Design, synthesis, and characterization of linear fluorinated poly(benzyl ether)s: A comparison study with isomeric hyperbranched fluoropolymers

Article abstract of DOI:10.1039/b511555h

A well-defined compositionally-equivalent linear analog to a previously reported hyperbranched fluoropolymer (HBFP) was synthesized and each was subjected to characterization studies as a fundamental investigation of the role of architecture on solution a

Full text of DOI:10.1039/b511555h

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Design, synthesis, and characterization of linear fluorinated poly(benzyl
ether)s: A comparison study with isomeric hyperbranched fluoropolymers
Kenya T. Powell, Chong Cheng, Chakravarthy S. Gudipati and Karen L. Wooley*
Received 15th August 2005, Accepted 29th September 2005
First published as an Advance Article on the web 24th October 2005
DOI: 10.1039/b511555h
A well-defined compositionally-equivalent linear analog to a previously reported hyperbranched
fluoropolymer (HBFP) was synthesized and each was subjected to characterization studies as a
fundamental investigation of the role of architecture on solution and solid-state properties.
Condensation polymerization of 3-{[(tert-butyl)dimethylsilyl]oxy}-5-[(29,39,49,59,69-
pentafluoro)oxy]benzyl alcohol in the presence of an excess of elemental sodium dispersion,
followed by removal of the TBDMS protecting group, and finally alkylation with 2,3,4,5,6-
pentafluorobenzyl bromide afforded linear fluorinated poly(benzyl ether)s (LFP)s. Molecular
n
weights were typically 7000 to 15000 Da (M ) with molecular weight distributions of ca. 2, as
determined by size exclusion chromatography. Confirmation of the isomeric structures of LFP
1
and HBFP was made by H, F, and C NMR, and IR spectroscopies. Evaluation of the
19
13
1
effects of molecular architecture on solution behavior were examined by solubility and F NMR
9
diffusion measurements. There was no significant difference in solubility in a wide range of organic
26
1
9
2 21
solvents. F NMR diffusion experiments measured diffusion coefficients of ca. 3 6 10 cm s
˚
and estimated Stokes radii of 15–26 A, depending upon the solvent, regardless of polymer
architecture. Differential scanning calorimetry and thermogravimetric analysis studies revealed
similar thermolytic profiles with a glass transition temperature of 53 uC for both systems and
thermal stability up to 290 uC. Our studies show that the difference in polymer architecture (linear
versus hyperbranched) does not necessarily mandate obvious discrepancies in spectroscopic or
solution behavior, although the molecular weights for these polymers were maintained at
relatively low values.
Introduction
to advanced functional materials, there is an ever-increasing
need for the ability to predict with precision the composition,
structure and properties of these complex, heterogeneous
systems.
In only the past two decades dendritic macromolecules have
1
experienced a rich history, and their significance continues to
grow as interesting macromolecular frameworks inspire new
synthetic methodologies, improved analytical characterization
To understand the unique properties of a novel polymer
architecture, comparisons are made with polymeric structural
analogs. These comparisons, however, often are not absolute
due to differences in the end-group or backbone function-
2
–4
tools and advanced product developments. Coincident with
developments in dendritic macromolecules have been exten-
sions to alternate architectures, most predominantly hyper-
alities, which are the result of the synthetic approaches to
24–32
5
–7
branched polymers, which are imperfectly-branched analogs
8
and are generally prepared more conveniently. The most
prepare the distinct architectures.
In order to extract
more definitive conclusions about hyperbranched systems,
exact compositional analogs are a vital piece of this complex
13,14,33,34
prominent unique behaviors offered by dendritic and hyper-
9
,10
branched polymers include lower viscosity,
1
higher solubi-
investigation.
1–13
lity and a greater ability to encapsulate and shield a core unit
when compared to their linear polymeric counterparts.
