J. Phys. Chem. 1987, 91, 1659-1663
1659
Structures and Thermal and Hydrothermal Stabilities of Sulfonated Poly(organosi1oxanes) by *‘Si and 13C CP/MAS NMR Sadakatsu Suzuki, Yoshio Ono,* Department of Chemical Engineering, Tokyo Institute of Technology, Ookayama, Meguro- ku. Tokyo 152, Japan
Shin-ichi Nakata, and Sachio Asaoka Research and Development Center, Chiyoda Chemical Engineering and Construction Company, Ltd., Moriyacho. Kanagawaku, Yokohama 221, Japan (Received: August 5, 1986; In Final Form: October 14, 1986)
High-resolution 29Siand 13Ccross polarization/magic-angle spinning (CP/MAS) NMR spectroscopies have been applied to poly((sulfopheny1)siloxane) and poly((sulfopropy1)siloxane) in order to examine their thermal and hydrothermal stability. The effects of the treatments on the catalytic activity for the alcohol dehydration were also studied. Under nonsteaming conditions, both siloxanes have much higher thermal stability than Amberlyst-15. Thermal stability is in a decreasing order, poly((sulfopheny1)siloxane) (573 K) > poly((sulfopropy1)siloxane) (543 K) > Amberlyst-15 (468 K), while the thermal stability under steaming conditions is in the order of poly((sulfopropy1)siloxane) (543 K) > poly((sulfopheny1)siloxane) = Amberlyst-15 (468 K). The thermal degradation of the poly((sulfopheny1)siloxane) mainly occurs by the rupture of the C-Si bonds between the benzene ring and the siloxane chain. The steam greatly affects the thermal stability of poly((su1fophenyl)siloxane). Thus, under steaming conditions, thermal degradation occurred at much lower temperatures than under nonsteaming conditions. The thermal degradation of the poly((sulfopropy1)siloxane) mainly occurs at the C-C bond in the sulfopropyl groups. Steam does not affect the thermal stability of poly((sulfopropy1)siloxane).
Introduction Cation-exchange resins like Amberlyst-15 have been used as acid catalysts for industrial processes.’-2 Owing to the presence of sulfo groups, they are highly acidic and active catalysts for proton-catalyzed reactions. The thermal stability of the resins is, however, not satisfactory. Thus, most of the resins are stable only up to 423 K,3 except for the perfluorinated resins which are supposed to be stable up to 463 K.4 Cross-linked poly(organosi1oxanes) are one of the most heatresistant class of polymers. Poly(dimethy1siloxane) starts to decompose at about 653 K,5 while poly(phenylsi1oxane)is more stable and starts to decompose at about 753 K.6 In a previous paper, we reported that sulfonated poly(organosiloxanes) have high catalytic activities for the dehydration of alcohols and the esterification of acetic acid with 2-methylpropan01.~ They are much more active than Amberlyst-15 for the vapor-phase nitration of benzene with nitrogen dioxide.8 It was also suggested from the effect of the pretreatment of the catalysts that they were thermally more stable than the organic resins. High-resolution solid-state CP/MAS N M R has been proven to be a powerful technique for structural elucidation of polymeric organosilanes or silane-modified silica gel.”3 In this work, we used 29Siand 13CN M R spectroscopy to monitor the structure of sulfonated poly(organosiloxanes), with special emphasis on their structural change with the thermal and hydrothermal treatments. The structural change as observed by N M R is correlated with the change in the catalytic activity for the dehydration of alcohols. (1) Bochermer, M. B.; Gerber, S. M.; Vieth, W.; Rodger, A. J. Ind. Eng. Chem. Fundam. 1965, 4,4. ( 2 ) Carlyle, R. M. Chem. Ind. 1982, 21, 561. (3) Kapura, J. M.; Gates, B. C. Ind. Eng. Chem. Prod. Res. Deu. 1973, 12, 62. (4) Waller, F. J. Coral. Rev. Sci. Eng. 1986, 28, 1. (5) Knight, G . J. Br. Polym. J . 1978, 10, 187.
