Homeotropically aligned self-organizing dendronized polymer

Article abstract of DOI:10.1021/ma502522s

Self-organizing dendronized polymers embody the bottom-up paradigm for the self-assembly of nanostructured materials. The presence of a dendritic side chain on each repeat unit of the linear polymer backbone gives dendronized polymer chains a nanometer-sized diameter, and this dimension can be tailored though the generation number of the dendrons, the peripheral groups on the dendrons, or the branching number of the repeating unit in the dendrons. Self-assembling dendrons with semifluorinated peripheral groups and polymers dendronized via supramolecular interactions with these dendrons have been reported to homeotropically align on glass surfaces. However, most derivatives of these semifluorinated dendrons.

Full text of DOI:10.1021/ma502522s

Note
pubs.acs.org/Macromolecules
Homeotropically Aligned Self-Organizing Dendronized Polymer
Deborah A. Barkley,† Tadanori Koga,*,†,‡ and Jonathan G. Rudick*,†
†Department of Chemistry and ‡Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York
11794-3400, United States
S
* Supporting Information
the size of the dendron will prevent dendronized polymers
from self-organizing. We previously investigated the synthesis
and bulk structure of poly(oxanorbornenedicarboximide)s
dendronized with amphiphilic poly(alkyl ether) dendrons.11
We polymerized dendritic macromonomers up to the third
generation in a living manner and varied the length of the
peripheral hydrocarbon chains from 10 to 22 carbons. All of the
polymers are isotropic in the melt phase. Percec has reported
dendronized poly(oxanorbornene)s that exhibit liquid crystal-
line phases based on amphiphilic benzyl ether-type dendron-
s.5a,7a−c We speculated that the number of dendrons attached to
each repeat unit was a critical factor contributing to the marked
difference in the phase behavior of Percec’s dendronized
polymers with two attached dendrons per repeat unit and ours
with only one dendron per repeat unit. Dendronized polymer 1
retains the polymerizable group and linker from our previous
study11 and incorporates the first-generation dendron from
Percec’s seminal work7a on dendronized poly(oxanorbornene)-
s. Numerous polymers have been dendronized with the
dendron in 1, and in each case the dendronized polymers
exhibit liquid crystalline phases.2d,7a,12 The absence of a liquid
crystalline phase in 1 would confirm that dense packing of the
dendrons around the polymer backbone is critical to the
emergent property of self-organization in dendronized
polymers.
INTRODUCTION
■
Self-organizing dendronized polymers embody the bottom-up
paradigm for the self-assembly of nanostructured materials.1
The presence of a dendritic side chain on each repeat unit of
the linear polymer backbone gives dendronized polymer chains
a nanometer-sized diameter, and this dimension can be tailored
though the generation number of the dendrons,2 the peripheral
groups on the dendrons,3 or the branching number of the
repeating unit in the dendrons. An additional degree of size and
shape control is available by controlling the degree of
polymerization of the dendronized polymer.4 Short dendron-
ized polymers can adopt a spherical shape or self-assemble to
form larger cylindrical polymer objects, whereas long
dendronized polymers are cylindrically shaped.4a,5 Self-organ-
ization of these nanoscale molecular building blocks makes it
possible to create ordered arrays over large areas.6 Herein, we
describe the synthesis and phase behavior of a dendronized
polymer (Figure 1) that spontaneously orients perpendicular to
the surface when sandwiched between glass slides.
RESULTS AND DISCUSSION
■
Figure 1. Structure of the dendronized polymer 1.
