Thermally activated, single component epoxy systems

Article abstract of DOI:10.1021/ma200673v

A single component epoxy system in which the resin and hardener components found in many two-component epoxies are combined onto the same molecule is described. The single molecule precursor to the epoxy resin contains both multiple epoxide moieties and a

Full text of DOI:10.1021/ma200673v

ARTICLE
pubs.acs.org/Macromolecules
Thermally Activated, Single Component Epoxy Systems
David A. Unruh,† Stefan J. Pastine,† Jessica C. Moreton,† and Jean M. J. Frꢀechet*,†,‡
†College of Chemistry, University of California, Berkeley, California 94720, United States
‡King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 Saudi Arabia
ABSTRACT: A single component epoxy system in which the
resin and hardener components found in many two-component
epoxies are combined onto the same molecule is described. The
single molecule precursor to the epoxy resin contains both
multiple epoxide moieties and a diamine held latent by ther-
mally degradable carbamate linkages. These bis-carbamate
“single molecule epoxies” have an essentially infinite shelf life
and access a significant range in curing temperatures related to the structure of the carbamate linkages used.
’ INTRODUCTION
environmental or health problems. An alternative strategy is to
use the blocking agent as the connecting linchpin between the
hardener and resin. With this design, the atom economy of the
curing reaction is increased and the production of toxic bypro-
ducts eliminated. Herein we describe such a strategy by using the
susceptibility of the carbamate functional group to decompose
under a thermal stimulus, and demonstrate its applicability toward
the synthesis and characterization of “single component epoxies”.
Epoxies are an important class of thermosetting polymers with
diverse applications including adhesives, structural materials,
paints, coatings, concrete, printed circuit boards, microelectronic
encapsulation, the aerospace industry, and other consumer
applications. In addition, recent interest has surfaced for using
epoxies as self-healing materials,1 chemical resists,2 and compo-
sites with nanotubes.3 The widespread utility of epoxy formula-
tions can be explained by a combination of their exceptional
processability prior to curing and their excellent postcure adhe-
sion, mechanical strength and chemical resistance after curing.
Additionally, the high-density three-dimensional network of
epoxies makes them extremely robust materials, making them
the thermoset of choice for many long-term applications.
The most common epoxy formulation consists of a multi-
valent epoxide (“resin”) and multivalent amine (“hardener”) to
form a polymeric network of essentially infinite molecular weight.
This reaction traditionally requires the two components to be
stored separately and mixed immediately prior to use. Attempts
to increase the amine latency traditionally take advantage of solu-
bility or phase differences between the epoxy and the amine.4ꢀ9
While these can still be packaged and marketed as single com-
ponent systems, they have limitations most particularly with
respect to shelf life. Additionally, amines can be made more latent
through chemical modification, for example as their ketimine
derivatives.10ꢀ12 This strategy is indeed effective in increasing
latency, but it requires rigorous processing to ensure that all com-
ponents are water free due to the well-known lability of ketimines.
In the design of latent amine epoxies, we wanted to take advan-
tage of the ability to block an amine with a thermally removable
group. While the use of blocking agents is a strategy that has seen
some recent and limited use in amine epoxies,13,14 it has historically
been muchmoreprevalentinpolyurethanechemistry.15ꢀ19 Although
blocking groups are effective in rendering a functional group
unreactive until an appropriate stimulus is applied, most blocking
agents once removed do not participate in the polyurethane cure.
Typically the blocking agents remain as unreactive byproduct
diluents, which can leach out over time and possibly present
’ EXPERIMENTAL SECTION
Materials. All reagents were obtained from commercial sources and
used without further purification unless otherwise noted. All solvents
used were reagent grade (99.9%) unless otherwise noted. Tetrahydrofuran,
toluene anddichloromethanewerepurifiedunderargonbypassingthrough
two columns of neutral alumina on a commercial apparatus. Water was
purified using a Barnstead NANOpure Diamond purification system.
Characterization. Elemental analysis was performed by the UC
Berkeley analytical facilities. 1H and 13C NMR measurements were
conducted on a Bruker AVB-400 nuclear magnetic resonance spectro-
meter. Differential scanning calorimetry (DSC) measurements were
performed with a TA Instruments Q200 differential scanning calori-
meter with standard aluminum pans. Monomers were used neat in all
DSC experiments, with the exception of entry 1 of Table 1, where
equimolar amounts of 1,6-diaminohexane and compound 10c were
mixed together prior to pan weighing. Ramped DSC scans were
performed at a rate of 10 °C/min, and reported cure enthalpy values
are an average of two measurements. Isothermal DSC analyses were
performed by rapidly ramping the sample to the desired cure tempera-
ture before the starting time. Thermogravimetric analyses (TGA) were
performed with a TA Instruments G5000 thermogravimetric analyzer,
and were performed at a rate of 10 °C/min. Infrared spectra were taken
with a Thermo Scientific Nicolet 6700 Fourier transform infrared spectro-
meter. Films were prepared by gently heating and stirring a mixture of
the epoxy precursor in an 11 wt % poly(methacrylonitrile) solution in
Received: March 25, 2011
Revised:
June 26, 2011
Published: July 29, 2011
r
2011 American Chemical Society
6318
dx.doi.org/10.1021/ma200673v Macromolecules 2011, 44, 6318–6325
|

Macromolecules
ARTICLE
Table 1. Deprotection and Curing Characteristics for Epoxy Monomers and Model Compoundsa
TGA deprotection
DSC exotherm
maximum of DSC
enthalpy of cure
Tg (∞)
(°C)
compound
onset (°C)
onset (°C)
exotherm peak (°C)
(kJ/equiv of epoxide)
10c + 1,6-diaminohexane
-
252
222
227
176
211
170
58
271
239
247
192
220
174
74
304
265
291
222
236
205
105
74
87
78
89
85
93
112
123
-
12a
12b
13a
13b
22
156
-
114
163
23
a TGA and DSC data were obtained at a heating rate of 10 °C/min.
nitromethane until homogeneous, and then spin-coating onto NaCl
disks at 1500 rpm for 60 s, drying at 90 °C for 15 min and placement in a
vacuum desiccator until use. Relative peak ratios calculated using FTIR
are an average of three films. Optical microscopy was performed with a
Fisher Scientific Micromaster inverted digital microscope on samples
with uniform (10 mm) thickness. Samples were cured at temperatures
for time limits that were determined by isothermal DSC measurements
with CO2 evolution permitted.