(6) Wada, T.; Ishizaka,
Zassi 1963, 66, 631.
M.; Iwamatu, I.; Kawasumi, K. Kougyoukagaku
(7) Manuscript in preparation. (8) Suzuki, S.; Tohmori, K.; Ono, Y . Chem. Left.1986, 747. (9) Sindorf, D. W.; Maciel, G . E. J . Am. Chem. SOC.1983, 105, 1487. (10) Lippmaa, E.; Magi, M.; Samoson, A.; Engelhardt, G.; Grimmer, A.-R. J . Am. Chem. SOC.1980, 102, 4889. (11) Pines, A,; Gibby, M. G.; Waugh, J. S. J . Chem. Phys. 1973, 59, 569. (12) Maciel, G. E.; Sindorf, D. W. J . Am. Chem. SOC.1980, 102, 7606. (13) Zaper, A. M.; Koehig, J. L. Adv. ColloidInterfaceSci. 1985, 22, 113.
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TABLE I: Content of Organic Groups in Poly(pheny1siloxane) and Its Sulfonated Form no.
monomer ratiob
R~~
RNMRd
1
0.1 1
2
0.43
2 3
1.oo
0.19 0.42 0.19 0.92
0.25 0.59 0.42 1.15
“Polymer no. 2 after sulfonation. *The ratio in starting monomers; triethoxyphenylsilane/tetraethoxysilane. The ratio of ( RSi03) and (SO,), estimated from elemental analysis. “The ratio of the signal area of the peaks due to (RSiO,) and those (SO,) in the 29SiNMR spectrum. The mechanism of the thermal degradation of sulfonated organosilanes is also discussed.
Experimental Section Preparation of Poly(organosi1oxanes). Two types of poly(organosiloxanes) were prepared by cocondensation of tetraalkoxysilane and organotrialkoxysilane according to the method described by Unger et al.14 Polysiloxanes with phenyl groups were prepared from triethoxyphenylsilane and tetraethoxysilane. Polysiloxanes with 3-mercaptopropyl groups were prepared from trimethoxy(3-mercaptopropy1)silane and tetramethoxysilane. Further details of the preparation method are describeds elsewhere. Tetraalkoxysilane (Kanto Chemical Co.) and trialkoxyorganosilane (Shin-etsu Silicon Co.) were used without further purification. Polysiloxane with phenyl groups was sulfonated by refluxing a solution of chlorosulfuric acid and chloroform (molar ratio 1:4) containing 10 g of the polymer for 3 h. The number of sulfo groups of the polymer which was prepared from the monomer mixture with the molar ratio of phenyltriethoxysilane and tetraethoxysilane of 3:7 was estimated as 2.0 mmol g-I by the titration method. Poly( (3-mercaptopropy1)siloxane)was converted to the sulfonated polymer by oxidizing the mercapto groups with potassium permanganate.15 The sulfonated polymer thus obtained has sulfo groups of 0.8 mmol g-I. Catalytic Reactiom The dehydration of ethanol and 2-propanol was carried out with a continuous flow reactor operating at (14) Unger, K. K.; Becker, N.; Roumeliotos, P. J . Chromafogr. 1976, 125, 115. (1 5) Wheals, B. B. J . Chromatogr. 1979, 1 1 7, 263.
0 1987 American Chemical Society
1660 The Journal of Physical Chemistry, Vol. 91, No. 6, 1987
Suzuki et al.
-GO -90 -120 -60 -90 -120 -60 -90 -120 6 P P ~ Figure 2. Effect of the cross-polarization time on the 29SiNMR of poly(phenylsi1oxane). CP contact time: (a) 0.5 ms, (b) 3 ms, (c) I O ms.
