Bein, Thomas

Brinker, Jeffrey

Brown, Kelly D.

Frye, Gregory C.

English

Universität München: Elektronischen Publikationen

7640 J.  Am. Chem. SOC. 1989,111, 7640-7641 
Acknowledgment. This research was supported by PHS Grant 
CA28824. N M R  spectra were obtained through the auspices of 
the Northeast Regional NSF/NMR Facility at  Yale University, 
which was supported by N S F  Chemistry Division Grant C H E  
7916210. An N.I.H. Postdoctoral Fellowship to J.N.H. (Grant 
1 F32 CA08341-02) is gratefully acknowledged. In addition, we 
thank Dr. Nathan B. Mantlo of Merck Sharp & Dohme Research 
Laboratories, Rahway, N J  for helpful discussions. 
Supplementary Material Available: Spectral data (IR, 'H  
NMR,  and MS) for compounds 8-16, 18, and 20, tables of 
fractional coordinates, bond distances, torsional angles, and an- 
isotropic temperature factors and summary of the X-ray crys- 
tallographic determinations and structures of compounds 13 and 
20 (17 pages). Ordering information is given on any current 
masthead page. 
Molecular Sieve Sensors for Selective Detection at the 
Nanogram Level 
Thomas Bein* and Kelly Brown 
Department of Chemistry, University of New Mexico 
Albuquerque, New Mexico 871 31 
Gregory C. Frye and C. Jeffrey Brinker 
Sandia National Laboratories, P.O. Box 5800 
Albuquerque, New Mexico 871 85 
Received April 17, 1989 
Zeolites have long been known for their molecular sieving 
properties based upon crystalline pore structures of molecular 
dimensions. We explore strategies to introduce molecular sieving 
functions into inorganic thinfilms and membranes which are of 
current interest for sensor coatings and gas-phase separations.24 
The zeolite films offer high thermal stability (>770 K) and 
chemical resistance. Surface acoustic wave (SAW, Figure 1 A) 
devices5 can be operated as highly sensitive piezoelectric balances 
that respond to small fractions of single-crystal monolayer ad- 
sorption via frequency changes of an oscillator circuit. Since the 
response is nonselective, a number of organic and organometallic 
coatings on SAW devices have previously been explored to impart 
chemical selectivity.6 The SAW device7** (97 MHz, detection 
limit ca. 100 pg/cm2) used in the present study to measure selective 
adsorption of organic vapors (0.1% of saturation in nitrogen flow, 
295 K) consists of a single-crystal quartz substrate with interdigital 
transducers which was coated with zeolite-silica thin films and 
mounted in a test chamber with gas inlet and outlet. 
(1) Breck, D. W. Zeolite Molecular Sieves; Krieger: Malabar, FL, 1984. 
(2) Bein, T.; Brown, K.; Enzel, P.; Brinker, C. J. Mat. Res. SOC. Symp. 
Proc.; Materials Research Society: Pittsburgh, PA, 1988; Vol. 121, p 761. 
(3) Bein, T.; Brown, K.; Brinker, C. J. Studies in Surface Science and 
Catalysis (Zeolites: Facts, Figures, Future); Jacobs, P. A., van Santen, R. 
A., Eds.; Elsevier: Amsterdam, 1989; No. 49, p 887. 
(4) Bein, T.; Brown, K.; Brinker, C. J. J .  Non-Cryst. Solids, in press. 
( 5 )  (a) Wohltjen, H. Sens. Actuators 1984, 5, 307. (b) Venema, A.; 
Nieuwkoop, E.; Vellekoop, M. J.; Nieuwenhuizen, M. S.; Barendsz, A. W. 
Sens. Actuators 1986, 10, 47. 
(6) (a) Wohltjen, H.; Snow, A. W.; Barger, W. R.; Ballantine, D. S .  ZEEE 
Trans. Ultrasonics, Ferroelectrics Freq. Contr. 1987,34, 172. (b) Snow, A.; 
Wohltjen, H. Anal. Chem. 1984,56, 141 1. (c) Bryant, A.; Poirier, M.; Riley, 
G.; Lee, D. L.; Vetelino, J. F. Sens. Actuators 1983, 4, 105. (d) Nieuwen- 
huizen, M. S.; Barendsz, A. W. Sens. Actuators 1987, 1 1 ,  45. (e) Nieu- 
wenhuizen, M. S.; Nederlof, A. J.; Barendsz, A. W. Anal. Chem. 1988.60, 
230. 