Preparation of 3,5-Diglycidoxyacetophenone, 10a. To a
solution of 3,5-dihydroxyacetophenone, 9a (1.01 g, 6.65 mmol), in
DMF (20 mL) was added epibromohydrin (2.20 mL, 26.6 mmol)
followed by cesium carbonate (4.77 g, 14.6 mmol). This reaction was
stirred overnight, after which 100 mL anhydrous ether was added to the
reaction mixture. The organic layer was washed with 0.1 M NaOH, water,
and brine and dried over anhydrous MgSO4. Solvent was evaporated to
yield 975 mg (53%) of a light yellow solid. 1H NMR (CDCl3, 400 MHz):
δ 2.57 (s, 3H), 2.77ꢀ2.78 (dd, 2H), 2.92ꢀ2.94 (t, 2H), 3.36ꢀ3.39 (m, 2H),
3.93ꢀ3.97 (dd, 2H), 4.29ꢀ4.33 (dd, 2H), 6.72ꢀ6.73 (t, 1H), 7.13ꢀ
7.14 (d, 2H); 13C NMR (CDCl3, 100 MHz): δ 26.7, 44.5, 49.9, 69.0,
69.1, 106.5, 107.2, 139.0, 159.6, 197.4. IR (CHCl3, cmꢀ1) 3051, 2970,
2923, 1684, 1595, 1444, 1363, 1298, 1177, 1156, 1063, 910. Anal. Calcd
for C14H16O5: C, 63.6; H, 6.1. Found: C, 63.48, H, 5.99.
Preparation of 4-Glycidoxyacetophenone, 10b. To a solu-
tion of 4-hydroxyacetophenone, 9b (3.67 g, 27.0 mmol), in dry DMF
(50 mL) were added cesium carbonate (13.17 g, 40.4 mmol) and
epibromohydrin (3.33 mL, 40.4 mmol). This reaction was stirred
overnight, after which 250 mL water was added. The organics were
extracted with ether, washed with 0.1 M NaOH and brine, dried over
anhydrous magnesium sulfate, and solvents were removed in vacuo to
yield 3.14 g (62%) of a clear oil. 1HNMR(CDCl3, 400MHz):δ2.56 (s, 3H),
2.77ꢀ2.79 (dd, 1H), 2.92ꢀ2.94 (dd, 1H), 3.36ꢀ3.39 (m, 1H), 3.97ꢀ
4.02 (dd, 1H), 4.30ꢀ4.34 (dd, 1H), 6.95ꢀ6.97 (d, 2H), 7.92ꢀ7.95 (d,
2H). 13C NMR (CDCl3, 100 MHz): δ 26.39, 44.59, 49.91, 68.88,
114.29, 130.62, 162.29, 196.74. IR (CHCl3, cmꢀ1): 3061, 3003, 2930,
1684, 1676, 1598, 1510, 1420, 1360, 1271, 1243, 1176, 1026, 959, 915.
Anal. Calcd for C11H12O3: C, 68.7; H, 6.3. Found: C, 68.43; H, 6.12.
Preparation of 2-(3,5-Diglycidoxyphenyl)propene, 10c. A
methyltriphenylphosphine bromide (1.66 g, 4.66 mmol) in dry THF
(25 mL) was cooled to ꢀ78 °C, and n-butyllithium (2.5 M in hexanes,
4.66 mmol) was added dropwise. After 10 min, a solution of acetophe-
none 10a (1.23 g, 4.66 mmol) in dry THF was added dropwise, and the
solution was allowed to stir at room temperature for 12 h. The mixture
was then filtered through a plug of Celite, concentrated in vacuo, and
purified via silica gel chromatography (1:10ꢀ1:4 ethyl acetate in
hexanes). Solvents were removed to yield 285 mg (23%) of a white
solid. 1H NMR (CDCl3, 400 MHz) δ 2.11 (s, 3H), 2.75ꢀ2.77 (dd, 2H),
2.90ꢀ2.92 (t, 2H), 3.34ꢀ3.36 (m, 2H), 3.93ꢀ3.97 (dd, 2H), 4.21ꢀ4.24
(dd, 2H), 5.08 (s, 1H), 5.34 (s, 1H), 6.44ꢀ6.45 (t, 1H), 6.65ꢀ6.66
(d, 2H); 13C NMR (CDCl3, 100 MHz) δ 22.1, 45.0, 50.4, 69.1, 100.9,
105.5, 113.3, 143.3, 143.9, 159.7. IR (CHCl3, cmꢀ1) 3084, 2926, 1770,
1593, 1435, 1346, 1253, 1176, 1131, 1063, 909. Anal. Calcd for C15H18O4:
C, 68.7, H, 6.9. Found: C, 68.75, H, 7.01.
Preparation of 1-(3,5-Diglycidoxyphenyl)ethanol, 11a. A
solution of acetophenone 10a (6.96 g, 26.3 mmol) in THF (50 mL) and
methanol (100 mL) was cooled to 0 °C, and then sodium borohydride
(1.99 g, 52.7 mmol) was added. The reaction was allowed to stir at room
temperature for 2 h, at which point starting material was completely
consumed by thin layer chromatography (1:1 ethyl acetate:hexanes) and
the reaction was quenched with aqueous 1 M NaHSO4. The mixture was
concentrated and extracted with diethyl ether. The organic portion was
washed with brine, dried over magnesium sulfate, and solvent was
1
removed to afford 6.28 g (89%) of a light yellow oil. H NMR (CDCl3,
400 MHz): δ 1.48ꢀ1.50 (d, 3H), 2.32 (br s, 1H), 2.78ꢀ2.80 (t, 2H),
2.93ꢀ2.95 (t, 2H), 3.36ꢀ3.39 (m, 2H), 3.74ꢀ3.83 (dd, 2H), 4.17ꢀ4.21
(dd, 2H), 4.83ꢀ4.88 (q, 1H), 6.44 (s, 1H), 6.60 (s, 2H). 13C NMR
(CDCl3, 100 MHz): δ 25.2, 44.7, 50.1, 68.8, 70.3, 100.6, 104.5, 148.8,
159.7. IR (neat, cmꢀ1): 3422, 2973, 2928, 2876, 1601, 1449, 1346, 1294,
1176, 1131, 1055, 909. Anal. Calcd for C14H18O5: C, 63.2; H, 6.8.
Found: C, 62.89; H, 7.07.
