Disassembly via an environmentally friendly and efficient fluorous phase constructed with dendritic architectures

Article abstract of DOI:10.1002/pola.24046

Traditionally the fluorous phase is generated with perfluorinated alkyl groups that are usually perfluorooctyl or longer and are bioaccummulative and biopersistent and therefore, are considered environmentally unfriendly. Here we report a new concept for the construction of the fluorous phase. This concept is based on the amplification of the fluorous effect with the help of dendritic architectures containing very short semifluorinated groups on their periphery. This new concept was demonstrated by the convergent synthesis of the first and second generation AB₃ and AB₂ benzyl ether dendrons functionalized on their periphery via catalytic nucleophilic addition of their phenolates to perfluoropropyl vinyl ether. The resulting dendrons are liquids. Their fluorous phase affinity was analyzed and demonstrated that the dendritic architecture amplifies the fluorous phase at a specific generation by the number of functional groups on the dendron periphery, and at different generations by increasing their generation number. Therefore, this concept is very efficient for the design and synthesis of new fluorous materials. In addition, by contrast with dendrons containing perfluoroalkyl groups on their periphery, the current dendrons mediate the disassembly of their parent building blocks but do not mediate the self-assembly in a supramolecular architecture.

Full text of DOI:10.1002/pola.24046

Disassembly via an Environmentally Friendly and Efficient Fluorous Phase
Constructed with Dendritic Architectures
CHRISTOPHER J. WILSON, DANIELA A. WILSON, ANDREW E. FEIRING, VIRGIL PERCEC
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia,
Pennsylvania 19104-6323
Received 17 March 2010; accepted 26 March 2010
DOI: 10.1002/pola.24046
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Traditionally the fluorous phase is generated with
perfluorinated alkyl groups that are usually perfluorooctyl or
longer and are bioaccummulative and biopersistent and there-
fore, are considered environmentally unfriendly. Here we
report a new concept for the construction of the fluorous
phase. This concept is based on the amplification of the fluo-
rous effect with the help of dendritic architectures containing
very short semifluorinated groups on their periphery. This new
concept was demonstrated by the convergent synthesis of the
first and second generation AB3 and AB2 benzyl ether den-
drons functionalized on their periphery via catalytic nucleo-
philic addition of their phenolates to perfluoropropyl vinyl
ether. The resulting dendrons are liquids. Their fluorous phase
affinity was analyzed and demonstrated that the dendritic
architecture amplifies the fluorous phase at a specific genera-
tion by the number of functional groups on the dendron peri-
phery, and at different generations by increasing their
generation number. Therefore, this concept is very efficient for
the design and synthesis of new fluorous materials. In addi-
tion, by contrast with dendrons containing perfluoroalkyl
groups on their periphery, the current dendrons mediate the
disassembly of their parent building blocks but do not mediate
C
V
the self-assembly in a supramolecular architecture.
2010
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48:
2498–2508, 2010
KEYWORDS: biodegradable; dendrimers; fluorous dendrons;
perfluoropropyl vinyl ether; self-assembly
INTRODUCTION In the past decade fluorous chemistry1
emerged as an influential strategy that facilitates new and ef-
ficient methodologies for catalysis,2 protecting groups,3 tags,4
separation processes,5 microarrays,6 organic electronics,7
medicine,8 self-assembly,9–11 liquid crystals,12 mediate the
solubility of polymers,13 and that of proteins and peptoids
folding.14,15 Many societal conveniences, ranging from non-
stick frying pans, to optics, electronics, displays, fuel and so-
lar cells, rechargeable batteries, drugs, and medical applica-
tions rely on the same building blocks, namely, various
combinations of linear hydrocarbons with perflooctyl or lon-
ger perfluorinated fragments that are used currently to gen-
erate the fluorous phase. These compounds degrade to the
environmentally biopersistent and potentially toxic perfluoro
acids (PFOA).16 The Environmental Protection Agency (EPA)
has the goal to reduce emissions and product content of
PFOA by 95% no later than 2010, and completely eliminate
it by 2015.17 Thus, there is a pressing challenge to develop
new innovative strategies of chemical design and synthesis
that will allow the field of fluorous chemistry not only to
continue but to expand into new technological frontiers pre-
viously prohibited by cost and environmental concerns. The
key requirement is to achieve an efficient fluorous effect by
molecular design using a minimum amount of expensive flu-
orine and short perfluoroalkyl groups. Perfluorobutanoic
acid and shorter acids do not bioacumulate in the human
body and are not persistent.16,18 Self-assembling dendrons
and dendrimers containing perfluoroalkyl groups on their
periphery,9 and dendrons and dendrimers containing per-
fluoroalkyl and perfluoroaryl groups on their periphery19
have been reported. The amplification of the fluorous phase
and fluorous or fluorophobic effect via the dendritic architec-
ture have been recognized since 1995.9a,b,e However, to our
knowledge no attempts have been made to elaborate an
environmentally friendly and efficient fluorous phase by
using the amplification effect of the dendritic architecture.
This manuscript reports the design of an environmentally
friendly and efficient fluorous phase based on dendritic
architectures. It is expected that the concept reported here
can be expanded to other perfluoroalkyl groups and will
impact many technological applications dominated by envi-
ronmentally less friendly fluorous phases.
RESULTS AND DISCUSSION
Self-Assembling Fluorous Dendrons. The Fluorous Phase
via Complex Architectures
Linear semifluorinated dodecyl groups containing perfluour-
obutyl, hexyl, and octyl segments on their periphery were
Additional Supporting Information can be found in the online version of the article. Correspondence to: V. Percec (E-mail: percec@sas.upenn.edu)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2498–2508 (2010) 2010 Wiley Periodicals, Inc.
