Poly Methylsilane Research Articles

A polymer blend containing polycarbosilane and polysilaethylene for designing improved silicon carbide based fibers

This study elucidates the characterization of silicon carbide fibers synthesized from a polymer blend comprising polycarbosilane (PCS) and polysilaethylene (PSE). Given that PSE lacks oxygen in its molecular structure and possesses a C/Si ratio of 1, akin to polymethylsilane (PMS)—which historically has been combined with polycarbosilane to enhance ceramic yields—it was anticipated that PSE would similarly augment the ceramic yield of the fibers post-pyrolysis. Unlike PMS, PSE exhibits compatibility with PCS up to 15 wt%, with a notable reduction in melt spinnable temperature when the PSE content surpasses 5 wt%. Fibers containing 5 wt% PSE, melt-spun at 603 K, developed a central hollow in the cross-section, attributed to hydrogen gas evolution from PSE. Incorporating 10 wt% or more PSE improved spinnability and facilitated the production of fibers with finer diameters. Ceramic yield after pyrolysis at 1273 K for 1 h was improved compared to fibers without PSE or with PMS, and after holding at 573 K for 2 h, the yield increased when subjected to an additional hold at 573 K for 2 hours, due to an increase of cross-linking in the samples.

Polymethyl(1-Butyric acidyl)silane-Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single-Walled Carbon Nanotubes.

Individual single–walled carbon nanotubes (SWNTs) with distinct electronic types are crucial for the fabrication of SWNTs–based electronic and magnetic devices. Herein, the water–soluble polymethyl(1–butyric acidyl)silane (BA–PMS) was synthesized via the hydrosilylation reaction between 3–butenoic acid and polymethylsilane catalyzed by 2,2′–azodibutyronitrile. As a new dispersant, BA–PMS displayed a quite good dispersing capacity to arc–discharged SWNTs and moderate selectivity for metallic species. The application of sucrose–DGU, the density gradient ultracentrifugation with sucrose as the gradient medium, to the co–surfactants (BA–PMS and sodium dodecyl sulfonate) individually dispersed SWNTs yielded metallic SWNTs of 85.6% purity and semiconducting SWNTs of 99% purity, respectively. This work paves a path to the DGU separation of the SWNTs dispersed by polymer–based dispersants with hydrophobic alkyl chains.

Oxidation effect of graft polysilane on fluorescence properties

Abstract Tritium is radioactive hydrogen isotope which can be easily absorbed by organisms. The release of tritium is harmful to human health and environment. For monitor tritium directly, the development of new scintillator with low excitation energy, high scintillation efficiency and enhanced oxidative resistance, is desired. Polysilane has unique fluorescence characteristics for the σ conjugate structure which allow the excited electrons delocalizing in the whole Si-Si main chain. Polysilane modified by functional side groups would be used as novel tritium-releasing scintillation if it had enough oxidative resistance. In this paper, preliminary study about modified polymethylsilane (PMS) is carried out on the relationship between oxidative resistance and fluorescence properties. The mechanism of oxidation which causes the fluorescence degradation is also discussed. Polymethylsilane grafting aniline groups (PA-PMS) preforms the most prominent fluorescence for the smaller electronegativity of N, but it shows a poor oxidative stability in the air. Its fluorescence properties decline significantly after being placed for a period of time, which is related to the oxidation of the amino group. By contrast, O bridging σ-n-π structure could acceptably provide both fluorescence properties and oxidative resistance at the same time, which are the pressing needs for the scintillator material in tritium monitor.

Raman Spectroscopic Evidence of the Selective Extraction of Metallic SWNTs By Polymethyl(1-undecylic acidyl)Silane

Water soluble polymethyl(1-undecylic acidyl)silane was synthesized by the hydrosilylation of 10-undecylenic acid with polymethylsilane catalyzed by 2,20-azobisisbutyronitrile. The arc-discharged SWNTs were ultrasonically dispersed in an aqueous solution of polymethyl(1-undecylic acidyl)silane and then subjected to ultracentrifugation. Raman spectroscopic characterization confirmed that the supernatant is enriched in the metallic SWNTs, especially those with chiral indexes of (14,2), (15,0), (13,1), (12,3) and (19,1) metallic SWNTs. In this work, the SWNTs of larger diameters and smaller chiral angles than those reported previously were selectively extracted. Moreover, FT-IR spectroscopy and Raman scattering evidence the charge transfer between polymethyl(1-undecylic acidyl)silane and SWNTs. It is assumed that polymethyl(1-undecylic acidyl) silane could wrap chiral-index-selectively onto SWNTs through a fairly weak CH–p interaction, and that the stiffness and length of main chains and side chains as well as the charge state of the polymethylsilane derivative play vital roles in the selective extraction of metallic SWNTs.