Preparation of 1-(4-Glycidoxyphenyl)ethanol, 11b. A solu-
tion of acetophenone 10b (3.10 g, 16.1 mmol) in methanol (50 mL) was
cooled to 0 °C, and then sodium borohydride (1.20 g, 32.3 mmol) was
added. The reaction was allowed to stir at room temperature for 2 h, at
which point starting material was completely consumed by thin layer
chromatography (1:1 ethyl acetate:hexanes) and the reaction was
quenched with aqueous 1 M NaHSO4. The mixture was concentrated
and extracted with diethyl ether. The organic portion was washed with
brine, dried over magnesium sulfate, and solvent was removed to afford
3.02 g (96%) of a clear oil. 1H NMR (CDCl3, 400 MHz): δ 1.51ꢀ1.52
(d, 3H), 1.76 (br s, 1H), 2.79ꢀ2.81 (dd, 1H), 2.93ꢀ2.96 (dd, 1H),
3.37ꢀ3.41 (m, 1H), 3.98ꢀ4.02 (dd, 1H), 4.24ꢀ4.28 (dd, 1H),
4.87ꢀ4.92 (q, 1H), 6.92ꢀ6.96 (d, 2H), 7.32ꢀ7.34 (d, 2H). 13C
NMR (CDCl3, 100 MHz): δ 25.1, 44.8, 50.2, 68.8, 70.0, 114.6, 126.7,
138.6, 157.9. IR (neat, cmꢀ1): 3404, 2971, 2925, 1610, 1513, 1453, 1241,
1178, 1088, 1035, 902. Anal. Calcd for C11H14O3: C, 68.0; H, 7.26.
Found: C, 67.75; H, 7.28.
Preparation of N,N0-Bis[[1-(3,5-diglycidoxyphenyl)ethoxy]-
carbonyl]hexane-1,6-diamine, 12a. The alcohol 11a (2.0 g,
7.68 mmol) and 1,6-diisocyanatohexane (968 mg, 5.76 mmol) were
added to 3 mL of toluene in a microwave reaction vial. The reaction
was heated to 120 °C for 5 h in microwave, at which time no starting
material was observed via thin layer chromatography (2:1 ethyl acetate:-
hexanes). The entire reaction contents were purified with silica gel
chromatography (1:1 to 3:1 ethyl acetate:hexanes). Solvent was removed in
vacuo to yield 954 mg (35%) of a clear oil. 1H NMR (CDCl3, 400 MHz):
δ 1.28 (br s, 4H), 1.45ꢀ1.47 (d, 10 H), 2.72ꢀ2.74 (dd, 4H), 2.87ꢀ
2.89 (t, 3.85), 3.11ꢀ3.12 (br d, 4H), 3.31ꢀ3.33 (dd, 4H), 3.87ꢀ3.91
(dd, 4H), 4.18ꢀ4.20 (d, 4H), 4.83 (br s, 2H), 5.64ꢀ5.68 (q, 2H),
6319
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
6.39 (s, 2H), 6.50ꢀ6.51 (d, 4H). 13C NMR (CDCl3, 100 MHz): δ
22.7, 26.3, 30.0, 40.9, 44.8, 50.2, 69.0, 72.4, 100.7, 105.3, 145.2, 156.0,
159.8. IR (neat, cmꢀ1): 3341, 2979, 2931, 2861, 1707, 1599, 1529,
1450, 1355, 1262, 1178, 1050, 910. Anal. Calcd for C36H48N2O12: C,
61.7; H, 6.9; N, 4.0. Found: 61.84; H, 6.79; N, 4.10.
DMF (50 mL) was added potassium carbonate (12.3 g, 89.1 mmol) and
allyl bromide (4.66 mL, 74.3 mmol). This reaction was stirred overnight,
after which 250 mL diethyl ether was added, and the organic layer was
washed with 0.1 M NaOH, brine, and dried over magnesium sulfate.
Solvent was removed in vacuo and recrystallized in ethyl acetate and hexanes
1
Preparation of N,N0-Bis[[1-(4-glycidoxyphenyl)ethoxy]-
carbonyl]hexane-1,6-diamine, 12b. The alcohol 11b (1 g, 5.15
mmol) and 1,6-diisocyanatohexane (519 mg, 3.09 mmol) were added to
3 mL toluene. This mixture was heated to 90 °C and stirred overnight.
The reaction was purified via silica gel chromatography (1:1 ethyl acetate:-
hexane) to yield 871 mg (61%) of a white solid. 1H NMR (CDCl3, 400
MHz): δ 1.28 (br s, 4H), 1.45 (br s, 4H), 1.49ꢀ1.51 (d, 6H), 2.74ꢀ2.75
(dd, 2H), 2.89ꢀ2.91 (t, 2H), 3.09ꢀ3.15 (m, 4H), 3.32ꢀ3.36 (m, 2H),
3.92ꢀ3.95 (dd, 2H), 4.19ꢀ4.22 (dd, 2H), 4.69 (s, 2H), 5.71ꢀ5.76
(q, 2H), 6.87ꢀ6.89 (d, 4H), 7.25ꢀ7.29 (d, 4H). 13C NMR (CDCl3,
100 MHz): δ 22.3, 26.4, 30.0, 40.9, 44.9, 50.3, 68.9, 72.3, 114.7, 127.7,
135.1, 156.2, 158.2. IR (CHCl3, cmꢀ1): 3340, 2931, 1701, 1612, 1514,
1242, 1179, 1063, 1034, 912. Anal. Calcd for C30H40N2O8: C, 64.7; H,
7.2; N, 5.0. Found: C, 64.74; H, 7.24; N, 5.28.
to yield 6.7 g (91%) of a white solid. H NMR (CDCl3, 400 MHz):
δ 3.90 (s, 3H), 4.54ꢀ4.55 (d, 4H), 5.28ꢀ5.31 (d, 2H), 5.40ꢀ5.44
(d, 2H), 6.01ꢀ6.05 (m, 2H), 6.69 (s, 1H), 7.20 (s, 2H). 13C NMR
(CDCl3, 100 MHz): δ 52.26, 69.04, 107.12, 108.12, 117.94, 131.94,
132.81, 159.57, 166.79. IR (CHCl3, cmꢀ1): 2973, 1723, 1597, 1446,
1323, 1301, 1235, 1168, 1053, 930. Anal. Calcd for C14H16O4: C, 67.7;
H, 6.5. Found: C, 67.74; H, 6.53.
Preparation of 1-(3,5-Diallyloxyphenyl)-1-methylethanol,
17. To a solution of the preceding methyl ester 16 (6.4 g, 25.9 mmol) in
dry THF (100 mL) was added a 3 M solution of methylmagnesium
bromide in ether (19 mL, 57 mmol). This reaction was stirred overnight
and quenched with saturated aqueous ammonium chloride. The mixture
was concentrated and extracted with diethyl ether. The organic layers
were combined, washed with brine, and dried over magnesium sulfate.