-60
-90
-120
-60
6
-90
-120
ppm
Figure 1. 29SiNMR spectra of poly(phenylsi1oxane) and poly((sulf0pheny1)siloxane): (a) no. 1, (b) no. 2, (c) no. 3, (d) no. 2'; for sample numbers, see Table I.
atomospheric pressure. The catalysts were pelleted, crushed, and assorted into grains of 9-16 mesh. The gas withdrawn from the outlet of the reactor was analyzed periodically by gas chromatography. NMR Measurements. 29Siand I3Ccross polarization and magic angle spinning (CP/MAS) N M R spectra were recorded on a JEOL JNM-GX270 FT N M R with a solid-state CP/MAS unit (NM-GSH 27 MU) at 53.7 and 67.9 MHz, respectively. The spinning rate used was close to 3.5 kHz and all measurements were carried out at rmm temperature. 29Siand I3C NMR spectra were run with a 4-s recycle time and 3-ms C P contact, and obtained by madding 1880-9000 acquisitions, the sweep widths being 20 000 and 27 027 Hz, respectively.
Results and Discussion 1 . Structure of Poly(organosi1oxanes). Poly(phenylsi1oxane). Three kinds of poly(phenylsi1oxanes) were prepared by changing the ratios of starting monomers, triethoxyphenylsilane and tetraethoxysilane. From the concentration of phenyl groups determined with the elemental analysis for carbon, the ratios (RE) of silicon atoms bound to an organic group, ( RSi03), and those not bound to an organic group, ( S O 4 ) ,were estimated. As shown in Table I, the RE values are in close agreement with the molar ratios of the starting monomers except for sample 1 . The 29SiCP/MAS N M R spectra of the three polymers are shown in Figure 1, a-c, where fiv: peaks are resolved at -70, -78 to -79, -90 (shoulder), -101, and -109 to -110 ppm. Based on the work of Engelhardt et a1.16 on methyl(pheny1)silicone resin, the peaks at -70 and -78 to -79 ppm can be assigned to silicon nuclei with the local environment of Ph(HO)Si*(OSi=)2 and p h S i * ( O S i ~ )respectively. ~, The rest of the signals is similar to those observed in the spectrum of silica and easily assigned as follows: -90 ppm, (HO),Si*(OSi=),; -101 ppm, (HO)Si(OSi=)3;-109 to -1 10; s i * ( O S i ~ ) ~Thus, . the signals in the 29Si NMR spectra are divided into two groups: signals due to silicon nuclei in R S i 0 3 and those due to the nuclei in SiO+ In Table I, the ratios of the integrated intensities of signals of the two types of silicon nuclei (RNMR) are listed. The values of RNMv are larger than those of RE.This is probably because the relative sensitivity of 29SiC P N M R depends on the local environment of silicon atoms. For example, Maciel et al." studied the 29SiN M R of silica gel and reported that Si nuclei in Si*(OS=), are relatively insensitive compared with Si nuclei bound to OH groups, where protons exist near silicon nuclei. It is (16) Engelhardt, G.; Jancke, H.; Lippmaa, E.: Samoson, A. J . Organometal. Chem. 1981, 210, 295. (17) Maciel. G . E.; Sindorf, D. W. J . Am. Chem. Soc. 1980, 102. 7606.