(7) Frye, G. C.; Ricco, A. J.; Martin, S. J.; Brinker, C. J. Mat. Res. SOC. 
Symp. Proc.; Materials Research Society: Pittsburgh, PA, 1988; Vol. 121, 
(8) Ricco, A. J.; Frye, G. C.; Martin, S. J. Lungmuir 1989, 5,  273. 
p 349. 
0002-7863/89/1511-7640$01.50/0 
I TO CIRCUITRY AREA Ill 
Perf luorot r ibuty lamine 
Before Adsorption 71 I 
4000 3600 3200 1800 1400 
Wavenumbers 
Figure 1. A. Schematics of the surface acoustic wave device. B. Ad- 
sorption of pyridine and perfluorotributylamine vapor (1 Torr a t  295 K) 
on HY-zeolite film embedded in silica matrix derived from base-cata- 
lyzed sol (B2), degassed a t  570 K, lo-' Torr. FTIR spectra were taken 
a t  8-cm-' resolution in a stainless steel UHV cell, equipped with CaF2 
windows and connected to a steel apparatus with turbomolecular pump 
and mass spectrometer. The features in the C-H stretch region (ca. 
2800-3000 cm-') a re  due to decomposition products of the sol matrix 
deposited on the cell windows after initial heating. 
I 
I 
Figure 2. Scanning electron micrograph of crystals of zeolite H-ZSM-5 
embedded in an A2-sol derived matrixI6 on a Si wafer. 
The zeolite-silica composites are prepared from suspensions of 
small zeolite crystals in alcoholic solutions of tetraethylorthosilicate 
(TEOS) that is hydrolyzed and polymerized by acid- and base- 
catalyzed reactions resulting in extended, weakly branched 
0 1989 American Chemical Society 
J. Am. Chem. SOC. 1989, 111, 7641-7643 764 1 
structures or compact, colloidal particles, re~pec t ive ly .~~ '~  During 
deposition of the zeolite/silicate suspensions by dip-coating, the 
solvent is evaporated, and the silicate films gel, "freezing in" the 
incorporated zeolite crystals (Figure 2). Final consolidation of 
the porous matrix structure to a nonporous film occurs by viscous 
The molecular sieving behavior of zeolite YI3 (Y, crystal size, 
0.2 pm; pore size, 7.5 A), chabazite14 (CHA, crystal size, 1-3 pm; 
pore size, 3.7 A),  ZSM-515 (crystal size, 0.5 ym; pore size, 5.4 
X 5.6 A), and zeolite A (LTA, crystal size, 3 hm; pore size, 4.1 
A) crystals is maintained when they are embedded in TEOS sol-gel 
derived glassy thin  film^.^^,^' For example, the acid form of zeolite 
Y'* embedded in a silicate-based film adsorbs pyridine (5.9 8, 
kinetic diameter) as shown by consumption of the intrazeolite 
bridged hydroxyl groups (at 3540 and 3640 cm-I) and the for- 
mation of pyridinium ions (band a t  1545 cm-'; Figure 1B). 
However, exposure of a similar film to perfluorotributylamine 
(10.2 A) does not indicate any reaction with the internal bridged 
hydroxyls. Similarly, acidic chabazite-based films (pore size 3.7 
A) react with ammonia (2.6 A) but not with tributylamine (8.1 
The selectivity of zeolite films is maintained even in aqueous 
systems. For example, pyridine or N H 3  diffused into Cu(I1)- 
containing faujasite-silica thin filmsI9 from aqueous solution co- 
ordinate to intrazeolite Cu(I1) to form [CuL4I2+ complexes as 
shown by the appearance of corresponding ligand vibrations, e.g., 
at 1610, 1543, 1487, and 1450 cm-' for [ C ~ ( p y ) ~ ] ~ + .  When CHA 
(3.7 A) or LTA (4.1 A) are incorporated in the glassy matrix, 
pyridine is completely excluded from the pores. In aqueous phase, 
the pyridine molecules bind selectively to Cu-FAU films but not 
to the corresponding N a  or NH,  forms. 