Solvent was removed in vacuo, and was purified via silica gel chroma-
tography, eluting with 1:3 ethyl acetate:hexanes to yield 4.7 g (73%) of a
Preparation of N,N0-Bis[[1-(3,5-diglycidoxyphenyl)ethoxy]-
carbonyl]toluene-2,4-diamine, 13a. The alcohol 11a (1.05 g,
3.94 mmol) and 2,4-tolylenediisocyanate (343 mg, 1.97 mmol) were
added to dry toluene (3 mL) and heated to 90 °C overnight. The entire
contents were purified via silica gel chromatography (1:1 to 3:1 ethyl
acetate:hexanes). Solvent was removed in vacuo to yield 510 mg (36%)
1
clear oil. H NMR (CDCl3, 400 MHz): δ 1.53 (s, 6H), 2.18 (s, 1H),
4.49ꢀ4.51 (dt, 4H), 5.25ꢀ5.29 (dq, 2H), 5.38ꢀ5.43 (dq, 2H), 5.99ꢀ
6.09 (m, 2H), 6.37ꢀ6.38 (t, 1H), 6.65ꢀ6.66 (d, 2H). 13C NMR (CDCl3,
100 MHz): δ 31.7, 68.9, 72.6, 99.8, 104.0, 117.8, 133.3, 152.0, 159.6. IR
(neat, cmꢀ1) 3415, 2977, 1595, 1438, 1423, 1362, 1293, 1166, 1053, 927.
Anal. Calcd for C15H20O3: C, 72.6; H, 8.1. Found: C, 72.22; H, 8.10.
Preparation of N,N0-Bis[[1-(3,5-diallyloxyphenyl)-1-
methylethoxy]carbonyl]hexane-1,6-diamine, 18. The alcohol
17 (9.67 g, 39.0 mmol) was added to 30 mL of dry tetrahydrofuran. A
solution of 1.6 M methyllithium in ether (2.44 mL, 3.90 mmol) was
added dropwise, and the resulting solution was heated to reflux for 1 h.
The reaction was cooled to room temperature, and a solution of 1,
6-diisocyanatohexane (3.91 g, 23.3 mmol) in 20 mL tetrahydrofuran was
added dropwise via addition funnel. The reaction was heated back to reflux
overnight, after which it was cooled to room temperature and concen-
trated. The residue was dissolved in ethyl acetate, washed with water, dried,
and purified via silica gel chromatography (1:2 ethyl acetate:hexane) to
1
of a colorless solid. H NMR (CDCl3, 400 MHz): δ 1.52ꢀ1.56 (dd,
6H), 2.18 (s, 3H), 2.74ꢀ2.75 (m, 4H), 2.89ꢀ2.91 (m, 4H), 3.32ꢀ3.36
(m, 4H), 3.89ꢀ3.93 (m, 4H), 4.19ꢀ4.23 (m, 4H), 5.74ꢀ5.80 (m, 2H),
6.40ꢀ6.43 (m, 2H), 6.51 (br s, 1H), 6.55ꢀ6.56 (m, 4H), 6.81 (br s, 1H),
7.03ꢀ7.05 (d, 1H), 7.18ꢀ7.20 (d, 1H), 7.77 (s, 1H). 13C NMR (CDCl3,
100 MHz): δ 17.1, 22.4, 22.6, 25.3, 44.8, 50.2, 68.9, 70.4, 101.0, 104.6,
105.2, 105.3, 105.4, 105.5, 130.9, 159.8. IR (CHCl3, cmꢀ1): 2917, 1721,
1598, 1530, 1446, 1224, 1177, 1046, 904. Anal. Calcd for C37H42N2O12:
C, 62.9; H, 6.0; N, 4.0. Found: C, 62.62; H, 6.12; N, 3.60.
Preparation of N,N0-Bis[[1-(4-glycidoxyphenyl)ethoxy]-
carbonyl]toluene-2,4-diamine, 13b. The alcohol 11b (1 g, 5.15
mmol) and tolylene 2,4-diisocyanate (538 mg, 3.09 mmol) were added
to 3 mL toluene. This mixture was heated to 90 °C and stirred overnight.
The reaction was purified via silica gel chromatography (1:1 ethyl acetate:
hexane) to yield 341 mg (24%) of a white solid. 1H NMR (CDCl3, 400
MHz): δ 1.55ꢀ1.60 (m, 6H), 2.16 (s, 3H), 2.74ꢀ2.76 (dd, 2H),
2.89ꢀ2.92 (m, 2H), 3.34ꢀ3.36 (m, 2H), 3.94ꢀ3.98 (dd, 2H), 4.19ꢀ
4.24 (m, 2H), 5.82ꢀ5.88 (d, 2H), 6.39 (s, 1H), 6.58 (s, 1H), 6.88ꢀ6.92
(m, 4H), 7.02ꢀ7.04 (d, 1H), 7.18 (br s, 1H), 7.30ꢀ7.34 (t, 4H), 7.77 (s, 1H).
13C NMR (CDCl3, 100 MHz): δ 17.2, 22.1, 22.3, 44.9, 50.3, 69.0, 73.3,
109.4, 114.9, 127.8, 127.9, 130.9, 134.6, 136.9, 153.2, 158.5, 164.2. IR
(CHCl3, cmꢀ1): 3320, 2980, 2922, 1718, 1611, 1514, 1227, 1179, 1063,
1035, 913. Anal. Calcd for C31H34N2O8: C, 66.2; H, 6.1; N, 5.0. Found:
C, 65.82; H, 5.96; N, 5.21.