Joining of SiC ceramics via a novel liquid preceramic polymer (V-PMS)

A novel liquid preceramic polymer (V-PMS) was synthsized by modifying polymethylsilane (PMS) with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane ([CH3(CH2CH)SiO]4, D4Vi), for joining SiC ceramics under ambient pressure. The obtained V-PMS with a viscosity of 125Pas at room temperature exhibits excellent thermal properties and bonding strength. The ceramic yield of V-PMS treated at 1200°C under Ar atmosphere is 84.5%, which is 38.3% higher than the original PMS. The shear strengths of the SiC joints joined by V-PMS at 800°C, 1000°C and 1200°C under N2 atmosphere are 11.9MPa, 34.5MPa and 29.9MPa, respectively. The excellent performances make the obtained V-PMS promising candidates for joining SiC ceramics in high-temperature applications.

Phenol substituted polymethylsilane: a soluble conducting polymer with low cross-linking density

Polymethylsilane (PMS) is made up of backbone of –Si–Si–, which is potentially a semi-conducting or conducting polymer after doping. Different phenolic groups are introduced into the main chain through Si–H substitution reaction. The polymer structures, optical properties and conducting performance are characterized. The aromatic modified PMS show a significant red-shift in UV absorption and fluorescent emission, higher oxidation resistance in the air and better film-forming properties. The conductivity values are about 10−6 S cm−1 and reach as high as 10−5 S cm−1 after I2-doping. At the same time, they also keep a good solubility in several organic solvents. The effect of functional groups in improving optical and conductive performance is studied, and the relationship between crosslink structure and oxidation resistance is discussed.

Selective extraction of metallic arc-discharged single-walled carbon nanotubes by a water soluble polymethylsilane derivative

Arc-discharged metallic SWNTs are selectively extracted with an aqueous solution of polymethyl(1-undecylic acidyl)silane by the formation of a charge donor–acceptor complex.

Preparation of Amorphous Silicon Carbide Nanostructures via Solvothermal Method

A solvothermal method was developed to synthesize silicon carbide nanoflakes and nanowires through pyrolysis of polymethylsilane (PMS) at 550 °C in solution. Evidences from HRTEM, SAED, FTIR and XPS indicated that the products were amorphous nanostructures which mainly consisted of Si, C elements and trace amount O element. Owing to concrete quantum confinement effects, the unique nanostructures have strong photoluminescence centered at 410-430 nm under excitation wavelength of 350 nm

Synthesis, characterization and ceramization of a novel vinyl-rich liquid precursor for Si(O)C ceramic

Abstract Polymethylsilane (PMS) was partially modified with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane ([CH 3 (CH 2 aCH)SiO] 4 , D4Vi) via conventional hydrosilylation. The as-synthesized vinyl-rich liquid precursor (V-PMS) was characterized by the viscosity test, gel-permeation chromatography, Fourier-transform infrared spectroscopy, nuclear magnetic resonances spectroscopy. The results indicate that the obtained precursor is well soluble in common solvents and exhibits a controllable viscosity of 326.9–714.6 mPa s at room temperature. The thermal properties of V-PMS were investigated by differential scanning calorimetry and thermogravimetric analysis. The V-PMS can be cured readily at 150 °C in inert atomosphere. The ceramic yield of V-PMS reaches 81% at 1200 °C, 38% higher than that of PMS. The final pyrolytic residue is hard, dense monolithic up to 1400 °C under Ar atmospheres. The controllable viscosity, excellent thermal curability and high ceramic yield enable the liquid precursor a promising material to shape various Si(O)C ceramic materials for high-temperature application.