Additionally, from the synthetic point of view, devising
synthetic routes that allow for preparations of compositional
analogs is interesting and of significance. As reported herein,
14–17
Many families of hyperbranched polymers, having varied
compositions and structures, have been afforded by the
development of synthetic methodologies based upon a number
we have developed a method for the preparation of isomeric
35
analogs to hyperbranched fluoropolymers,
which have
1
8
of different mechanisms,
including advances with the
exhibited interesting properties attributed to the combined
traditional condensation polymerization of multi-functional
20
fluorocarbon content, high degree of branching, and large
36–43
1
monomer(s), and also unique adaptations of ring-opening
9
number of chain end groups,
to elucidate the importance
2
1–23
and living vinylic polymerizations.
As the chemistry of
of the hyperbranched architecture. Thus, adding to other
equivalent analog studies, this study offers the exploration
of the effects of molecular architecture on spectroscopic
and solution behavior in compositionally-equivalent poly-
fluoroaromatic polymer systems, one hyperbranched and
the other linear (Fig. 1). In addition to the synthetic pathway,
hyperbranched polymers evolves beyond laboratory curiosities
Center for Materials Innovation and the Department of Chemistry,
Washington University, One Brookings Drive, Saint Louis, MO, 63130-
4899, USA. E-mail: klwooley@wustl.edu; Fax: +1 314 935 9844;
Tel: +1 314 935 7136
5
128 | J. Mater. Chem., 2005, 15, 5128–5135
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we compare the linear and hyperbranched polymers’ spectro-
scopic and thermal properties, solubility, and translational
diffusion.
alcohol, 6, in excellent yield. Selective alkylation of the
phenolic site of 6 by reaction with 2,3,4,5,6-pentafluorobenzyl
bromide in acetone at room temperature for 3 days in the
presence of potassium carbonate and 18-crown-6 afforded
the AB monomer, 3, with a yield of 97%. Polymerization of
Results and discussion
3
was accomplished to afford 7, by allowing the monomer
Synthesis
to undergo reaction with sodium (,0.1 mm in diameter
suspended in toluene at 25 wt%) in THF to form the
benzyloxide anion in situ and proceed with nucleophilic
aromatic substitution of the pentafluorobenzyl groups. With
As illustrated in Fig. 1, LFP and HBFP are of the same
compositions, having a benzyl phenyl ether-based backbone
with each repeat unit containing a tetrafluoroaryl and a
branching aryl group. The large number of pentafluorobenzyl
2
the evolution of H gas and heat upon the addition of the
sodium dispersion, the polymerization was accomplished in a
cooled reaction flask, which was then allowed to warm to
room temperature gradually, to ensure the stability of the silyl
protecting group.
‘
‘terminal groups’’ present in the hyperbranching structure
which are actually terminal groups for dendritic repeat units
(
and side chain groups for linear repeat units) are accommo-
dated in the linear form as side chain substituents. Since these
pentafluorobenzyl groups are utilized as reactive sites for the
Growth of 7 from 3 was monitored by size exclusion
1
19
chromatography, H NMR spectroscopy and F NMR
spectroscopy. Upon establishment of the polymer backbone
by arylation of the benzylic alcohol of 3, the intensity of
the hydroxyl proton decreased and the benzylic methylene
protons shifted downfield from 4.56 ppm in 3 to 5.15 ppm for
the ether linkage of 7 (labeled as methylene protons ‘‘a’’ in
Figs. 2a and 2b). In addition, the benzylic ether protons of 3
shift downfield slightly from 5.22 ppm to 5.25 ppm for 7
2
preparation of the HBFP from an A B monomer, a synthetic
route was required to allow for the establishment of the LFP
backbone while maintaining the pentafluorobenzyl side chains.
Thoughtful care was taken, therefore, in designing both the
synthetic approach and the functionality of the LFP monomer.
The reaction conditions that produce the hyperbranched
polymer were adopted for the linear analog (Scheme 1).
