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Pont de Nemours & Company for the measurement and interpretation of the NMR spectra. Registry No' I' 60950-97-2; 'I' 65288-70-2; 12633-21-5; M50, 12725-39-2; Fomblin Z, 64772-82-3.
Literature Cited Gumprecht, W. H. ASLE Trans. 1968, 9 , 24. Gumprecht, W., H. "The preparation and h r m l &havior of Hemfluorpropylene Epoxlde Polymers", paper presented at the Fourth International Symposium on Fluorine Chemistry, Estes Park, CO. July 1967. Jones, W. R., Jr. "Friction Wear and Thermal Stability Studies of Some Organo Tin and Organ0 Silicon Compounds", NASA TN D-7175, March 1973. Jones, W. R., Jr.; Johnson, R. L.; Wlner, W. 0.; Sanborn, D. M. ASLE Trans 1975, 78. 249. Jones, W. R., Jr.; Snyder, C. E., Jr. ASLE Trans. 1980, 23, 253.
Kratrer, R. H.; Paciorek, K. J. L.; Kaufman, J.; Ito, T. I. J. Fluorine Chem. 1977, 10, 231. Paciorek, K. J. L.; Kratzer, R. H.; Kaufman, J.; Nakahara, J. H. J. Appl. Poiym. Scl. 1979, 2 4 , 1397. Sianesl, D.; Zamboni, V.; Fontanelii, R.; Blnaghi, M. Wear 1971, 78, 85. Sianesi, D.: Pasetti. A.: Fontanelll. R.: Bernardi. G. C.: Canoriccio. G. Chlm. Ind. (Mllan) 1973, 55, 208. Sianesi, D.: Pasetti, A.; Belardineili, G.. US. Patent 3715378. 1973. Snyder, C. E., Jr.; Doiie, R. E., Jr. ASLE Trans. 1978, 79, 171. Snyder, c. E., Jr.; Tamborski, c.; @pal, H.; Svisco, C. A. Lubr. fngr. 1979, 35, 451. Snyder, C. E., Jr.; Gschwender, L. J.; Tamborski, C. Lubr. fngr. 1981, 3 7 , 344. Snyder. c. E., Jr.; Oschwellder, L. J.; Campbell. W. 8. Lubr. Engr. 1982, 3 8 , 41.
Received for review August 18, 1982 Accepted November 18, 1982
Syntheses and Characterizations of Poly(pentafluorosu1fur diacetylenes) T. A. Kovacina,' R. A. De Marco, and A. W. Snow Naval Research Laboratory, 4555 Overlook Avenue, S. W., Washlngton, DC 20375
Mono- and bis(pentafluorosu1fur)-substituted diacetylenes were thermally polymerized in both the bulk liquid and vapor phases at temperatures between 25 and 80 "C. The polymer formed in the liquid phase at 25 O C with S F , D H was insoluble, while the polymer derived from SF5-mSF5 at 80 "C was soluble in fluorinated solvents. The vapor phase polymerization of both monomers occurred at 25 O C ; the rate of polymerization of SF,C=C--VH was rapid compared to SF5CsC=-1;SF5. The newly formed polymers were characterized by a variety of spectroscopic and physical property measurements.