Synthesis and pyrolysis of a novel preceramic polymer PZMS from PMS to fabricate high‐temperature‐resistant ZrC/SiC ceramic composite

As a valuable ultra‐high‐temperature ceramic (UHTC), ZrC was introduced to SiC ceramic for the preparation of high‐temperature‐resistant ZrC/SiC composite by a polymer‐derived method through the reaction between Cp2Zr(CH=CH2)2 and polymethylsilane (PMS). The composition, structure, element distribution and pyrolysis process of the preceramic polymer polyzirconomethylsilane (PZMS) were investigated by nuclear magnetic resonance, infrared, gel permeation chromatography, X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy and thermogravimetric analysis. The obtained ZrC/SiC ceramic composites had very good high‐temperature resistance with a weight loss of 7.1% after being subjected to temperatures ranging from 1200 to 2200°C, as the introduction of ZrC prevented the fast growth of crystalline β‐SiC. The ceramic composites prepared by this method were homogeneous with well‐distributed element components, and the ceramic yield reached as high as 78.4%. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis and Electronical Property of Antimony-Substituted Polysilanes and Iron-Substituted Polysilanes

Novel polysilanes, antimony-substituted polysilanes (APS) and iron-substituted polysilanes (IPS), were synthesized and characterized in this paper. To prepare these new metal-containing polymers, high reactive polymers, polymethylsilane (PMS) and polychloromethylsilane (PCMS) were used as mother polymers. The APS was synthesized directly by the reaction of PMS with SbCl3, while IPS was obtained from the reaction of PCMS with Na2Fe(CO)4 in the solvent of n-hexane. The polymers were characterized by elemental analysis, FT-IR, 1H-NMR, 29Si CP/MAS NMR, GPC, and UV. The number average molecular weights of these two polymers are between 1400 and 1600. These polymers show good semiconductive properties, whose intrinsic conductivities are in the range of 10-8~10-7S/cm, and can be increased to10-5S/cm after being doped with iodine.

A Novel SiC Precursor with High Ceramic Yield: Antimony-Substituted Polysilane (APS)

A novel SiC precursor antimony-substituted polymethylsilane (APS) is present in this paper. First, pre-APS was synthesized from polymethylsilane (PMS) and SbCl3 at room temperature. Pre-APS was a liquid mixture and could be used in PIP process without solvent. After the elemination of HCl and the crosslinking of pre-APS, the novel precursor APS with the ceramic yield 91% was prepared.

A modified polymethylsilane as the precursor for ceramic matrix composites

A novel SiC precursor, A-PMS, was synthesized through a reaction of polymethylsilane (PMS) with SbCl 3, where the Si–H in PMS reacts with Sb–Cl to form Si–Sb bond with HCl evaporated. A-PMS was used as a precursor to prepare C f/SiC ceramic matrix composites (CMCs) via polymer infiltration and pyrolysis (PIP) process. It is evident that SbCl 3 plays a very important role in promoting chain crosslinking, transforming of the Si–Si into Si–C bonds and stabilizing PMS from very high oxidation trend of the active Si–H bonds. A-PMS keeps liquid at room temperature that is suitable for the infiltration in the absence of any solvent. A-PMS can be cured into a fully crosslinked structure at 320 °C that leads to a very high ceramic yield up to 91% and an Si/C ratio near 1.12 after pyrolysis. The resulted CMCs samples reached a density of 1.76 g cm −3 and a flexural strength of 381 MPa after only four infiltration–pyrolysis cycles.

Silicon Carbide Base Ceramic Fiber Synthesis from Polycarbosilane-Polymethylsilane Blend Polymers by Melt Spinning

A melt-spinnable precursor for SiC based fibers was prepared from blend polymers of polycarbosilane (PCS) and polymethylsilane (PMS). After melt spinning, thermal oxidation curing, and pyrolysis, Si-C-O fibers were obtained. The addition of a small amount of PMS (0.2 or 0.5 mass%) to PCS was effective in increasing the resulting ceramic yield at 1273 K. Fiber decomposition temperature of the obtained Si-C-O fibers shifted to higher temperature (~100 K) by the PMS addition. For high PMS content (20 mass%), however, cross-linking of the blend polymers made the spinning process impossible. Doping of a radical trapping agent in the starting blend polymers was effective in preventing the cross-linking process. Si-C-O fibers with high oxygen content and reduced C/Si ratio were obtained in this case.

Synthesis and Ceramization of Polymethylsilane Precursors Modified with Metal Chlorides

Polymethylsilane (PMS) modified with titanium chloride (TiCl 4 ) or molybdenum chloride (MoCl 5 ) was pyrolyzed at various temperatures to enable a detailed investigation of stable phases formed during pyrolysis. The existence of TiSi 2 in PMS-TiCl 4 precursor and β-MoSi 2 in the PMS-MoCl 5 precursor below 1273 K suggested a strong interaction between Si-H and the metal chlorides during mixing. During pyrolysis of the PMS-10 mass% TiCl 4 precursor, a silicon rich Si-Ti-C state was obtained below 973 K, which simultaneously formed crystalline Si, TiSi 2 , and SiC phases at relatively low temperatures below 1273 K. During pyrolysis of the PMS-MoCl 5 precursors, however, formation of crystalline Si and SiC phases were not accelerated, while the crystalline β-MoSi 2 or α-MoSi 2 phase was formed rapidly.

