Octa(aminophenyl)silsesquioxane as a nanoconstruction site

Full text of DOI:10.1021/ja011781m

12416
J. Am. Chem. Soc. 2001, 123, 12416-12417
A key problem with almost all of the materials explored to
Octa(aminophenyl)silsesquioxane as a
Nanoconstruction Site
date is that the aliphatic components limit the thermal stability
of the resulting nanocomposites, strongly influence (lower) Tg,
and decrease mechanical properties potentials. Hence we sought
more rigid, thermally stable nanoplatforms while expanding the
types of functionality available for nanoconstruction projects.
We report here the synthesis of octa(aminophenyl)silsesqui-
oxane (OAPS), an aromatic amine-functionalized silsesquioxane
free from aliphatic components. OAPS appears to offer excellent
potential as a nanoconstruction site for preparing materials ranging
from high-temperature nanocomposites, to precursors to organic
light-emitting diodes, to multiarmed stars, to templates for high-
temperature porous materials of use in catalysis, sensing, separa-
tions, etc.
Ryo Tamaki,† Yasuyuki Tanaka,‡ Michael Z. Asuncion,
Jiwon Choi, and Richard M. Laine*
Department of Materials Science and Engineering
Macromolecular Science and Engineering Center
UniVersity of Michigan, Ann Arbor, Michigan 48109-2136
ReceiVed July 23, 2001
The field of nanomaterials science and engineering has a
continuing need for well-defined building blocks that allow the
construction of a wide variety of materials nanometer-by-
nanometer with precise control of the nanoarchitecture and that
imbue functionality.1,2 Octahedral or cubic silsesquioxanes (cubes)
and the related polyhedral oligomeric silsesquioxanes (POSS)
offer one solution to this need in that they provide the opportunity
to design and “construct” materials with extremely well-defined
dimensions and behavior.3-11 In this regard, we have prepared a
wide variety of octafunctional cubes with polymerizable moieties
that offer access to highly cross-linked (thermoset) nanocompos-
ites having: (1) controlled porosities with high surface areas,9
(2) novel mechanical properties,10-12 and (3) high thermal
stabilities (see below). In a complementary fashion, POSS
materials offer access to robust thermoplastics with good-to-
excellent properties including resistance to atomic oxygen.3-7
Our approach to generating functionalized cubic silsesquioxane
macromonomers that offer access to nanocomposites has relied
OAPS is easily prepared in two steps by nitration of octaphe-
nylsilsesquioxane (OPS)18 in fuming nitric acid to form octa-
(nitrophenyl)silsesquioxane (ONPS),19 followed by mild reduction.
OPS nitration was described briefly 40 years ago, but the resulting
product was poorly characterized, and the material was reported
to be unreactive. Slight modification of this procedure20 provides
ONPS with one nitro group per phenyl (see Supporting Informa-
tion). ONPS is easily transformed to OAPS by hydrogen-transfer
reduction21-23 using formic acid and triethylamine (Pd/C catalyst
60 °C/N2/5 h) resulting in quantitative conversion (Scheme 1).21
1H and 13C NMR data (Supporting Information) support the
formation of equal quantities of the meta and para nitration and
amine products. 29Si NMR spectra of ONPS show two peaks at
-79.2 and -83.0 ppm for the para and meta isomers, respectively.
Likewise, 29Si NMR spectra of OAPS also show two respective
peaks at -73.3 and -77.4 ppm. Thermal gravimetric and chem-
ical analyses (TGA) of the ONPS and OAPS products are shown
in Table 1. The TGA ceramic yield for ONPS was 33.7 versus
34.5 wt % theory. The TGA ceramic yield for OAPS was 41.1
versus 41.7 wt % theory. More importantly C, H, and N analyses
agree with the calculated values. These results support formation
of monosubstituted ONPS and its quantitative conversion to
primarily on introducing functionality by hydrosilylation using
(HSiO1.5 8
13
)
or (HMe2SiOSiO1.5)8 nanoplatforms.13-15 We have
successfully introduced functional groups including methacry-
lates,1 mesogenic groups,8 epoxies,2,10 and alcohols.11
In a departure from this approach, we recently reported the
synthesis of octa(aminopropyl)silsesquioxane which offers access
to novel amides and imides with good high-temperature properties
and hints of liquid crystalline behavior.16 Feher et al. reported
the same synthesis almost simultaneously.17
(17) Feher, F. J.; Wyndham, K. D. Chem. Commun. 1998, 323.
