Stereoregular Anionic Ring-Opening Polymerization of Silacyclopent

37 Stereoregular Anionic Ring-Opening Polymerization of Silacyclopent-3-enes 1

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Downloaded by TUFTS UNIV on June 20, 2017 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1990-0224.ch037

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Xuehai Zhang, Qingshan Zhou, William P. Weber, Raymond F. Horvath, Tak-Hang Chan, and Georges Manuel 3

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Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1661 Department of Chemistry, McGill University, Montreal, Quebec H3A 2K6, Canada Laboratoire des Organométalliques, UA 477 Université Paul-Sabatier, 31062 Toulouse Cedex, France

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The ring-opening polymerization of 1,1-dimethyl-1-silacyclopent-3– ene,1-methyl-1-phenyl-1-silacyclopent-3-ene, 1,1-diphenyl-1-silacyclopent-3-ene, and 1,1,3-trimethyl-1-silacyclopent-3-ene was catalyzed by alkyllithium reagents in the presence of hexamethylphosphoramide or Ν,Ν,Ν',Ν'-tetramethylethylenediamine and yielded poly(1,1-dimethyl-1-sila-cis-pent-3-ene), poly(1-methyl-1phenyl-1-sila-cis-pent-3-ene), poly(1,1-diphenyl-1-sila-cis-pent-3ene), and poly(1,1,3-trimethyl-1-sila-cis-pent-3-ene), respectively. The polymer products were characterized byH, 3C, and Si NMR spectroscopy; gel permeation chromatography; and thermogravimetric analysis. The mechanism of this polymerization is discussed. 1

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THE ANO INC I RN IG-OPENN IG POLYMERZ IATO IN

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of 1,1-dimethyl-l-silacyclopent-3-ene (I) has been reported recently, although the polymer has not been fully characterized (I). The properties of poly(l,l-dimethyl-l-sila-dspent-3-ene) (Π), as well as several related systems, are reported in this chapter. Anionic polymerization of I yields high-molecular-weight materials with weight-average (Mw) and number-average (Mn) molecular weights of 158,000 ^Author to whom correspondence should be addressed.

0065-2393/90/0224-0679$06.00/0 © 1990 American Chemical Society

Zeigler and Fearon; Silicon-Based Polymer Science Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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SILICON-BASED POLYMER SCIENCE: A COMPREHENSIVE RESOURCE

and 69,000, respectively. By comparison, ring-opening metathesis polym erization of I (2, 3) gives low-molecular-weight materials. Anionic polymerization requires a cocatalyst system composed of an alkyllithium reagent and either N,N,N',IV'-tetramethylethylenediamine (TMEDA) or hexamethylphosphoramide (HMPA). 1-Methyl-l-phenyl-l-silacyclopent-3-ene ( I I I ) , l,l-diphenyl-l-silacyclopent-3-ene ( I V ) , and 1,1,3trimethyl-l-silacyclopent-3-ene ( V ) were polymerized under similar condi tions.


Experimental Procedures Ή and 1 3 C NMR spectra were obtained with a JEOL FX-90FT (Fourier transform) spectrometer. 1 3 C NMR spectra were run with broad-band proton decoupling. 2 9 Si NMR spectra were obtained with a Brucker WP-270-SY FT spectrometer. Solutions of 10-15% in CDC1 3 or C 6 D 6 were used to obtain 2 9 Si NMR spectra, whereas 5% solutions were used for Ή and 1 3 C NMR spectra. A DEPT (distortionless enhance ment by polarization transfer) pulse sequence was used to obtain 2 9 Si NMR spectra. This technique was effective, because all the silicon atoms are bonded to at least one methyl group (4). IR spectra were recorded on a Perkin-Elmer PE 281 spectrometer. The spectra were taken from neat oils between NaCl plates or from chloroform solutions in NaCl cells. Gel permeation chromatographic (GPC) analysis of the molecular weight dis tribution of the polymers was performed with a Perkin-Elmer series 10 liquid chromatograph equipped with an LC-25 RI detector (25 °C), a 3600 data station, and a 660 printer. A Perkin-Elmer PL 10-μπι particle mixed-pore-size cross-linked poly styrene gel column (32 cm by 7.7 mm) was used for the separation. The eluting solvent was reagent-grade tetrahydrofuran (THF) at a flow rate of 0.7 mL/min. The retention times were calibrated against known monodispersed polystyrene standards with M p s of 194,000, 87,000, or 10,200 and for which the ratio M w / M n is less than 1.09. Thermogravimetric analyses (TGA) were carried out with a Perkin-Elmer TGS-2 analyzer at a nitrogen flow rate of 50 cm 3 /min. The temperature program for the analysis was 50 °C for 10 min followed by an increase of 5 °C/min to 600 °C. Elemental analysis was performed by Galbraith Laboratories, Knoxville, T N . Satisfactory analytical results (±0.4%) were obtained for all new polymers. Polymerization of I. I was polymerized in flame-dried equipment under N 2 at -40 °C as follows. A 25-mL round-bottom flask equipped with a poly(tetrafluoroethylene) (Teflon)-covered magnetic stirring bar and rubber septum was charged with I (1.2 g, 10.9 mmol) (5, 6), T H F (10 mL), and either HMPA (5 drops) or T M E D A (5 drops). w-Butyllithium (0.8 mL, 1.2 M , 0.96 mmol) was added slowly to this mixture. The mixture quickly became thick. The mixture was stirred for 1 h at -40 °C and then warmed to -20 °C, and saturated aqueous ammonium chloride was added. The organic layer was separated, washed with brine and water, and dried over molecular sieves (4 A). After filtration, the solvent was removed by evaporation under vacuum; 1.10 g (92% yield) of polymer was isolated. The yields of polymer (±2%) and their spectral properties were identical regardless of whether HMPA or T M E D A was used as cocatalyst. With n-butyllithium-TMEDA, a polymer with M w and M n of 158,000 and 69,000, respectively, was obtained, whereas with n-butyllithium-HMPA, a polymer with M w and M n of 120,000 and 30,400, respectively, was isolated.