The synthesis of dendronized polymer 1 is described in Figure
2. Anhydride 2 was obtained as a single diastereomer from the
Diels−Alder reaction of furan and maleic anhydride.13 In a two-
step, one-pot sequence, anhydride 2 was reacted with β-alanine
tert-butyl ester to afford 3 in 81% yield. Carboxylic acid 4 was
obtained from 3 by TFA-catalyzed hydrolysis of the ester. We
previously reported11 that other routes14 to prepare 4 were
unsatisfactory in our hands, so we were pleased to obtain 4 in
good overall yield. The first-generation dendritic alcohol 7 was
prepared according to an established procedure.4b Williamson
etherification of propyl gallate (5) with 1-bromododecane
provided 6 in good yield. The alcohol was obtained by
reduction of the ester with LiAlH4. Carbodiimide-mediated
condensation of alcohol 7 with carboxylic acid 4 proceeded
smoothly, and the dendritic macromonomer 8 was obtained in
good yield after purification by column chromatography. The
identity and purity of the macromonomer were confirmed on
Thermotropic self-organization of dendronized polymers in
bulk is a general phenomenon that has been demonstrated for a
large number of different polymer backbones, but only with a
narrow subset of dendrons. Percec and co-workers have
meticulously investigated polymers dendronized with self-
assembling benzyl ether-type dendrons.2d,3−5,7 Mezzenga,
Schluter, and co-workers have demonstrated that complexes
̈
of anionic surfactants with cationic dendronized polymers form
long-range liquid crystalline order in bulk.8 Many of these
dendrons exhibit liquid crystal mesomorphism in bulk based on
phase segregation of peripheral hydrocarbon groups from the
branched dendron.9 Polymerization of these dendritic macro-
monomers stabilizes the liquid crystal mesophase through a
molecular weight effect similar to that observed with side-chain
liquid crystalline polymers.5 Polymers dendronized with
amphiphilic polyamide dendrons10 or with amphiphilic poly-
(alkyl ether) dendrons11 do not exhibit mesomorphism in bulk
despite their apparent similarity to the examples noted above.
Dendronized polymer 1 was designed to investigate whether
a mismatch between the size of the main-chain repeat unit and
Received: December 15, 2014
Revised: April 2, 2015
Published: April 16, 2015
© 2015 American Chemical Society
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Note
Figure 2. Synthesis and polymerization of dendritic macromonomer 8.
the basis of 1H and 13C NMR spectroscopy, MALDI-TOF mass
spectrometry, gel permeation chromatography (GPC), and
elemental analysis.
Figure 3. (a) DSC Thermograms from first and second heating−
cooling cycles for dendronized polymer 1 (10 °C/min). Polarized
optical micrographs of polymer 1 (b) sandwiched between glass slides
and (c) sandwiched between silanized glass slides.
Macromonomer 8 was subjected to ring-opening metathesis
polymerization (ROMP) initiated with the first-generation
Grubbs catalyst ([M]0/[I]0 = 50). The polymerization reaction
was allowed to proceed until monomer was no longer observed
in GPC of the reaction mixture and was then quenched by
addition of ethyl vinyl ether. The polymerization reaction was
complete after 5 h, and 1 was obtained in high yield.
Dendronized polymer 1 was characterized by 1H NMR
spectroscopy to determine the ratio of cis:trans alkenes
(33:77) and by GPC to confirm that the sample has a narrow
distribution of molecular weights (Mn = 50 600, Mw/Mn =
1.06). The microstructure and molecular weight characteristics
of the sample are similar to the polymers dendronized with
poly(alkyl ether) dendrons previously reported by our group.11
Polymer 1 was characterized by observing the sample under
polarized optical microscopy while heating the sample in a hot
stage. When polymer 1 was sandwiched between a glass
microscope slide and a glass coverslip, we observed the sample
to undergo a melting transition from a birefringent solid to an
isotropic liquid at 112 °C. Upon cooling to room temperature,
the sample remained optically isotropic. Differential scanning
calorimetry (DSC) experiments confirmed several first-order
phase transitions up to the isotropization temperature (108 °C)
in the first heating cycle and revealed two first-order phase
transitions in subsequent cooling and heating cycles (Figure
3a). The DSC data are tabulated in Table 1, and these
suggested that polymer 1 forms a mesophase that had been
overlooked in our polarized optical microscopy experiments.
To determine whether the optically isotropic appearance of
polymer 1 was due to homeotropic alignment, we reexamined
the sample sandwiched between a silanized glass microscope
slide and coverslip. Indeed, the sample that was sandwiched
between hydrophilic glass slides appears optically isotropic
(Figure 3b) while the sample sandwiched between hydrophobic
glass slides appears birefringent (Figure 3c). Planar alignment
was also observed from a sample of polymer 1 prepared on a
glass slide with no coverslip (see Supporting Information).15 As
is typical for liquid crystalline dendronized polymers, the
birefringent texture did not contain any characteristic defects
upon which to assign the phase. The difference between the
appearances of polymer 1 in the two sample configurations
suggests that the sample is homeotropically aligned.