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FIGURE 1 Comparison of the self-assembly of (3,4,5)RfG1-CO2H, (3,4,5)2RfG2-CO2H, and (3,4,5)212G2-CO2H.20
discovered in our laboratory to enhance the ability of the
first generation AB3 dendrons toward self-assembly and thus
mimic, at the first generation, the capabilities encountered
only in higher generations of hydrogenated homologous com-
pounds20 (Fig. 1). The fluorous effect was responsible for
this trend.9a,b,e
by a
variety of electrophiles.23 Feiring and Wonchoba
reported that the reaction of a phenol with perfluoropropyl
vinyl ether (PPVE) in DMF in the presence of a catalytic
amount of potassium tert-butoxide produced the addition
product in 72–96% yield (Scheme 1).
In this study we applied this method to the synthesis of a
library of first and second generation AB3 and AB2 semi-
fluorinated dendrons. Methyl 3,4,5-tris(1,1,2-trifluoro-2-(per-
fluoropropoxy)ethoxy)benzoate [(3,4,5)PPVEG1-COOCH3] and
methyl 3,4-bis(1,1,2-trifluoro-2-(perfluoropropoxy)ethoxy)-
benzoate [(3,4)PPVEG1-COOCH3] first generation dendrons
were synthesized by using the 3,4,5- and 3,4-polyhydroxy
methyl benzoate building blocks (Scheme 2).24
The corresponding dendronized polymers,9a,b and higher
generation dendrons, exhibit a decreased solubility in or-
ganic solvents even at high temperature while becoming
soluble only in fluorinated solvents. Thus, although semi-
fluorinated molecules are known to exhibit enhanced solubil-
ity in organic solvents (oleophilicity), semifluorinated den-
drons were shown to provide a pathway to oleophobic
compounds. This solubility effect is the simplest assay for
the fluorous phase and supports the concept of fluorous den-
drons. Subsequent results from other laboratories demon-
strated the chemical synthesis of oligonucleotides on theses
fluorous dendrons.20h Although these preliminary results
were not originally directed toward the solution of the PFOA
problem they provide crucial support for the research hy-
pothesis of the experiments to be reported here.
The short nomenclature for these compounds follows the no-
menclature used for the benzyl ether dendrons.20a,11 We
term the PPVE chain to be semifluorinated due to the pres-
ence of a single H that results from electrophilic trapping of
the carbanion generated from nucleophilic addition of the
phenolate to the perfluorinated vinyl ether. Although these
chains are closer to perfluorinated chains in structure than
to semifluorinated ones the prefix per- should only be
applied in cases where all hydrogens are replaced by fluo-
rine. In addition to the ease of preparation, the incorporation
of an ether bond into the perfluoroalkyl chain fulfills the
requirement of higher solubility and eventual degradability
to shorter nonbiopersistent molecules. In the case of
Design and Synthesis of New Fluorous Dendrons
The addition reaction of nucleophiles to fluorinated olefins is
an efficient reaction in organofluorine chemistry.21 Therefore,
this can be considered a new ‘‘click reaction’’.22 The carban-
ions resulted from this nucleophilic addition can be trapped
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SCHEME 1 The mechanism of addi-
tion of phenol to perfluoropropyl
vinyl ether.24
(3,4,5)PPVEG1-COOCH3 and (3,4,5)2PPVEG2-COOCH3, the
resulting degradation products are nonpersistent perfluo-
propyl chains and the naturally occurring gallic acid.
mixture was poured into ice water. Following an acidic
workup and purification by column chromatography using
neutral alumina and ethylacetate/hexane eluent, a colorless
oil was obtained in 70–90% yield. No mono- or di-addition
products were recovered from the reaction mixture.
Synthesis of the higher generation PPVE dendrons follows a
convergent synthesis method previously developed in our
laboratory (Schemes 3 and 4).20a
The ester groups of (3,4,5)PPVEG1-COOCH3 and (3,4)
PPVEG1-COOCH3 were reduced to the corresponding benzyl
alcohols (3,4,5)PPVEG1-CH2OH and (3,4)PPVEG1-CH2OH with
LiAlH4 in THF at 0 ꢀC until complete consumption of the start-
ing material was observed by TLC (30 min). After purification
on a short plug of silica gel the dendritic benzyl alcohols were
obtained as colorless oils in 85–88% yield. The dendritic ben-
zylic alcohols were transformed into dendritic benzyl
Functionalization of both AB3 methyl 3,4,5-trihydroxyben-
zoate and AB2 methyl 3,4-dihydroxybenzoate was achieved
via the nucleophilic addition of the corresponding phenolate
to PPVE. This reaction is carried out in anhydrous DMF at
25 ꢀC with a catalytic amount of potassium tert-butoxide.
The reaction reaches 100% conversion in 18 h as deter-
mined by thin layer chromatography (TLC). The reaction
SCHEME 2 Synthesis of first generation dendritic benzyl chlorides (3,4,5)PPVEG1-CH2Cl and (3,4)PPVEG2-CH2Cl.
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SCHEME 3 Synthesis of second generation AB3 (3,4,5)2PPVEG2-COOCH3 and AB2 (3,4)2PPVEG2-COOCH3 dendrons.
chlorides (3,4,5)PPVEG1-CH2Cl and (3,4)PPVEG1-CH2Cl by
quantitative chlorination in methylene chloride at 23 C with
the PPVE dendrons was estimated by NMR, GPC, and
MALDI-TOF. NMR and GPC data are available in the support-
ing informations (Figs. S1–S17).
