Macromolecules 1990,23, 1911-1915 (3) Jacobs, S. D.; Cerqua, K. A.; Marshall, K. L.; Schmid, A.; Guardalben. M. J.: Skerrett. K. J. J. ODt. SOC.Am. B: O D ~ . Phys. 1988,5, 1962. Ortler, R.; Brauchle, C.; Miller, A.; Riepl, G. Makromol. Chem., Rapid Commun. 1989, I O , 189. Eich, M.; Wendorff, J. H. Makromol. Chem., Rapid Commun. 1987, 8 , 467. Nakamura. T.: Ueno, T.: Tani. C. Mol. Cryst. Lia. . C r -y s t . 1989, 169, i67.' Kriabaum, W. R.; Ciferri, A.; Asrar, J.; Toriumi, H. Mol. Cryst. Liq. Cryst. 1981, 76, 79. Finkelmann, H.; Rehage, G. Makromol. Chem., Rapid Commun. 1982, 3, 859. Freidzon, Ya. S.; Boiko, N. I.; Shibaev, V. P.; PlatB, N. A. Eur. Polym. J . 1986, 22, 13. Watanabe, J.; Fukuda, Y.; Gehani, R.; Umematsu, I. Macromolecules 1984, 17, 1004. Watanabe, J.; Nagase, T. Macromolecules 1988, 21, 171. Tseng, S. L.; Laivins, G. V.; Gray, D. G. Macromolecules 1982, 15, 1262. Bhadani, S. N.; Gray, D. G. Mol. Cryst. Liq. Cryst. 1983,99, 29. Watanabe, J.; Goto, M.; Nagase, T. Macromolecules 1987,20, 298. Freidzon, Ya. S.; Tropsha, Y. G.; Shibaev, V. P.; PlatB; N. A. Makromol. Chem., Rapid Commun. 1985,6,625. Janini, G. M.; Laub, R. J.; Shaw, T. J. Makromol. Chem., Rapid Commun. 1985,6, 57.
1911
(16) Yamaguchi, T.; Hayashi, T.; Nakamura, N. Mol. Cryst. Liq. Cryst. 1987,5, 23. (17) Finkelmann, H.; Ringsdorf, H.; Siol, W.; Wendorff, H. Mukromol. Chem. 1978, 179,829. (18) Pinsl, J.; Brauchle, C.; Kreuzer, F. H. J . Mol. Electron. 1987, 3, 9. (19) Finkelmann, H.; Koldehoff, J.; Ringsdorf, H. Angew. Chem., Int. Ed. Engl. 1978, 17, 935. (20) Toyne, K. J. In Thermotropic Liquid Crystals; Gray, G. W., Ed.; Wiley: New York, 1987; pp 43, 44. (21) Ringsdorf, H.; Zentel, R. Makromol. Chem. 1982, 183, 1245. (22) Shannon, P. J. Macromolecules 1983, 16, 1677. (23) Van Meter, J. P.; Klanderman, B. H. Mol. Cryst. Liq. Cryst. 1973, 22, 285. (24) Hassner, J.; Alexanian, V. Tetrahedron Lett. 1978, 4475. (25) Daux, W. L.; Norton, D. A. Atlas of Steroid Structure; Plenum: New York, 1975; Vol. 1. (26) (a) Kelker, H.; Hatz, R. Handbook of Liquid Crystals; Verlag Chemie; Weinheim, 1980; pp 320, 321. (b) Oron, N.; KO, K.; Yu, L. J.; Labes, M. M. In Liquid Crystals and Ordered Fluids; Plenum: New York, 1974; Vol. 2, pp 403-410. (27) Van Kreveln, D. W.; Hoftyzer, P. J. In Properties of Polymers; Elsevier: Amsterdam, 1976; Chapter 10. (28) Hiebert, M.; Solladie, G. Mol. Cryst. Liq. Cryst. Lett. 1981, 64, 211. Finkelmann, H.; Stegemeyer, H. Ber. Bunsenges. Phys. Chem. 1978,82,1302.
