ChEMISTRyOf
MATERIALS
VOLUME 5,NUMBER 9
SEPTEMBER 1993
0 Copyright 1993 by the American Chemical Society
C‘ommunzcatzons Bridged Polygermsesquioxanes. Organically Modified Germanium Oxide Materials Gregory M. Jamison,+Douglas A. Loy,’J and Kenneth J. Shea* Org. 1812, Properties of Organic Materials Department, Sandia National Laboratories Albuquerque, New Mexico 87185, and Department of Chemistry, University of California Irvine Irvine, California 92717 Received May 19, 1993 Revised Manuscript Received July 19, 1993
Sol-gel processed polysilsesquioxanes are hybrid organic-inorganic materials with potential applications as photoresists, membranes, or catalytic supports.’ Hydrolytic conversion of trichloro- or trialkoxysilanes often leads to amorphous or crystalline oligosilsesquioxanes instead of high polymers.2 In light of the intimate dependence of polysilsesquioxaneproperties of tightly controlled reaction conditions and processing,recent emphasis has been placed on control of polymer microarchitecture via the introduction of arylene-, acetylene-, and alkylene-bridging groups.s Another strategy for modifying the properties of Sandia National Laboratories. University of California. (1) (a) Brinker, C. J.; Scherer, G. W. Sol-Gel Science; Academic Press: London, 1990. (b) Gesser, H. D.; Goswami, P. C. Chem. Rev. 1989,89, 765. (c)Sol-Gel Technologyfor ThinFilms,Fibers,Preforms,Electronics, and Specialty Shapes; Klein, L. C., Ed.; Noyes: Park Ridge, NJ, 1988. (2) (a) Brown, J. F., Jr.; Vogt,L. H., Jr.; Prescott, P. I. J. Am. Chem. SOC. 1964,86,1120. (b)Brown, J. F., Jr. J.Am. Chem. SOC. 1966,87,4317. (c) Feher, F.J.; Newman, D. A.; Walzer, J. F. J.Am. Chem. SOC. 1989, 111,1741. (d) Feher, F.J.; Budzichowski,T. A.; Blanksky, R. L.; Weller, K. J.; Ziller, J. W. Organometallics 1991,10, 2526. (3) (a) Shea, K. J.; Loy, D. A.; Webster, 0. J. Am. Chem. SOC.1992, 114,6700. (b) Shea, K. J.;Loy, D. A.; Webster, 0.W. Chem.Mater. 1989, Through 1,572. (c) Shea,K. J.;Webster,O.;Loy,D.A.InBetterCeramics Chemistry IV; Mater. Res. Soc. Proc.; Zelinski, B. J. J., Brinker, C. J., Clark, D. E., Ulrich, D. R., Eds.; MRS: Pittaburgh, PA, 1990; Vol. 180, p 975. (d) Shea, K. J.; Loy, D. A.; Webster, 0.W. h o c . ACS Diu. Polym. Mater., Sci. Eng. 1990,63,281.(e) Shea, K. J.; Loy, D. A.; Small, J. H. t t
hybrid organic-inorganic polymers is to substitute a group IVA metal, such as germanium, for silicon. We report here the synthesis and characterization of bifunctional hexylene-bridged organogermanium monomers XsGe(CH2)sGeXs (X = C1 (1); OEt (2)) and the formation of polymeric materials through sol-gel hydrolysis-condensation of the monomers (Scheme I). Incorporation of organic spacers into bis(alkoxysily1) monomers is designed to impart an influence on the polymers’ porosity by virtue of the spacer length. While porosity in rigid arylene-bridged polysilsesquioxanes is arylene-independent4 (and therefore probably a function of polymer growth and aggregation phenomena) ,5 gel porosity derived from bis(triethoxysily1)terminated alkanes is dependent upon alkylene spacer length and pH. However, under acid-catalyzed conditions the porosity collapses when more than five methylene units comprise the spacer; base-catalyzed gels retain porosity with up to eight methylene spacer units.sh In all cases secondary modification of porosity and surface areas has been achieved by chemical removal of the organic substituent in the bulk material.6 In contrast to polysilsesquioxane networks, microstructure in organogermanate gels may be modified by taking Better Ceramics Through Chemistry V; Mater. Res. Soc. Proc.; HampdenSmith, M. J., Klemperer, W. G., Brinker, C. J., Eds.; MRS: Pittsburgh, PA,1992;Vol.271,p711.(f)Loy,D.A.;Shea,K.J.;Russick,E.M.Better Ceramics Through Chemistry V; Mater. Res. Soc.Proc.; Hampden-Smith, M. J., Klemperer, W. G., Brinker, C. J., E&.; MRS: Pittsburgh, PA, 1992,Vol. 271,p 699. (9) Corriu, R. J. P.; Moreau, J. J. E.; Thepot, P.; Man, M. W. C. Chem. Mater. 1992,4,1217. (h) Oviatt, H. W., Jr.; Shea, K. J.; Small, J. H. Chem. Mater. 1993,5,943. (i) Small, J. H.; Shea, K. J.; Loy, D. A. J. Non-Cryst. Solids, in press. (4) (a)Reference 3a. (b) Loy, D. A. Ph.D. Dissertation, University of California, Irvine, 1991. (5) (a) Reference la, Chapter 9. (b) Brinker, C. J. The Structure of Sol-Gelsilica. In Glass:Scienceand Technology;UhLmann,D.R.,Kreidl, N. J., Eds.; Academic Press: Boston, 1990; Vol. 4. (c) Brinker, C. J.; Scherer, G. W. J. Non-Cryst. Solids 1986,70,301. (6) Hydrocarbon-bridging groups in polysilseequioxanes have been studied as “pore templates.” Oxygen plasma treatments quickly remove the bridging group leaving porous silica. Loy, D. A.; Buss, R.J.; M i n k , R. A.; Shea, K. J.; Oviatt, H. Polym. Prepr. 1993,34,244.