Table 1. Thermal Transition Temperatures (°C) and
Corresponding Enthalpy Changes (kcal/mol)
cycle
first heating
k 95 (0.27) k 108 (0.73) i
first cooling
k −14 (0.94) Colh 88 (0.12) i
k −8.36 (1.11) Colh 107 (0.10) i
k −14 (0.92) Colh 88 (0.12) i
second heating
second cooling
Wide- and small-angle X-ray scattering studies of 1 were
undertaken to confirm the presence of and assign the liquid
crystalline phase. Data were acquired after cooling the sample
from the isotropic melt phase to the liquid crystalline phase. A
diffuse peak (d = 2π/q ∼ 0.455 nm) corresponding to the
melted peripheral alkyl chains was observed in the wide-angle
scattering pattern. The small-angle scattering pattern contained
one intense scattering peak and two weaker peaks in the ratio
q1:q2:q3 = 1:√3:2 (Figure 4a) from which we conclude that the
dendronized polymer organizes in a hexagonal columnar lattice.
The lattice parameter for polymer 1 at 80 °C was calculated to
be 4.34 nm from eq 1.16 The lattice parameter dimension is
equivalent to the diameter of an individual column in the
hexagonal lattice, so the diameter of a single chain of
dendronized polymer 1 is 4.3 nm at this temperature (Figure
4b). The diameter of polymer 1 is similar to other polymers
dendronized with the same first-generation dendron2d,7a,12
including the poly(oxanorbornene) to which two of these
dendrons are attached to each repeat unit.7a We calculated the
end-to-end length for a molecular model of monomer 8 in an
all-trans conformation to be 2.8 nm, so the diameter of the
cylindrical polymer in the liquid crystalline phase is
approximately twice the length of the dendronized polymer
repeat unit. Tilting of the dendron relative to the column axis
and gauche conformations in the alkyl chains would account for
the difference between the calculated and observed column
diameters (i.e., 5.6 nm vs 4.3 nm). The degree of tilting (∼50°)
required to match the experimental column diameter has been
observed in X-ray diffraction experiments with oriented fiber
samples of dendronized polymers.2d,3b,17 Close agreement
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Note
composed of a single poly(oxanorbornene) chain encapsulated
by the self-assembling dendrons attached to each repeat unit.
Self-organization of polymer 1 is in marked contrast to the
phase behavior of polymers dendronized with amphiphilic
poly(alkyl ether) dendrons previously reported by us.11 The
diameter of polymer 1 in the liquid crystalline phase is similar
to the diameters of the polymers dendronized with poly(alkyl
ether) dendrons, so the poly(alkyl ether) dendrons are likely
large enough to fully encapsulate the polymer backbone. A
mismatch between the size of the polymer repeat unit and the
size of the dendrons is an unlikely reason for why the
amphiphilic poly(alkyl ether) dendrons did not endow the
dendronized polymer with liquid crystalline properties. A
plausible explanation for the difference between these
dendronized polymers is that shape incompatibility between
the branching groups and peripheral groups is critical to
achieving phase segregation of the core and peripheral groups.
The poly(alkyl ether) branching units are too similar to the
peripheral alkyl groups, whereas the aromatic rings in polymer
1 segregate from the peripheral alkyl chains.
In the homeotropically aligned sample of dendronized
polymer 1 the optically isotropic appearance of the sample
results from the cylindrical polymers spontaneously orienting
perpendicular to the glass surfaces. Self-assembling dendrons
with semifluorinated peripheral groups9b and polymers
dendronized via supramolecular interactions6 with these
dendrons have been reported to homeotropically align on
glass surfaces. However, most derivatives of these semi-
fluorinated dendrons21 and covalently dendronized polymers
with these semifluorinated dendrons2d,7d exhibit planar align-
ment rather than homeotropic alignment. There are no reports
of dendronized polymers that spontaneously align perpendic-
ular to the substrate surface. Dendronized polymer 1 is unique
from other dendronized polymers because it exhibits
homeotropic alignment.