140 120
140 120
1LO 120
140 120
6 PPm Figure 3. "C NMR spectra of polyphenylsiloxane (a-c) and poly((sulfopheny1)siloxane)(d): (a) no. 1, (b) no. 2, (c) no. 3, (d) no. 2'; for sample numbers, see Table I. TABLE II: Effects of Thermal and Hydrothermal Treatments on the Composition of Poly( (sulfopheny1)siloxane)
elemental analysis treatment none N2" N2
+ H20b
temp, K wt 9% C wt % S 12 468 503 603 468 503 603
14 15 13
5 5 6
6
14
5
9
5
5
2
(SO3H)/
(RSi03) 0.9 0.8 0.8 0.9 0.8 1.3 1.1
REC R N M R d 0.19 0.18
0.42 0.39
0.21
0.42
0.18 0.18 0.11 0.04
0.34 0.41 0.17 0.09
"Under a stream of N2 (101 kPa) for 12 h. bUnder a stream of N 2 kPa) + H 2 0 (25 kPa) for 12 h. 'The ratio of (RSiO,) and ( S O 4 ) ,estimated from elemental analysis. dThe ratio of the signal area of the peaks due to (RSi03) and those ( S O 4 )in the 29SiNMR spectrum. (76
reasonable to assume that a similar situation exists in poly(organosiloxanes). Thus, the intensity ratios, RNMR, must be larger than the actual atomic ratios, R E . This is further supported by the following experiments. (1) The increase in CP contact time resulted in the relative enhancement of the Si*(OSi=)4 signal, as is shown in Figure 2. The values of RNMR are 0.48, 0.52, and 0.54 for the spectra with contact times of 0.5, 3, and 10 ms, respectively. (2) The use of the gate-decoupling method instead of the cross-polarization method also led to the relative enhancement of S i * ( o S i ~signal. )~ Thus, RNMR does not represent the real values of the ratio of silicon atoms bound to an organic group and those not bound to an organic group. The relative value of RxMR can still be a convenient measure of the ratio for discussing the chemical transformation of particular samples. Figure 3 shows the 13CN M R spectra of poly(phenylsiloxane). Based on the work of Nguyen-Duc-Chuy et aI.'* on triethoxyphenylsiloxane, the peaks at 134 and 127 ppm can be assigned to ortho and meta carbon nuclei in a phenyl group, respectively. (1 8) Nguyen-Duc-Chuy:Chvalovsky, V.; Schraml, J.; Magi, M.;Lippmaa, E. Collecf. Czech. Chem. Commun. 1975, 40, 875.
The Journal of Physical Chemistry, Vol. 91, No. 6, 1987
Stability of Sulfonated Poly(organosi1oxanes) TABLE III: Effects of Thermal and Hydrothermal Treatments on the Composition of Poly( (sulfopropy1)siloxane) elemental analysis
(SO,H)/ treatment none' none N2b N2
+ H20C
temp, K
468 603 468 603
wt % C 13 12 13 11 14 11
wt % S 11 11 11 3 11 3
(RSiO,) 1.o 1.o 0.9
0.3 0.8 0.3
RNMRd
0.97
1.oo 1.03 0.86 1.03 0.74
'Poly((mercaptopropy1)siloxane). bUnder a stream of N2 (101 kPa) for 12 h. cUnder a stream of N2 (76 kPa) + H 2 0 (25 kPa) for 12 h. dThe ratio of the signal area of the peaks due to ( R S i 0 3 ) and those ( S O 4 ) in the 29Si N M R spectrum
-110 50 20 -IO 29Si NMR ppm 13c NMR Figure 4. N M R spectra of poly((mercaptopropy1)siloxane) and poly((su1fopropyl)siloxane): (a and b), poly((mercaptopropy1)siloxane); (c and d), poly((sulfopropy1)siloxane).
-50 -80
A shoulder peak around 130 ppm may be assigned to overlapped signals due to the ipso and para carbon. Poly( (sulfopheny1)siloxane). Poly((sulfopheny1)siloxane) was prepared by sulfonating poly(phenylsi1oxane) (no. 2, see Table I). From elemental analysis data of carbon and sulfur listed in Table 11, the ratios of the numbers of sulfo groups and phenyl groups, (SO,H)/(RSiO,), and the ratios (RE) of the numbers of silicon atoms bound to an organic group and those not bound to an organic group were estimated and are listed in Table I. The value of REdecreased by sulfonation (Table I), indicating that the part of phenyl groups in the poly(phenylsi1oxane) is removed during sulfonation. The ratio ( S03H)/(RSiO,) was estimated to be 0.9. This shows that the most of remaining phenyl groups are sulfonated. The 29SiN M R spectrum of the sulfonated polymer is shown in Figure Id. Compared with the spectrum of poly(pheny1siloxane), Figure Ib, the relative intensity of the peaks due to 29Si nuclei bound to a phenyl group becomes smaller after sulfonation, and the ratio RNMR decreased to 0.42 from the value of 0.59 for poly(phenylsi1oxane). This gives a clear evidence for the cleavage of Si-C bond during sulfonation. The 13CN M R spectrum of the polymer changed by sulfonation (Figure 3d). The signal at 142.2 ppm is assigned to the carbon nuclei bound to a sulfo group, for the chemical shift of the carbon atom at the ipso position in benzenesulfonic acid is reported to be 145.7 ppm.lg It seems that the chemical shifts of other carbon atoms overlaps around 130 ppm. Poly( (mercaptopropyl)siloxane). From the elemental analysis of carbon and sulfur, the number of mercaptopropyl groups in (19) Breitmaier, E.; Voelter, W. ' ) C N M RSpectroscopy; Verlag Chemie: New York, 1978.
