Polymerizability of Isomerically Trimethylsilyl Substituted Styrenes

Polymer Journal, Vol. 23, No. 4, pp 285-296 (1991) Polymerizability of Isomerically Trimethylsilyl Substituted Styrenes Yusuke KAWAKAMI* and Ruben Walter CAIRO Department of Synthe1ic Chemislry, School of Engineering, Nagoya University, Chikusa, Nagoya 464, Japan (Received October 8, 1990) ABSTRACT: Polymerizability of isomerically trimethylsilyl and pentamethyldisiloxanyl substituted styrenes was studied. In the polymerization, a-substituted isomers gave low molecular weight polymer in low yield. Chain transfer constant to the a-trimethylsilyl substituted monomer was estimated to be quite large as a styrene type monomer. In NMR spectrum, ix-vinyl proton of a-isomers shifted to the lower field compared with that of m- or p-isomers, and 9% of nuclear Overhauser enhancement (NOE) was observed for ix-vinyl proton of a-trimethylsilylstyrene under irradiation on silylmethyl proton. The characteristic polymerization behavior of the a-isomers is discussed. KEY WORDS Trimethylsilyl Group / Steric Effect / Radical Polymerization / Anionic Polymerization / cl-Orbital / Nuclear Overhauser Enhancement / Reaction Mechanism / As reported in previous papers, 1 - 5 > poly- of the vinyl proton, and also on the polymmers from oligodimethylsiloxanyl substituted erizability of the monomer. In this article, styrenes are good materials for selective oxygen we would like to report mainly the study of separation from air. The high permeability of the effects of the isomerically substituted trigas was attributed to the lowered glass tran- methylsilyl group on the phenyl ring of styrene sition temperature of the polymer and high dif- on the chemical shifts in NMR spectra and to fusivity of gas brought about by highly mo- give possible explanation on the low reactivity bile oligodimethylsiloxanyl side chains even of the a-substituted monomer in polymerizain the solid state. tion. Trimethylsilyl substituted polystyrene, which does not have siloxane linkage, also EXPERIMENTAL exhibited enhanced permeation of gases compared with polystyrene. However, the General reason for the high permeability seems differIR, 1 H, and 13 C NMR spectra were recorded ent from that for the oligodimethylsiloxanyl on a JASCO FT-IR spectrometer model substituted polymers. It will be interesting to FT7000, and on a Varian NMR spectrometer elucidate the role of bulky groups such as model Gemini 200 (200 MHz for 1 H, 50 MHz trimethylsilyl group on the polymerizability of for 13 C). Chemical shifts are given as b in ppm monomers and the gas permeation behavior. from tetramethylsilane as an internal standard. In the synthesis of polymers of isomerically Nuclear Overhauser enhancement (NOE) trimethylsilyl substituted styrenes along with analysis was made on a Varian 500 MHz 1 H the direction of our study, we noticed an NMR spectrometer model VXR-500. Monointeresting effect of the o-trimethylsilyl group mers were purified by column chromatography on proton and carbon NMR chemical shifts (Wako Silica gel 60) with hexane as the eluent. 285 Y. KAWAKAMI and R. w. CAIRO Wittig 0-HO--- X).