Figure 4. (a) Plot of the small-angle X-ray scattering intensity profile
of polymer 1 at 80 °C. (b) Schematic diagram of hexagonally ordered
cylindrical dendronized polymers in the liquid crystalline phase. The
lattice parameter (a) calculated from the scattering data is equivalent
to the diameter (Dcol) of a dendronized polymer chain.
between the structure of the self-organized lattices of polymer 1
and the poly(oxanorbornene) with two dendrons attached to
each repeat unit7a suggests that intramolecular self-assembly of
the dendrons is able to overcome any mismatch between the
size of the dendron and the size of the main chain repeat unit.
⎛
⎝
⎞
⎠
4π
3 3
1
3
q2
2
q3
⎜
⎜
⎟
⎟
a =
+
+
q
(1)
1
A model for the hexagonal columnar lattice and core−shell
structure of an individual cylindrical dendronized polymer is
shown in Figure 4b. Such a model is intuitively reasonable
based on the composition and shape of the dendrons. The
peripheral alkyl chains constitute a majority of the repeat unit
(falkyl = 0.80) and should make up the continuous domain of
the mesophase. The tapered shape of the dendrons imposes a
packing preference for the narrow apex of the dendron to form
the core of the cylinder and the peripheral alkyl chains at the
exterior of the cylinder18 (i.e., an exo-recognition process19).
The covalent connection between the dendron and the
polymer backbone also restricts the arrangement of the
dendrons and reinforces the packing of taper-shaped dendrons
with the apex at the core of the cylinder.18 Direct visualization
through transmission electron microscopy experiments with
self-assembling dendrons9d and polymers dendronized with
self-assembling dendrons20 has confirmed that the aromatic
portion of the dendrons form the core of the cylinders and that
the alkyl chains make up the continuous phase of the hexagonal
lattice. It is worth noting that an alternative model in which
alkyl chains comprise the cylinders and the dendronized
polymers constitute the matrix of various columnar mesophases
has been reported for self-organizing supramolecular complexes
of dendronized polyelectrolytes with surfactants.8c Dendron-
ized polymer 1 and other polymers dendronized with self-
assembling dendrons are different from those supramolecular
complexes because the arrangement of the alkyl chains in self-
assembling benzyl ether-type dendrons is restricted by the
conformations available to the dendron end groups. We
conclude that the dendronized polymer 1 forms a hexagonally
ordered two-dimensional lattice of cylinders that are each
Figure 5. (a) Illustration of homeotropic alignment of dendronized
polymer 1 between hydrophilic surfaces. (b) Illustration of planar
alignment of dendronized polymer 1 between hydrophobic surfaces.
Homeotropic alignment of columnar mesophases on glass is
attributed to interactions between polar functional groups in
the mesogen with the polar surface.22 We speculate that the
polar functional groups of the poly(oxanorbornene-
dicarboximide) backbone provide a similar driving force for
homeotropic alignment. This is consistent with a model of the
dendronized polymer in which the peripheral alkyl groups of
the dendron make up the continuous domain of the
mesophase. Increasing the number of dendrons covalently
attached to the poly(oxanorbornene) backbone causes the self-
organizing dendronized polymers to adopt a planar orientation
parallel to the glass surface.5a,7a Self-organizing dendronized
poly(oxanorbornene)s that exhibit planar alignment have a
larger fraction of nonpolar functional groups than polymer 1,
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Note
with a G1956A single quadrupole mass spectrometer (accuracy 0.1
amu). The MALDI-TOF data were recorded on a Bruker Autoflex II
TOF/TOF workstation. MALDI-TOF samples (10 mg/mL) were
prepared in THF with 2,5-dihydroxybenzoic acid as the matrix and
silver trifluoroacetate as the ionizing species. Gel permeation
chromatography (GPC) was performed on a LC-20AD liquid
chromatography pump equipped with a DGU-20A5 degasser, CBM-
20A controller, RID-10A RI detector, and CTO-20A column oven (all
from Shimadzu) equipped with three American Polymer Standards
AM GPC gel columns of 100 Å (5 μm), 500 Å (5 μm), and 10 000 Å
(5 μm). Relative molecular weights and molecular weight distributions
were determined according to a calibration made from narrow
polydispersity polystyrene standards (American Polymer Standards).