1661
'60.RC
.P 40 -
f
g20U
O'LOO
'
' 480 ' ' 560 ' ' 640 Pretreatment Temperture / K
Figure 5. Effect of the temperature of the thermal and hydrothermal treatment on the catalytic activity of poly((sulfopheny1)siloxane) for 2-propanol dehydration. Pretreatment conditions: 0, thermal treatment (12 h in a nitrogen stream); 0,hydrothermal treatment (12 h in a steam (25 kPa)-nitrogen stream). Reaction conditions: 373 K, 2-propanol = 20 kPa, W/F = 6.2 g h mol-'.
the poly((mercaptopropy1)siloxane) was found to be slightly smaller than that in the mixture of the starting silanes (Table 111). The 29Siand I3CN M R spectra of poly( (mercaptopropy1)siloxane) are shown in Figure 4a,b. Here again, five peaks are resolved in 29SiN M R spectrum. Relying upon the assignments made for the 29Si N M R spectra of silica gel modified by trimethoxy(chloropropy1)silane and trimethoxy(aminopropyl)silane,20 we ascribed the peaks at -57 and -65 ppm to HS(CH2),(HO)Si*and HS(CH2)3Si*(OSi=)3,respectively. The peaks at -91.0, -100.6, and -109.8 ppm are assigned (HO)2Si*(OSi=)2, (HO)Si*(OSi=),, and Si*(OSi=)4, respectively. The 13CN M R spectrum of poly((mercaptopropy1)siloxane) showed three peaks at 12.5, 28.5, and 42.5 ppm. Based on the work of Zaper et al.?l the peaks at 12.5 and 28.5 ppm can be assigned to the methylene carbon attached to silicon atom and to the remaining two methylene carbons, respectively. The peaks at 42.5 ppm may be assigned to the carbon from impurities, because its appearance depended upon samples. For comparison, the I3C N M R spectrum of trimethoxy( 3-mercaptopropy1)silane dissolved in CDCI3 was measured. Four peaks appeared at 8.32,27.71, 27.59, and 50.40 ppm. Three peaks at 8.32, 27.71, and 27.59 ppm are assigned to the methylene carbon in the mercaptopropyl groups and the signal at 50.40 ppm is assigned to the methoxy carbon. This confirms that the chemical shifts of methylene carbon attached sulfur atom and methylene carbon in the middle of the propyl group are almost same. Thus, the chemical shift at 28.5 ppm of poly((mercaptopropy1)siloxane) is ascribed to overlapped peaks due to -S-C*-C- and -C-C*-C-. Poly( (suljopropy1)siloxane). Poly( (sulfopropy1)siloxane) was prepared by oxidizing poly((mercaptopropy1)siloxane). As listed in Table 111, after oxidation of the mercapto groups to sulfo groups another small loss of organic groups was observed. 29Siand 13CN M R spectra of poly((sulfopropy1)siloxane) are shown in Figure 4c,d. 29Siand I3C N M R spectra and elemental analysis data were quite similar between poly((mercapt0propy1)siloxane) and poly( (sulfopropy1)siloxane). 2. Thermal and Hydrothermal Stability of Poly( (suljoorgano)siloxanes). Poly( (suljopheny1)siloxane). The thermal stability of poly((sulfopheny1)siloxane) was studied. The polymer was packed in a reactor and kept at constant temperature for 12 h under a nitrogen stream. When it was used for the catalytic reaction, the temperature of the reactor was decreased to the reaction temperature (373 K) and then the reaction was started. For the N M R measurements or elemental analyses, the sample was treated under the same conditions. In Figure 5, the conversion of 2-propanol is plotted as a function of the pretreatment temperature. The reaction products were propylene (90%) and isopropyl ether (10%). The activities for dehydration were constant with running time under the reaction conditions. The activity did not depend on the pretreatment temperature up to 573 K and gradually decreased over 603 K. (20) Sudholter, E. J. R.; Huis, R.; Hays, G. R.; Alma, N. C. M. J . Colloid Interface Sci. 1985, 103, 554. (21) Zaper, A. M.; Cholli, A,; Koenig, J. L. "Molecular Characterization of Composite Interface"; Polymer Science and Technology; Plenum: New York, 1985; Vol. 27.