0897-4756/93/2805-ll93$04.00/00 1993 American Chemical Society
Communications
1194 Chem. Mater., Vol. 5, No. 9,1993 Scheme I
I
EtOH / NEt3 25°C
X3Ge -GeX3
2
'of, 3a-d, X = C1 3e-h, X = OEt
advantage of the lability of the germoxane linkage' to affect partial depolymerization and reorganization of the germanium oxide lattice. Our interest in germanium-based materials was directed toward postpolymerization modification of the germoxane network and also whether or not porosity collapse would occur upon polymerization of the germanium analogues of hexylene-bridged polysilsesquioxanes. Organogermanate materials constitute a new area of sol-gel research. Previous investigations into the behavior of nonbridged alkylgermanium chlorides or alkoxides under hydrolysis-condensation conditions have not detailed properties of the resulting polymers (eq 1).8Our nR-GeX,
-
+ 1.5nH20
(R-GeOl&,
(1)
work in this area involved the hydrolysis and condensation of RGeX3 (R = Me, Ph; X = C1, OEt). Monomer concentrations as high as 2 M under avariety of conditions were employed. No gels were obtained, only amorphous precipitates were formed.9 Terminal hexyl substitution (i.e., hydrolysis of n-hexyltriethoxygermane)under similar conditions does not lead to gels. a,w-Bia(germy1)alkanes can be readily prepared by reduction of the appropriate dienes. Hydrogermylation of 1,5-hexadienewith HGeCl3 in the absence of catalystlo proceeds smoothly in benzene to give l,Sbis(trichloro(7) (a) Aylett, B. J. Organometallic Compounds, 4th ed.; Chapman and Halk London, 1979; Vol. 1, Part 11. (b) Anderson, H. H. J . Am. Chem. SOC.1950, 72, 2089. (c) Griffiths, J. E.; Onyszchuk, M. Can. J. Chem. 1961,39, 339. (8) (a) Viktorov, N. A.; Gar, T. K.; Mironov, V. F. Zh. Obsh. Khim. 1986, 55, 1051. (b) Zueva, G. Y.; Manucharova, I. F.; Yakovlev, I. P.; Ponomarenko, V. A. Zzv. Akad. Nauk SSSR, Neorg. Mat. 1966,2,229. (c) Kimura, T. JP Patent 03259924 A2; Chem. Abstr. 1992,116,130385d. (9) Loy, D. A:; Jamison, G. M., unpublished results. (10) (a) Schmidbauer, H.;Rott, J. 2.Naturf0rsch.B 1990,45,961. (b) Petrov, A. D.; Mironov, V. F.; Dzhurinskaya, N. G. Dokl. Akad. Nauk SSSR 1959,128, 302.