Introduction Fluorocarbon materials generally are more chemically inert and thermally and oxidatively stable compared to their hydrocarbon analogues. However, whether fluorinated heteroatoms, such as the pentafluorosulfur (SF,) group, also impart these properties is unknown. The recent syntheses (Kovacina et al., 1981) of mono(pentafluorosu1fur)diacetylene (SF,C=CC=CH) and bis(pentafluorsu1fur)diacetylene (SF,C=CC=CSF,) has shown that these compounds are considerably more stable than the unsubstituted diacetylene. Properties such as density, molecular weight, and boiling point are significantly increased by the presence of SF, group!. Mono- and bis(pentafluorosulfur)diacetylene are relatively stable liquids at room temperature. However, on standing at room temperature the liquids were found to discolor gradually (Kovacina et al., 1981) either in the presence of light or in the dark. Depending on the length of time the liquids were left at 25 "C, the color change was from colorless to various shades of amber. An infrared analysis of the head gases above liquid samples of either monomer that had been left at room temperature and an analysis of the redistilled monomers were the same and indicated that the materials did not decompose. We did observe that traces of amber-colored solids were left in the Pyrex traps when the monomers were distilled, suggesting that a polymerization had occurred. In addition, we observed that Teflon stopcock plugs exposed to SF,CrCCGCH vapors became permanently discolored with a nonvolatile, insoluble coating that appeared to penetrate
into the Teflon, again suggesting the possibility of a polymerization reaction. In the interest of developing new, high density materials with stable fluorocarbon-like properties, and in view of the highly unsaturated molecular structure of these diacetylenes, the bulk and vapor phase polymerizations of these monomers were investigated. Results and Discussion Both SF,C=CC=CH and SFSC=CC=CSF5 were found to undergo polymerization in the liquid phase at relatively low temperatures. Poly(SF5C4SF5)is formed at 80 "C and is soluble in fluorinated solvents and partially soluble in hydrocarbon solvents. In contrast, poly(SF5C4H) is formed at room temperature and was not found to be soluble in any of these solvents. The presence of unreacted acetylenic functions in both polymers is characteristic of melt or vapor-deposited diacetylene polymers (Snow, 1981). The initial step in the polymerization of diacetylenes is believed to result in an open chain conjugated polyene system, followed by the formation of a polyacene structure. The poly(SF5C4H)and poly(SF5C4SF5)are believed to have the former structure based on infrared evidence. The infrared spectrum of poly(SF,C,H) contains a single C=C stretch (2230 cm-') that is comparable to the monomer SF5C=Cstretch (2260 cm-') rather than the CECH stretch at 2080 cm-l. In a similar comparison, the difference in the CEC stretch for the SF5C4SF5monomer and polymer is 10 cm-'. Further heating of the bis-substituted polymer converts it to an insoluble material suggesting that cross-linking had oc-
This article not subject to U.S. Copyright. Published 1983 by the American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 171
Y = H. SF5
Y = H, SF, curred, but this material was not characterized. The phenomenon of polymerization of diacetylene on the surface of polymers was reported previously (Snow et al., 1982). The polymerization of SF5C4Hon fluorinated and hydrocarbon polymers was studied and the order of decreasing affinity for vapor phase polymerization determined. The corresponding weight gains on the polymers after 10 days exposure were found to be poly(tetrafluoroethylene) (PTFE) 51% , poly(ethy1ene) (PE) 11%, poly(fluorinated ethylene propylene) (FEP) 4%, and poly(vinylidene fluoride) (PVF2)1%. Similar experiments (Snow, 1981) with unsubstituted diacetylene showed a different preference for the same substrate materials: PVF2 (81% ), PE (61%), PTFE (23%), and FEP (0.3%). Clearly, a difference in the order of preference between the monomers was demonstrated, but we have not determined if this was related to the surface characteristics of the host polymer or physical and chemical properties of the monomers. The polymerization of the monomers on polymer films gave us the opportunity to measure some surface properties of these materials. The contact angle 6, (Le., the angle formed between the polymer surface, through a drop of liquid on the polymer, to a tangent line drawn where the drop contacts the polymer) was measured using water and methylene iodide. Poly(SF,C,H) and poly(SF5C4SF5),each on FEP, gave the same results; approximately 102" for water and 75O for CH&. In comparison, PTFE typically gives values of 108O for water and 85" for CH212,while FEP gives values of 110" and 86O, respectively. The size of 6 is an indication of the ability of liquids to wet the surface (Zisman, 1964); larger values indicate less wetting. Therefore, the SF,-containing polymers are more easily wetted by water and CHJ2 than is PTFE or FEP. The critical surface tension was measured using a series of n-alkanes with known surface tension values. The surface tension for the alkane was plotted against the cosine of the measured contact angle. The critical surface tension is defined as the surface tension that corresponds to cos 6 = 1, and this means that any liquid with a lower surface tension will completely wet the surface of the polymer. The critical surface tension (dyn/cm) for poly(SF,C,H) on FEP was 26.8, and for poly(SF,C,SF,) on FEP a value of 20.4 was determined. The lower critical surface tension for poly(SF,C,SF,) illustrates that the SF, group reduces the wettability of the polymer compared to the hydrogen containing poly(SF,C,H). In comparison to typical polymers, the wettability of the SF,-containing polymers is much lower than PE (critical surface tension of 31.0) but higher than FEP or PTFE (critical surface tension of each is 18.0). Experimental Section Mono- and bis(pentafluorosu1fur)diacetylene were prepared by the reported method (Kovacina et al., 1981). Gases and volatile liquids were handled in a conventional Pyrex vacuum line, and quantities were determined by PVT measurements. Infrared spectra were taken on a Perkin-Elmer Model 567 double beam spectrometer; NMR
spectra were taken on a Varian Model EM390 spectrometer using Freon-11 as an internal reference; XPS data were obtained from a McPherson Model ESCA-36 photoelectron spectrometer; ESR data were obtained on a Bruker ER 200D spectrometer; thermal gravimetric analysis was conducted using a DuPont 951 thermogravimetric analyzer; the polymer molecular weight was determined on a Corona Wescan molecular weight apparatus using benzil to calibrate the instrument; and mass spectra were obtained at 70 eV on a CVC MA-2 time-offlight instrument. The critical surface tension and contact angles were measured with a conventional contact angle goniomemter.