2
Polycondensation polymerizations of an A B and an AB
(
labeled as methylene protons ‘‘b’’ in Figs. 2a and 2b). Upon
monomer were performed to afford the HBFP, 1, and LFP, 2,
respectively. The monomer precursor for LFP, 3, contains a
protected site that serves to block the reactivity of what would
be the branching site of HBFP, and reserves that position
for a key functional group, namely the pentafluorobenzyl
moiety. The HBFP precursor, 4, contains the two penta-
fluorobenzyl groups that were allowed to react to give the
highly branched framework.
polymerization, diminishment of the para-fluorine resonance
intensity at 2156.2 ppm was monitored, together with shifts in
the ortho- and meta-fluorines from 2144.6 to 2146.3 ppm and
from 2164.7 to 2157.9 ppm, respectively (Fig. 2d and 2e).
Retention of the TBDMS protecting group was confirmed by
2
9
Si NMR and also by comparison of the tert-butyl and methyl
proton resonance intensities at 0.98 and 0.20 ppm, respectively,
with the benzylic and aryl protons of the remainder of the
1
structure in the H NMR spectra (Fig. 2a and 2b).
The production of LFP began with the preparation of
monomer 3. The reaction of methyl 3,5-dihydroxybenzoate
4
4
with tert-butyldimethylsilyl chloride allowed for isolation
of the mono-protected product, 5. Reduction with lithium
aluminum hydride then introduced the B functionality of
the AB monomer, by affording the mono-phenolic benzylic
After the successful polymerization of the protected AB
monomer came the deprotection of 7 and subsequent alkyla-
tion with 2,3,4,5,6-pentafluorobenzyl bromide. Initially, potas-
sium fluoride in the presence of 18-crown-6 was used to
Fig. 1 The linear and hyperbranched fluoropolymers have equivalent compositions, and differ only in the topology. The condensed repeat unit
structures indicate the differences in architecture by noting that the polymer backbone proceeds through only two sites in the linear structure,
whereas there is a possibility for reaction through the pentafluorobenzyl site of the hyperbranched polymer. In the expanded form of each structure,
six repeat units are illustrated to emphasize the different architectures, for which the hyperbranched form is shown with the statistical 50%
branching.
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Scheme 1 Synthetic routes for the preparation of the linear and hyperbranched fluoropolymers, 2 and 1, respectively.
remove the silyl protecting group, but no reaction occurred.
A stoichiometric amount of tetrabutylammonium fluoride
reaction with 2,3,4,5,6-pentafluorobenzyl bromide through
nucleophilic substitution to give LFP, 2, in a 60% yield, after
(
TBAF) was used for desilylation, but resulted in the
repeated precipitation into hexanes. Introduction of the
1
pentafluorobenzyl groups was observed by H and F NMR
19
cumbersome removal of excess TBAF salts. For a cleaner
reaction and more facile purification, AgF was used as a
desilylation agent both with and without a catalytic amount of
1
spectroscopies (Fig. 2c and 2f). In the H NMR spectrum, the
benzylic methylene protons of the unique pentafluorobenzyl
side chain groups appeared at 5.28 ppm, intermediate between
the resonances observed for the benzylic backbone groups.
4
5,46
TBAF, but with little or no removal of the TBDMS group.
An alternate route was attempted in order to circumvent the
production of the deprotected polymer and form the alkylated
final product in situ with the reaction of potassium fluoride, a
catalytic amount of TBAF, and 2,3,4,5,6-pentafluorobenzyl
bromide. This resulted, however, in an incomplete reaction
and a complex product mixture. The protected polymer was
finally deprotected successfully using potassium fluoride in
THF at reflux in the presence of a catalytic amount of TBAF
1
9
19
The F NMR spectrum observed the reintroduction of
F
resonances due to the ortho-, meta- and para-positions of 2 vs.
only tetrafluoroaryl resonances observed for 7 (Fig. 2f vs. 2e),
similar to those of the monomer (Fig. 2d). Integration of the
ortho-, meta- and para-fluorine resonances indicated that
alkylation had occurred by selective displacement of the more
reactive benzylic bromide, without substantial side reaction
involving nucleophilic aromatic substitution upon the penta-
fluorobenzyl ring. A lack of increase in molecular weight, as
observed by size exclusion chromatography, provided further
confirmation of the clean alkylation procedure.