ꢀ
SOCl2 and a catalytic amount of DMF. Consumption of the
alcohol was monitored by TLC (30 min). Following an aque-
ous work up and purification by using a short plug of alu-
mina, a pale yellow oil was obtained in 80–95% yield. This
product was used directly in the alkylation step. Our labora-
tory reported a robust methodology for the quantitative alkyl-
ation of dendritic benzyl chlorides with polyhydroxy methyl
benzoates in DMF using K2CO3 as base that has been efficient
in the synthesis of diversity of benzyl ether dendrons.20 The
dendrons (3,4,5)PPVEG1-CH2Cl and (3,4)PPVEG1-CH2Cl were
alkylated onto methyl 3,4-dihydroxybenzoate, methyl 3,5-
dihydroxybenzoate, andꢀmethyl 3,4,5-trihydroxybenzoate in
DMF using K2CO3 at 65 C. The reactions were monitored by
TLC until complete consumption of the phenol starting mate-
rial was observed (4–5 h). This was also indicated by the
change in the color of the reaction from the dark brown to an
off white indicating complete consumption of the phenolate.
The second generation dendrons (3,4,5)2PPVEG2-COOCH3,
(3,4)2 PPVEG2-COOCH3, (3,4,5-3,5)PPVEG2-COOCH3, and
(3,4,5-34)PPVEG2-COOCH3 were obtained in 65–90% yield
after purification by column chromatography.
The PPVE peripheral groups can be identified by their diag-
nostic 13C NMR splitting patterns arising from the splitting
of the 13C signal by adjacent 19F that also has a nuclear spin
of 1/2. Three groups of signals were observed, a doublet of
triplets at ꢁ97 ppm, a triplet of quartets at ꢁ106 ppm and
a multiplet arising from overlapping of three signals appear-
ing as a triplet of doublets, a triple triplet and a quartet of
triplets at ꢁ116 ppm (Fig. 2). The PPVE group can be identi-
fied in the 1H NMR as a doublet again split by the adjacent
spin 1/2 19F at ꢁ6.09 ppm (Fig. 3). As with the previously
1
reported hydrogenated analogues H NMR analysis of Gener-
ation 2 dendrons showed a shift in the central benzene unit
aromatic proton signals defined as tier 1 to higher field with
increasing generation number.20a In the case of
(3,4,5)2PPVEG2-COOCH3 a shielding of the aromatic protons
in the central benzene unit is observed in comparison to the
first generation (3,4,5)PPVEG1COOCH3 dendron as a 0.76
ppm upfield shift (Fig. 3).20a
Calculation of the Partition Coefficients of Fluorinated
Dendrons by Gravimetric Method
Partition coefficients of fluorinated compounds represent the
equilibrium distribution of the fluorous compound between
It was found that the addition of FREON 113 (ꢁ3%) to the
chromatographic solvent facilitated purification by column
chromatography for second generation dendrons. Purity of
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 4 Synthesis of constitutional isomeric fluorous dendrons (3,4,5-3,5)PPVEG2-COOCH3 and (3,4,5-3,4)PPVEG2-COOCH3.
FIGURE 2 Diagnostic 13C NMR spectrum showing splitting in (3,4,5)PPVEG1-CH2OH substituted dendron. Expansion of 94–123
ppm region.
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ARTICLE
in the fluorous phase. Although first generation dendron has,
as expected, lower fluorophilicity, second generation
(3,4,5)2PPVEG2-COOCH3 showed complete affinity in the flu-
orous phase.
Dissasembly and the Lack of Self-Assembly of PPVE
Dendrons
The disassembly and the self-assembly properties of PPVE
dendrons were investigated by a combination of differential
scanning calorimetry (DSC), thermal optical polarized mi-
croscopy (OPM), and by X-ray diffraction (XRD) experiments.
Surprisingly, all dendrons are liquids when the parent poly-
phenol building blocks are crystalline. Therefore, at room
temperature no self-assembly was observed for any of the
fluorous dendrons reported. Only glass transitions at low
temperatures were observed for compounds (3,4,5)2PPVEG2-
COOCH3, (3,4,5-3,4)PPVEG2-COOCH3 and (3,4)2PPVEG2-
COOCH3 (Fig. 4) coupled with slow crystallization peaks on
ꢀ
ꢀ
heating at ꢃ11 C and ꢃ12 C, followed by immediate melt-
ing at ꢃ4 ꢀC and ꢃ6 ꢀC, respectively for (3,4,5-3,4)PPVEG2-
COOCH3 and (3,4)2PPVE-COOCH3 (Fig. 4). Attempts to char-
acterize the phase formed by (3,4,5-3,4)PPVEG2-COOCH3 and
(3,4)2PPVE-COOCH3 by X-ray diffraction experiments were
unsuccessful due to overlap of crystallization and melting
transitions. In contrast to the semifluorinated benzyl ether
dendrons reported previously,9a,b,e where self-assembly into
supramolecular columns and spheres at the first and second
generation was observed, the new fluorous dendrons
reported here mediate only the disassembly process. The
term disassembly refers to the dismantling of the original
crystalline, liquid crystalline or amorphous state prior to
self-assembly into a new supramolecular structure.11 The
lack of self-assembly may be due to the enhanced flexibility
of the semifluorinated ether derivative combined with the
ability of the acidic –H from the dendron structure to H-
bond intramolecularly with the ether oxygen. These results
are in line with previous experiments in which semifluori-
nated ethers were used as spacers in side-chain and main-
chain liquid crystalline polymers.25
FIGURE 3 500 MHz 1H NMR spectra (a) (3,4,5)PPVEG1-CH2OH3
and (b) (3,4,5)2PPVEG1-COOCH3 (CDCl3, TMS, 25 ꢀC).