Having demonstrated the chemical and size-based molecular 
selectivity of zeolite-silica films, we present the first application 
of these films as coatings on SAW devices. W e  note that thin 
silica films alone, processed similarly, have extremely low porosity 
(<2%) and surface areas ( 1  cm2/cm2).8 A glassy silica matrix 
of ca. 150 nm thickness, embedding crystals of ZSM-5 (pore size 
5.4 X 5.6 A), was coated on the active surface of a S A W  device. 
A striking difference in frequency response to different probe 
molecules was observed. While vapors of MeOH (ca. 3.8 kinetic 
diameter) and PrOH (ca. 4.7 A) adsorb a t  levels of 500-800 
ng/cm2 in the film, the response to isooctane (2,2,4-trimethyl- 
pentane; 6.2 8) is minimal (below 5 ng/cm2). This dramatic 
difference can be understood if the kinetic diameters of these 
molecules are compared to the pore size of the zeolite film. The 
amount of vapor adsorbed in the film is in reasonable agreement 
with that calculated from crystal area densities observed in electron 
micrographs. 
A). 
(9) Brinker, C. J.; Keefer, K. D.; Schaefer, D. W.; Ashley, C. S. J .  Non- 
(10) Brinker, C. J.; Scherer, G. W. J .  Non-Cryst. Solids 1985, 70, 301. 
(11) Brinker, C. J.; Scherer, G. W.; Roth, E. P. J .  Non-Cryst. Solids 1985, 
Cryst. Solids 1982, 48, 47. 
72  769 . _, 
(12) Brinker, C. J.; Drotning, W. D.; Scherer, G. W. In Better Ceramics 
through Chemisrry; Brinker, C. J., Clark, D. E., Ulrich, D. R., Eds.; Elsevier: 
Amsterdam, 1984; p 25. 
(13) Synthesized according to U S .  Patent 4,175,059, 1979, example 3. 
(14) Synthesized according to ref 1, p 288. 
(15) Synthesized according to van Santen, R. A,; Keijsper, J.; Ooms, G.; 
Kortbeek, A. G. T. G. In New Deuelopments in Zeolite Science and Tech- 
nology; Murakami, Y., Iijima, A,, Ward, J. W., Eds.; Kodansha: Tokyo, 
Japan, 1986; p 169. 
(16) Silica sols were prepared from a stock solution of 61.0 mL of TEOS 
(tetraethylorthosilicate), 61.0 mL of EtOH, and 5.0 mL of 0.04 M HC1. For 
the preparation of A2 sol, IO mL of the stock solution was combined with 0.12 
mL of 1 .O M HCI and 0.4 mL of H 2 0 .  B2 sol was obtained by adding 1.0 
mL of 0.05 M N H 4 0 H  to 10 mL of the stock solution. See: Brinker, C. J.;  
Keefer, K. D.; Schaefer, D. W.; Assink, R. A,; Kay, B. D.; Ashley, C. S. J .  
Non-Cryst. Solids 1984, 63, 45. 
(17) Dip-coated composites were made from suspensions of 0.5-2.5 g 
zeolite in 2.5 mL of silica sol which was diluted with 5 mL of EtOH and 
coated on Si wafers at 50 mm/min vertical pulling rate. All wafers were dried 
in air at 360 K. 
(18) Obtained by degassing the NH4-exchanged form at 670 K in vacuo. 
(19) Zeolites were 50% ion-exchanged with 0.1 M CU(NO,)~ prior to 
dispersion in  the sol. 
We have established that (i) zeolite-silica thin films with mo- 
lecular sieving properties can be prepared, (ii) the films can be 
modified such that different chemical selectivities result, and (iii) 
these zeolite films can be utilized to introduce chemical selectivity 
to highly sensitive surface acoustic wave devices. Other zeolite 
thin film coatings with modified chemical selectivities are presently 
being explored. 
Acknowledgment. Financial support from the National Science 
Foundation (DMR-8706 167) is gratefully acknowledged. A 
portion of the work was performed a t  Sandia National Labora- 
tories and supported by the U S .  Department of Energy under 
contract number DE-AC-04-76DP00789. W e  appreciate the 
technical assistance of Barbara Lammie. 