(18) Brown, J. F., Jr.; Vogt, L. H., Jr.; Prescott, P. I. J. Am. Chem. Soc.
1964, 86, 1120.
† Current address: Tyco Electronics Corporation, Technology Division,
Menlo Park, CA 94025. E-mail: ryo.tamaki@tycoelectronics.com.
‡ Current address: Department of Applied Chemistry, Kyushu Institute of
Technology, Sensui, Tobata, Kitakyushu, 804-8550, Japan.
(1) Sellinger, A.; Laine, R. M. Macromolecules 1996, 29, 2327.
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28, 8435.
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(5) Feher, F. J.; Soulivong, D.; Eklud, A. G.; Wyndham, K. D. Chem.
Commun. 1997, 1185.
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453. (b) Haddad, T. S.; Mather, P. T.; Jeon, H. G.; Romo-Uribe, A.; Farris,
A. R.; Lichtenhan, J. D. In Organic/Inorganic Hybrid Materials; Laine, R.,
Sanchez, Brinker, Giannelis, Eds.; MRS Symp. Ser. 519; Materials Research
Society: Warrendale, PA, 1998; pp 381-386.
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Sci. 1996, 60, 591. (b) Gonzalez, R. I.; Phillips, S. H.; Hoflund, G. B. J.
Spacecr. Rockets 2000B, 37, 463.
(8) Sellinger, A.; Laine, R. M.; Chu, V.; Viney, C. J. Polym. Sci., Part A:
Polym. Chem. 1994 32, 3069.
(9) Zhang, C.; Babonneau, F.; Bonhomme, C.; Laine, R. M.; Soles, C. L.;
Hristov, H. A.; Yee, A. F. J. Am. Chem. Soc. 1998, 120, 8380.
(10) Laine, R. M.; Choi, J.; Lee, I. AdV. Mater. 2001, 13, 800.
(11) Zhang, C.; Laine, R. M. J. Am. Chem. Soc. 2000 122, 6979.
(12) Laine, R. M.; Asuncion, M.; Baliat, S.; Dias Filho, N. L.; Harcup, J.;
Sutorik, A. C.; Viculis, L.; Yee, A. F.; Zhang, C.; Zhu, Q. In Organic/Inorganic
Hybrid Materials; Klein, L., De Guire, M., Lorraine, F., Mark, J., Eds.; MRS
Symp. Ser. 576; Materials Research Society: Warrendale, PA, 1999; pp 3-14.
(13) (a) Agaskar, P. A. Inorg. Chem. 1991, 30, 2707. (b) Hasegawa, I.;
Kuroda, K.; Kato, C. Bull. Chem. Soc. Jpn. 1986, 59, 2279.
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Soc., Chem. Commun. 1989, 208.
(19) Olsson, K.; Gro¨nwall, C. ArkiV. Kemi. 1961, 17, 529.
(20) ONPS was prepared per Olsson and Gro¨nwall19 with several modifica-
tions. OPS, 50 g (48.4 mmol) was added in small portions to 300 mL of fum-
ing nitric acid with stirring at 0 °C. After addition was complete, the solution
was stirred for an additional 30 min and then at room temperature for 20 h.
After filtration through glass wool, the solution was poured onto 250 g of
ice. A very faintly yellow precipitate was collected, washed with water (∼100
mL × 5 until pH ≈ 6.0) and then with ethanol (∼100 mL × 2). The obtained
powder was dried at ambient to remove residual solvent to yield 60.8 g (43.6
1
mmol, 90.1%) of material. H NMR (acetone-d6, ppm): 8.7 (t, 1.0H), 8.4-
8.0 (m, 4.1H), 7.8 (m, 2.7H); 13C NMR (acetone-d6, ppm): 154.0, 148.9, 141.0,
138.6, 136.5 (small), 135.3, 134.1, 132.3 (small), 130.8, 129.5, 127.0, 125.2,
123.6 (small); 29Si NMR (THF, TMS, acetone-d6, ppm): -79.2, -83.0.