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Stereoregular Anionic Ring-Opening

Polymerization

681


The analysis of poly(l,l-dimethyl-l-sila-ci5-pent-3-ene) (Π) gave the following results. Ή N M R spectrum (values are chemical shifts [δ] expressed in parts per million [ppm]): 0.125 (s [singlet], 6 H), 1.58 (d [doublet], 4 H, / [coupling constant] = 7 Hz), and 5.485 (t [triplet], 2 H , / = 7 Hz). 1 3 C NMR spectrum (δ, ppm): -3.26 (2 C), 16.72 (2 C), and 123.45 (2 C). 2 9 Si NMR spectrum (δ, ppm): 2.17. IR spectrum (values are frequencies [v]): 1710 (br [broad]), 1670 (br), 1630 (C = C), 1345, 1248, and 840 cm" 1 . The polymerization of 1,1-dimethyl-l-silacyclopentane (7) was carried out as described for I, but only the starting material was recovered. Poly(l,l,3-trimethyl-l-sila-cis-pent-3-ene) (VHI). VIII was prepared by po lymerization of V (5, 6) as described for I; an 84% yield was obtained. With nbutyllithium-HMPA, a polymer with M w and M n of 23,500 and 11,400, respectively, was obtained, whereas with methyllithium-TMEDA, a polymer with M w and M n of 32,000 and 15,000, respectively, was found. The polymer products had identical spectral properties. Analysis gave the following results. Ή NMR (δ, ppm): -0.056 (s), -0.018 (s), and 0.030 (s) at a peak intensity ratio of -1:2:1 (6 H); 1.30 (d, 2 H , / = 8 Hz); 1.455 (d, 2 H , / = 1 Hz); 1.655 (d, 3 H, / = 1 Hz); and 5.01 (t, 1 H , / = 8 Hz). 1 3 C N M R (δ, ppm): -3.34, -2.36, -1.28, 17.34, 17.43, 18.26, 18.34, 21.41, 21.47, 22.33, 22.38, 117.09, 117.25, 117.40, 117.42, 130.58, 130.74, 130.96, and 131.08. 2 9 Si NMR (δ, ppm): 1.926. IR (v): 1720-1610 (br), 1345, and 830 c m 1 . Poly( 1-methyl-l-phenyl-l-sila-cis-pent-3-ene) (IX). IX was prepared by polym erization of HI (8, 9) as described for I; a 93% yield was obtained with n-butyllithium-HMPA. The polymer, which was purified by precipitation from methanol, was a viscous oil. Analysis gave the following results. M w = 23,000. M n = 10,000. Ή NMR (δ, ppm): 0.226 (s, 3 H), 1.61 (d, 4 H, / = 6 Hz), 5.30 (t, 2 H , / = 6 Hz), and 7.5-7.27 (m [multiplet], 5 H). 1 3 C NMR (δ, ppm): -5.45, 15.30, 123.26, 127.65, 129.01, 133.88, and 137.84. 2 9 Si N M R (δ, ppm): -4.33. IR (v): 1640, 1435, 1370, 1250, 1120, and 830 c m 1 . Poly( 1,1-diphenyl- l-sila-eis-pent-3-ene) (VI). VI was prepared as described previously by polymerization of IV (5, 10). Methyllithium with either HMPA or T M E D A and n-butyllithium with T M E D A were effective catalysts. The polymer was purified by addition of methanol to a T H F solution of the crude reaction product. The polymer precipitated to give an 89% yield (mp = 130-136 °C). With n-butyllithium-TMEDA, a polymer with M w and M n of 13,400 and 7,900, respectively, was obtained. When methyllithium-TMEDA was used, M w = 12,400 and M n = 6,900 were found. Finally, with methyllithium-HMPA, M w and M n were 8000 and 4350, respectively. All the polymer products had identical spectral properties. Ή N M R (δ, ppm): 1.76 (d, 4 H , / = 6 Hz), 5.31 (t, 2 H , / = 6 Hz), and 7.40-7.66 (m, 10 H). 1 3 C NMR (δ, ppm): 13.67, 123.48, 127.60, 129.22, 134.91, and 135.51. 2 9 Si NMR (δ, ppm): -10.54. IR (v): 1420, 1360, and 1100 c m 1 . Isomerization of VI. AIBN [azobis(isobutyronitrile)] (15 mg) and VI (100 mg) were dissolved in 4 mL of dry T H F in a quartz tube. The solution was purged with argon and sealed with a rubber septum, and then, 10 mL of thiophenol was added. This solution was irradiated with a 450-W medium-pressure Hanovia Hg lamp for 24 h at 25 °C. After precipitation with methanol, a polymer with the following properties was obtained, mp = 62-70 °C. Ή NMR (δ, ppm): 1.76 (br m, 4 H), 4.70 (br m), 5.3 (br m), and 7.3 (br m, 10 H) (the ratio of peak intensities for ds-vinyl