Polarized optical microscopy was performed on an Olympus BX43
optical microscope with a FP82HT hot stage and FP900 controller
(both from Mettler Toledo). Melting point determinations were
performed on a Thomas-Hoover Unimelt capillary melting point
apparatus.
and the polar interactions between the backbone and the
surface contribute less to polymer−substrate interfacial energy.
CONCLUSION
■
Individual molecules and supramolecules that spontaneously
produce functional nanostructured arrays are critical compo-
nents to fulfill the vision of bottom-up self-assembly.23 Self-
organization into liquid crystalline lattices is an emergent
property that can be exploited for simple processing of
molecules into ordered nanostructures.23 Dendronized poly-
mers offer a combination of tunable structural features that can
be exploited to endow these materials with desirable functions,1
while only a narrow subset of dendronized polymers self-
organize into lattices. We have identified from our unsuccessful
attempt to observe self-organization in polymer dendronized
with amphiphilic poly(alkyl ether) dendrons that shape
incompatibility between the branching and peripheral groups
is critical for creating self-organizing dendronized polymers.
Furthermore, we have uncovered a unique example of a
dendronized polymer that exhibits homeotropic alignment.
exo,exo-5,6-(Dicarboxylic anhydride)-7-oxabicyclo[2.2.1]-
hept-2-ene (2).13 To a round-bottom flask, maleic anhydride
(3.8432 g, 39.192 mmol), Et2O (30 mL), and furan (4.4 mL, 61
mmol) were added. The mixture was refluxed for 16 h. The mixture
was cooled, and the precipitate was collected by filtration and then
rinsed three times with cold Et2O. Compound 2 was obtained as a
1
EXPERIMENTAL SECTION
colorless solid (4.3131 g, 66%). TLC (CH2Cl2): Rf = 0.51. H NMR
■
(400 MHz, CDCl3, δ): 6.59 (s, 2H), 5.47 (s, 2H), 3.20 (s, 2H). 13C
NMR (100 MHz, CDCl3, δ): 169.9, 137.0, 82.2, 48.7. Spectral data
agree with the literature.25
Materials. Anhydrous tetrahydrofuran (THF, 99.9%), anhydrous
dichloromethane (CH2Cl2, 98%), 4-(dimethylamino)pyridine
(DMAP, 99%), trifluoroacetic acid (TFA, 99%), furan (≥99%), maleic
anhydride (99%), β-alanine tert-butyl ester hydrochloride (98%), 2,5-
dihydroxybenzoic acid (98%), ethyl vinyl ether (99%), and bis-
(tricyclohexylphosphine)benzylidine ruthenium(IV) dichloride
(Grubbs catalyst, first generation, 97%) were used as received from
Aldrich. Dichloromethane (CH2Cl2, A.C.S. reagent), chloroform
(CHCl3, A.C.S. reagent), N,N-dimethylformamide (DMF, 99.9%),
and hydrogen chloride (HCl, A.C.S reagent) were used as received
from EMD. Ethyl acetate (EtOAc, A.C.S. reagent), diethyl ether
(Et2O, A.C.S. reagent), acetone (A.C.S. reagent), and sodium
hydroxide (NaOH, A.C.S. reagent) were used as received from Fisher.
For the polymerization reactions, anhydrous CH2Cl2 was degassed by
subjecting the solvent to three to four freeze−pump−thaw cycles.
Sodium chloride (NaCl, A.C.S. reagent), anhydrous magnesium sulfate
(MgSO4, 99.9%), and potassium carbonate (K2CO3, A.C.S. reagent)
were used as received from J.T. Baker. Triethylamine (NEt3, 99%), 1-
(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC·
HCl, 98%), lithium aluminum hydride powder (LiAlH4, 97%), n-
butyltrichlorosilane (97+%), and n-propyl gallate (5, 98%) were used
as received from AlfaAesar. Hexanes (hex, A.C.S. reagent), methanol
(MeOH, A.C.S. reagent), and tetrahydrofuran (THF, A.C.S. reagent)
were used as received from BDH. 1-Bromododecane (98.0%) was
used as received from TCI America. Chloroform-d with 0.03% v/v
tetramethylsilane (CDCl3, 99.8% D) and methanol-d4 (CD3OD,
99.9% D) were used as received from Cambridge Isotope Laboratories.