(
rather than stoichiometric) in a manner similar to that
4
7
employed by Beers et al. Due to the highly polar nature of
the phenolic OH groups, purification was achieved by repeated
precipitations, but with difficulty. Under optimized conditions,
therefore, the alkylation was conducted subsequent to the
deprotection without isolation of 7.
Characterization
Alkylation to yield 2 was performed according to the
reaction conditions employed for the preparation of the
monomers 3 and 4. Potassium carbonate was used as a mild
base to deprotonate the phenolic hydroxy group with the
assistance of 18-crown-6. The phenoxide then underwent
As expected, spectroscopic analyses revealed the compositional
3
5
equivalence of the LFP and HBFP materials, as evaluated by
1
IR, H NMR, C NMR, and F NMR spectroscopies. In the
13
19
1
H NMR spectra of LFP (Fig. 3a) and HBFP (Fig. 3b), the
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1
Fig. 2 H (300 MHz, acetone-d
19
) and F (282 MHz, acetone-d
1
) NMR spectra for the monomer, 3, linear polymer, 7, and LFP, 2. The H NMR
6
6
19
spectra are shown in (a), (b) and (c), respectively, and the F NMR spectra are included as (d), (e), and (f), respectively.
benzylic methylene protons of the backbone and the side
chain/terminal groups (labeled as a, b and f, respectively, in
Fig. 2c and Fig. 3), resonate as broad singlets from 5.0 to
phase was observed from 340 uC (onset) to 540 uC (Fig. 5).
DSC measured a single glass transition temperature (T ) for
g
each polymer at 53 uC (Fig. 6). In contrast to the crystallinity
observed for a similar linear non-fluorinated benzyl ether
5
.5 ppm. The aromatic proton c resonates at 6.7 ppm and
the resonances for the aromatic protons d and e coincide at
.8 ppm.
3
3
48
m
polymer, LFB did not exhibit a T .
6
Qualitative solubility studies were performed for 2 and 1 in
several organic solvents having various polarities, including
tetrahydrofuran, methylene chloride, benzene, toluene, and
acetone. In each case, the polymers were found to be highly
soluble at room temperature. No significant enhancement in
solubility was observed for HBFP relative to LFP, a result
inconsistent with most reports on solubility comparisons
between compositionally-equivalent linear and hyperbranched
polymers. Non-solvents for these polymers included water,
hexanes, methanol, as would be expected.
1
9
In the F NMR spectrum of LFP (Fig. 4a), the two ortho
o) one para (p), and two meta (m) fluorines of the side
chain pentafluorobenzyl group appear at 2144.6, 2155.8, and
164.5 ppm, respectively, while the two ortho (o9) and two
(
2
meta (m9) fluorines of the tetrafluorobenzyl moiety along the
backbone resonate at 2146.3 and 2158.0 ppm, respectively. A
1
9
direct comparison with the F NMR spectrum of HBFP
Fig. 4b) demonstrates agreement with both the chemical shifts
(
and peak integrations.
1
9
Thermal analyses were performed by thermogravimetric
analysis (TGA) and differential scanning calorimetry (DSC).
TGA indicated that both polymers displayed excellent thermal
stability up to 290 uC (onset) with 25% mass loss at 340 uC. An
additional 25% mass loss occurred as another decomposition
Pulsed-field gradient spin-echo F correlation spectro-
4
scopy was performed on a series of LFP and HBFP polymer
9
1
samples using high resolution (470 MHz) F NMR, by the
9
5
0–52
method reported by Wu, Chen, and Johnson.