(21) OAPS was prepared by introducing ONPS (10.0 g, 7.16 mmol, -NO2
57.4 mmol) and 5 wt % Pd/C (1.22 g, 0.574 mmol) into a 250-mL Schlenk
flask equipped with a condenser under N2. Distilled THF (80 mL) and
triethylamine (80.0 mL, 0.574 mmol) were then added. The mixture was heated
to 60 °C, and 85% formic acid (10.4 mL, 0.230 mol) was added slowly at 60
°C. Carbon dioxide evolved, and the solution separated into two layers. After
5 h, the THF layer was separated, and 50 mL of THF and 50 mL of water
were added until the slurry formed a black suspension. The suspension and
the THF solution separated previously were mixed and filtered through Celite.
Another 20 mL of THF and 20 mL of water were added to the flask to dissolve
the remaining black slurry, and the suspension was filtered again. All of the
filtrates were combined with 50 mL of ethylacetate and washed 4× with 100
mL H2O. The organic layer was dried after 5 g of MgSO4 and precipitated by
addition to 2 L of hexane. A white precipitate was collected by filtration, re-
dissolved in 30:50 THF/ethyl acetate and reprecipitated into 1 L hexane. The
obtained powder was dried under vacuum. Yield 6.80 g (5.89 mmol, recovery
82%). 1H NMR (acetone-d6, ppm): 7.8-6.2 (b, 4.0H), 5.2-3.7 (b, 2.0H);
13C NMR (acetone-d6, ppm): 154.0, 148.1, 136.6, 132.8, 129.3, 123.4, 120.8,
117.3, 115.8, 114.4; 29Si NMR (THF, TMS, acetone-d6, ppm): -73.3, -77.4.
(22) Cortese, N. A.; Heck, R. F. J. Org. Chem. 1977, 42, 3491.
(15) Hasegawa, I.; Motojima, S. J. Organomet. Chem. 1992, 441, 373.
(16) Gravel, M.-C.; Zhang, C.; Dinderman, M.; Laine, R. M. Appl.
Organomet. Chem. 1999, 13, 329.
(23) Johnstone, R. A. W.; Wilby, A. H. Chem. ReV. 1985, 85, 129.
10.1021/ja011781m CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/13/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 49, 2001 12417
Scheme 1
simply on heating an NMP solution of OAPS and phthalic
anhydride at 350 °C/N2/4 h (Supporting Information). The
obtained powder is soluble in common polar organic solvents and
behaves as expected per NMR, TGA, and GPC analyses. The
corresponding maleimide (OMIPS) was also easily made (Sup-
porting Information). Both compounds are stable to ∼430 °C (5%
mass loss temperature). No exotherms corresponding to maleimide
polymerization were observed by DSC although the heated
product was no longer soluble. The maleimide group offers access
to diverse thermosets via self-polymerization or via Michael-
addition reactions with dithiols or diamines to form high-
temperature resins.24, 25
Nanocomposites. OAPS when reacted with diepoxides or
dianhydrides should provide high cross-link density materials with
good thermal stability, and good-to-excellent tensile and compres-
sive strengths.10 Reacting OAPS, with pyromellitic anhydride
(PMA) at >300 °C, provides complete curing and a material that
exhibits a 5% mass loss temperature of 540 °C (air and N2) and
75 wt % char yield at >1000 °C/N2. This robustness is exemplary
and offers potential for many diverse applications. The properties
of these materials will be discussed elsewhere.26
Table 1. Properties of the Silsesquioxanesa
ceramic
C % H % N % yield (%)b
POSS
(FW)
Mn
Mw Mw/Mn (cal) (cal) (cal)
(cal)
OPS
(1033.5)
ONPS
(1393.5)
OAPS
(1153.7)
718
733 1.022
-
-
-
9.1c
(46.5)
33.7d
(43.5)
41.1e
(41.7)
1030 1111 1.078
1057 1133 1.072
41.3
2.3
8.0
(41.4) (2.4) (8.0)
49.4 4.3 9.2
(50.0) (4.2) (9.7)
a Obtained by GPC using THF as eluent and calibrated with
polystyrene standards. b Calculated by TGA at 1000 °C in air. c OPS
sublimes. d Allowing for residual solvent (slight decrease below 300
°C) the ceramic yield was calculated as 33.7% at 1000 °C. e The OAPS
ceramic yield was calculated as 41.1 wt TGA for both ONPS and OAPS
demonstrated the decomposition onset temperatures of ∼350 °C.
