Ind. Eng. Chem. Res. 1996,34, 1390-1393
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Polysilahydrocarbon Synthetic Fluids. 4. Quantitative Structure-Activity Relationships Kazimiera J. L. Paciorek* and Steven R Masuda Technolube Products Division, Lubricating Specialties Company, 3365 E. Slauson Avenue, Vernon, California 90058
Quantitative structure-activity relationships (QSAR) were developed for the viscosity of polysilahydrocarbons, specifically tri- and tetrasilahydrocarbons, as a function of the number of carbons, the carbon to silicon ratio, and the bridge length. lowing the approaches utilized earlier in fluoroelastomer/ chlorofluorocarbonswell studies (Paciorek et al., 1991b).
Introduction Lubricants are used extensively in a variety of space hardware. Long-term reliable performance with the absence of outgassing, under different speeds, loads, temperatures, and type of motions, is mandatory (Jones et al., 1994). For the different applications lubricants of specific viscositykemperature profiles are necessary. Among other compounds silahydrocarbons were identified as exhibiting promising characteristics. Initial investigations were limited to monosilahydrocarbons (Rosenberg et al., 1960; Baum and Tamborski, 1961; Tamborski et al., 1983). In these compositions, due t o the presence of only one silicon, the increases in molecular weights (hydrocarbon chain lengths) cancel the "plasticizing" action of silicon (Petrov et al., 1964) resulting in properties approaching those of hydrocarbon systems. Subsequent development of trisilahydrocarbons (Paciorek et al., 1988, 1990) and tetrasilahydrocarbons (Paciorek et al., 1991a) provided families of materials of very broad viscosity/molecular weight ranges. The diversity of potential compositions permits very specific structure-property tailoring. To allow ready identification of arrangements having particular viscosity/molecular weight profiles, quantitative structure-activity relationships (QSAR)were developed fol-
'
Results and Discussion The tri- and tetrasilahydrocarbons studied are listed in Table 1. In both series the effect of the bridge length and the silicon substituents on viscosity characteristics was investigated. For the trisilahydrocarbons there is a definite linear relationship betweeen the total number of carbons and viscosity; this does not hold for the tetrasilahydrocarbons as shown in Figure 1. One is tempted to speculate that the discrepancy is at least partly due t o the large proportional difference in the number of carbons in the bridging groups. In the tetrasilahydrocarbons two-carbon and three-carbon bridges are present compared to six-carbon and eightcarbon bridges in the trisilahydrocarbons. In the former case the short two-carbon linkage apparently imparts a degree of rigidity which is reflected in the higher viscosity of the approximately equivalent molecular weight materials, e.g., CH3Si[CzH4Si(CsH17)313 (MW 1231) and CH3Si[C3HsSi(CsH17)313(MW 12731, 40 "C viscosities 78 versus 62 cSt, respectively. To address the different aspects of structural arrangements and to provide for a meaningful predictive
4 0 % Triailahydrocarbon
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60 80 100 120 140 Total Number of Carbon Atoms Figure 1. Viscosities of trisilahydrocarbons and tetrasilahydrocarbons at 40 and 100 "C as a function of total carbon number. 0
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0888-588519512634-1390$09.00/0
0 1995 American Chemical Society
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Figure 2. Calculated 40 and 100 "C viscosities versus actual as a function of carbon to silicon ratio for tri- and tetrasilahydrocarbons.
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Figure 3. Calculated 40 and 100 "C viscosities versus actual as a function of number of carbons and carbon to silicon ratio for tri- and tetrasilahydrocarbons.
1392 Ind. Eng. Chem. Res., Vol. 34,No. 4, 1995
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60 80 100 120 140 Calculated Viscosity cSt Figure 4. Calculated 40 and 100 "C viscosities versus actual as a function of number of carbons, carbon to silicon ratio, and bridge length for tri- and tetrasilahydrocarbons. 0
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Table 1. Silahydrocarbon Listing, Viscosities, and Descriptors compound
genformula
viscosity, cSt 100 "C
MW
40°C
372.86 1158.37 428.98 990.24 1214.46 1439.02 1230.56 1483.04 487.14 1272.64 1370.92 1525.12 1623.32 1875.80
8.7 89.7 12.6 73.9 95.5 133.0 78.0 92.8 10.5 61.6 66.2 76.2 89.7 105.0