Novel Anionic Polymerization of Masked Disilenes to 
Polysilylene High Polymers and Block Copolymers' 
Kenkichi Sakamoto, Kuninori Obata, Hiroki Hirata, 
Masashi Nakajima, and Hideki Sakurai* 
Department of Chemistry, Faculty of Science 
Tohoku University, Aoba- ku, Sendai 980, Japan 
Received February 8, 1989 
Polysilylenes, the linear silicon-silicon bonded polymers, have 
several interesting properties and are a subject of current intense 
investigations.2 Polysilylenes are prepared mostly by the 
Wurtz-type coupling reactions of dichlorodialkylsilanes which, 
however, have several difficulties such as the poor control of 
structure, molecular weight, and polydispersity. The yields of 
polymers are also usually In this paper, we will describe 
an entirely novel method of preparing polysilylenes based on 
anionic polymerization of masked d i~ i l enes .~  
After examination of several possibilities, we have found that 
l-phenyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes ( lb- ld)  can be 
used for anionic p01ymerization.l~ Alkyllithiums such as n- and 
(1) Chemistry of Organosilicon Compounds 257. 
(2) (a) West, R. J .  Organomet. Chem. 1986, 300, 327. (b) West, R. 
Organopolysilanes. In Comprehensive Organometallic Chemistry; Abel, E., 
Ed.; Pergamon: Oxford, England, 1982; Chapter 9.4, pp 365. Recent ap- 
plications of polysilylenes as S i c  precursors,' in microlithography,4 as pho- 
to initiator^,^ and in reprography6 are noteworthy. 
(3) (a) Yajima, S.; Hayashi, J.; Omori, M. Chem. Lert. 1975, 931. (b) 
Yajima, S.; Shishido, T.; Kayano, H. Nature 1976, 264, 237. (c) Yajima, S.; 
Omori, M.; Hayashi, J.; Okamura, K.; Matsuzawa, T.; Liaw, C. Chem. Lett. 
1976, 551. (d) West, R.; David, L. D.; Djurovich, P. I . ;  Yu, H.; Sinclair, H. 
Am. Ceram. Soc. Bull. 1983, 62, 899. 
(4) (a) Gobbi, G. C.; Fleming, W. W.; Sooriyakumaran, R.; Miller, R. D. 
J .  Am.  Chem. SOC. 1986, 108, 5624. (b) West, R.; Wolff, A. R.; Peterson, 
D. J .  Radiation Curing 1986, 13, 35. 
( 5 )  Wolff, A. R.; West, R. Appl. Organomet. Chem. 1987, 1, 7 .  
(6) Abkowitz, M.; Knier, F. E.; Yuh, H.-J.; Weagley, R. J.; Stolka, M. 
Solid State Commun. 1987, 62, 547. 
(7) A few other routes are indicated for the preparation of polysilylenes 
such as catalyzed dehydrogenative coupling of primary organosilanes, but at 
this moment the method is limited to the preparation of low molecular weight 
oligomers of arylsilanes.* 
(8) (a) Aitkin, C. T.; Harrod, J. F.; Samuel, E. J .  Organomet. Chem. 1985, 
279, C11. (b) Aitkin, C. T.; Harrod, J .  F.; Samuel, E. J .  Am. Chem. Soc. 
1986, 108, 4095. (c) Aitkin, C. T.; Harrod, J. F.; Samuel, E. Can. J .  Chem. 
1986, 64, 1677. 
(9) Conceptually, polymerization of disilenes, the silicon-silicon double 
bonded species, may be a straightforward route to linear polysilylenes. It is 
not possible in practice though, because disilenes are not stable enough to be 
isolated except for those with very bulky substituents.1° Incidentally, 7,8- 
disilabicyclo[2.2.2]octa-2,5-dienes have been known as precursors of disilenes; 
Roark and Peddle" reported generation of disilenes by thermolysis of la. We 
have also reported that a 2,3-benzo-7,8-disilabicyclo[2.2.2]octa-2,5-diene 
system afforded cis- and trans- 1,2-diphenyl-l,2-dimethyldisilenes by ther- 
molysis.'2 Therefore, we have expected that these 7,8-disilabicyclo[2.2.2]- 
octa-2,5-diene systems could behave as masked disilenes even in ionic reac- 
tions. 