two immiscible phases.1b It was expected that 3,4,5-trisubsti-
tuted fluorinated dendrons would create a high concentration
of fluorous component and an increased partition coefficient
into the fluorous solvent. The gravimetric method of partition
coefficient utilizes the miscibility of 1,3-perfluorodimethyl cyclo-
hexane and cyclohexane at elevated temperatures and demixing
on cooling to partition the fluorinated material between the
two phases. The gravimetric determination method was applied
to the fluorinated dendrons (3,4,5)PPVEG1-COOCH3, (3,4,5-
3,4)PPVEG2-COOCH3, (3,4,5)2PPVEG2-COOCH3 possessing 3, 6,
and 9 fluorinated groups on their periphery. This method has
the advantage that it is simple and economical with respect to
the quantity of fluorinated solvent required especially for large
molecular mass compounds. The partition coefficient (eq 1)
was calculated as the ratio between the masses of fluorinated
dendron in the two layers (fluorous versus organic).
EXPERIMENTAL
Materials
Aluminum oxide (activated, basic, and neutral Brockmann I,
standard grade, ꢁ150 mesh, 58 Å) (all from Fisher), silica
gel (60 Å, 32–63 lm) (Sorbent Technology), N,N-dimethylfor-
mamide (DMF, dry), ethyl acetate, hexane, diethyl ether (all
from Fisher, ACS reagents), 3,4-dihydroxybenzoic acid (98%),
3,5-dihydroxybenzoic acid (97%), and 3,4,5-trihydroxyben-
zoate, potassium tert-butoxide, LiAlH4 (95þ%) and perfluor-
ovinylether were used as received. Tetrahydrofuran (Fisher,
ACS reagent grade) was refluxed over sodium/benzophenone
and freshly distilled before use. Dichloromethane (Fisher,
ACS reagent grade) was refluxed over CaH2 and freshly dis-
tilled before use. All other chemicals were commercially
available and were used as received. Methyl 3,4-dihydroxy-
benzoate and methyl 3,5-dihydroxybenzoate were prepared
from the corresponding acids by esterification with MeOH in
the presence of a catalytic amount of H2SO4.
½cfꢂ
P ¼
;
(1)
½coꢂ
where cf is the concentration of dendron in the fluorous
phase and co is the concentration of dendron in the organic
phase (molꢃ1 dm3). When 100% recovery was obtained in
the fluorous phase, the partition coefficient P was denoted at
P > 100.1b The dendrons (3,4,5)PPVEG1-COOCH3, (3,4,5-
3,4)PPVEG2-COOCH3, and (3,4,5)2PPVEG2-COOCH3 showed
excellent fluorous phase affinities of P ¼ 18, 49, and >100,
respectively, with 95, 98, and 100% recovery of the dendron
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
experiments. The purity of the products was determined by
a combination of TLC on silica gel coated aluminum plates
(with F254 indicator; layer thickness, 200 lm; particle size,
2–25 lm; pore size 60 Å, SIGMA-Aldrich) and high pressure
liquid chromatography (HPLC) using THF as mobile phase at
1 mL/min, on a Shimadzu LC-10AT high pressure liquid
chroꢀmatograph equipped with a Perkin Elmer LC-100 oven
(40 C), containing two Perkin Elmer PL gel columns of 5 ꢄ
102 and 1 ꢄ 104 Å, a Shimadzu SPD-10A UV detector (k ¼
254 nm), a Shimadzu RID-10A RI-detector, and a PE Nelson
Analytical 900 Series integrator data station. Thermal transi-
tions were determined on a TA Instruments Q100 differen-
tial scanning calorimeter (DSC) ꢃe1quipped with a refrigerated
cooling system with 10 ꢀC min heating and cooling rates.
Indium was used as calibration standard. The transition tem-
peratures were reported as onset of the maxima and minima
of their endothermic and exothermic peaks. Matrix-assisted
laser desorption/ionization time-of-flight (MALDI-TOF) mass
spectrometry was performed on a PerSeptive Biosystems-
Voyager-DE (Framingham, MA) mass spectrometer equipped
with a nitrogen laser (337 lm) and operating in linear
mode. Internal calibration was performed using Angiotensin
II and Bombesin as standards. The analytical sample was
obtained by mixing the THF solution of the sample (3–15
mg/mL) and THF solution of the matrix [3,5-dihydroxyben-
zoic acid, 99% (Acros) or 1:1 mixture of 3,5-dihydroxyben-
zoic acid, 99% (Acros) and silver(I) trifluoroacetate, 98%
(Lancaster) dissolved in acetone, 10 mg/mL] in a 1/5 v/v ra-
tio. A total of 0.5 lL of sample-matrix solution was loaded
onto the MALDI plate and allowed to dry at rt before the
plate was inserted into the vacuum chamber of the MALDI
instrument. The laser steps and voltages applied were
adjusted depending on both the molecular weight and the
nature of each analyzed compound. Several runs from differ-
ent regions of the sample were collected and the results are
presented as accumulated data.
Synthesis of Fluorous Dendrons
(3,4,5)PPVEG1-COOCH3
In a dry two-neck round bottom flask containing methyl
3,4,5–trihydroxybenzoate (5.38 g, 0.03 mol) and potassium
tert-butoxide (0.49 g, 8.76 mmol) dissolved in dry DMF (60
mL) was added perfluorovinyl ether (23.32 g, 0.08 mol)
under N2. The reaction was stirred at 23 ꢀC for 18 h. The
reaction mixture was then poured into ice water containing
hydrochloric acid (2 mL) and extracted three times with 100
mL of ether. The organic fractions were combined, washed
with water, and dried over magnesium sulphate. The solvent
was removed under reduced pressure and the crude product
was purified on neutral alumina with hexane: ethyl acetate
mixture (7:1) yielding 22.3 g of a clear liquid; (78%). Purity
FIGURE 4 DSC traces (10 ꢀC/ min) for the PPVE functionalized
dendrons (3,4,5)2G2PPVE-COOCH3, (3,4,5-3,4)G2PPVE-COOCH3,
and (3,4)2G2PPVE-COOCH3. (a) first heating, (b) second heat-
ing, and (c) first cooling scans. The phase transitions and the
corresponding enthalpy changes are indicated.
