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Anionic Ring-Opening Polymerization of Phenylsilacyclobutanes

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Anionic Ring-Opening Polymerization of Phenylsilacyclobutanes Polymer Journal, Vol. 32, No. 4, pp 354-360 (2000) Anionic Ring-Opening Polymerization of Phenylsilacyclobutanes Kozo MATSUMOTO, t Masaaki SHINOHATA, and Hitoshi YAMAOKA Department ofPolymer Chemistry, Kyoto University, Kyoto 606-8501, Japan (Received October 23, 1999) ABSTRACT: Buty]]jthium-induced anionic ring-opening polymerization of phenyl-substituted silacyclobutanes was investigated. Polymerization of 1,1-dimethyl-3-phenylsilacyclobutane in tetrahydrofuran (THF) at - 78°C proceeded in a living fashion. A linear relationship between ln[M]of[M] and time ([M] 0 is the initial concentration of the monomer and [Ml is the concentration of monomer) and a linear relationship between number-average molecular weight (Mn) and monomer conversion were observed. The molecular weight of the obtained polymer was very narrow (M,)Mn = 1.09, Mw is weight-average molecular weight). In contrast, neither 1,1-dimethyl-2-phenylsilacyclobutane nor 1-methyl-1- phenylsilacyclobutane showed a living nature under the same polymerization conditions, which were confirmed by two­ step monomer addition experiments. 13C NMR and 29Si NMR spectrum of the poly(l,1-dimethyl-2-phenylsilacy­ clobutane) indicated that polymerization of 1,1-dimethyl-2-phenylsilacyclobutane proceeded without regioselectivity. By differential scanning calorimetry (DSC) measurements, glass transition temperatures (Tg)s were determined at -5"C for poly(l,1-dimethyl-3-phenylsilacyclobutane), 27°C for poly(l,1-dimethyl-2-phenylsilacyclobutane), and -29°C for poly(l­ methyl-1-phenylsilacyclobutane). KEY WORDS Silacyclobutane / Phenylsilacyclobutane / Living Anionic Polymerization / Ring- Opening Polymerization/ Polysilacyclobutane / Silacyclobutane is an important monomer to synthe­ silacyclobutane with phenylmagnesium bromide. size polycarbosilanes and many researchers have stud­ Triphenylphosphine, tetrachloromethane, magnesium, ied the polymerization of silacyclobutanes in detail dur­ hexachloroplatinic acid, lithium, and butyllithium hex­ 1 2 ing the last half century. • Recently, we reported the liv­ ane solution were purchased from Wako Pure Chemical ing anionic polymerization of 1,1-dimethyl and 1,1- Industry, chlorodimethylsilane and 3-chloropropyl­ diethyl-substituted silacyclobutanes.3 Knischka and co­ methyldichlorosilane from Shin-Etsu Chemical, and workers reported the living anionic polymerization of used as delivered. Tetrahydrofuran (THF) was freshly 1,1-dipropylsilacyclobutane.4 However, the living poly­ distilled over sodium benzophenone ketyl under argon merization of silacyclobutane derivatives other than 1,1- atmosphere before use. Phenylmagnesium bromide was dialkylsilacyclobutanes remains unknown. prepared by treatment of phenyl bromide with magne­ Phenyl group substituted monomers are quite attrac­ sium in THF. Lithium naphthalene was prepared by tive because the physical and mechanical properties of treatment of naphthalene with lithium metal in THF. polymeric materials are strongly affected by aromatic substituents. Therefore, we studied the anionic ring­ Measurements opening polymerization of 1-phenyl, 2-phenyl, and 3- Gel-permeation chromatography was carried out in phenyl substituted silacyclobutanes in detail. The poly­ chloroform on a JASCO 880-PU chromatograph merization of 1,1-dimethyl-3-phenylsilacyclobutane gave equipped with four polystyrene gel columns (Shodex K- a living polysilacyclobutane, while those of the other two 802, K-803, K-804, and K-805 ; exclusion limit = 5 X 3 5 6 monomers did. 10 , 7X104, 4X10 , and 4X10 , respectively) and JASCO 830-RI refractive index detector. Molecular EXPERIMENTAL weights of the polymers were calibrated with polysty­ rene standards. 1H and 13C NMR spectra were recorded 29 Materials on a JEOL GSX 270 spectrometer in CDC13. Si NMR 1,1-Dimethyl-3-phenylsilacyclobutane (1) was synthe­ sized in four steps from a-methylstyrene (Scheme 1). 2- 5 Phenyl-2-propen-1-ol was prepared as reported. 2- t-BuOOH I Se02 (OH Phenyl-3-chloro-1-propene was prepared by treatment of Ph~ PhA 2-phenyl-2-propene-l-ol with triphenylphosphine in tet­ salicylic acid rachloromethane.6 Platinum-catalyzed hydrosilation of CH2Cl2 the olefin with chlorodimethylsilane and successive ex­ c, HSiMe2CI Le, posure of the product to magnesium provided the desired Ph -H""'2P""t"'c""1e=,=6=H'-2-0- Ph SiMe2CI monomer 1 in good yield. 1,1-Dimethyl-2-phenylsilacyclobutane (2) was pre­ Ph pared as reported.7 1-Methyl-1-phenylsilacyclobutane Mg (3) was prepared by treatment of 1-chloro-1-methyl- THF D.iMe2 1 tTo whom correspondence should be addressed. Scheme 1. 