Self-
diffusion studies have previously been found to be valuable
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Fig. 5 TGA profiles of 2 (lower trace) and 1 (upper trace).
a Varian Unity-plus (282 MHz) spectrometer in acetone-d
2
6
9
and referenced internally with CFCl
3
.
Si NMR spectra were
recorded using standard INEPT (insensitive nuclei enhanced
by polarization transfer) experiments on a Varian Unity-plus
1
6
Fig. 3 H (300 MHz, acetone-d ) NMR spectra of 2 (a) and 1 (b).
6
spectrometer at 59.6 MHz in acetone-d and were referenced
externally with tetramethylsilane at 0.0 ppm. IR spectra
were recorded on a Perkin-Elmer Spectrum BX FT-IR
system as thin films on KBr disks and were analyzed using
FT-IR Spectrum v2.00 software (Perkin-Elmer Corporation,
Beaconsfield, Bucks, England).
in the characterization of dendritic aliphatic polyesters of
5
3
generations one to four. The values for the diffusion coeffi-
cients for LFP and HBFP were measured to be 2.0–3.4 6
2
0
6
2 21
cm s , which gave estimated Stokes radii of 15–26 A.
˚
1
The LFP gave distinctly larger Stokes radii in acetone
Size exclusion chromatography was conducted using a
Waters 1515 Isocratic HPLC pump and detection was by a
Waters 2414 refractive index detector; data analysis was
performed with PrecisionAcquire32 Acquisition Program and
Discovery32 Light Scattering Analysis software (Waters,
Milford, MA). Three Polymer Laboratories (PL) gel columns
connected in series in the order of decreasing pore size
˚
22–25 A) than in tetrahydrofuran (15–19 A), whereas the
˚
(
HBFP did not undergo a significant conformational size
˚
change, rather exhibiting similar Stokes radii (21–26 A) in both
solvents.
Experimental
4
2
˚
˚
(
Mixed C, 10 A, and 10 A) were used at 35 uC with THF as
Measurements
the eluent. The instrument was calibrated using polystyrene
standards (Polymer Laboratories Ltd., Amherst, MA).
Thermogravimetric analyses were done under nitrogen with
1
H NMR spectra were recorded on a Varian Unity-plus
(
300 MHz) spectrometer in acetone-d with the residual solvent
6
1
3
proton signal used as a reference. C NMR spectra were
recorded on a Varian Unity-plus spectrometer (75 MHz) in
acetone-d6 with solvent carbon signal as a chemical shift
21
21
a flow rate of 50 mL min and a heating rate of 10 uC min
using a Mettler Toledo TGA/DST A851 and a DSC822 .
e
e
1
9
1
standard. F ( H decoupled) NMR spectra were recorded on
1
9
Fig. 4
F (282 MHz, acetone-d
6
) NMR spectra of 2 (a) and 1 (b).
Fig. 6 DSC thermograms for 2 (lower trace) and 1 (upper trace).
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e
21 1
Data were analyzed using STAR 7.01 software. The decom-
position temperature, T , was taken from the onset of the mass
loss up to 900u C and the glass transition temperature, T , was
1591, 1446, 1345, 1256, 1161, 1020, 839, 752 cm ; H NMR
(acetone-d ): d 0.23 (s, 6H, SiCH ), 0.99 (s, 9H, CCH ), 3.84 (s,
3H, OCH ), 6.63 (m, 1H, ArH), 7.00 (m, 1H, ArH), 7.13
(m, 1H, ArH); C NMR (acetone-d
109.9, 112.0, 112.5, 132.4, 156.9, 158.7, 166.3; Si NMR
(acetone-d ): d 21.7 (s); mp 5 78–79 uC; T 5 233 uC; Anal.