1-Hydroxybenzotriazole hydrate (HOBt) was used as received from
Creosalus. Alumina basic powder (50−200 μm) was used as received
from Dynamic Adsorbents. 4-(Dimethylamino)pyridinium tosylate
(DPTS) was prepared according to a literature procedure.24
N-[2-(tert-Butoxycarbonyl)ethyl]-7-oxabicyclo[2.2.1]hept-5-
ene-2,3-exo,exo-dicarboxylic Imide (3). A solution of 2 (4.2116 g,
25.351 mmol) and β-alanine tert-butyl ester hydrochloride (4.6437 g,
25.563 mmol) in dry THF (15 mL) was stirred for 7 h. To the
solution, NEt3 (3.6 mL), EDC·HCl (9.6940 g, 50.569 mmol), and
HOBt (7.7942 g, 50.893 mmol) were added, and the mixture was
stirred for 21 h. The solvent was removed in vacuo; the product was
purified by column chromatography (SiO2, hex to 1:1 hex/EtOAc)
and then recrystallized from CH2Cl2 to give a solid weighing 6.01 g
(81%). TLC (1:1 hex/EtOAc): Rf = 0.08. 1H NMR (400 MHz,
CDCl3, δ): 6.52 (s, 2H), 5.29 (s, 2H), 3.77 (t, J = 7.5 Hz, 2H), 2.87 (s,
2H), 2.07 (t, J = 7.5 Hz, 2H), 1.46 (s, 9H). 13C NMR (100 MHz,
CDCl3, δ): 175.9, 169.8, 136.6, 80.9, 53.4, 47.4, 34.7, 33.2, 28.0.
N-[2-(Hydroxycarbonyl)ethyl]-7-oxabicyclo[2.2.1]hept-5-
ene-2,3-exo,exo-dicarboxylic Imide (4). In a Schlenk tube, 3
(5.7142 g, 19.481 mmol) and cold TFA were combined. The solution
was stirred for 2 h at room temperature. The product was precipitated
into cold water, collected by filtration, rinsed with cold hexanes, and
1
dried to obtain 4 as a colorless solid (3.5239 g, 76%). H NMR (400
MHz, CD3OD, δ): 6.56 (s, 2H), 5.17 (s, 2H, CH(O)), 3.72 (t, J = 7.8
Hz, 2H), 2.93 (s, 2H), 2.56 (t, J = 7.8 Hz, 2H). 13C NMR (100 MHz,
CD3OD, δ): 176.8, 172.8, 136.2, 80.8, 48.2, 34.1, 31.2. mp 135−136
°C (lit.26 mp 132−134 °C). Spectral data agree with the literature.26
Propyl 3,4,5-Tris(n-dodecan-1-yloxy)benzoate (6).7a A sol-
ution of 5 (3.25 g, 15.3 mmol) in DMF (100 mL) was added dropwise
to a solution of K2CO3 (18.72 g, 138.2 mmol) and 1-bromodecane
(15.0 g, 60.2 mmol) in DMF (200 mL). The solution was stirred at 80
°C for 20 h. The reaction mixture was poured onto ice and filtered,
and the resulting solid was dissolved in Et2O and washed with water,
dilute HCl, water, and saturated NaCl(aq). The organic layer was
dried over MgSO4. The solids were removed by filtration, and the
volatiles were removed in vacuo. The resulting solid was purified by
column chromatography (SiO2, hex to 95:5 hex/EtOAc), giving 2 as a
Techniques. Thin layer chromatography (TLC) was performed on
60 Å silica gel plates (250 μm, Whatman) and observed using a UV
lamp (254 nm) or with KMnO4 stain. Flash column chromatography
was performed on a Teledyne Isco CombiFlash Rf with RediSep Rf