1
(HPLC), 99þ%; H NMR (500 MHz, CDCl3/Freon113, TMS) d
¼ 7.99 (s, 2H, Ar), 6.06 (d, 2J ¼ 53.5, 3H, ACHF), 3.96 (s,
3H, ACH3). 13C NMR (126 MHz, CDCl3/HFB, TMS) d ¼
163.75, 143.39, 136.58, 130.20, 121.37, 120.42–104.22
(ACF2A), 98.50–96.56 (ACHFA), 52.78; MALDI-TOF MS calc.
for C23H8F30O8 þ Naþ: 1004.96; found m/z: 1005.20[M þ
Na]þ.
Techniques
1H NMR (500 MHz) and 13C (125 MHz) NMR spectra in solu-
tion were recorded on a Bruker DRX 500 instrument using
TMS as internal standard and Advance 500 fitted with
Bruker Cold (Cryogenic) probe for higher sensitivity 13C
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ARTICLE
(3,4,5)PPVEG1-CH2OH
1.60 g, 93%. Purity (HPLC), 99þ%; 1H NMR (500 MHz,
CDCl3/Freon113, TMS) d ¼ 7.73 (m, 2H, Ar), 7.45 (d, 2J ¼
9.1, 3H, Ar), 7.00 (m, 1H, Ar), 6.06 (m, 6H, ACHF), 5.18 (m,
4H, ACH2), 3.91 (s, 3H, CH3); 13C NMR (126 MHz, CDCl3/
HFB, TMS) d ¼ 165.41, 152.11, 147.90, 143.76, 143.67,
132.41, 132.32, 124.03, 123.75, 118.51, 118.31, 115.97,
114.89, 120.32-104.06 (ACF2A), 98.72-96.77 (ACHFA),
A solution of 3,4,5-PPVE-methyl ester (5.3 g, 5.4 mmol) in
dry THF (45 mL) was added dropwise under N2 atmosphere
to a stirred suspension of LiAlH4 (0.3 g, 8.14 mmol) in dry
ꢀ
THF (30 mL) cooled to 0 C in an ice bath. The mixture was
stirred at 20 ꢀC for 30 min and the reaction progress was
monitored by TLC (ethyl acetate/hexane 1/7 v/v). The
excess of hydride was quenched under cooling in an ice bath
with H2O (0.3 mL) followed by NaOH (0.3 mL) and H2O (1
mL). The organic layer was separated by filtration and the
crude compound was passed through a short column of neu-
tral alumina with hexane/ethyl acetate (1/7). Removal of the
solvent yielded a clear oil, 4.4 g (85%). Purity (HPLC),
99þ%; 1H NMR (500 MHz, CDCl3/Freon113, TMS) d ¼ 7.35
(s, 2H, Ar), 6.10 (d, 2J ¼ 44.7, 3H, ACHF), 4.69 (s, 2H,
ACH2A); 13C NMR (126 MHz, CDCl3/HFB, TMS) d ¼ 143.37,
142.12, 131.80, 117.74, 120.49–104.30 (ACF2), 98.66–96.72
69.31, 69.14, 52.24; MALDI-TOF MS calc. for C52H20F60O16
þ
Naþ: 2062.97; found m/z: 2062.67[M þ Na]þ.
(3,4,5-3,5)PPVEG2-COOCH3
Into a three-neck round bottom flask equipped with mag-
netic stirring, heating bath, condenser, and dropping funnel
with pressure-equalization arm was added a suspension of
finely ground dry K2CO3 (0.76 g, 0.5 mmol) in dry DMF (25
mL) that was subsequently degassed for 1 h, under stirring.
Methyl 3,5-dihydroxybenzoate (0.15 g, 0.91 mmol) was
added, while purging the system with N2. The 3,4,5-PPVE-
CH2-Cl (1.75 g, 1.83 mmol) was dissolved in DMF (15 mL)
and added to a dropping funnel and flushed with N2 for 30
min. After the complete dissolution of the phenol in DMF,
the chloride was added dropwise to the reaction mixture
(ACHFA), 63.27; MALDI-TOF MS calc. for C22H8F30O7
þ
Naþ: 976.97; found m/z: 976.30[M þ Na]þ.
