Takahiro Gunji

Preparation and properties of polysilsesquioxanes: Polysilsesquioxanes and flexible thin films by acid‐catalyzed controlled hydrolytic polycondensation of methyl‐ and vinyltrimethoxysilane

Polymethylsilsesquioxane (PMS) and polyvinylsilsesquioxane (PVS) were prepared by acid-catalyzed controlled hydrolytic polycondensation of methyl- and vinyltrimethoxysilane (MTS and VTS), respectively. The spinnabilities and molecular weights of polysilsesquioxanes were easily controlled by the reaction conditions, such as the molar ratios of water, hydrochloric acid, and methanol to MTS or VTS; nitrogen flow rate; temperature; and stirring rate. PMS and PVS showed spinnability of more than 200 cm when their molecular weights were up to 42,000 (PMS) and 19,000 (PVS) Mw. Transparent, colorless, and flexible films of 0.02–0.10 mm thick were prepared by casting a 20 wt % acetone–methanol (V/V = 1) solution of PMS and PVS on a polymethylpentene shale, followed by heating at 80°C for 3 weeks. The tensile strength of the films, approximately 26 (PMS) and 17 (PVS) MPa, was found to be correlated with the structure of the polysilsesquioxanes. The surface contact angle and electroconductivity of films were also measured.

Preparation of continuous zirconia fibres from polyzirconoxane synthesized by the facile one-pot reaction

A one-pot reaction of zirconium oxychloride octahydrate (ZOC) with ethyl acetoacetate (Hetac) in the presence of triethylamine was investigated. The reaction was carried out in molar ratios of Hetac/ZOC=1.0, 1.5, 2.0 to give highly viscous solutions with good spinnability and stability to self-condensation. Polyzirconoxanes (PZOs) were isolated as white powders by reprecipitation of the solutions with tetrahydrofuron (THF)-hexane that were soluble in acetone, methanol and THF. The molecular weight of PZO was Mn=1000–2000, and was dependent on the molar ratio and the reaction time. Dry spinning of the solution (Hetac/ZOC=1.5) containing 3mol% tris(acetylacetonato)yttrium [Y(acac)3] gave continuous precursor fibres (3.0Y–PZO). Yttria stabilized zirconia fibres of 12–18 μm diameter with a tensile strength of 1.4GPa were obtained by heat treatment of the 3.0Y–PZO at 1100 or 1200 °C. The fibre consisted of submicrometre-sized particles of tetragonal crystallites.

Preparation of silicon oxycarbide ceramic films by pyrolysis of polymethyl- and polyvinylsilsesquioxanes

The sol-gel reactions of methyl- and vinyltrimethoxysilane under controlled conditions provided the corresponding polysilsesquioxanes and flexible thin films on further condensation of the precursors. Silicon oxycarbides containing a large amount of free carbon 58 mol% and 90 mol% were obtained in high yields 90 wt% on pyrolyzing the precursors of polymethyl-and polyvinylsilsesquioxane at 1400°C under N2 atmosphere, respectively. Moreover, pyrolytic polycondensation of polyvinylsilsesquioxane was found to give the silicon oxycarbide ceramic films without deformations and cracks. The composition and properties of films were investigated.

Preparation and properties of silicon-containing polymer hybrids from 3-methacryloxypropyltrimethoxysilane

The preparation of organic‐inorganic polymer hybrids consisting of carbon‐carbon and siloxane chains was investigated by radical polymerization of 3-methacryloxypropyltrimethoxysilane (MAS) followed by acid-catalyzed hydrolytic polycondensation. The condensation of poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) of various molecular weights Mn = 830‐12000 prepared by polyaddition provided transparent and flexible free-standing hybrid gel films. The mechanical properties of these films were highly dependent on the carbon‐carbon chain length: with an increase in the carbon‐ carbon chain length, the elasticity of gel films increased, while the tensile strength and Young’s modulus decreased. Hydrolyzability of S-PMA decreased with an increase in the carbon‐carbon chain length, resulting in the formation of rubber-like films with flexibility. # 1998 John Wiley & Sons, Ltd.

Preparation and properties of polysilsesquioxanes. Function and characterization of coating agents and films

Abstract Coating characteristics of polysilsesquioxanes with various molecular weights prepared by acid-catalyzed hydrolytic polycondensation of trimethoxysilane RSi(OMe) 3 (R=Me, Vinyl) were investigated in relation to the structure. Homogeneous, smooth and crack-free coating films of thickness from 0.25 to 0.95 μm were prepared by 1–10 times dip-coating of an acetone–methanol solution of polysilsesquioxanes on polymer, metal and ceramic substrates. Their mechanical, optical and electrical properties were investigated. The adhesion and hardness of coating films showed the maximum values based on the evaluation of JIS (Japanese Industrial Standard) K5400. They also increased with increasing molecular weight, T 3 unit of polysilsesquioxanes, heating time and sintering temperature. The coating films were revealed to be thermally stable on heating to 800°C. The refractive index of coating films decreased gradually with increasing temperatures up to about 800°C. The transmittance of coating films was higher than 98% at 500 nm. The surface resistivity of the coating films increased with the increase of sintering temperature.

Preparation of SiO2TiO2 fibers from polytitanosiloxanes

Abstract Continuous oxide fibers SiO 2 ue5f8TiO 2 were obtained by drying spinning of precursor fibers from polytitanosiloxanes (PTS) prepared by the reaction of silicic acid (SA) with titanium chelate (PTP) in the molar ratio of SA/PTP = 0.5 (PTS-0.5) and 1.0 (PTS-1). The precursor fibers, being golden-yellow, turned black and then white on pyrolysis. The fibers underwent decomposition with removal of organic groups to form black fibers at 200–500°C and white fibers at about 1000°C. Crystallization of TiO 2 took place at 850°C (PTS-0.5) and 950°C (PTS-1). Rearrangement of Siue5f8Oue5f8Ti linkage of the polymer back-bone into Siue5f8Oue5f8Ti m ay lead to the formation of TiO 2 clusters and subsequent crystallization of TiO 2 .

Preparation of polymetalloxanes as a precursor for oxide ceramics

The reaction of di-t-butoxysilanediol with bis(acetylacetonato)titanium di-iso-propoxide gave cyclic titanosiloxane. Silicon tetraacetate was reacted with boron tri-n-butoxide in THF to form polyborosiloxanes with molecular weight around one thousand. Monolithic SiO2ue5f8B2O3 gels were obtained on aging a solution of the reaction product. High molecular weight polyborosiloxanes, capable of forming gel fibers, were obtained by the reaction followed by partial alkoxylation and subsequent hydrolysis. The hydrolysis of bis(ethyl acetoacetato)zirconium diethoxide was investigated to obtain polyzirconoxanes as a precursor for the oxide materials. The product was found to be a low molecular weight polymer formed by condensation of the partial hydrolysis product which showed good spinnability and gave gel fibers.

Hydrolytic polycondensation of vinyltrimethoxysilane and formation of vinylpolysiloxane films

AbstractHydrolytic polycondensation of vinyltrimethoxysilane (VTM) was investigated in detail to prepare vinylpolysiloxanes (VPS) having spinnability and tough gel films. VTM was hydrolyzed in various molar ratios r1 (H2O/VTM) = 0.5–1.6 (HCl/VTM = 0.105, EtOH/VTM = 1.44) at 70°C under a N2 stream with stirring at 150 rpm to give vinylpolysiloxanes with n

Preparation and Properties of Polysilsesquioxanes - Polysilsesquioxanes as a Candidate to a Low Dielectrics for Electronic Devices -

overline {{text{Mn}}}