(10) (a) West, R.; Fink, M. J.; Michl, J. Science (Washington, D. C . )  1981, 
214, 1343. (b) Masamune, S.; Hanzawa, Y.; Murakami, S.; Bally, T.; Blout, 
J. F. J .  Am. Chem. SOC. 1982, 104, 1150. 
0002-7863/89/1511-7641$01.50/0 0 1989 American Chemical Society 


Molecular sieve sensors for selective detection at the nanogram level

Open Access LMU ( Ludwig-Maximilians-Univ. München)

7640 J.  Am. Chem. SOC. 1989,111, 7640-7641 Acknowledgment. This research was supported by PHS Grant CA28824. N M R  spectra were obtained through the auspices of the Northeast Regional NSF/NMR Facility at  Yale University, which was supported by N S F  Chemistry Division Grant C H E  7916210. An N.I.H. Postdoctoral Fellowship to J.N.H. (Grant 1 F32 CA08341-02) is gratefully acknowledged. In addition, we thank Dr. Nathan B. Mantlo of Merck Sharp & Dohme Research Laboratories, Rahway, N J  for helpful discussions. Supplementary Material Available: Spectral data (IR, 'H  NMR,  and MS) for compounds 8-16, 18, and 20, tables of fractional coordinates, bond distances, torsional angles, and an- isotropic temperature factors and summary of the X-ray crys- tallographic determinations and structures of compounds 13 and 20 (17 pages). Ordering information is given on any current masthead page. Molecular Sieve Sensors for Selective Detection at the Nanogram Level Thomas Bein* and Kelly Brown Department of Chemistry, University of New Mexico Albuquerque, New Mexico 871 31 Gregory C. Frye and C. Jeffrey Brinker Sandia National Laboratories, P.O. Box 5800 Albuquerque, New Mexico 871 85 Received April 17, 1989 Zeolites have long been known for their molecular sieving properties based upon crystalline pore structures of molecular dimensions. We explore strategies to introduce molecular sieving functions into inorganic thinfilms and membranes which are of current interest for sensor coatings and gas-phase separations.24 The zeolite films offer high thermal stability (>770 K) and chemical resistance. Surface acoustic wave (SAW, Figure 1 A) devices5 can be operated as highly sensitive piezoelectric balances that respond to small fractions of single-crystal monolayer ad- sorption via frequency changes of an oscillator circuit. Since the response is nonselective, a number of organic and organometallic coatings on SAW devices have previously been explored to impart chemical selectivity.6 The SAW device7** (97 MHz, detection limit ca. 100 pg/cm2) used in the present study to measure selective adsorption of organic vapors (0.1% of saturation in nitrogen flow, 295 K) consists of a single-crystal quartz substrate with interdigital transducers which was coated with zeolite-silica thin films and mounted in a test chamber with gas inlet and outlet. (1) Breck, D. W. Zeolite Molecular Sieves; Krieger: Malabar, FL, 1984. (2) Bein, T.; Brown, K.; Enzel, P.; Brinker, C. J. Mat. Res. SOC. Symp. Proc.; Materials Research Society: Pittsburgh, PA, 1988; Vol. 121, p 761. (3) Bein, T.; Brown, K.; Brinker, C. J. Studies in Surface Science and Catalysis (Zeolites: Facts, Figures, Future); Jacobs, P. A., van Santen, R. A., Eds.; Elsevier: Amsterdam, 1989; No. 49, p 887. (4) Bein, T.; Brown, K.; Brinker, C. J. J .  Non-Cryst. Solids, in press. ( 5 )  (a) Wohltjen, H. Sens. Actuators 1984, 5, 307. (b) Venema, A.; Nieuwkoop, E.; Vellekoop, M. J.; Nieuwenhuizen, M. S.; Barendsz, A. W. Sens. Actuators 1986, 10, 47. (6) (a) Wohltjen, H.; Snow, A. W.; Barger, W. R.; Ballantine, D. S .  ZEEE Trans. Ultrasonics, Ferroelectrics Freq. Contr. 