(3,4,5)PPVEG1-CH2Cl
Into two-neck round bottom flask was added 3,4,5PPVE-
CH2OH (3.72 g, 3.88 mmol) dissolved in 40 mL of dry
CH2Cl2 and 1 drop of dry DMF. The flask was flushed with
N2 and cooled to 0 ꢀC in an ice bath. SOCl2 (0.35 mL, 4.8
mmol) dissolved in 16 mL of dry CH2Cl2 was added drop-
wise via a dropping funnel. The reaction was stirred at 23
ꢀC until completion followed by TLC (ethyl acetate/hexane
1/9 v/v) (ꢁ30 min). The solvent was removed and the crude
oil was redissolved in diethyl ether, washed twice with water
and brine and dried over MgSO4. The crude product was
passed through a short plug of alumina, concentrated and
ꢀ
and the temperature was increased to 60 C. The suspension
was stirred at 60 ꢀC under N2 and monitored by TLC. After
4 h the reaction mixture was poured into ice-cold water (15
mL), stirred for 5 min and then extracted five times with
ethyl acetate (100 mL). The combined organic extracts were
washed with water (100 mL), brine (100 mL), and dried on
anhydrous MgSO4. Evaporation of the solvent yielded the
crude product, which was purified by flash chromatography
(basic alumina, hexane/ethyl acetate, 8/1). The pure frac-
tions were collected, and after evaporation resulted in a vis-
cous oil, 1.2 g, 65%. Purity (HPLC), 99þ%; 1H NMR (500
MHz, CDCl3/Freon113, TMS) d ¼ 7.64 (s, 4H,Ar), 7.26 (s, 2H,
Ar, 6.91 (m, 1H, Ar), 6.20 (m, 6H, ACHF), 5.24 (s, 4H, ACH2),
3.99 (s, 3H, -CH3); 13C NMR (126 MHz, CDCl3/HFB, TMS) d
¼ 161.98, 159.23, 143.61, 132.57, 132.43, 132.38, 120.51–
104.33 (ACF2), 98.69–96.75 (ACHF), 118.70, 107.87, 106.40;
MALDI-TOF MS calc. for C52H20F60O16 þ Naþ: 2062.97; found
m/z: 2062.54 [M þ Na]þ.
used without further purification, 3.0
g (80%). Purity
1
(HPLC), 99þ%; H NMR (500 MHz, CDCl3/Freon113, TMS) d
¼ 7.40 (s, 2H, Ar), 6.06 (d, J ¼ 53.3, 3H, ACHF), 4.56 (s, 2H,
ACH2).
(3,4,5-3,4)PPVEG2-COOCH3
A suspension of finely ground dry K2CO3 (0.7 g, 0.5 mmol)
in dry DMF (25 mL) was added to a three-neck round bot-
tom flask equipped with magnetic stirring, heating bath, con-
denser, and dropping funnel with pressure-equalization arm
and degassed at 50 ꢀC for 1 h, under stirring. Methyl 3,4-
dihydroxybenzoate (0.14 g, 0.85 mmol) was added, while
purging the system with N2. The 3,4,5-PPVE-CH2-Cl (1.65 g,
1.7 mmol) was dissolved in DMF (15 mL) and added to a
dropping funnel and flushed with N2 for 30 min. Following
the complete dissolution of the phenol in DMF, the chloride
was added dropwise to the reaction mixture while the tem-
(3,4,5)2PPVEG2-COOCH3
A suspension of finely ground dry K2CO3 (1.5 g, 0.01 mol) in
dry DMF (50 mL) was added to a three-neck round bottom
flask equipped with magnetic stirring, heating bath, con-
denser, and dropping funnel with pressure-equalization arm
and degassed at 50 ꢀC for 1 h, under stirring. Methyl 3,4,5-
trihydroxybenzoate (0.22 g, 1.23 mmol) was added, while
purging the system with N2. The 3,4,5-PPVE-CH2-Cl (3.22 g,
1.23 mmol) was dissolved in DMF (20 mL) and added to a
dropping funnel and flushed with N2 for 30 min. Following
the complete dissolution of the phenol in DMF, the chloride
was added dropwise to the reaction mixture while the tem-
ꢀ
perature was increased to 60 C. The suspension was stirred
ꢀ
at 60 C under N2 and monitored by TLC. After 4 h the reac-
tion mixture was poured into cold water (1.5 L), stirred for
5 min, and then extracted five times with ethyl acetate (100
mL). The combined organic extracts were washed with water
(100 mL), followed by brine (100 mL), and dried over anhy-
drous MgSO4. Evaporation of the solvent yielded the crude
product, which was purified by flash chromatography (basic
alumina, hexane/ethyl acetate, 8/1). The pure fractions were
collected, and after evaporation resulted in a viscous oil,
ꢀ
perature was increased to 60 C. The suspension was stirred
ꢀ
at 60 C under N2 and monitored by TLC. After 4 h the reac-
tion mixture was poured into ice-cold water (20 mL), and
stirred for 5 min, and then extracted five times with ethyl
acetate (100 mL). The combined organic extracts were
washed with water (100 mL), brine (100 mL), and dried on
FLUOROUS PHASE DENDRONS MEDIATED DISASSEMBLY, WILSON ET AL.
2505

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
anhydrous MgSO4. Evaporation of the solvent yielded the
crude product, which was purified by flash chromatography
(basic alumina, hexane/ethyl acetate, 8/1). The pure frac-
tions were collected, and after evaporation resulted in a vis-
cous oil, 2.5 g, 70%. Purity (HPLC), 99þ%; 1H NMR (500
MHz, Freon113/CDCl3, TMS) d ¼ 7.43 (s, 6H, Ar), 7.23 (s,
2H, Ar), 6.0 (m, 9H, ACHF), 5.16 (s, 6H, ACH2A), 3.90 (s,
3H, ACH3); 13C NMR (126 MHz, CDCl3/HFB, TMS) d ¼
165.46, 151.72, 143.77, 143.40, 141.40, 132.44, 126.20,
120.50–104.33 (ACF2), 118.29, 108.71, 98.66-96.72 (ACHF),
69.29, 51.41; MALDI-TOF MS calc. for C52H20F60O16 þ Agþ:
3098.85; found m/z: 3099.20 [M þ Na]þ.
completion followed by TLC (ethyl acetate/hexane 1/8 v/v)
(ꢁ1 h). The solvent was removed and the crude oil was
redissolved in diethyl ether, washed twice with water and
brine and dried over MgSO4. The crude product was passed
quickly through a short plug of alumina concentrated and
used immediately in the next step, 2.5 g (95%).