682

(δ 5.3 ppm) and trans-vinyl (δ 4.7 ppm) hydrogens is 2.2). 1 3 C N M R (δ, ppm): 13.67, 17.9, 123.4, 124.7, 127.6, 129.2, 134.9, and 135.5. 29Si N M R (δ, ppm): -10.54 and -11.2.


Discussion The stereochemistry about the C - C double bonds of II was assigned by comparison of 1 3 C NMR chemical shifts with those of model compounds (II) (Chart I). Poly(l,l-diphenyl-l-sila-d5-pent-3-ene) (VI) (mp 130-136 °C) undergoes phenylthio-radical-catalyzed isomerization (12, 13) to a mixture of poly(l,l-diphenyl-l-sila-cis-pent-3-ene) and poly(l,l-diphenyl-l-silatrans-pent-3-ene) (VII) (mp 62-70 °C). 1 3 C NMR chemical shifts support these assignments, as shown in Scheme I.

-3.26

16.70

123.45

Chart I. C NMR chemical shifts of II compared with those of model com pounds. 13

The anionic ring-opening polymerization of I is unexpected because under similar conditions, allyltrimethylsilane undergoes metallation to yield an α-trimethylsilyl-substituted allyl anion (14-16). Relief of ring strain may be an important factor in facilitating this ring-opening polymerization. For example, the polymerization of silacyclobutanes is catalyzed by various nuZeigler and Fearon; Silicon-Based Polymer Science Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

37.

ZHANG ET AL.

Stereoregular Anionic Ring-Opening Polymerization

δ : 13.67

123.5

Ce Η '6π5

CgHgSH

C6H5

AIBN/h v

13.67


r

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H

123.5

* J

J

- — Si-CH^ /

L

ru

17.9

η

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124.7

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683

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- S I - C H ^ ^ H

C=C

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C=C

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Scheme I. Isomerization of VI as followed by C NMR chemical shifts. 13

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cleophiles (17-21). However, we were unable to polymerize 1,1-dimethyl1-silacyclopentane. The retention of stereochemistry of the double bonds in the polymer provides evidence against the intermediacy of a free allyl anion, which would be expected to undergo bond rotation to yield a polymer pos sessing both cis and trans double bonds. On the basis of these facts, chain propagation probably proceeds by reaction of a negatively charged pentacoordinated siliconate anion with a molecule of I to yield a new pentacoordinated siliconate anion (Scheme II). The molecular weights of these polymers are high with respect to the ratio of monomer to alkyllithium. This result suggests that the attack by alkyllithium reagents on the silyl center of the monomer may be slow or reversible. The microstructure of polymer formed by anionic polymerization of V was analyzed by H and 1 3 C NMR spectroscopy. Both *H and 1 3 C NMR spectra indicate that the methyl groups bonded to silicon may be in one of three distinct environments. l