__~ Reaction H t1._ o=C/ \ X... r. tK o,m,p-S 2 Scheme 1. o,m,p-S 1 Synthetic route to a-substituted styrenes. Number-average molecular weights of polymers were determined by a Corona vapor phase osmometer model 114. Gel permeation chromatograms were recorded on a JASCO high pressure liquid chromatograph model 880. Thermal analysis of polymers were made on a SEIKO thermal analysis system model SSC5000 equipped with DSC I 00. Synthesis of Monomers Halogenostyrenes were synthesized from halogenobenzaldehyde via Wittig reaction. o-, m-, p-Trimethylsilylstyrenes (o-, m-, p-S 1 ) were synthesized via Grignard reaction from o-, m-, p-halogenostyrene in the presence of trimethylcholorosilane (TMCS) according to Scheme 1. Reaction with dimethyldichlorosilane (DMCS) first and then the coupling of remaining chlorosilane group with lithium trimethylsilanolate (L TMS) gave o-, m-, ppentamethyldisiloxanylstyrenes (o-, m-, p-S 2 ). In NMR assignment, vinyl protons of the monomers, Ha, Hb, and He and number of carbon atoms in the aromatic ring are as follows. 286 o-Trimethylsilylstyrene (o-S 1 ) To a solution of triphenylphosphine (24.50 g, 93.41 mmol) in benzene (90 ml), 5 N aq. sodium hydroxide solution (226 ml), o-bromobenzaldehyde (8.20 g, 44.30 mmol) and methyl iodide (12.58 g, 88.62 mmol) were added, and the reaction mixture was stirred vigorously for 24 h at 40°C. After the reaction, the organic layer was separated, followed by repeated extraction with l N aq. sodium hydroxide solution to remove triphenylphosphine oxide as much as possible. The benzene solution was dried over magnesium sulfate. A small amount of hexane was added to produce further precipitation of triphenylphosphine oxide. After benzene was evaporated, the product, o-bromostyrene 6 was obtained in 75% yield and purified by column chromatography (Rf= 0.6). Carefully dried Mg turnings (1.06 g, 43.60 mmol) was activated by mechanical agitation without solvent under nitrogen atmosphere in Polym. J., Vol. 23, No. 4, 1991 a-Substituted Styrene a three-necked flask. Dry tetrahydrofuran (THF) was added to cover Mg, and few drops of 1,2-dibromoethane were added to activate Mg. Then, trimethylchlorosilane (3.56 g, 32. 78 mmol) in THF (3.6 ml) was introduced into the flask. To this mixture, o-bromostyrene (4.00 g, 21.85mmol) in THF (8.0ml) was added dropwise for 1 h, and the reaction mixture was stirred for further 2 days. After 2 days, the reaction mixture was poured into hexane, and the formed solid was removed by filtration. After evaporation of the solvent, the product, o-trimethylsilylstyrene in solution was separated and purified on column chromatography (Rf =0.53) in 58% yield. Chemical shifts in 1 H NMR: 0.33 (s. 9H, -Si(CH 3 h), 5.27 (dd, lH, 1 2 = 10.9 Hz, 1 2 = 1.4 Hz, He), 5.63 (dd, lH,11 = 17.3 Hz, 1 2 = 1.4 Hz, Hb), 7.07 (dd, lH, 1 1 = 17.3 Hz, 1 2 = 10.9 Hz, Ha), and 6.99--7.56ppm (m, 4H, aromatic). m-Trimethylsilylstyrene (m-S 1 ) Chemical shifts in 1 H NMR: 0.25 (s, 9H, -Si(CH 3 h), 5.23 (dd, lH, 1 1 = 10.9 Hz, 1 2 = 1.0 Hz, He), 5.74(dd, lH,1 1 = 17.5Hz,J2 = 1.0 Hz, Hb), 6.72 (dd, lH, 1 1 = 17.5 Hz, 1 2 = 10.9 Hz, Ha), and 7.27-7.51 ppm (m, 4H, aromatic). p-Trimethylsilylstyrene (p-S 1 ) Synthesis and chemical shifts of this compound were already reported. 1 o-Pentamethyldisiloxanylstyrene (o-S 2 ) The Grignard reagent prepared from obromostyrene (3.50 g, 19.12 mmol) and Mg turnings (0.93 g, 38.24 mmol) in THF (7.6 ml) was added dropwise to a solution of dimethyldichlorosilane (4.60 ml, 38.24 mmol) in THF (4.3 ml) at room temperature, and allowed to react for 15 h at the temperature. After the reaction, the solution was concentrated to about one third in volume, dry hexane was added, and the formed solid was filtered under nitrogen atmosphere. The desired compound was purified by distillation, bp 35-40°C/0.2 mmHg. 53% Yield. To a solution of lithium trimethyls (...truncated)