1662
-60 -90 -120
-60
-90
-120
-60 -90 -120
6 P P ~ Figure 6. 29SiNMR spectra of poly((sulfophenyl)siloxane) after thermal or hydrothermal treatment. Thermal treatment at (a) 468 K, (b) 503 K, (c) 603 K; hydrothermal treatment at (d) 468 K, (e) 503 K, (f) 603 K.
The effect of hydrothermal treatment of poly((sulfopheny1)siloxane) on the catalytic activity is shown in Figure 5. The catalysts were kept under a stream of steam (25 kPa)-nitrogen mixture at constant temperature for 12 h. The activity for 2propanol dehydration depressed by steaming over 473 K. Under the steaming conditions, the thermal stability of poly((sulf0pheny1)siloxane) was much lower than under the nonsteaming conditions. The thermal and the hydrothermal stability of Amberlyst-15 was also studied in a similar manner. Under both the steaming and nonsteaming conditions, the activities were constant up to 468 K and sharply decreased over 473 K. These results show that poly( (su1fophenyl)siloxane) has higher thermal stability than Amberlyst- 15 in the absence of steam. In the presence of steam, the thermal stability of siloxane polymer is almost same as the resin. 29SiN M R spectra of the samples treated at 468,503, and 603 K under nitrogen are shown in Figure 6. The 29SiN M R spectra of the samples treated at 468 and 503 K were almost the same as the spectrum of the untreated sample (Figure la). This indicates that there is no structural change in the polymer by the thermal treatment below 503 K. The elemental analysis confirmed that the amount of carbon and sulfur of the samples treated at 468 and 503 K were almost same as that of the untreated sample (Table 11). The intensity ratio, RNMR,of 29SiN M R signals of the sample treated at 603 K was smaller than those of the sample treated at 468 and 503 K. These results are in conformity with the change in the catalytic activity with the thermal treatment temperature. 29SiN M R spectra of the samples treated at 468, 503, and 603 K under steaming conditions are also shown in Figure 6. The treatment at 468 K caused no appreciable change in the elemental analysis data and N M R spectra. However, after the treatment at 503 and 603 K, the intensities of the peaks due to silicon nuclei attached to a phenyl group became smaller compared with those of nontreated sample. These results were also in agreement of the change in the catalytic activities and elemental analysis data. When poly(pheny1siloxane) was treated at 603 K, 29SiN M R showed no indication of degradation whether under steaming condition or under nonsteaming conditions. It is known that the bond between the silicon atom and benzene ring in the poly(phenylsiloxane) ruptures and benzene is released.22 The differential gas-evolution curve of poly(phenylsi1oxane) measured by Chubarov et al.23had two well-defined maxima at 873-933 K and 1073 K. The product of the first reaction is benzene, and (22) Andrianov, K. A.; Manucharova, I. F. I m . Akad. Nauk SSSR, Otd. Khim. Nauk. 1962, 420. (23) Chubarov, V. A.; Masenkis, M. A.; Zherdev, Yu, V.; Korolev, A. Ya.; Arasin, Ya. D.; Andrianov. K. A. Vysokomol. Soedin.. Ser. A. 1973,A15, 2627.