I -SiThe thermal stability of these polymers was determined by TGA in a nitrogen atmosphere. Poly(l,l,3-trimethyl-l-sila-cw-pent-3-ene) (VIII) was stable up to 150 ° C . VIII lost weight at a rate of 3-5%/50 ° C increase in temperature between 150 and 350 °C. Rapid weight loss occurred between 350 and 425 °C. By 500 ° C 97% weight loss had occurred. The TGA of Π gave similar results. Poly(l-methyl-l-phenyl-l-sila-d5-pent-3-ene) (IX) was stable up to 200 ° C , whereas VI was stable up to 250 ° C . IX lost weight rapidly at >350 °C, whereas VI started to lose weight rapidly at 300 ° C . Zeigler and Fearon; Silicon-Based Polymer Science Advances in Chemistry; American Chemical Society: Washington, DC, 1989.


684


Scheme II. Polymerization

of 1.

Acknowledgments This work was supported by the Air Force Office of Scientific Research (grant 89-0007). Manuel and Weber thank the North Atlantic Treaty Organization (NATO) for a travel grant. Chan and Horvath acknowledge the support of the Natural Science and Engineering Research Council of Canada and the Fond pour la Formation de Chercheurs et L aide a la Recherche of Quebec.

References 1. Horvath, R. F.; Chan, T. H. J. Org. Chem. 1987, 52, 4489. 2. Lammens, H . ; Sartori, G.; Siffert, J.; Sprecher, N. J. Polym. Sci. 1971, 89, 341. 3. Finkel'shtein, E. S.; Portnykh, E. P.; Ushakov, Ν. V.; Vdovin, V. M . Izv. Akad. Nauk SSSR, Ser. Khim. 1981, 3, 641.

4. Pegg, D. T.; Doddrell, D. M.; Bendall, M . R. J. Chem. Phys. 1982, 77, 2745. 5. Manuel, G.; Mazerolles, P.; Cauquy, G. Synth. React. Inorg. Met.-Org.

Chem.

1974, 4, 133. 6. Weyenberg, D. R.; Toporcer, L. H . ; Nelson, L. E. J. Org. Chem. 1968, 33, 1975.


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ZHANG ET AL.

Stereoregular Anionic Ring-Opening

Polymerization

685

7. Fessenden, R.; Coon, M . D. J. Org. Chem. 1961, 26, 2530.


8. Manuel, G.; Cauquy, G.; Mazerolles, P. Synth. React. Inorg. Met.- Org. Chem.

1974, 4, 143. 9. Manuel, G.; Mazerolles, P.; Darbon, J. M . J. Organomet. Chem. 1973, 59, C7. 10. Dunoques, J.; Calas, R.; Dedier, J.; Pisciotti, F. J. Organomet. Chem. 1970, 25, 51. 11. Marchand, Α.; Gerval, P.; Joanny, M . ; Mazerolles, P. J. Organomet. Chem. 1981, 217, 19. 12. Kobayashi, Y.; Okamoto, S.; Shimazaki, T.; Ochiai, Y.; Sato, F. Tetrahedron Lett. 1987, 3959. 13. Golub, M . A. J. Polym. Sci. 1957, 25, 373. 14. Ayalon-Chass, D.; Ehlinger, E.; Magnus, P. J. Chem. Soc., Chem. Commun. 1977, 772. 15. Lau, P. W. K.; Chan, T. H . Tetrahedron Lett. 1978, 2383. 16. Ehlinger, E.; Magnus, P. Tetrahedron Lett. 1980, 11. 17. Nametkin, N . S.; Vdovin, V. M.; Grinberg, P. L.; Babich, E. D. Dokl. Akad. Nauk. SSSR 1965, J61,

358.

18. Nametkin, N. S.; Vdovin, V. M.; Zav'yalov, V. I. Izv. Akad. Nauk. SSSR, Ser. Khim. 1964, 191, 2003. 19. Nametkin, N. S.; Vdovin, V. M.; Poletaev, Y. Α.; Zavialov, V. I. Dokl. Akad.

Nauk. SSSR 1967, 175, 1068. 20. Nametkin, N . S.; Vdovin, V. M . ; Zav'yalov, V. I. Dokl Akad. Nauk. SSSR

824. 21. Topchiev, Α. V. Ger. Patent 1,226,310, 1966; Chem. Abstr. 1967, 66, 76763j.

1965,

162,

RECEIVED for review May 27, 1988. ACCEPTED revised manuscript March 13, 1989.


Stereoregular Anionic Ring-Opening Polymerization of Silacyclopent

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