1987,34, 172. (b) Snow, A.; Wohltjen, H. Anal. Chem. 1984,56, 141 1. (c) Bryant, A.; Poirier, M.; Riley, G.; Lee, D. L.; Vetelino, J. F. Sens. Actuators 1983, 4, 105. (d) Nieuwen- huizen, M. S.; Barendsz, A. W. Sens. Actuators 1987, 1 1 ,  45. (e) Nieu- wenhuizen, M. S.; Nederlof, A. J.; Barendsz, A. W. Anal. Chem. 1988.60, 230. (7) Frye, G. C.; Ricco, A. J.; Martin, S. J.; Brinker, C. J. Mat. Res. SOC. Symp. Proc.; Materials Research Society: Pittsburgh, PA, 1988; Vol. 121, (8) Ricco, A. J.; Frye, G. C.; Martin, S. J. Lungmuir 1989, 5,  273. p 349. 0002-7863/89/1511-7640$01.50/0 I TO CIRCUITRY AREA Ill Perf luorot r ibuty lamine Before Adsorption 71 I 4000 3600 3200 1800 1400 Wavenumbers Figure 1. A. Schematics of the surface acoustic wave device. B. Ad- sorption of pyridine and perfluorotributylamine vapor (1 Torr a t  295 K) on HY-zeolite film embedded in silica matrix derived from base-cata- lyzed sol (B2), degassed a t  570 K, lo-' Torr. FTIR spectra were taken a t  8-cm-' resolution in a stainless steel UHV cell, equipped with CaF2 windows and connected to a steel apparatus with turbomolecular pump and mass spectrometer. The features in the C-H stretch region (ca. 2800-3000 cm-') a re  due to decomposition products of the sol matrix deposited on the cell windows after initial heating. I I Figure 2. Scanning electron micrograph of crystals of zeolite H-ZSM-5 embedded in an A2-sol derived matrixI6 on a Si wafer. The zeolite-silica composites are prepared from suspensions of small zeolite crystals in alcoholic solutions of tetraethylorthosilicate (TEOS) that is hydrolyzed and polymerized by acid- and base- catalyzed reactions resulting in extended, weakly branched 0 1989 American Chemical Society J. Am. Chem. SOC. 1989, 111, 7641-7643 764 1 structures or compact, colloidal particles, re~pec t ive ly .~~ '~  During deposition of the zeolite/silicate suspensions by dip-coating, the solvent is evaporated, and the silicate films gel, "freezing in" the incorporated zeolite crystals (Figure 2). Final consolidation of the porous matrix structure to a nonporous film occurs by viscous The molecular sieving behavior of zeolite YI3 (Y, crystal size, 0.2 pm; pore size, 7.5 A), chabazite14 (CHA, crystal size, 1-3 pm; pore size, 3.7 A),  ZSM-515 (crystal size, 0.5 ym; pore size, 5.4 X 5.6 A), and zeolite A (LTA, crystal size, 3 hm; pore size, 4.1 A) crystals is maintained when they are embedded in TEOS sol-gel derived glassy thin  film^.^^,^' For example, the acid form of zeolite Y'* embedded in a silicate-based film adsorbs pyridine (5.9 8, kinetic diameter) as shown by consumption of the intrazeolite bridged hydroxyl groups (at 3540 and 3640 cm-I) and the for- mation of pyridinium ions (band a t  1545 cm-'; Figure 1B). However, exposure of a similar film to perfluorotributylamine (10.2 A) does not indicate any reaction with the internal bridged hydroxyls. Similarly, acidic chabazite-based films (pore size 3.7 A) react with ammonia (2.6 A) but not with tributylamine (8.1 The selectivity of zeolite films is maintained even in aqueous systems. For example, pyridine or N H 3  diffused into Cu(I1)- containing faujasite-silica thin filmsI9 from aqueous solution co- ordinate to intrazeolite Cu(I1) to form [CuL4I2+ complexes as shown by the appearance of corresponding ligand vibrations, e.g., at 1610, 1543, 1487, and 1450 cm-' for [ C ~ ( p y ) ~ ] ~ + .  