Anionic Ring-Opening Polymerization of 1,1,3-Trimethyl-l-silacyclopent-3-ene. Effect of Temperature on Poly(l,l,3-trimethyl-l-sila-cis-pent-3-ene) Microstructure Young Tae Park, Georges Manuel, and William P. Weber' K. B. and D. P. Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661. Received August 7, 1989; Revised Manuscript Received October 10, 1989
ABSTRACT: 1,1,3-Trimethyl-l-silacyclopent-3-ene (I) undergoes anionic ring-opening polymerization on treatment with n-butyllithium and HMPA cocatalysts in THF to yield poly(l,l,3-trimethyl-l-sila-cis-pent3-ene) (11). Comparison of 'H, 13C, and ? 3 i NMR spectra of I1 with those of model compounds, (2)and (E)-2-methyl-l,4bis(trimethylsilyl)-2-butene (IV), permits assignment of polymer I1 microstructures. When the polymerization of I is conducted a t -42 "C, the NMR spectra of I1 are consistent with a polymer in which cis-1,4-isoprene units are joined to dimethylsilylene units. A 1:2:1 distribution of head-to-head, headto-tail, and tail-to-tail arrangements of adjacent cis-1,4-isoprene units is found. On the other hand, when the polymerization is conducted at -78 OC, the microstructure of I1 is predominantly head-to-tail. The mechanism of polymerization, which may account for the observed regioselectivity, is discussed.
'H and 13C NMR signals assigned to the methyl groups bonded to silicon changed (Figures 1 and 2). To clarify this situation, we have prepared both (2)and (E) - 2-methyl- 1,4-bis (trimethylsilyl)-2-butene [(2)IV and (E)-IV]. While these model compounds are methylethylenediamine (TMEDA) in THF solvent at -40 "C leads to poly(l,l,3-trimethyl-l-sila-cis-pent-3-ene) known,3 neither high-field 'H,"C, nor "Si NMR spectra of them have been reported. The assignment of 13C (II).' While the microstructure of the closely related sysNMR chemical shifts was done on the basis of 'H-coutem, poly(l,l-dimethyl-l-sila-cis-pent-3-ene) (111) was pled 13C NMR spectra. The significant difference in the assigned on the basis of comparison of 13C NMR chem13C chemical shift of the methyl and the proximate methical shifts with model compouunds,2 the assignment of ylene carbons bonded to a cis carbon-carbon double bond the microstructure of I1 was made on the basis of less compared to those bonded to a trans carbon-carbon doufirm evidence. Several experiments have led us to more ble bond should be noted (Figures 3-5). thoroughly s t u d y this system. Chief among these was Of great significance, we have found that when I is the observation that when we conducted the polymerizatreated with n-butyllithiumlHMPA cocatalysts in THF tion at different temperatures, the intensity ratio of the
We have previously reported that anionic ring-opening polymerization of 1,1,3-trimethyl-l-silacyclopent-3ene (I) catalyzed b y n-butyllithium/hexamethylphosphoramide (HMPA) or m e t h y l l i t h i u m / t e t r a -
0024-9291 19012223-191 1$02.50/0
0 1990 American Chemical Society
Macromolecules, Vol. 23, No. 7, 1990
1912 Park et al.
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at -78 "C for 3 h, regioselective polymerization occurs. Thus the NMR spectra of I1 produced in this way is consistent with a polymer microstructure in which 1,4-isoprene units are preferentially joined to dimethylsilane groups in a head-to-tail manner. The methyl groups bonded to silicon give rise to three resonances in both the 'H and I3C NMR spectra (2:27:2). This is expected if a single microenvironment is dominant. Comparison of the peak heights of these 13C NMR signals indicates that the head-to-tail microstructure is favored over the head-to-head plus tail-to-tail microstructures by approximately 7:l. Further, the 'H and 13C NMR chemical shifts
This information has permitted us to fully analyze the lH, 13C,and 29SiNMR spectra of I1 produced at -42 "C. The methyl groups bonded to silicon give rise to three 'H and three 13C resonances. Both of these sets have a 1:2:1 intensity ratio. These may be interpreted in terms of diad microstructures in which 1,4-isoprene units are bonded to dimethylsilyl groups in head-to-head, headto-tail, and tail-to-tail arrangements (1:2:1) (Figure 7). On the other hand, the 'H and 13CNMR resonances due to the 1,4-isoprene units can be accounted for by triad analysis. This leads to a prediction of eight unique methylene signals, as well as eight distinct vinyl and four methyl resonances, in the 13C NMR. These have in fact been observed (Figure 8). Of particular importance, no 13C NMR signal is observed near 30 ppm. A signal in this region would be expected for one of the methylene carbons if trans-1,4-isoprene units were present. Apparently, ring-opening polymerization of I occurs in a stereoregular cis manner at both -42 and -78 "C. We have previously proposed a mechanism for the anionic ring-opening polymerization 1,l-dimethyl-lsilacyclopent-3-ene (V) that involves hypervalent pentacoordinate siliconate intermediates. Chain growth occurs by ring opening of these anionic species to yield an allylic anion, which reacts rapidly with another molecule of V. To account for the cis stereospecificity observed, this reac-
Macromolecules, Vol. 23, No. 7, 1990
Anionic Ring-Opening Polymerization 1913
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