1
yield 3.86 g (30%) of a clear oil that solidified over time. H NMR
(CDCl3, 400 MHz): δ 1.28 (br s, 4H), 1.43 (br s, 4H), 1.71 (s, 12H),
3.05ꢀ3.07 (d, 4H), 4.48ꢀ4.50 (dt, 8H), 4.76ꢀ4.77 (d, 2H), 5.25ꢀ5.29
(dq, 4H), 5.37ꢀ5.43 (dq, 4H), 5.99ꢀ6.09 (m, 4H), 6.36ꢀ6.37 (t, 2H),
6.53ꢀ6.54 (d, 4H). 13C NMR (CDCl3, 100 MHz): δ 26.3, 29.1, 30.0,
40.4, 68.9, 80.4, 99.6, 104.0, 117.8, 133.4, 149.4, 149.4, 155.2, 159.6. IR
(CHCl3, cmꢀ1): 3348, 2980, 2932, 2860, 1701, 1596, 1521, 1448, 1363,
1260, 1149, 1053, 928. Anal. Calcd for C38H52N2O8: C, 68.6; H, 7.9; N,
4.2. Found: C, 68.49, H, 7.96; N, 4.54.
Preparation of N,N0-Bis[[1-(3,5-diallyloxyphenyl)-1-
methylethoxy]carbonyl]toluene-2,4-diamine, 19. Methyllithium
(756 uL, 1.6 M) was added to a solution of the alcohol 17 (3 g, 12.1 mmol)
in dry tetrahydrofuran (20 mL). This was heated to reflux for 1 h, then
allowed to cool to room temperature before cooling on an ice bath. A solution
of tolylene 2,4-diisocyanate (1.26 g, 7.26 mmol) in dry tetrahydrofuran
(10 mL) was added dropwise to the reaction mixture. After addition was
complete, the reaction was heated to reflux overnight. The mixture was
concentrated, and the resulting residue was extracted with ethyl acetate,
washed, dried, evaporated, and purified via silica gel chromatography (1:2 to
1:1 ethyl acetate:hexane) to yield 1.523 (38%) of a clear oil that had traces
of starting material. 1H NMR (CDCl3, 400 MHz): δ 1.74 (s, 6H), 1.78
(s, 6H), 2.18 (s, 3H), 4.47ꢀ4.54 (m, 8H), 5.23ꢀ5.29 (m, 4H), 5.36ꢀ5.43
(m, 4H), 6.00ꢀ6.05 (m, 4H), 6.36ꢀ6.37 (t, 1H), 6.38 (t, 1H), 6.44 (br s,
1H), 6.54ꢀ6.57 (dd, 4H), 6.66ꢀ6.67 (d, 2H), 7.00ꢀ7.02 (d, 1H), 7.59 (br s,
1H). 13C NMR (CDCl3, 100 MHz): δ 17.1, 28.9, 31.7, 53.5, 68.9, 72.7,
81.7, 99.7, 99.8, 103.9, 104.0, 117.7, 117.8, 130.7, 133.3, 136.3, 136.9, 148.6,
Preparation of N,N0-Bis[[1-(4-methoxyphenyl)ethoxy]-
carbonyl]hexane-1,6-diamine, 14. To a solution of 1-(4-Methox-
yphenyl)ethanol (1.04 g, 6.82 mmol) in dry toluene (3 mL) was added
1,6-diisocyanatohexane (690 mg, 4.11 mmol). This reaction was heated
at 90 °C for 10 h, and then purified via silica gel chromatography (1:2 to
1
2:1 ethyl acetate:hexanes) to yield 986 mg (61%) of a white solid. H
NMR (CDCl3, 400 MHz): δ 1.26ꢀ1.29 (m, 4H), 1.42ꢀ1.46 (m, 4H),
1.50ꢀ1.52 (d, 6H), 3.10ꢀ3.15 (m, 4H), 3.79 (s, 6H), 4.70 (br s, 2H),
5.74ꢀ5.75 (q, 2H), 6.86ꢀ6.88 (d, 4H), 7.27ꢀ7.29 (d, 4H). 13C NMR
(CDCl3, 100 MHz): δ 22.3, 26.4, 30.0, 55.4, 72.4, 113.9, 127.6, 134.5,
156.2, 159.3. IR (CHCl3, cmꢀ1): 3552, 2933, 1700, 1614, 1516, 1247,
1178, 1065, 1035. Anal. Calcd for C26H36O6: C, 66.1; H, 7.7; N, 5.9.
Found: C, 66.36; H, 7.74; N, 6.07.
Preparation of Methyl 3,5-Diallyloxybenzoate, 16. To a
solution of methyl 3,5-dihydroxybenzoate, 15 (5 g, 29.7 mmol), in dry
6320
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
Scheme 1. Overview of Thermal Deprotection and Curing of Model Compound 1 and Epoxy Precursor 5 To Give Oligomer 4 and
Cross-Linked Epoxy 8
Scheme 2. Synthesis of Secondary Benzylic Epoxy Precursors 12 and 13 and Non-Curing Control Precursor 14a
a Reagents and conditions: (i) epibromohydrin, Cs2CO3, DMF; (ii) NaBH4, MeOH/THF; (iii) CH3PH3PBr, n-BuLi, THF; (iv) 1,6-diisocyanatohex-
ane, toluene; (v) 2,4-tolylene diisocyanate, toluene.
148.7, 151.9, 159.6, 159.7. IR (CHCl3, cmꢀ1): 2982, 1712, 1597, 1528,
1449, 1166, 1142, 1054, 927. Anal. Calcd for C38H52N2O8: C, 69.8; H, 6.9;
N, 4.2. Found: C, 70.3, H, 7.5; N, 2.9.
with CH2Cl2, ethyl acetate, and hexanes to give 978 mg (95%) of a light tan
solid. 1H NMR (DMSO-d6, 400 MHz): δ 1.19 (br s, 4H), 1.33 (br s, 4H),
1.57 (s, 12 H), 2.84ꢀ2.85 (q, 4H), 6.05ꢀ6.06 (t, 2H), 6.17 (d, 4H),
6.95ꢀ6.98 (t, 2H), 9.08 (s, 4H). 13C NMR (DMSO-d6, 100 MHz): δ 14.6,
26.5, 29.6, 29.9, 79.3, 101.1, 103.1, 149.8, 155.3, 158.4. IR (KBr, cmꢀ1): 3343,
2976, 2928, 1684, 1597, 1516, 1441, 1332, 1266, 1139, 996, 959. Anal. Calcd
for C26H36N2O8: C, 610.9; H, 7.2; N, 5.6. Found: C, 61.87; H, 7.29; N, 5.55.
Preparation of N,N -Bis[[1-(3,5-hydroxyphenyl)-1-methylethoxy]-
carbonyl]toluene-2,4-diamine, 21. The bis-carbamate 19 (1.5 g,
2.2 mmol) was added to tetrahydrofuran (25 mL) and methanol (20 mL).