When CHA (3.7 A) or LTA (4.1 A) are incorporated in the glassy matrix, pyridine is completely excluded from the pores. In aqueous phase, the pyridine molecules bind selectively to Cu-FAU films but not to the corresponding N a  or NH,  forms. Having demonstrated the chemical and size-based molecular selectivity of zeolite-silica films, we present the first application of these films as coatings on SAW devices. W e  note that thin silica films alone, processed similarly, have extremely low porosity (<2%) and surface areas ( 1  cm2/cm2).8 A glassy silica matrix of ca. 150 nm thickness, embedding crystals of ZSM-5 (pore size 5.4 X 5.6 A), was coated on the active surface of a S A W  device. A striking difference in frequency response to different probe molecules was observed. While vapors of MeOH (ca. 3.8 kinetic diameter) and PrOH (ca. 4.7 A) adsorb a t  levels of 500-800 ng/cm2 in the film, the response to isooctane (2,2,4-trimethyl- pentane; 6.2 8) is minimal (below 5 ng/cm2). This dramatic difference can be understood if the kinetic diameters of these molecules are compared to the pore size of the zeolite film. The amount of vapor adsorbed in the film is in reasonable agreement with that calculated from crystal area densities observed in electron micrographs. A). (9) Brinker, C. J.; Keefer, K. D.; Schaefer, D. W.; Ashley, C. S. J .  Non- (10) Brinker, C. J.; Scherer, G. W. J .  Non-Cryst. Solids 1985, 70, 301. (11) Brinker, C. J.; Scherer, G. W.; Roth, E. P. J .  Non-Cryst. Solids 1985, Cryst. Solids 1982, 48, 47. 72  769 . _, (12) Brinker, C. J.; Drotning, W. D.; Scherer, G. W. In Better Ceramics through Chemisrry; Brinker, C. J., Clark, D. E., Ulrich, D. R., Eds.; Elsevier: Amsterdam, 1984; p 25. (13) Synthesized according to U S .  Patent 4,175,059, 1979, example 3. (14) Synthesized according to ref 1, p 288. (15) Synthesized according to van Santen, R. A,; Keijsper, J.; Ooms, G.; Kortbeek, A. G. T. G. In New Deuelopments in Zeolite Science and Tech- nology; Murakami, Y., Iijima, A,, Ward, J. W., Eds.; Kodansha: Tokyo, Japan, 1986; p 169. (16) Silica sols were prepared from a stock solution of 61.0 mL of TEOS (tetraethylorthosilicate), 61.0 mL of EtOH, and 5.0 mL of 0.04 M HC1. For the preparation of A2 sol, IO mL of the stock solution was combined with 0.12 mL of 1 .O M HCI and 0.4 mL of H 2 0 .  B2 sol was obtained by adding 1.0 mL of 0.05 M N H 4 0 H  to 10 mL of the stock solution. See: Brinker, C. J.;  Keefer, K. D.; Schaefer, D. W.; Assink, R. A,; Kay, B. D.; Ashley, C. S. J .  Non-Cryst. Solids 1984, 63, 45. (17) Dip-coated composites were made from suspensions of 0.5-2.5 g zeolite in 2.5 mL of silica sol which was diluted with 5 mL of EtOH and coated on Si wafers at 50 mm/min vertical pulling rate. All wafers were dried in air at 360 K. (18) Obtained by degassing the NH4-exchanged form at 670 K in vacuo. (19) Zeolites were 50% ion-exchanged with 0.1 M CU(NO,)~ prior to dispersion in  the sol. We have established that (i) zeolite-silica thin films with mo- lecular sieving properties can be prepared, (ii) the films can be modified such that different chemical selectivities result, and (iii) these zeolite films can be utilized to introduce chemical selectivity to highly sensitive surface acoustic wave devices. Other zeolite thin film coatings with modified chemical selectivities are presently being explored. Acknowledgment. Financial support from the National Science Foundation (DMR-8706 167) is gratefully acknowledged. A portion of the work was performed a t  Sandia National Labora- tories and supported by the U S .  