(3,4)2PPVEG2-COOCH3
In a three-neck round bottom flask equipped with magnetic
stirring, heating bath, condenser, and dropping funnel with
pressure-equalization arm was added a suspension of finely
ground dry K2CO3 (1.57 g, 0.01 mol) ꢀin dry DMF (35 mL)
that was subsequently degassed at 50 C for 1 h, under stir-
ring. Methyl 3,4-dihydroxybenzoate (0.32 g, 1.89 mmol) was
added, while purging the system with N2. The 3,4-PPVE-CH2-
Cl (2.62 g, 3.79 mmol) was dissolved in DMF (35 mL) and
added to a dropping funnel while flushed with N2 for 30
min. After the complete dissolution of the phenol in DMF,
the chloride was added through the dropping funnel to the
reaction mixture while the temperature was increased to
60 ꢀC. The suspension was stirred at 60 ꢀC under N2 and
monitored by TLC. After 5 h the reaction mixture was poured
into ice-cold water (0.5 L), stirred for 5 min, and then
extracted five times with ethyl acetate (100 mL). The com-
bined organic extracts were washed with water (100 mL),
brine (100 mL), and dried on anhydrous MgSO4. Evaporation
of the solvent yielded the crude product, which was purified
by flash chromatography (basic alumina, hexane/ethyl ace-
tate, 8/1). The pure fractions were collected, and after the
evaporation of the solvent resulted in a viscous oil, 2.40 g,
(87%). Purity (HPLC), 99þ%; 1H NMR (500 MHz, CDCl3/
Freon113, TMS): d ¼ 7.70–7.62 (m, 6H, Ar), 7.53 (s, 1H, Ar),
(3,4)PPVEG1-COOCH3
Into a dried two-neck round bottom flask containing methyl
3,4 –dihydroxybenzoate (2 g, 0.01 mol) and potassium tert-
butoxide (0.2 g 1.0 mmol) dissolved in dry DMF (20 mL)
was added perfluorovinyl ether (6.33 g, 0.02 mol) under N2
ꢀ
and left stirring at 23 C for 18 h. The reaction mixture was
than poured into ice water containing hydrochloric acid (2
mL), and extracted three times with ether (100 mL), and
washed with water and dried over MgSO4. The solvent was
removed under reduced pressure and the crude product was
purified on neutral alumina with hexane: ethyl acetate mix-
ture (7:1) yielding a colorless liquid; 7.5 g (90%). Purity
1
(HPLC), 99þ%; H NMR (500 MHz, CDCl3/Freon113, TMS) d
¼ 8.03 (m, 2H, Ar), 7.47 (d, 2J ¼ 8.6, 1H, Ar), 6.09 (d, 2J ¼
53.6, 2H, ACHF), 3.81 (s, 3H, ACH3); 13C NMR (126 MHz,
CDCl3/HFB, TMS) d ¼ 164.67, 144.58, 140.37, 129.39,
128.54, 124.77, 122.45, 120.40–104.25 (ACF2), 98.67–96.69
(ACHF), 51.99; MALDI-TOF MS calc. for C18H8F20O6 þ Agþ:
722.99; found m/z: 723.45 [M þ Na]þ.
2
7.43 (m, 1H, Ar), 6.20 (d, J ¼ 53.8, 1H, ACHF), 5.37 (s, 2H,
ACH2-O), 5.31 (s, 2H, ACH2AO), 3.96 (s, 3H, ACH3); 13C
NMR (126 MHz, CDCl3/HFB) d 165.75, 152.31, 148.03,
140.98, 140.94, 140.39, 140.30, 125.36, 123.59, 121.74,
115.98, 114.49, 112.46, 120.52–104.36 (ACHF2), 98.65–
98,62 (ACHF), 69.41, 69.24, 50.83; MALDI-TOF MS calc. for
(3,4)PPVEG1-CH2OH
A solution of 3,4-PPVE-methyl ester (3.16 g, 4.5 mmol) in
dry THF (15 mL) was added dropwise under N2 atmosphere
to a stirred suspension ofꢀLiAlH4 (0.25 g, 6.76 mmol) in dry
THF (10 mL) ꢀcooled to 0 C in an ice bath. The mixture was
stirred at 20 C for 30 min when the reaction was shown to
be completed by TLC (ethyl acetate/hexane 1/7 v/v). The
excess of hydride was quenched under cooling on ice bath
with 0.3 mL H2O followed by 0.3 mL NaOH and 1 mL of
H2O. The organic layer was separated by filtration and the
crude compound was passed through a short column of neu-
tral alumina with hexane/ethyl acetate (1/7). Removal of the
solvent resulted in a clear oil, 2.66 g (88%). Purity (HPLC),
C
42H20F40O12 þ Naþ: 1499.53; found m/z: 1497.75 [M þ
Na]þ.
Gravimetric Determination of Partition Coefficients
A known quantity of fluorinated dendron was dissolved in
ꢀ
1:1 homogeneous mixture obtained at 60 C of 1,3-perfluoro-
dimethyl cyclohexane: cyclohexane. The solution was allowed
to cool slowly to room temperature when the two solvents
become immiscible. The solutions were allowed to sit in a
sealed flask at 25 ꢀC for 12 h prior to separation to allow
the solution to reach an equilibrium state. The partition coef-
ficient was obtained as the ratio between the mass deter-
mined gravimetrically of fluorinated dendron in the two
layers. The results are averaged over three experiments.