Tetrakis(triphenylphosphino)palladium (2.07 g, 0.179 mmol) was added,
and the solution was cooled to 0 °C before adding sodium borohydride
(500 mg, 13.2 mmol). This reaction was stirred for 2 h, when it was
quenched with saturated aqueous ammonium chloride, concentrated,
Preparation of N,N0-Bis[[1-(3,5-dihydroxyphenyl)-1-
methylethoxy]carbonyl]hexane-1,6-diamine, 20. The bis-
dicarbamate 18 (1.36 g, 2.04 mmol) was dissolved in methanol (12 mL)
and tetrahydrofuran (22 mL). Tetrakis(triphenylphosphino)palladium
(231 mg, 0.20 mmol) was added, and the solution was cooled in an ice
bath before adding sodium borohydride (771 mg, 20.4 mmol). This was
stirred for 4 h before thin layer chromatography (2:1 ethyl acetate:hexane)
showed reaction completion. The reaction was quenched with sodium
bisulfate and concentrated. The residue was extracted with ethyl acetate, and
the combined extracts were washed, dried, and evaporated, purified via silica
gel chromatography (1:1 to 5:1 ethyl acetate:hexane), and finally triturated
6321
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
Scheme 3. Synthesis of Tertiary Benzylic Epoxy Precursors 22 and 23a
a Reagents and conditions: (i) allyl bromide, K2CO3, DMF; (ii) methylmagnesium bromide, THF; (iii) 1,6-diisocyanatohexane, cat. methyllithium,
THF; (iv) 2,4-tolylene diisocyanate, cat. methyllithium, THF; (v) Pd(PPH3)4, NaBH4, MeOH/THF; (vi) epibromohydrin, Cs2CO3, DMF.
the reaction was stirred overnight. The reaction was diluted with water
and extracted with diethyl ether. The combined extracts were washed
with 0.1 M aqueous NaOH, dried, evaporated, and purified via silica gel
chromatography, eluting with 2:1 CH2Cl2:ethyl acetate, to yield 600 mg
(45%) of a light yellow oil. 1H NMR (CDCl3, 400 MHz): δ 1.27 (br s,
4H), 1.43 (br s, 4H), 1.70 (s, 12H), 2.72ꢀ2.74 (dd, 4H), 2.88ꢀ2.90
(t, 4H), 3.05ꢀ3.06 (br d, 4H), 3.31ꢀ3.34 (m, 4H), 3.89ꢀ3.93 (dd, 4H),
4.16ꢀ4.19 (dd, 4H), 4.80 (br s, 2H), 6.37 (s, 2H), 6.55ꢀ6.56 (d, 4H).
13C NMR (CDCl3, 100 MHz): δ 26.2, 29.0, 30.0, 40.4, 44.8, 50.1, 68.8,
80.2, 99.4, 104.2, 149.6, 155.2, 159.4. IR (CHCl3, cmꢀ1): 3362, 2980,
2931, 1711, 1597, 1521, 1448, 1257, 1176, 1153, 1058, 912. Anal. Calcd for
C38H52N2O12: C, 62.6; H, 7.2; N, 3.8. Found: C, 62.74; H, 7.43; N, 3.67.
Preparation of N,N0-Bis[[1-(3,5-diglycidoxyphenyl)-1-
methylethoxy]carbonyl]toluene-2,4-diamine, 23. Dry N,N0-
dimethylformamide (2 mL) was added to the tetrahydroxy bis-carbamate
21 (750 mg, 1.46 mmol) and cesium carbonate (2.26 g, 5.86 mmol)
under nitrogen atmosphere. Epibromohydrin (2.9 mL, 35.2 mmol) was
Figure 1. Comparison of TGA traces for monomer 12b (blue) and
control 14 (red).
added via syringe, and the mixture was stirred for 48 h. The mixture was
then diluted with water and extracted with diethyl ether. The combined
extracts were washed with water, dried, evaporated, and purified via silica
and extracted with ethyl acetate. The combined extracts were washed,
dried, evaporated, and purified via silica gel chromatography (1:1 to 5:1
ethyl acetate:hexanes) to yield a dark oil that was triturated with ethyl
acetate, CH2Cl2, and hexanes to yield 900 mg (78%) of an off-white
solid. 1H NMR (DMSO-d6, 400 MHz): δ 1.64 (s, 12H), 2.09 (s, 3H),
6.06ꢀ6.07 (q, 2H), 6.22ꢀ6.24 (dd, 4H), 6.97ꢀ6.99 (d, 1H), 7.07ꢀ7.10
(d, 1H), 7.40 (s, 1H), 8.63 (br s, 1H), 9.12 (s, 2H), 9.13 (s, 2H), 9.44 (br
s, 1H). 13C NMR (DMSO-d6, 100 MHz): δ 17.2, 20.8, 29.1, 31.2, 70.5,
79.9, 100.1, 100.8, 100.9, 102.5, 102.6, 103.0, 114.6, 125.3, 130.0, 136.6,
137.4, 148.7, 148.9, 152.0, 152.7, 152.9, 157.8, 158.0, 158.1. IR (KBr, cmꢀ1):
3295, 2967, 1683, 1587, 1432, 1227, 1125, 1037, 993, 958. Anal. Calcd for
C27H30N2O8: C, 63.5; H, 5.9; N, 5.4. Found: C, 63.29; H, 6.12; N, 5.29.
Preparation of N,N0-Bis[[1-(3,5-diglycidoxyphenyl)-1-
methylethoxy]carbonyl]hexane-1,6-diamine, 22. A 10 mL ali-
quot of dry N,N0-dimethylformamide was added to the tetrahydroxybis-
carbamate 20 (900 mg, 1.80 mmol) and cesium carbonate (2.85 g,
7.39 mmol). Epibromohydrin (4.93 g, 36 mmol) was then added, and
gel chromatography (1:20 to 1:5 ethyl acetate:dichloromethane) to yield
575 mg (53%) of a white solid. 1H NMR (CDCl3, 400 MHz): δ 1.74ꢀ
1.78 (d, 12H), 2.19 (s, 3H), 2.73ꢀ2.74 (m, 4H), 2.87ꢀ2.89 (m, 4H),
3.31ꢀ3.33 (m, 4H), 3.91ꢀ3.93 (m, 4H), 4.15ꢀ4.21 (m, 4H), 6.36ꢀ
6.40 (dt, 2H), 6.46 (br s, 1H), 6.56ꢀ6.60 (dd, 4H), 6.65 (br s, 1H),
7.00ꢀ7.02 (d, 2H), 7.22 (br s, 1H), 7.59 (s, 1H). 13C NMR (CDCl3,
100 MHz): δ 17.9, 29.0, 44.9, 50.3, 68.9, 69.0, 99.8, 99.9, 104.3, 104.4,
130.9, 136.4, 137.0, 149.1, 149.0, 149.1, 159.6, 159.7. IR (CHCl3, cmꢀ1):
3340, 2983, 2928, 1729, 1598, 1530, 1448, 1232, 1176, 1138, 1051, 910.