Fluorene Derivative (OFPS). Pd-catalyzed coupling of bro-
mofluorene to OAPS (Supporting Information) provides a po-
tential route to hole-transport materials for organic light-emitting
diodes.27,28 Potassium phosphate was found to be superior to other
bases tested27 in limiting Si-O bond cleavage. On average, 0.66
fluorene groups/N (∼5 fluorene groups/cube) were introduced as
Scheme 2. Reactions of Octaminophenylsilsesquoxanea
1
confirmed by H NMR. Steric hindrance may make complete
substitution difficult. Diverse coupling reactions are available for
27, 28
adding other functional species to the aromatic nitrogen.
Schiff Base Derivative (OSPS). OAPS reacts rapidly with the
2-pyridinecarboxaldehyde under mild conditions, giving an imine
that emits green light under UV illumination. This type of imine
offers potential for forming metal chelate complexes for sensor,
electrochemical, photonic, and catalytic applications.29-31
OAPS contains an inorganic core as a foundation and rigid
arylamine moieties that serve as highly functional anchors to this
foundation. As suggested in Scheme 2, it provides access to
numerous materials with a high density of functional groups in a
very small volume, ∼1 nm. Some of these materials can be used
as starting points to construct a large number of thermally robust
nanocomposite materials nanometer-by-nanometer. For example,
we successfully prepared core-shell materials.26 Still other
derivatives appear to offer potential for numerous nonstructural
applications. OAPS represents the first example of a new class
of materials that are very promising nanoconstruction sites. In
future papers, we will describe the syntheses of ketones, esters,
bromo- and acid-functionalized octaphenylsilsesquioxane nano-
construction sites.
a i) 1:8.4 OAPS:phthalic anhydride in NMP 350 °C/N2 /4 h. ii) 1:8
OAPS:maleic anhydride in DMA 60 °C/N2/3 h with acetic anhydride
and Et3N. iii) 1:8 OAPS:pyromellitic anhydride in NMP 350 °C/N2/3 h;
iv) 1:8 OAPS:epoxy neat at 200 °C/6 h/N2; v) 1:8.8 OAPS:2-bromo-
9,9-dimethylfluorene, Pd2(dba)3, (dcbp)P, glyme 100 °C/N2/5.5 h; vi) 1:8
OAPS:2-pyridinecarboxaldehyde Na2SO4/ THF/rt/N2/22 h.
Acknowledgment. We thank the FAA (Grant No. 95-G-026) and the
U.S. Air Force (Phillips Labs, Edwards AFB) for partial support of this
work.
Supporting Information Available: NMR data (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
OAPS. The decomposition onset for both ONPS and OAPS is
∼350 °C.
JA011781M
Table 1 also provides GPC (THF) data giving molecular
weights for ONPS, OAPS, and OPS of 1394, 1154, and 1034
Da, respectively. These values differ from calculated values
because polystyrene was used as a calibration standard. All of
the compounds exhibit narrow polydispersities, even after reaction,
indicating the absence of polymeric materials resulting from core
decomposition.
(24) White, J. E.; Snider, D. A. J. Appl. Polym. Sci. 1984, 29, 891.
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Polym. Sci. Polym. Chem. Ed. 1975, 13, 961.
(26) (a) Laine, R. M.; Choi, J.; Lee, I. AdV. Mater. 2001, 13, 800 and
references therein. (b) Choi, J.; Harcup, J.; Yee, A. F.; Zhu, Q.; Laine, R. M.
J. Am. Chem. Soc. 2001, 123. ASAP on Web October 26, 2001. (c) Tamaki,
R.; Choi, J.; Laine, R. M. Abstracts of Papers, 221st National Meeting of the
American Chemical Society, San Diego, CA, April 1-5, 2001; American
Chemical Society: Washington, DC, 2001; PMSE 312.
To demonstrate the potential OAPS offers as a nanoconstruction
site, several model compounds were synthesized per Scheme 2.
See Table 2 for yields and derivatization details (Supporting
Information).
Phthalimide Derivatives. As a prelude to making 3-D imide
nanocomposites, efforts were directed toward making a prototype
imide, a potential nanofiller. The octaphthalimide (OPIPS) forms
(27) Harris, M. C.; Buchwald, S. L. J. Org. Chem. 2000, 65, 5327.
(28) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L. J.
Org. Chem. 2000, 65, 1158.
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Heming, A. M.; Kukulj, D.; Shooter, A. J. Macromolecules 1999, 32, 2110.