1
99þ%; H NMR (500 MHz, CDCl3/Freon113, TMS): d ¼ 7.40
(s, 1H, Ar), 7.35 (d, 2J ¼ 8.6, 1H, Ar), 7.30 (d, 2J ¼ 9.0, 0H,
1H, Ar), 6.06 (d, 2J ¼ 53.8, 1H, ACHF), 4.73 (s, ACH2);
MALDI-TOF MS calc. for C17H8F20O5 þ Agþ: 649.99; found
m/z: 650.12 [M þ Na]þ.
(3,4)PPVEG1-CH2Cl
P ¼ ½cꢂf=½cꢂo; P ¼ ½mðgÞꢂf=½mðgÞꢂo;
Into a two-neck round bottom flask was added 3,4 PPVE-
CH2OH (2.55 g, 3.8 mmol) dissolved in dry CH2Cl2 (45 mL)
and 1 drop of dry DMF. The flask was flushed with N2 and
cooled to 0 ꢀC in an ice bath. SOCl2 (0.35 mL, 4.74 mmol)
dissolved in dry CH2Cl2 (5 mL) was added dropwise via a
f ¼ fluorous phase; o ¼ organic phase:
Typical procedure: Into a 25-mL conical separating flask was
measured 1.09 g of dendron and added 20 mL of hot 1:1
mixture of PFCy:Cy. The flask was sealed and allowed to
ꢀ
dropping funnel. The reaction was left stirring at 23 C until
2506
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
ꢀ
Colloid Interface Sci 2003, 8, 251–258; (c) Krafft, M. P.; Riess, J.
G. J Polym Sci Part A: Polym Chem 2007, 145, 1185–1198; (d)
Fast, J. P.; Perkins, M. G.; Mark, G.; Pearce, R. A.; Mexozzi, S.
Anesthesiology 2008, 109, 651–656.
stand at 25 C for 12 h. The phases were separated and the
partition coefficient was determined gravimetrically by
determining the amount of dendron in each organic and flu-
orous phase
9 (a) Percec, V.; Schluter, D.; Kwon, Y. K.; Blackwell, J.; Moller,
M.; Slangen, P. J. Macromolecules 1995, 28, 8807–8818; (b)
Johansson, G.; Percec, V.; Ungar, G.; Zhou, J. P. Macromole-
cules 1996, 29, 646–660; (c) Johansson, G.; Percec, V.; Ungar,
G.; Smith, K. Chem Mater 1997, 9, 164–175; (d) Percec, V.;
Schluter, D.; Ungar G. Macromolecules 1997, 30, 645–648; (e)
Percec, V.; Johansson, G.; Ungar, G.; Zhou, J. J Am Chem Soc
1996, 41, 9855–9866; (f) Hudson, S. D.; Jung, H. T.; Percec, V.;
Cho, W.-D.; Johansson, G.; Ungar, G.; Balagurusamy, V. S. K.
Science 1997, 278, 449–452; (g) Percec, V.; Glodde, M.; Bera, T.
K.; Miura, Y.; Shiyanovskaya, I.; Singer, K. D.; Balagurusamy,
V. S. K.; Heiney, P. A.; Schnell. I.; Rapp, A.; Spiess, H.-W.
Dunan, H. Nature, 2002, 419, 384–387; (h) Percec, V.; Bera, T. K.
Tetrahedron 2002, 58, 4031–4040; (i) Percec, V.; Glodde, M.;
Johansson, G.; Balagurusamy, V. S. K.; Heiney, P. A. Angew
Chem Int Ed 2003, 42, 4338–4342; (j) Dukeson, D. R.; Ungar, G.;
Balgurusamy, V. S. K.; Percec, V.; Johansson, G. A.; Glodde,
M. J Am Chem Soc 2003, 125, 15974–15980; (k) Percec, V.;
Imam, M. R.; Bera, T. K.; Balagurusamy, V. S. K.; Peterca, M.;
Heiney, P. A. Angew Chem Int Ed 2005, 44, 4739–4745; (l) Per-
cec, V.; Glodde, M.; Peterca, M.; Rapp, A.; Schnell, I.; Spiess, H.
-W.; Bera, T. K.; Miura, Y.; Balagurusamy, V. S. K.; Aqad, E.;
Heiney, P. A. Chem—Eur J 2006, 12, 6298–6314; (m) Percec, V.;
Aqad, E.; Peterca, M.; Imam, M. R.; Glodde, M.; Bera, T. K.;
Miura, Y.; Balagurusamy, V. S. K.; Ewbank, P. C.; Wuthner, F.;
Heiney, P. A. Chem Eur J 2007, 13, 3330–3345; (n) Ungar, G.;
Noble, K.; Percec, V.; Johansson, G. J Mater Sci 2000, 35,
5241–5246; (o) Tomalia, D. A. Nat Mater 2003, 2, 711–712; (p)
Martin-Rapun, R.; Marcos, M.; Omenat, A.; Serrano, J. L.; De
Givenchy, E. T.; Guittard, F. Liq Cryst 2007, 34, 395–400; (q)
Yoon, D. K.; Lee, S. R.; Kim. Y. H.; Choi, S.-M.; Jung, H.-T. Adv
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CONCLUSIONS
A series of first and second generation AB3 and AB2 benzyl
ether dendrons containing short semifluorinated segments
on their periphery were synthesized and their fluorous
phase behavior was analyzed. The fluorous phase effect is
amplified at the same generation by the number of semi-
fluorinated groups and for the same number of semifluori-
nated groups on the dendron periphery by increasing the
generation number. These new fluorous dendrons mediate
disassembly of their parent building blocks but do not pro-
mote their self-assembly. The disassembly process via fluo-
rous phase is significant for a variety of technological
applications.
Financial support by the National Science Foundation (DMR-
0548559 and DMR-0520020) and the P. Roy Vagelos Chair at
the University of Pennsylvania are gratefully acknowledged.
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