Anal. Calcd for C39H46N2O12: C, 63.7; H, 6.3; N, 3.8. Found: C, 63.45;
H, 6.51; N, 3.92.
’ RESULTS AND DISCUSSION
The synthetic design of these single component amine epoxy
precursors are inspired by previous work with a carbamate
deprotection mechanism using ultraviolet light as the trigger.20ꢀ25
6322
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
Figure 2. (a) Selected IR spectra of films and (b) relative peak ratios of carbonyl and nitrile stretches of precursor 13b (as a 200 mM solution in a
mixture of 11% poly(methacrylonitrile) in nitromethane) as a function of curing times at 160 °C.
The synthetic route to access these epoxy precursors depends
upon the degree of substitution of the benzylic carbon. Scheme 2
outlines the preparation of bis-carbamate epoxy precursors 13
and 15, which are derived from a secondary benzylic alcohol in a
facile three-step process. For example, 13a is prepared from 3,
5-dihydroxyacetophenone, 9a, by alkylation with epibromohy-
drin in the presence of cesium carbonate to afford 10a followed
by reduction with sodium borohydride and bis-carbamation with
a diisocyanate to yield the desired secondary bis-carbamate.
In the case of tertiary bis-carbamates 22 and 23, the synthetic
sequence starting from methyl 3,5-dihydroxybenzoate is somewhat
lengthier requiring five steps due to the need for a protectionꢀ
deprotection sequence (Scheme 3). The starting material 15 was
first bis-allylated to afford 16, which was then treated with two
equivalents of methylmagnesium bromide to afford the tertiary
benzylic alcohol 17. Allyl protection of the phenols of 15 was
crucial to enable the selective methyllithium-catalyzed bis-carba-
mation of the tertiary alcohol to produce alkyl bis-carbamate 18
and aryl bis-carbamate 19. The allyl groups were then removed
via palladium-catalyzed sodium borohydride reduction to give
the hydroxylated bis-carbamates 20 and 21. Finally, four epoxide
groups were installed using epibromohydrin and cesium carbo-
nate to afford the desired epoxies 22 and 23. Direct epoxidation
of the allyl groups using conventional reagents (mCPBA or DMDO)
were unsuccessful. Although the two synthetic pathways differ in
length and ease of preparation, the overall synthetic scheme has
flexibility with respect to the substitution of the benzylic carbon,
the substitution around the phenyl ring, and the nature of the
diisocyanate. This flexibility allowed access to a small library of
epoxy precursors with a significant range of deprotection and
curing temperatures.
Figure 3. Combined DSC and TGA traces for monomer 23.
Rather than using this motif as a UV-curable system, which
operates at an inefficient wavelength for large-scale use (280 nm)
and has a poor quantum yield (with many deleterious side reactions),
we decided to take advantage of the thermal instability of the
carbamate functional group.19 The overall process of thermal
deprotection and curing of our “single component epoxies” is
summarized in Scheme 1. In contrast to phenyl carbamate, the
functionality commonly used in a blocked isocyanate, which
thermally decomposes into an isocyanate and a phenol, the
carbamate moieties of our epoxy precursors (e.g., 1 and 5) are
designed to undergo the entropically favorable thermal decom-
position to yield carbon dioxide, an eliminated alkene (2 and 6),
and a primary diamine (3 and 7). Because the eliminated alkene
contains at least one epoxide moiety, it can react with the newly
formed primary amine, thus realizing the key step in the for-
mation of an epoxy thermoset. In practice, the epoxy precursor
should contain at least two latent amines and four epoxy moieties
(such as 5) in order to produce a cross-linked epoxy thermoset.
Epoxy precursors that have a low epoxy/amine ratio and cannot
cross-link (such as 1) were still used as model compounds to
illustrate the structure/function relationship between molecular
design and deprotection temperature.
When heated past the deprotection temperature of the
carbamate moiety, the epoxy precursors display a decomposition
with two inflection points. TGA monitoring confirmed the first
inflection, corresponding to the weight change expected from the
loss of 2 CO2 molecules from the epoxy material, as well as some
evaporation of the diamine and glycidyl ether formed postde-
protection. Following initial weight loss, the weight of the sample
subjected to TGA analysis only decreases slowly, likely as a result
of evaporation, until the second inflection point occurs at an
elevated temperature (>350 °C). Only bis-carbamates that include
6323
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
Figure 4. DSC isothermal comparison of monomers 13b and 23.
Figure 5. Comparison of CO2 bubbles produced in cured resins of epoxy 23, cured fully at different temperatures: (a) 160 °C for 1 h; (b) 180 °C for
30 min; (c) 200 °C for 15 min. Scale bar is 200 μm.
epoxy groups displayed this relative stability after loss of CO2, as
seen by TGA comparison between epoxy 12b and 14 (Figure 1).
The control epoxy 14 was designed to release CO2 at a similar
temperature as epoxy 12b, but without the ability to cure. IR
monitoring of the deprotection of epoxy precursor 13b diluted in
a matrix of poly(methacrylonitrile) heated to 160 °C (Figure 2)
shows that the carbamate NH peak at 3329 cmꢀ1 is replaced by a
broader peak centered at 3386 cmꢀ1, primarily due to the amine of
the deprotected monomer. Although this precursor is diluted in a
polymer matrix, it is possible that background curing may give rise
to hydroxyls in this region of the spectrum. In addition, the IR
spectra showed a relative increase in transmission at 1717 cmꢀ1
corresponding to the loss of the carbamate carbonyl as it is con-
verted to CO2, compared to the nitrile stretch of the polymer matrix
which changes minimally during the heating period.
The curing of epoxies is also known to produce a large DSC
exotherm, specifically due to epoxide ring-opening by the amine.
As shown by Figure 3, the cure exotherm only appears once the
temperature of CO2 release is reached. A subsequent DSC scan
shows no further exotherm as the cure is complete. As shown in
Table 1 for a variety of precursors, cure always follows deprotec-
tion, the onsets of which may differ by as little as 4 to as much
as 16 °C. Interestingly, while the Tg values of the cured ther-
mosets match well with those obtained from cured amine epoxies
and depend upon the aliphatic or aromatic nature of the amine
curing agent,26 the measured enthalpy of cure is less than that
typical of amine epoxies, generally regarded to be on the order of
100 kJ/equivalent of epoxide.27
When compared to the first entry in Table 1, a control system
consisting of the byproducts of thermal carbamate deprotection,
the lower energies of the bis-carbamate monomers are likely due
to small amounts of evaporation of one or both byproducts
during the release of CO2. Because the carbamate deprotection
follows Arrhenius kinetics, a statistical portion of the monomer
will deprotect and thus cure at temperatures below the measured
TGA onset. Isothermal DSC curing studies with precursors 13b
and 23, the two lowest-curing monomers, reflect this behavior
where both molecules can cure completely at 160 °C in ca. 90 and
50 min (Figure 4), despite having very similar deprotection onsets
(170 and 176 °C, respectively).