Suzuki et al.
The Journal of Physical Chemistry, Vol. 91, No. 6,1987
-
T
150
_
c
150
120
120
6 P P ~ Figure 7. I3C NMR spectra of poly((su1fophenyl)siloxane) after thermal or hydrothermal treatment. Thermal treatment at (a) 468 K, (b) 503 K, (c) 603 K; hydrothermal treatment at (d) 468 K, (e) 503 K, (f) 603 K.
-50
-so
-80 -110
-a0
-110
6 P P ~ Figure 8. 29SiNMR spectra of poly((sulfopropy1)siloxane) after thermal or hydrothermal treatment. Thermal treatment at (a) 468 K, (b) 603 K; hydrothermal treatment at (c) 468 K, (d) 603 K.
that of the second, hydrogen. The reactions are represented by the following scheme:23 =Si-OH + c6H~Si' C6H6 ZSi-O-Sil (1)
-
+
2 ~ S ~ - C ~ HC6H6 S + zSi-(C6H4)-Si= -+
2 =Si-C&s
-+
H2 4- "Si-(C&)z-Si=
(2) (3)
Reactions 1 and 2 occur more easily and require lower temperature than reaction 3. For poly((sulfophenyl)siloxane), reaction 1 or 2 is plausibly operative during the thermal treatment under nitrogen at 603 K. The lower degradation temperature for a sulfonated sample indicates that the reaction is catalyzed by its own acidic property. Another degradation mechanism is required to explain lower hydrothermal stability. Thus, the hydrolysis of Si-C bond may occur in the presence of steam. =Si-c6H4So3H H 2 0 C6HsS0,H + S i O H (4)
+
-
The mechanism is supported by the relative increase of the signal due to (HO)Si*(OSi=)3 compared with that of Si*(OSi=)4after the hydrothermal treatment. I3C N M R spectra of the samples treated at 468, 503, and 603 K in the absence and the presence of steam are shown in Figure 7. All the samples gave similar spectra to that of untreated sample, even though the partial loss of the phenyl group at 603 K was evidenced by 29SiNMR spectra. There are no signals originating from decomposed organic moieties.
J . Phys. Chem. 1987, 91, 1663-1668
/I
50
I
20 -10
150
120
90
60
30
0
6P P ~ Figure 9. "C NMR spectra of poly((su1fopropyl)siloxane) after thermal or hydrothermal treatment. Thermal treatment at (a) 468 K, (b) 603 K; hydrothermal treatment at (c) 468 K, (d) 603 K.
All spectra are greatly different from that of the sample before sulfonation, indicating that all the remaining organic groups after thermal or hydrothermal treatments are in the form of sulfophenyl groups. Widdecke et reported that catalytic activity of Amberlyst-15 in water decreased over 423 K and suggested the hydrolysis of sulfophenyl groups. @-C&SO3H 4- H2O @-C6H5 H2S04 (5) +
+
Though the desulfonation of arylsulfonic acids with water is a well-known fact, the invariance of the I3CNMR spectrum by the treatments indicates that the cleavage of S i 4 bond (reaction 4) proceeds faster than the desulfonation of sulfophenyl groups. Poly((sulfopropy1)siloxane). The thermal and hydrothermal stability of poly((sulfopropy1)siloxane) was also studied in a similar manner to poly( (sulfophenyl)siloxane), except for using dehy(24) Widdecke, H.; Klein, J. Chem. Ing. Tech. 1981, 53, 954.