Department of Energy under contract number DE-AC-04-76DP00789. W e  appreciate the technical assistance of Barbara Lammie. Novel Anionic Polymerization of Masked Disilenes to Polysilylene High Polymers and Block Copolymers' Kenkichi Sakamoto, Kuninori Obata, Hiroki Hirata, Masashi Nakajima, and Hideki Sakurai* Department of Chemistry, Faculty of Science Tohoku University, Aoba- ku, Sendai 980, Japan Received February 8, 1989 Polysilylenes, the linear silicon-silicon bonded polymers, have several interesting properties and are a subject of current intense investigations.2 Polysilylenes are prepared mostly by the Wurtz-type coupling reactions of dichlorodialkylsilanes which, however, have several difficulties such as the poor control of structure, molecular weight, and polydispersity. The yields of polymers are also usually In this paper, we will describe an entirely novel method of preparing polysilylenes based on anionic polymerization of masked d i~ i l enes .~  After examination of several possibilities, we have found that l-phenyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes ( lb- ld)  can be used for anionic p01ymerization.l~ Alkyllithiums such as n- and (1) Chemistry of Organosilicon Compounds 257. (2) (a) West, R. J .  Organomet. Chem. 1986, 300, 327. (b) West, R. Organopolysilanes. In Comprehensive Organometallic Chemistry; Abel, E., Ed.; Pergamon: Oxford, England, 1982; Chapter 9.4, pp 365. Recent ap- plications of polysilylenes as S i c  precursors,' in microlithography,4 as pho- to initiator^,^ and in reprography6 are noteworthy. (3) (a) Yajima, S.; Hayashi, J.; Omori, M. Chem. Lert. 1975, 931. (b) Yajima, S.; Shishido, T.; Kayano, H. Nature 1976, 264, 237. (c) Yajima, S.; Omori, M.; Hayashi, J.; Okamura, K.; Matsuzawa, T.; Liaw, C. Chem. Lett. 1976, 551. (d) West, R.; David, L. D.; Djurovich, P. I . ;  Yu, H.; Sinclair, H. Am. Ceram. Soc. Bull. 1983, 62, 899. (4) (a) Gobbi, G. C.; Fleming, W. W.; Sooriyakumaran, R.; Miller, R. D. J .  Am.  Chem. SOC. 1986, 108, 5624. (b) West, R.; Wolff, A. R.; Peterson, D. J .  Radiation Curing 1986, 13, 35. ( 5 )  Wolff, A. R.; West, R. Appl. Organomet. Chem. 1987, 1, 7 .  (6) Abkowitz, M.; Knier, F. E.; Yuh, H.-J.; Weagley, R. J.; Stolka, M. Solid State Commun. 1987, 62, 547. (7) A few other routes are indicated for the preparation of polysilylenes such as catalyzed dehydrogenative coupling of primary organosilanes, but at this moment the method is limited to the preparation of low molecular weight oligomers of arylsilanes.* (8) (a) Aitkin, C. T.; Harrod, J. F.; Samuel, E. J .  Organomet. Chem. 1985, 279, C11. (b) Aitkin, C. T.; Harrod, J .  F.; Samuel, E. J .  Am. Chem. Soc. 1986, 108, 4095. (c) Aitkin, C. T.; Harrod, J. F.; Samuel, E. Can. J .  Chem. 1986, 64, 1677. (9) Conceptually, polymerization of disilenes, the silicon-silicon double bonded species, may be a straightforward route to linear polysilylenes. It is not possible in practice though, because disilenes are not stable enough to be isolated except for those with very bulky substituents.1° Incidentally, 7,8- disilabicyclo[2.2.2]octa-2,5-dienes have been known as precursors of disilenes; Roark and Peddle" reported generation of disilenes by thermolysis of la. We have also reported that a 2,3-benzo-7,8-disilabicyclo[2.2.2]octa-2,5-diene system afforded cis- and trans- 1,2-diphenyl-l,2-dimethyldisilenes by ther- molysis.'2 Therefore, we have expected that these 7,8-disilabicyclo[2.2.2]- octa-2,5-diene systems could behave as masked disilenes even in ionic reac- tions. (10) (a) West, R.; Fink, M. J.; Michl, J. Science (Washington, D. C . )  1981, 214, 1343. (b) Masamune, S.; Hanzawa, Y.; Murakami, S.; Bally, T.; Blout, J. F. J .  Am. Chem. SOC. 1982, 104, 1150. 0002-7863/89/1511-7641$01.50/0 0 1989 American Chemical Society 

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