Calcd for C14 Si (282.41 Da): C, 59.54; H, 7.85%. Found
C, 59.70; H, 7.76%.
d
6
3
3
g
3
1
3
taken as the midpoint of the inflection tangent of the final of
6
): d 25.0, 18.1, 25.3, 51.7,
2
9
three runs from 0 uC to 150 uC.
Elemental analyses were performed for pure samples by
MHW Laboratories (Phoenix, AZ). Calculations of the
theoretical elemental percentages for the polymers were based
on the composition of the repeating units.
6
d
H O
22 4
1
9
F Pulsed gradient spin-echo diffusion ordered spectro-
3-{[(tert-Butyl)dimethylsilyl]oxy}-5-hydroxybenzyl alcohol
(6). With the reaction flask cooled in an ice bath, 5 (20.0 g,
70.9 mmol) in THF (250 mL) was added slowly via cannula to
a slurry of THF (50 mL) and lithium aluminum hydride (6.95 g,
183 mmol). The reaction was brought to room temperature
scopy was performed on a Varian Inova spectrometer operat-
ing at 470 MHz. A bipolar pulse pair (BPP) which utilizes a
5
0
9
0–180u pulse sequence was employed. In order to insure
19
quantification, relaxation delay times ¢5 times T1 (the
spin–lattice relaxation time) were applied. The diffusion time
F
1
and allowed to proceed for 2 h while being monitored by H
NMR spectroscopy. The reaction flask was cooled in an ice
bath and to it was added saturated aqueous ammonium
chloride (30 mL) slowly. The mixture was filtered and the
filter cake was rinsed with copious amounts of fresh THF,
which was removed in vacuo, and the resulting residue was
partitioned between ethyl acetate and water. The combined
was set to 0.06 ms and the pulsed field gradient was ramped
2
2
over a range of 0 to approximately 50 mgauss cm to provide
for at least three half-lives of signal decay for accurate
diffusion coefficient estimates. The amplitude was based on the
decay over time of the para fluorine peak. The samples were
charged into Shigemi tubes with deuterated solvents (acetone,
benzene, THF) and were filtered through a 0.2 mm filter prior
to each run. Concentrations were based on equal molar
amounts from the molecular weight of the polymer. The
diffusion coefficient was obtained from a linear regression fit
extrapolation of the natural log of the peak intensity versus the
square of the gradient strength change of the data acquisition
array using Origin (7.0) software (Microcal Software Inc.,
Northampton, MA).
organic layers were dried over MgSO
4
and concentrated to
give 17.6 g of pure product as a white solid: Yield 97.4%. IR:
3
1
500–3200, 3100–2850, 2336, 2218, 2089, 1983, 1865, 1734,
2
1 1
597, 1451, 1317, 1247, 1023, 959, 830, 772, 633, 512 cm ; H
): d 0.19 (s, 6H, SiCH ), 0.97 (s, 9H, CCH ),
.15 (t, 1H, J 5 6 Hz, CH OH), 4.50 (d, 2H, J 5 6 Hz,
OH), 6.25 (m, 1H, ArH), 6.39 (m, 1H, ArH), 6.48 (m, 1H,
NMR (acetone-d
6
3
3
4
2
CH
2
1
3
ArH), 8.18 (ArOH); C NMR (acetone-d ): d 25.0, 18.1, 25.3,
6
2
9
6
3.8, 105.7, 106.8, 109.4, 145.2, 156.8, 158.2; Si NMR
acetone-d ): d 20.0 (s); mp 5 78–79 uC; T 5 205 uC; Anal.
Calcd for C13 Si (254.40 Da): C, 61.43; H, 8.72%. Found
C, 61.50, H, 8.73%.