Bulk Liquid Phase Polymerization Poly(SF5C,SF5). Approximately 5 mmol of monomer was condensed into a 5-mm 0.d. X 15 mm long Pyrex NMR tube and the tube was sealed. When the sample was left overnight at room temperature, a dark bronze, nonviscous liquid formed. The tube was then placed in an oil bath heated to 80 "C for approximately 12 h, giving a totally solidified matrix. After cooling to room temperature, the tube was opened under a vacuum to remove trace quantities of gas, which was identified as monomer by IR. The polymer was characterized by spectroscopic and physical property measurements. The mass spectrum of the polymer contained no significant peaks above m/e 151 (SF5C2+)and was predominated by SF, cleavage fragments. The molecular weight of the polymer was determined by vapor phase osmometry (VPO) techniques using hexafluoro-m-xylene as a solvent. The extrapolated molecular weight was 2200 and corresponds to approximately 7.3 repeat units. A I9FNMR spectrum gave a very weak resonance and suggested the presence of paramagnetism in the material. The ESR of the neat polymer was a multiplet having a g value of 2.0027. The calculated spin density was 2 X lo1, spins/g or approximately 1spin/106 repeat units. The XPS spectrum of the solid indicated sulfur, carbon, and fluorine to be the only elements present and the sulfur to fluorine ratio was 2.510. The thermal stability of the polymer was determined by thermal gravimetric analysis in a nitrogen atmosphere. With a heating rate of 10°/min, a 10% weight loss was observed at 177 "C and continued to a 50% loss at 315 "C. An analysis of the volatile materials indicated that cleavage of the SF, group occurred to give SF,. Poly(SF,C,H). Samples of SF,C,H were sealed in NMR tubes as above and left overnight at room temperature. The monomer was found to be completely polymerized, when the tube was opened under vacuum. Attempts to enhance the rate of polymerization by heating the sample were unsuccessful, and temperatures as low as 50 "C resulted in severe detonations during the polymerization. Warning: Extreme caution must be exercised in heating this monomer above 25 "C. Also, we have found this polymer to be extremely sensitive to shock and pressure. Attempts to cut pieces of the polymer with a razor or break pieces by hand resulted in a rapid detonation and conflagration of the sample. Due to the insolubility of the polymer, characterizing this polymer was more limited. Again, the mass spectrum was not helpful to assign a molecular weight because the major fragments resulted from cleavage products of sulfur fluorides. VPO and NMR measurements were not conducted because a suitable solvent could not be found. The ESR spectrum consisted of a broad resonance having a g value of 2.0026 and a calculated spin density of 3 X 10ls spins/g or approximately 1 spin/1000 repeat units. Attempts to obtain an XPS spectrum of poly(SF,C,H) were
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unsuccessful due to decomposition of the sample during the analysis. The thermal stability of this polymer was determined by TGA as above and gave a 10% weight loss at 165 "C and gradually continued until a 50% weight loss was observed at 405 "C. Analysis of the volatile products also indicated that SF5cleavage had occurred. Vapor Phase Polymerizations The vapor phase polymerizations onto polymer surfaces were conducted by placing samples of weighed, commercially available polymers into a 1-L Pyrex flask equipped with a 12/30 standard-taper joint and a stopcock. The polymer samples were then exposed to the monomer vapors for varying times, then removed from the vessel and weighed to determine the relative amount of polymerization on each sample as a function of time. Poly(SF5C4H). A series of four polymer samples (PTFE, PVFB, FEP, and PE) were placed into the reaction flask. The percentage weight gain after 10 days exposure was PTFE (51%), PE (ll?