Examination of the deprotection parameters for the various
structures studied suggests the following: (i) 1,4--substitution
leads to a lower deprotection temperature than 1,3,5-substitu-
tion, (ii) increasing the substitution of the benzylic carbon results
in a lower deprotection temperature, and (iii) aryl bis-carbamates
deprotect at lower temperatures than alkyl bis-carbamates. These
patterns reflect an increase in the ability to stabilize a partial
positive charge arising in the benzylic carbon in the transition
6324
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325

Macromolecules
ARTICLE
state and the well-known fact15 that aryl carbamates are less
thermally stable than their alkyl counterparts, presumably due to
the electron-withdrawing effect of the aryl group.
(12) Suzuki, K.; Matsu-ura, N.; Horii, H.; Sugita, Y.; Sanda, F.; Endo,
T. J. Appl. Polym. Sci. 2003, 88, 878–882.
(13) Schile, R. D. U.S. Patent Application 20080227950, September
18, 2008.
As a result of curing, the gaseous carbon dioxide produced by
the decomposition of the carbamate moieties remains trapped
within the film forming spherical bubbles, shown by Figure 5. As
expected, the size of these bubbles varies according to the curing
temperature, with smaller bubbles formed within the film cured
at a lower temperature, and dramatically larger bubbles formed in
a film cured at a higher temperature. The size of the bubbles likely
vary due to a variety of factors, most notably the impact of temp-
erature on the rates of carbamate decomposition and curing. As
the curing temperature increases, CO2 is generated more quickly
and is trapped to a larger extent within the rapidly curing film,
resulting in larger bubbles. Lower curing temperatures both generate
CO2 more slowly and allow a greater amount of the generated gases
to diffuse or escape from the film before it is fully cured.
(14) Larsen, D. W. U.S. Patent 4,111,917, Sep. 5, 1978.
(15) Wicks, Z. W., Jr. Prog. Org. Coat. 1975, 3, 73–99.
(16) Wicks, Z. W., Jr. Prog. Org. Coat. 1981, 9, 3–28.
(17) Wicks, D. Prog. Org. Coat. 1999, 36, 148–172.
(18) Wicks, D. Prog. Org. Coat. 2001, 41, 1–83.
(19) Spindler, R.; Frꢀechet, J. M. J. Macromolecules 1993, 26,
4809–4813.
(20) Cameron, J. F.; Frꢀechet, J. M. J. J. Org. Chem. 1990, 55, 5919–
5922.
(21) Birr, C.; Lochinger, W.; Stahnke, G.; Lang, P. Liebigs. Ann.
Chem. 1972, 763, 162–172.
(22) Cameron, J.; Frꢀechet, J. M. J. J. Photochem. Photobiol. A 1991,
59, 105–113.
(23) Cameron, J. F.; Willson, C. G.; Frꢀechet, J. M. J. J. Chem. Soc.
Perkin Trans. I 1997, 2429–42.
In conclusion, we have developed a novel design strategy
toward single component latent amine epoxies, in which we combine
the latent amine and the epoxide onto the same molecule. The
thermal trigger used in this epoxy design is analogous to that used
for blocked isocyanates in polyurethane coatings. Utilizing a
small library of epoxy precursors, we have shown that the cure
temperatures can be adjusted through small structural changes to
yield a range of self-curing epoxy-urethane monomers which cure
in relatively short periods at elevated temperatures to give ther-
mosets that may be useful as foam dielectrics, adhesives, sealants,
and coatings.
(24) Cameron, J. F.; Willson, C. G.; Frꢀechet, J. M. J. J. Am. Chem. Soc.
1996, 118, 12925–12937.
(25) Cameron, J. F.; Willson, C. G.; Frꢀechet, J. M. J. J. Chem. Soc.,
Chem. Commun. 1995, 923–924.
(26) Petrie, E. M. Epoxy Adhesive Formulations; McGraw-Hill: Blacklick,
OH, USA, 2005; p 68.
(27) Klute, C. H.; Viehmann, W. J. Appl. Polym. Sci. 1961, 5, 86–95.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: frechet@berkeley.edu and jean.frechet@kaust.edu.sa.
’ ACKNOWLEDGMENT
Synthesis of the new materials and their characterization was
supported by the Director, Office of Science, Office of Basic
Energy Sciences, Division of Materials Sciences and Engineering
of the U.S. Department of Energy under Contract No. DE-AC02-
05CH11231; additional support by the Frꢀechet Various Donors
Gift Funds is also acknowledged.
’ REFERENCES
(1) Meng, L. M.; Yuan, Y. C.; Rong, M. Z.; Zhang, M. Q. J. Mater.
Chem. 2010, 20, 6030–6038.
(2) Wu, C.; Hsu, S. L. J. Micromech. Microeng. 2010, 20, 015006.
(3) Zhao, Y.; Barrera, E. V. Adv. Funct. Mater 2010.
(4) Gilbert, M. D.; Schneider, N. S.; MacKnight, W. J. Macromolecules
1991, 24, 360–369.
(5) G€uthner, T.; Hammer, B. J. Appl. Polym. Sci. 1993, 50, 1453–
1459.
(6) Fedtke, M.; Domaratius, F.; Walter, K.; Pfitzmann, A. Polym.
Bull. 1993, 31, 429–435.
(7) Hidekazu, I.; Masahiko, O.; Hideo, Y. European Patent 0193068,
September 3, 1986.
(8) Great Britain Patent 1,121,196, July 24, 1968.
(9) Dooley, J. U.S. Patent 5,077,376, May 21, 1990.
(10) Kayser, R. H.; Pollack, R. M. J. Am. Chem. Soc. 1977, 99,
3379–3387.
(11) Suzuki, K.; Matsu-Ura, N.; Horii, H.; Sugita, Y.; Sanda, F.;
Endo, T. J. Appl. Polym. Sci. 2002, 83, 1744–1749.
6325
dx.doi.org/10.1021/ma200673v |Macromolecules 2011, 44, 6318–6325