capability, a quantitative structure-activity relationship needed to be developed. Using multivariate linear regression analysis, the simplest treatment is the expression of the calculated versus actual viscosities as function of the ratio of number of carbons to number of silicons (C/Si). This is illustrated in Figure 2 and given by eqs 1and 2, where r = Pearson correlation coefficient, 40 "C viscosity = 4.2942(C/Si) - 19.9080
104 165 138 171 175 177 161 172 115 182 191 182 183 184
number C Si 20 76 24 64 80 96 79 97 26 82 89 100 107 125
3 3 3 3 3 3 4 4 4 4 4 4 4 4
bridge, C total length I
12 12 16 16 16 16 6 6 9 9 9 9 9 9
6 6 8 8 8 8 2 2 3 3 3 3 3 3
C/Si 6.66 25.33 8.00 21.33 26.67 32.00 19.75 24.25 6.50 20.50 22.25 25.00 26.75 31.25
higher temperature the viscosities tend to converge. The inclusion of descriptors for the total number of carbon atoms (TNOC) provides for somewhat better correlations as shown by the plots in Figure 3 and given by eqs 3 and 4. Further refinement incorporating the 40 "C viscosity = -0.3298(TNOC)
(1)
+ 5.4702(C/Si) - 19.7032 (3)
r = 0.981, s = 7.89, n = 14
r = 0.975, s = 8.53, n = 14 100 "C viscosity = 0.6494(C/Si) - 1.5974
2.5 14.3 3.3 12.6 16.1 20.4 12.6 15.1 2.8 11.4 12.5 13.5 15.4 17.5
VI
(2)
r = 0.990, s = 0.821, n = 14 s = error of the estimate, and n = number of data points. The 40 "C plots are more informative, since at the
100 "C viscosity = -0.0222(TNOC)
+ 0.7282(C/Si) - 1.5836 (4)
r = 0.991, s = 0.811, n = 14 bridge length (BL) term, pertaining to the number of carbons separating the silicons, illustrated in Figure 4
Ind. Eng.Chem. Res., Vol. 34,No. 4,1995 1393 and given by eqs 5 and 6 improves only slightly the
+
40 "C viscosity = -l.O168(TNOC) 7.8592(C/Si) 3.5405(BL) - 1.2997 ( 5 )
r = 0.985, s = 7.20, n = 14
+
100 "C viscosity = -0.0801(TNOC) 0.9299(C/Si) - 0.2982(BL) - 0.0336 (6)
r = 0.992, s = 0.778, n = 14 agreement between the actual and calculated values. On the other hand, for property tailoring the inclusion of the bridge length descriptor is of importance in structure design. Furthermore, as mentioned earlier, increasing the bridge length, in particular in tetrasilahydrocarbons, does provide for viscosity decrease and higher viscosity index (VI), i.e., flatter viscosity/temperature profile.
Acknowledgment The support of this investigation by the U.S.Air Force Wright Laboratoryhlaterials Directorate through Contract No. F33615-87-C-5328is gratefully acknowledged.
tions by Vacuum Tribometry. Preprint, 28th Aerospace Mechanisms Symposium, NASA Lewis Research Center, Cleveland, OH, May 18-20, 1994. Paciorek, K. J. L.; Pratt, R. E.; Shih, J. G. Trisilahydrocarbon Nov 29,1988. Lubricants. US.Patent 4,788,312, Paciorek, K.J. L.; Shih, J. G.; Kratzer, R. H.; Randolph, B. B.; Snyder, C. E., Jr. Polysilahydrocarbon Synthetic Fluids. 1. Synthesis and Characterization of Trisilahydrocarbons. Znd. Eng. Chem. Res. 1990,29,1855. Paciorek, K. J. L.; Shih, J. G.; Kratzer, R. H.; Randolph, B. B.; Snyder, C. E., Jr. Polysilahydrocarbon Synthetic Fluids. 2. Synthesis and Characterization of Tetrasilahydrocarbons. Znd. Eng. Chem. Res. 199la,30,2191. Paciorek, K. J. L.; Masuda, S. R.; Nakahara, J. H.; Snyder, C. E., Jr.; Warner, W. M. Quantitative Structure-Activity Relationships for Fluoroelastomer/Chlorofluorocarbon Systems. Znd. Eng. Chem. Res. 1991b,30,2531. Paciorek, K. J . L.; Lin, W.-H. Polysilahydrocarbon Synthetic Fluids. 3. Synthesis of Six Carbon-Bridged Trisilahydrocarbons. Znd. Eng. Chem. Res. 1995,34,1387. Petrov, A. D.;Mironov, B. F.; Ponomarenko, V. A.; Chernyshev, E. A. Synthesis of Organosilicon Monomers; Consultants Bureau, New York, 1964. Rosenberg, H.; Groves, J. D.; Tamborski, C. Organosilicon Compounds. I. Synthesis of Some Long-chain Tetraalkylsilanes. J . Org. Chem. 1960,25,243. Tamborski, C.; Chen, G. J.; Anderson, D. R.; Snyder, C. E., Jr. Synthesis and Properties of Silahydrocarbons, A Class of Thermally Stable, Wide-Liquid-Range Fluids. Znd. Eng. Chem. Prod. Res. Dev. 1983,22,172.
Literature Cited Baum, G.; Tamborski, C. Tetraalkylsilanes: A new Class of WideLiquid-Range Fluids. J . Chem. Eng Data 1961,6, 142. Jones, W. R., Jr.; Pepper, S. V.; Herrera-Fierro, P.; Feuchter, D.; Jayne, D. T.; Wheeler, D. R.; Abel, P. B.; Kingsbury, E.; Morales, W.; Jansen, R.; Ebihara, B.; Helmick, L. S.; Masuko, M. The Preliminary Evaluation of Liquid Lubricants for Space Applica-
Received for review June 22, 1994 Accepted December 21, 1994@
IE9403910 Abstract published in Advance ACS Abstracts, March 1, 1995. @