&), FEP (4%),and PVF2 (1%). The infrared spectrum of poly(SF,C,H) was obtained by double beam, subtractive techniques. The polymer on FEP was placed into the sample beam and a neat FEP film was placed in the reference beam. The resulting IR spectrum contained principal absorptions at 2230 (m, v(C=C)), 1720 (w, v(C=C)), and 900 cm-l (vs, v(SF)). Poly(SF5C4SF5).Due to the low volatility of this monomer, the vessel was equipped with a side arm that was used to contain a reservoir of monomer and ensure that a measurable quantity of monomer could polymerize on
the surfaces. The polymer surfaces were limited to PTFE and FEP, and due to polymerization of the excess monomer in the side arm,the reaction time was limited to approximately 2 weeks. The weight gain of each polymer was approximately 4%. The IR spectrum of poly(SF5C4SF5)was also obtained by subtractive IR techniques. The principal bands were found at 2160 (s, v(C=C)), and 900 cm-' (s, v(SF)). Acknowledgment The authors are respectfully indebted to M. K. Bernett for the surface property measurements and to D. M. Pace for the ESR measurements. Registry No. Poly(SF,C,H), 84864-30-2; poly(SF6C4SF5), 84864-31-3.
Literature Cited Kovaclna, T. A.; Berry, A. D.; Fox, W. B. J . Fluorine &em. 1978, 7 , 430-2. Kovacina, T. A.; De Marco, R. A.; Snow, A. W. submitted for publication in J. Fluorine Chem 198 1. Snow, A. W. Nature (London) 1981, 292, 40-1. Snow, A. W.; Grifflth, J. R., private communication, IUPAC International Symposium on Macromolecules; July 12-16, 1982. Zlsman, W. A. I n "Advances in Chemistry Series", No. 43: "Contact Angle, Wettabilii and Adhesion", Gould, R. F., Ed.; 1984; Chapter 1.
.
Receiued for review July 29, 1982 Reuised manuscript receiued November 16, 1982 Accepted November 30, 1982 Presented at the Division of Fluorine Chemistry Symposium on Fluoropolymers, 183rd National Meeting of the American Chemical Society, Las Vegas, NV, Mar 28, 1982.
I I I . Symposium on Synthetic and Petroleum Based Lubricants 183rd National Meeting of the American Chemical Society Las Vegas, Nevada, March 1982
Synthesis and Properties of Silahydrocarbons, a Class of Thermally Stable, Wide Liquid Range Fluids Chrlst Tamborskl,'' Grace J. Chen,' Denlre R. Anderson,' and Carl E. Snyder, Jr.' Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, Ohio 45433, and University of Dayton Research Instltute, Dayton, Ohio 45469
An improved synthesis procedure for stlahydrocarbons (tetraalkylsilanes)has been developed. Through the reaction between alkyllithium or alkylmagnesium halides with alkyltrichlorosilanes a series of silahydrocarbons has been prepared. Structure property correlations have been performed which provided the basis for the synthesis of thermally stable and wide liquid range fluM properties. Improvement in low-temperature properties was noted by the use of mixtures of the silahydrocarbon fluids. These mixtures of silahydrocarbons had improved rheological properties without affecting any of the desirable high-temperature properties. These new silahydrocarbon fluids are suitable for applicatlons where petroleumbased or synthetic hydrocarbon-basedfluids cannot meet performance specifications due to thermal and/or rheological deficiencies.
Introduction Several years ago (Tamborski and Rosenberg, 1960; Rosenberg et al., 1960; Baum and Tamborski, 1961) we Wright-Patterson Air Force Base. 'University of Dayton. 0196-432118311222-0172$01.50/0
reported our initial studies on the synthesis and properties of a class of fluids which we referred to at that time as tetraalkylsilanes (R4Si). These compounds can be readily synthesized via organometallic (organolithium or Grignard) intermediates. The synthesis procedure developed provided a means of preparing numerous compounds pos-
0 1983 American Chemical Society