Normal Phase disposable silica cartridges. NMR spectra were recorded
on a Bruker NanoBay (1H, 400 MHz; 13C, 100 MHz) instrument or a
Bruker AVANCE III instrument equipped with a Prodigy cold probe
(1H, 500 MHz; 13C, 125 MHz). Peak multiplicities are denoted as
follows: s = singlet, d = doublet, t = triplet, q = quartet, pent = pentet,
hept = heptet, sept = septet, and m = multiplet. Samples were
dissolved in deuterated solvent, and chemical shifts (δ) are reported in
ppm relative to tetramethylsilane signal at δ 0 ppm. Direct injection,
low-resolution electrospray ionization mass spectrometry (ESI-MS)
data were acquired in positive polarity mode on an Agilent LC-MSD
1
colorless solid (9.18 g, 84%). TLC (95:5 hex/EtOAc): Rf = 0.34. H
NMR (400 MHz, CDCl3, δ): 7.25 (s, 2H), 4.25 (t, J = 6.7 Hz, 2H),
4.01 (t, J = 6.5 Hz, 6H), 1.81 (m, 6H), 1.76 (m, 2H), 1.47 (m, 6H),
1.28 (overlapped m, 54H), 1.04 (t, J = 7.5 Hz, 3H), 0.90 (t, J = 6.8 Hz,
9H). 13C NMR (100 MHz, CDCl3, δ): 166.5, 152.7, 142.3, 124.9,
107.9, 73.4, 69.1, 66.4, 31.8, 30.3, 29.7, 29.6, 29.5, 29.4, 29.3, 26.0,
22.6, 22.1, 14.1, 10.5. ESI−MS (m/z): [M + H]+ calcd for C46H84O5,
717.2; found, 717.6. GPC: Mn = 830, Mw/Mn = 1.06. The spectral data
agree with literature.7a
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3,4,5-Tris(n-dodecan-1-yloxy)benzyl Alcohol (7).4b A solution
of 1 (9.75 g, 13.6 mmol) in dry THF (50 mL) was added dropwise to
a suspension of LiAlH4 (0.3 g, 8.5 mmol) in dry THF (125 mL) at 0
°C. The mixture was stirred at room temperature for 30 min. The
reaction mixture was quenched with 0.3 mL of deionized water, 0.3
mL of 5% NaOH(aq), and 1 mL of deionized water and filtered to
remove solids. Volatiles were removed in vacuo. The resulting solid
was purified by column chromatography (SiO2, 9:1 hex./EtOAc) and
then recrystallized from acetone to give a colorless solid (5.95 g, 66%).
Wide- and Small-Angle X-ray Scattering. Wide- and small-
angle X-ray scattering were obtained at the X27C beamline of the
National Synchrotron Light Source, Brookhaven Naitonal Laboratory
(Upton, NY). Scattering was detected from an X-ray wavelength of
0.137 nm with a Mar CCD 2-D area detector at temperatures
controlled by an Instec temperature controller. Samples were
sandwiched between Kapton tape in a steel washer which was loaded
onto the hot stage. Scattering was measured for 10 s and was
background corrected. The sample-to-detector distance for the wide-
angle X-ray scattering measurements was 118 mm. The sample-to-
detector distance for the small-angle X-ray scattering measurements
was 801 mm. The data were analyzed in xPolar version 1.4.1.0 software
from Precision Works NY.