(
6
d
Materials
22 3
H O
Tetrahydrofuran (HPLC grade) was purchased from Aldrich
Chemical Company and either used fresh or distilled from
sodium. Acetone (reagent grade) was purchased from Aldrich
and distilled from anhydrous potassium carbonate. All other
reagents and solvents were purchased from Aldrich and used
3
-{[(tert-Butyl)dimethylsilyl]oxy}-5-{[(2,3,4,5,6-pentafluoro)-
oxy}benzyl alcohol (3). To dry acetone (350 mL) was added 6
24.8 g, 97.3 mmol) and K CO (13.4 g, 97.3 mmol). The
(
2
3
as received. HBFP (M = 8 kDa, M /M = 2.0) was prepared
n
w
5,55
n
mixture was allowed to stir magnetically at ambient tem-
perature while 2,3,4,5,6-pentafluorobenzyl bromide (14.7 mL,
3
in a manner reported previously.
9
7.3 mmol) was added. After the addition of 18-crown-6
Methyl 3-{[(tert-butyl)dimethylsilyl]oxy}-5-hydroxybenzoate
5). To a solution of methyl 3,5-dihydroxybenzoate (74.6 g,
(
2.57 g, 0.1 equivalents) the reaction was allowed to proceed
1
(
for 3 d while monitored by H NMR. The reaction mixture
was filtered and the solvent was evaporated in vacuo. The
residue was partitioned between hexanes and water and the
4
44 mmol) and THF (400 mL) was added tert-butyldimethyl-
silyl chloride (66.9 g, 444 mmol). The resulting mixture was
cooled in an ice bath and imidazole (33.2 g, 488 mmol) was
added slowly. The reaction was allowed to warm to room
temperature and proceed for 24 h while being monitored by
TLC (15% ethyl acetate–cylcohexane). The solvent was
evaporated in vacuo and the resulting residue was partitioned
between water and ethyl acetate. The aqueous layer was
extracted with ethyl acetate and the combined organic layers
combined organic layers were dried over MgSO , filtered
4
through Celite 545, and evaporated in vacuo. Purification by
flash column chromatography over silica gel eluting with
hexanes and increasing polarity to THF gave 41.3 g of a yellow
oil: Yield 97.5%. IR: 3500–3200, 2900–2850, 1653, 1591, 1504,
1451, 1387, 1328, 1253, 1155, 1046, 1001, 973, 937, 841, 786,
2
1
1
755, 654, 514 cm
6
; H NMR (acetone-d ): d 0.20, (s, 6H,
4
were dried over MgSO . The solvent was again evaporated
SiCH ), 0.98 (s, 9H, CCH ), 4.27 (t, 1H, J 5 6 Hz, CH OH),
3
3
2
in vacuo and the benzoate starting material was removed by
precipitation into cylcohexane. Separation of the mono- and
di-protected products was accomplished via silica gel flash
column chromatography with 15% ethyl acetate–cyclohexane
as the eluent to yield the mono-protected product as a white,
waxy solid. Recrystallization in hexanes afforded 49.4 g of
white crystals: Yield 47.8%. IR: 3500–3200, 3100–2850, 1701,
4.56 (d, 2H, J 5 6 Hz, CH OH), 5.22 (s, 2H, C F CH O), 6.41,
2 6 5 2
1
3
(m, 1H, ArH), 6.57 (m, 1H, ArH), 6.60 (m, 1H, ArH);
C
NMR (acetone-d ): d 23.8, 19.0, 26.5, 58.8, 64.7, 106.6, 107.3,
6
1
9
112.3, 112.7, 139.0, 142.9, 147.1, 146.8, 158.1, 160.5;
F
2
NMR (acetone-d ): d 2164.7, 2156.2, 2144.6; Si NMR
9
6
(acetone-d ): d 20.9 (s); T 5 275 uC; Anal. Calcd for C H O Si
6
d
20 23 3
(434.47 Da): C, 55.28; H, 5.34%. Found C, 55.24; H, 5.33%.