germy1)hexane (1) in 46% yield following vacuum distillation (Scheme l). Halide-ethoxide exchange can be affected under mild conditions with an ethanol/ triethylamine solution in benzene; 1,6-bis(triethoxygermyl)hexane (2) is isolated in 64% yield following distillation. Both compounds are clear, colorless, high-boiling liquids which remain inert to atmospheric oxygen and moisture, and have been fully characterized.11 Monomer 1was subjected to hydrolysis (6 equiv of HzO) in tetrahydrofuran, in the presence of 6 equiv of triethylamine. At all monomer concentrations of 1 employed (0.1, 0.05, 0.025, 0.01 M), precipitation occured to yield white polygermoxanes 3a-d which were isolated in good yield by aqueous workup.12 In comparison to the polymerization of alkyltrichlorogermanes and the chlorinated hexylene-bridged monomer 1 (vide supra), homogeneous solutions of 1,6bis(triethoxygermy1)hexane (2) set as opaque white gels when subjected to the same conditions at monomer concentrations ranging from 0.1 to 0.01 M. In all cases the sols acquired a blue cast early in the hydrolysiscondensation process; with time the samples set as opaque white gels. Gel times ranged from 15 min (3e, from 0.1 M 2) and less than an hour for 3f (0.05 M 2) to 2.5 h for 3g (0.025 M 2; upon aging for 5 weeks the latter sample remained too fragile to process). Sols of 3h (from 0.01 M 2) gelled within 1day but ultimately collapsed, presumably due to the low molar volume of the hexylene-bridged polygermsesquioxane. Gels were aged approximately 1 week (duringwhich time there was no discernible shrinkage of the gels) and supercritically extracted with COz to give high yields of aerogels 3e-h. Hydrolysis-condensation of 2 at similar concentrations under acid-catalyzed conditions failed to give monoliths. Instead, reactions proceeded so swiftly that gelation occurred before mixing was complete, much like the polymerization of 1 (vide supra). Nitrogen sorption analysis of the resulting polymer indicated that, as in thecase of the hexylene-bridged polysilsesquioxane,3hthe material is nonporous (5.41 m2/g BET). 13C CP MAS NMR of aerogel 3e (Figure 1)generated three resonances at 32.2,23.4, and 20.5 ppm (assigned to the three different types of bridging carbons), indicating that a majority of the hexylene bridges have been maintained under the polymerization conditions. Infrared analysis of the polymeric material indicated the presence of some vinylic functionality, as a weak C-H stretch at 3026 cm-l is observed, accompanied by a C=C stretch observable at 1605cm-lm13Apparently there is some degree of Ge-C bond breaking under these base-catalyzed conditions. No terminal olefinic C-H stretch was observed in the acid-catalyzed polymer (as it is in acid catalyzed Y
(11) Spectroscopic data: 1, bp: 113-117 OC/100 mTorr. IR (KBr): = 2936,2864,1462,1402,701cm-l. lH NMR (200 MHz, CDCla): 6 2.05,
1.76,1.50 (eacha m, 4 H, ClsGe(CH2)BGeCls);13CNMR (50.3 MHz, CDCh) 6 32.5,30.2,22.8 (each a 8 , ClSGe(CH2)sGeCL). LRMS mlz = 406.8 (M+ - Cl). Elem Anal. Calcd C, 16.30;-H, 2.74. Found C, 16.12; H, 2.77. 2, bp: 133-138 OC/100 mTorr. IFt(KBr): Y = 2972, 2927, 2872, 1386, 1099, 1056, 913, 672 cm-l. 'H NMR (200 MHz, CDCh): 6 3.84, 1.21 (q, (12 H), t, (18 H), (EtO)aGe(CHn)eGe(OEt)s), 1.54, 1.37, 1.31 (each a s , 4 l8C NMR (50.3 MHz, CDClS): 6 59.8,18.7 H, (EtO)sGe(CH2)eGe(OEt)s); (each a 8, (EtO)sGe(CHz)eGe(OEt)s),31.6, 22.5, 14.5 (each a 8, (EtO)sGe(CHz)eGe(OEt)s). LRMS: mlz = 455.2 (M+-OEt). Elem. Anal. Calcd C, 43.26; H, 8.47. Found C, 42.06, H, 8.97. (12) The polymers were washed with 2 X 50 mL of deionized water and 50 mL of acetone before drying in vacuo at 85 OC for 48 h. (13) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification of Organic Compounds, 4th ed.; Wiley: New York, 1981.
Chem. Mater., Vol. 5, No. 9, 1993 1195
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I 20
40
60
0
PPm
Figure 1. 1*C CPMAS NMR spectrum of aerogel 3b. 4.01 3 61
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Relative Pressure (P/Po> Figure 2. Type IV isotherm for mesoporous polygermsesquioxane aerogel 3b.
gels from 0.4 M (EtO)aSi(CHz)eSi(OEt)3);the rapid polymerization kinetics of 2 at low pH may well preclude germanium-carbon bond cleavage. The discrepancy between the NMR and IR spectra of 3e lies in the relative insensitivity of the solid-state NMR experiment, where small amounts of impurity (
