comparison, a XPS analysis
of PTFMS shows 28% fluorine on the surface. The F/C
ratios in the surfaces of all the block copolymers are
depicted in Figure 9.
The same dramatic effect is observed in the contact
angle determinations of the block copolymer surfaces
also listed in Table 5. An approximately 10 mol % block
of the fluorinated monomer in the PS block copolymers
increases the contact angle to 105° and 111° for TF(F5)S
and TF(F15)S, respectively. The contact angle depen-
dence of the content of TF(F15)S in the block copolymers
is shown in Figure 10. The advancing contact angle of
water is also depicted in Figure 11 as a function of the
detected F/C ratio in the film surfaces. The two sets of
angles express that at the same F/C ratio the highest
contact angle will most likely be achieved in the
PTF(F15)S with the homopolymer PTF(F5)S being the
only exception. Furthermore, it is obvious that the
highest possible contact angle, 122°, can only be ob-
tained with the homopolymer of PTF(F15)S. On the other
hand, the PTF(F15)S blocks also have a much higher F/C
ratio per repeating unit of the main chain compared to
the PTF(F5)S blocks. This is due to the fluoroalkoxy side
chains in the TF(F15)S repeating units that contain 10
more fluorine atoms than the similar side chains in the
TF(F5)S repeating units. In other words, the higher

794 Borkar et al.
Macromolecules, Vol. 37, No. 3, 2004
copolymers with St and controlled characteristics can
be prepared by the macroinitiator approach. The new
homopolymers demonstrate different, but considerably
lower, Tgs than PFS and PS with comparable molecular
weights presumably resulting from a fluoroalkoxy side-
chain plasticizing effect. The block copolymers with PS
are characterized by strong phase separation reflected
in two Tgs, which can be observed when the smallest
block constitutes more than 10 mol %. The long fluori-
nated octaoxy side chain enriches surfaces of both
homopolymers and block copolymers with PS. Spin-
coated films containing the fluorinated octaoxy side
chain obtain very low surface energy as revealed by a
high advancing water contact angle on the order of 122°.
The influence of mixing small amounts of these block
copolymers in a PS matrix on the surface properties is
under investigation.
F igu r e 10. Advancing (9) and receding (b) contact angles of
water on block copolymer surfaces as a function of % PTF-
(F5)S in block copolymers.
Ack n ow led gm en t. We gratefully acknowledge the
financial support from Aage and J ohanne Louis-Hans-
en’s Foundation (DK) and Materials Research, Danish
Research Agency. We thank Lene Hubert, Risø National
Laboratory, DK, for recording the XPS spectra.
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contact angle is achieved due to more than twice as
many fluorine atoms per chain segment, thus at a
considerably higher consumption of fluorine. However,
the minimum necessary amount of fluorine in order to
obtain these contact angles has not been worked out
since the analysis is based on a relatively small and
limited number of block copolymers with styrene. On
the other hand, starting from the respective short
fluoropolymer macroinitiators, the styrene block length
and thus the F/C ratio of the block copolymer can to a
certain extent be controlled when this is needed.
In combination, both XPS analyses and contact angle
measurements strongly imply that the fluorinated
blocks preferentially segregate at the air surface of the
films when spin-coated. Furthermore, even a relatively
small fluorinated block in a PS block copolymer signifi-
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block copolymer.
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Con clu sion s
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Nucleophilic substitution on FS with the proper
fluorinated alcohols provides a facile route to novel,
highly fluorinated monomers. These can be polymerized
in a controlled manner by ATRP. Furthermore, block
(23) J ankova, K.; Borkar, S.; Hvilsted, S., unpublished results.
MA034952B