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Silyl protected LFP (7). The monomer (3) (19.4 g, 44.7 mmol)
was dissolved in THF (150 mL) and the reaction flask was
placed in an ice bath. A sodium dispersion in toluene 25 wt%
by mass (less than 0.1 mm in diameter), was added in aliquots
over 3 d until excess equivalents were delivered (total added
9 3 9
Calcd for repeat unit C21H O F (480.28 Da): C, 52.51; H,
1.89; F, 35.60%. Found C, 52.77; H, 1.92; F, 35.44%.
Conclusions
9
.50 mL, 89.9 mmol, 2.0 eq.). The polymerization was allowed
We have shown that protecting group chemistry allows for
the production of a well-defined compositionally-equivalent
linear analog to a hyperbranched fluoropolymer. The LFP
to proceed at room temperature as the reaction was monitored
1
19
by SEC, H NMR, and F NMR spectroscopies. The reaction
mixture was concentrated in vacuo and then cautiously
partitioned between ethyl acetate and water. The aqueous
phase was extracted with ethyl acetate, the organic layers
1
19
and HBFP exhibit similar H and F NMR spectroscopic
characteristics, display the same decomposition and glass
transition temperature, and also show similarity in solubility.
The only distinguishing data were obtained from diffusion
studies, which indicated a higher degree of radius change for
the linear polymer than for the hyperbranched structure, as a
function of solvent. Currently, we are investigating the surface
behavior of the LFP when cast into neat films and when
components within complex, amphiphilic networks crosslinked
by diamino-terminated poly(ethylene glycol). The studies with
LFP-PEG crosslinked networks are expected to ascertain the
importance of the hyperbranched component to the enhanced
antifouling results observed by the HBFP-PEG crosslinked
were combined, dried over MgSO
4
and filtered through
Celite 545 and then precipitated into hexanes to afford 15.0 g
of a light yellow solid: Yield 81.8%. Mw, GPC 5 25 000 Da,
M /M 5 2.5: IR: 2900–2850, 1650, 1598, 1496, 1460, 1375,
w
n
2
1 1
1
336, 1256, 1148, 1054, 998, 941, 781, 680 cm ; H NMR
acetone-d ): d 0.20 (br s, 6H, SiCH ), 0.98 (br s, 9H, CCH ),
.15 (br m, 2H, C F CH O), 5.27 (br m, 2H, ArCH O),
(
6
3
3
5
6
6
4
2
2
.50 (br s, 1H, ArH), 6.65 (br s, 1H, ArH), 6.80 (br s, 1H,
1
3
ArH); C NMR (acetone-d
6
): d 25.0, 18.1, 25.7, 58.8, 76.2,
1
1
05.9, 107.5, 113.4, 111.0, 137.8, 141.5, 146.1, 146.8, 159.1,
1
9
29
54–56
network system.
59.8; F NMR (acetone-d
): d 21.5 (m); T 5 320 uC; Anal. Calcd for repeat
unit C H O SiF (414.47 Da): C, 57.95; H, 5.35%. Found C,
6
): d 2157.9, 2146.3; Si NMR
(
acetone-d
6
d
2
0
22
3
4
Acknowledgements
5
6.32; H, 5.04%.
The authors thank Dr Andr e´ d’Avignon and Dr Jeff Kao
of the Washington University Chemistry Department
NMR Facilities. We also acknowledge the Office of Naval
Research (N00014-02-1-0326 and N00014-05-1-0057) for
financial support.
Deprotection and alkylation to give LFP (2). A solution of
KF (0.505 g, 8.69 mmol) and 7 (2.59 g, 6.25 mmol) in THF
30 mL) was prepared. A 1 M solution of tetrabutylammonium
(
fluoride (1.5 mL, 1.5 mmol) in THF was added and the
reaction was heated at reflux for approximately 24 h. Aqueous
saturated ammonium chloride solution was added and allowed
to stir magnetically. The residue obtained by solvent evapora-
tion was partitioned between ethyl acetate and water. The
organic layer was dried over MgSO4 and filtered through
Celite 545. The solution was concentrated in vacuo to give
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