354 Anionic Polymerizations of Phenylsilacyclobutanes spectra were recorded on a JEOL GSX 500 spectrometer merization. in CDC13• Tetramethylsilane was used as the internal standard for NMR measurement. IR spectra were meas­ Synthesis of 1, 1-Dimethyl-2-phenylsilacyclobutane (2) ured on a JASCO IR-810 spectrometer. Differential The title compound was prepared as reported, 7 and scanning calorimetry (DSC) measurements were per­ distilled twice over calcium hydride under reduced pres­ formed on a MAC Science DSC 3100 at - 100 to + 150°C sure before use. Spectral data were in accordance with and found to be reproducible with no apparent hystere­ those reported previously. sis over three heating and two cooling scans. Glass tran­ sition temperature (Tg) was determined from the inflec­ Synthesis of 1-Methyl-1-phenylsilacyclobutane (3) tion point on the DSC curve easily observed in the differ­ In a 500 mL round-bottomed flask equipped with a ential calculus of DSC curves (DDSC). magnetic stirring bar, reflux condenser, dropping fun­ nel, rubber septum, and rubber balloon, were placed Preparation of Chloro(3-chloro-2-phenylpropyl)dimethyl­ magnesium (2.91 g, 120 mmol) and THF (20 mL) under silane argon atmosphere. 0.8 mL of 1,2-dibromoethane was A magnetic stirring bar and catalytic amount ofhexa­ added, and the mixture was heated by a heat gun to chloroplatinic acid (10 mg) were charged in a two-necked activate the magnesium. A solution of 3-chloro­ 100 mL round bottomed flask equipped with a reflux propylmethyldichlorosilane (19.2 g, 100 mmol) in THF condenser, dropping funnel, and rubber balloon. The (80 mL) was slowly added to the magnesium over a pe­ flask was filled with argon. 3-Chloro-2-phenyl-1-propene riod of 1 h. After stirring the mixture for 2 h at room (13.0 g, 85 mmol) was added and the mixture was heated temperature, a solution of phenylmagnesium bromide to 50°C. Chlorodimethylsilane (11.0 mL, 99 mmol) was (1.76 Min THF, 65 mL, 114 mmol) was added at 0°C and slowly added to the mixture which was then stirred for 3 the mixture was stirred for 2 h at room temperature. h at 50°C. Excess chlorodimethylsilane was removed The solution was poured into 1 M aqueous HCl and the with a rotary evaporator under reduced pressure. Direct products were extracted with hexane (200 mL X 2). The distillation of the resulting residue under reduced pres­ organic layer was washed with water, dried over anhy­ sure gave the title compound (15.0 g, 61 mmol) in 72% drous Na2SO4, and concentrated. The residual oil was yield: hp 80°C (0.3 Torr) ; IR (neat) 3026, 2952, 1495, distilled over CaH2 under reduced pressure to give the 1 1 1256, 831, 808, 699 cm- ; H NMR (CDC13) o 0.11 (s, 3 title compound (13.3 g, 82.2 mmol) in 82% yield: hp 33 H), 0.19 (s, 3H), 1.28 (dd, J= 11.0, 14.7 Hz, lH), 1.57 °C (0.3 Torr) ; IR (neat) 2960, 2924, 1429, 1250, 1113, 1 (dd, J = 4.4, 14.7 Hz, lH), 3.19 (dddd, J = 4.4, 7.3, 7.3, 866, 771, 731, 696 cm -l; H NMR (CDC13) o 0.55 (s, 3 11.0 Hz, lH), 3.67 (dd, J = 7.3. 13.2 Hz, lH), 3.69 (dd, J H), 1.10-1.40 (m, 4H), 2.19 (tt, J = 8.8, 8.8 Hz, 2H), = 7.3, 13.2 Hz, lH), 7.20-7.41 (m, 5H); 13C NMR 7.30-7.43 (m, 3H), 7.58-7.70 (m, 2H); 13C NMR (CDC13) o 1.65, 2.50, 23.69, 43.80, 51.78, 127.40, 127.70, (CDC13) o - 1.87, 14.27, 18.19, 127.86, 129.36, 133.42, 128.64, 141.98. Anal. Calcd. for CuH16ChSi: C, 138.57. Anal. Calcd. for C10H 14Si: C, 74.00%; H, 8.69%. 53.44%; H, 6.52%. Found: C, 53.54%; H, 6.71%. Found : C, 73.84 % ; H, 8.83%. The monomer was redis­ tilled over CaH2 just before a polymerization. Synthesis of 1,1-Dimethyl-3-phenylsilacyclobutane (1) A magnetic stirring bar and magnesium (3.0 g, 123 Polymerizations of Phenylsilacyclobutanes mmol) were charged into a three-necked 300 mL round In a 50-mL round-bottomed flask equipped with a bottomed flask equipped with a reflux condenser, drop­ magnetic stirring bar, rubber septum, and rubber bal­ ping funnel, and rubber balloon. The flask was filled loon, was placed THF (6 mL) under argon atmosphere. with argon. First, THF (10 mL) and 1,2-dibromoethane The solvent was titrated with a THF solution of lithium (0.6 mL) were added and the mixture was heated by a naphthalene to eliminate all reactive impurities. The heat gun to activate the magnesium. After an exo­ mixture was cooled to -78"C, butyllithium (1.00 M hex­ thermic reaction, a solution of chloro(3-chloro-2- ane solution, 0.15 mmol) was added, and then phenylsi­ phenylpropyl)dimethylsilane (15.0 g, 61 mmol) in THF lacyclobutane (3.0 mmol). The reaction mixture was (90 mL) was slowly added over a period of 10 min. The stirred for the designated period. Water (0.5 mL) was mixture was then heated to reflux and stirred for 1 h. added to terminate the polymerization. The resulting The mixture was poured into ice-cooled 1 M HCl (200 mixture was poured into water (50 mL) and extracted mL) and the products were extracted with hexane (300 with ether (50 mL).
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