Preparation and characterization of 3-dimensionally ordered macroporous SiC

Three-dimensionally (3D) long range ordered macroporous SiC ceramics were prepared through infiltrating polymethylsilane (PMS) into the 3D ordered sacrificial silica template, pyrolysis and the template removal. It was found that the pore size (84–658 nm), BET surface area (299.44–584.64 m2/g) and micropore volume (0.25–0.64 cm3/g) of the achieved porous SiC can be tailored by utilizing different sizes silica sphere templates. There exist three kinds of pores in the porous ceramics: sphere inversed pores, windows and mesopores (2–5 nm). The sphere inversed pores were packed as hcp structure and three dimensionally penetrated through the windows, and the mesopores endowed the porous ceramics surprising high BET surface areas and micropore volumes.

Macroporous SiCMoSi2ceramics from templated hybrid MoCl5–polymethylsilane

AbstractA molybdenum‐containing preceramic polymer, MoPMS, was synthesized for the first time by HCl elimination of polymethylsilane (PMS) and MoCl5at room temperature in tetrahydrofuran. The insoluble MoPMS prepared was embedded into the void spaces of a silica colloidal crystal template within the pot life of the polymer and successfully transformed to a three‐dimensionally long‐range‐ordered macroporous SiCMoSi2ceramic after pyrolysis at 1400 °C in an argon atmosphere followed by template removal in HF. The bead‐inverse macroporous SiCMoSi2ceramic, with a ceramic yield of about 88%, exhibits high temperature stability, high BET surface area, and semiconducting behavior. In addition, the macroporous SiCMoSi2ceramic was used as a catalyst carrier for platinum–ruthenium coated on the surface of the pores. The preceramic polymer and the ceramic were characterized by IR, thermogravimetric analysis, X‐ray diffraction, scanning and transmission electron microscopy, and BET surface area. Copyright © 2005 John Wiley & Sons, Ltd.

Fabrication of Porous SiC Ceramics with Special Morphologies by Sacrificing Template Method

Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.

Fabrication and characterization of ordered macroporous PMS-derived SiC from a sacrificial template method

Three-dimensionally long range ordered macroporous SiC ceramics were prepared using a low molecular weight polymer precursor, polymethylsilane (PMS), by utilizing sacrificial colloidal silica crystalline arrays as templates which were subsequently etched off with HF (45%) after pyrolysis in an argon atmosphere. SEM, TEM, HRTEM and BET were used to specify the morphologies and BET surface areas of the porous materials. The pore sizes of about 84–658 nm and BET surface areas (pore volumes) of about 584.64 m2 g−1 (0.64 cm3 g−1)–299.44 m2 g−1 (0.25 cm3 g−1) of the achieved macroporous SiC ceramic were approximately proportional to the sizes 112–700 nm of the sacrificial silica sphere templates used. It was found for the first time that the unexpectedly high surfaces area and pore volumes of the achieved porous SiC ceramic were related to the microchannels on the walls that were caused by the interfacial diffusion of oxygen or silica from the silica sphere template into the walls of the SiC framework structures.

Ceramization of Reflux‐Treated Polymethylsilane Precursors to Silicon Carbide

The pyrolysis of polymethylsilane (PMS) in an argon gas environment with a flow rate of 1 L/min was investigated as a standard pyrolytic process, and the investigation showed SiSi network formation at 573 K. Subsequently, various condensed PMS resins were prepared by adjusting pre‐heat‐treatment or reflux conditions in the temperature range of 423–723 K. The effect of pre‐heat treatment or refluxing on the ceramic yield at 1273 K was quantitatively evaluated. Structural evolution in the PMS resins prepared under various reflux conditions was investigated during pyrolysis up to 1873 K. The X‐ray diffraction patterns of the pyrolysis products revealed crystallite growth of β‐SiC and silicon at 1273–1473 K. 29Si solid‐state nuclear magnetic resonance with the single‐pulse method was also conducted on the pyrolysis products at 1273 K.