1
TLC (9:1 hex/EtOAc): Rf = 0.21. H NMR (400 MHz, CDCl3, δ):
6.58 (s, 2H), 4.61 (d, J = 6.0 Hz, 2H), 3.99 (m, 6H), 1.81 (m, 6H),
1.79 (t, J = 6.0 Hz, 1H), 1.47 (m, 6H), 1.29 (overlapped m, 48H), 0.90
(t, J = 6.8 Hz, 9H). 13C NMR (100 MHz, CDCl3, δ): 153.3, 137.6,
136.0, 105.4, 73.4, 69.1, 65.7, 31.9, 30.3, 29.8, 29.7, 29.4, 26.2, 26.1,
22.7, 14.1. ESI-MS (m/z): [M + H]+ calcd for C43H80O4, 661.1; found,
661.5. GPC: Mn = 890, Mw/Mn = 1.05. The spectral data agree with
the literature.4b
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional micrographs, comparison of core−shell models, and
copies of NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
N-[2-([3,4,5-Tris(n-dodecyloxy)benzyloxy]carbonyl)ethyl]-7-
oxabicyclo[2.2.1]hept-5-ene-2,3-exo,exo-dicarboxylic Imide
(8). A solution of 4 (0.3342 g, 1.409 mmol), 7 (0.5200 g, 1.513
mmol), and DTPS (0.0457 g, 0.1463 mmol) in anhydrous CH2Cl2 (5
mL) was cooled in an ice−water bath. To this solution, EDC·HCl
(0.6158 g, 3.212 mmol) was added. After 5 min the solution was
allowed to warm to room temperature, and stirring was continued for
22 h. The reaction solution was concentrated in vacuo. The resulting
solid was purified by flash column chromatography (SiO2, hex to 5:1
hex/EtOAc), which yielded 8 as a colorless solid (0.3994 g, 58%).
AUTHOR INFORMATION
Corresponding Authors
*E-mail jon.rudick@stonybrook.edu (J.G.R.).
*E-mail tadanori.koga@stonybrook.edu (T.K.).
■
Notes
1
TLC (5:1 hex/EtOAc): Rf = 0.23. H NMR (400 MHz, CDCl3, δ):
The authors declare no competing financial interest.
6.56 (s, 2H), 6.53 (s, 2H), 5.27 (s, 2H), 5.01 (s, 2H), 3.97 (overlapped
m, 6H), 3.83 (t, J = 5.8 Hz, 2H), 2.83 (s, 2H), 2.69 (t, J = 5.9 Hz, 2H),
1.80 (m, 6H), 1.50 (m, 6H) 1.29 (overlapped m, 48H), 0.90 (t, J = 6.7,
9H). 13C NMR (100 MHz, CDCl3, δ): 175.8, 170.5, 153.2, 136.6,
130.4, 107.2, 80.9, 69.2, 67.1, 47.4, 34.6, 32.0, 29.7, 29.4, 26.1, 22.7,
14.1. MALDI-TOF (m/z): [M + Na]+ calcd for C54H89NNaO8,
902.65; found, 902.97. Anal. Calcd for C54H89NO8: C, 73.68; H, 10.19;
N, 1.59. Found: C, 73.80; H, 10.02; N, 1.47. GPC: Mn = 1080, Mw/Mn
= 1.06.
ACKNOWLEDGMENTS
■
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund (53195-DNI7 to
J.G.R.) and the National Science Foundation (DMR-1255245
to J.G.R. and CMMI-1332499 to T.K.) for support of this
research. We thank Dr. Steven D. Hudson (NIST) for helpful
discussions. Differential scanning calorimetry experiments were
carried out at the Center for Functional Nanomaterials,
Brookhaven National Laboratory, which is supported by the
U.S. Department of Energy, Office of Basic Energy Sciences,
under Contract DE-AC02-98CH10886 (Proposal No. 31906 to
J.G.R.). Use of the National Synchrotron Light Source was
supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Contract DE-AC02-
98CH10886.
Poly(N-[2-([3,4,5-tris(n-dodecyloxy)benzyloxy]carbonyl)-
ethyl]-7-oxabicyclo[2.2.1]hept-5-ene-2,3-exo,exo-dicarboxylic
Imide) (1). A Schlenk tube was charged with a magnetic stir bar, first-
generation Grubbs’ catalyst (0.0019 g, 0.0023 mmol), and 8 (0.1008 g,
0.1145 mmol) and capped with a rubber septum. The tube was
evacuated and filled with N2 to degas. Degassed, anhydrous CH2Cl2
(2.4 mL) was added under a N2 atmosphere. The reaction mixture was
stirred at room temperature for 4.5 h. Ethyl vinyl ether (1 mL) was
added to the reaction vessel, and the reaction mixture was stirred for 5
min. The solution was precipitated into cold MeOH (60 mL), and the
solid was collected by filtration. The product was taken up in 5:1 hex/
EtOAc and passed through a column of basic Al2O3. The product was
collected by filtration after precipitation into cold methanol (93.6 mg,
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