1663
dration of ethanol at 503 K for testing the catalytic activity. The conversion of ethanol over the untreated sample was 91%, and the selectivity was 86% to diethyl ether and 14% to ethylene. Whether under steaming or nonsteaming conditions, the activities were constant for pretreatment temperature up to 543 K and gradually decreased over 568 K. The conversion of ethanol for the samples treated at 603 and 633 K was 70% and lo%, respectively. The ethylene selectivity also decreased with decrease in catalytic activity. The presence of steam did not affect the stability of poly((sulfopropy1)siloxane). The 29Siand 13CNMR spectra of the samples after thermal and hydrothermal conditions are given in Figures 8 and 9. There are no great differences in the NMR spectra of the samples between thermal and hydrothermal treatment. As expected, 29Si and 13CNMR spectra of the sample treated at 468 K are the same as those of the untreated sample. However, by the treatment at 603 K, the intensity of the peaks of Si nuclei attached to an organic group in 29SiNMR spectrum became relatively smaller than that of the peaks due to Si nuclei not bound to an organic group, and a shoulder peak appeared at about -76 ppm. In the I3C NMR spectrum, chemical shifts and signal shapes of the sample treated at 603 K was greatly changed from that of the untreated sample. All the three signals of the original poly( (sulfopropy1)siloxane) became greatly smaller or disappeared, and new signals appeared at 150-120 and 50-10 ppm. This clearly shows that sulfopropyl groups were decomposed during the thermal treatment at 603 K. A shoulder peak at -76 ppm in the 29SiNMR spectra may be assigned to the silicon nuclei bound to organic groups that are newly produced during the decomposition of the sulfopropyl groups. Since the sample treated at 603 K becomes dark gray, the signals of 150-120 ppm at the I3C NMR spectra may be assigned the carbon nuclei of coke precursors having aromatic nature which are formed from the decomposed sulfopropyl groups. The results of the elemental analysis of the sample treated at 468 K were not different from the untreated sample (Table 111). For the sample treated at 603 K, the content of carbon did not change, but that of sulfur was greatly decreased. These changes in the composition of the polymer are well correlated to the change in the catalytic activity for ethanol dehydration. Registry No. H3CCH20H,64-17-5; H3CCHOHCH3,67-63-0; H2CeCHCH3, 115-07-1; (CH3)2CHOCH(CH3)2, 108-20-3.
Simultaneous Measurement of Gaseous Diffusivity and Solubility in Liquids'' Roger J. Combdband Paul E. Field* Chemistry Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received: August I I , 1986)
Diffusion of gases into nonpolar liquids has previously been measured by two techniques: (1) a pseudo-steady-statetechnique developed by Hildebrand with diffusion through multiple capillaries and (2) a method by Walkley with diffusion through an open tube. Each of these methods requires prior knowledge of solubility of the gas in the liquid. An apparatus is constructed which combines these methods into a single experiment. Simultaneoussolution of the two equations that describe the combined experiment yields both the solubility and diffusion coefficient. Diffusivities and solubilities of nitrogen, argon, and oxygen into liquids of carbon tetrachloride and benzene as well as oxygen in water have been studied. The results compare favorably with the literature.
Introduction the literature on diffusion of gases into liquids two facts are apparent. First, the paucity of diffusion data is a consequence (1) (a) Presented in part at the 36th Southeastern Regional Meeting of the American Chemical Society, Raleigh, NC, October 1984. (b) From the Ph.D. Thesis of Roger J. Combs, Virginia Polytechnic Institute and State University, April 1986.
0022-3654/87/2091-1663$01.50/0
of the experimental difficulties which attend measurements with slightly soluble gases. Second, diffusion results of the various techniques2 show large variation. Difficulty in the evaluation of diffusion coefficients is compounded since a knowledge of gas solubilities is also required.- Most diffusion method; rely-on independent literature values as a source of these solubilities. (2) St Dennis, C. E.; Fell, C. J. D. Can. J . Chem. Eng. 1971, 49, 8 8 5 .
0 1987 American Chemical Society
