Organosilicon Compounds

A new class of cyclotrisiloxanes having hydridosiloxanylalkyl substituents on one, two, or three of the ring silicon atoms and a method for their preparation are provided. These compounds undergo living anionic ring-opening polymerization to generate unique polymer structures.

Organic trihydridosilanes provide an elegant route for generating self-assembled monolayers (SAM)s by vapor phase transport on a variety of substrates. Under mild conditions, these precursors can be made to interact with a variety of clean metal and hydrogenated metalloid surfaces such as Ti, Cu, and Si to form near-zero-thickness SAMs. These SAMs can be customized with specific functionality to activate or deactivate subsequent Co deposition on the underlying substrate, leading to area specific Co deposition.

Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinctive advantage over conventional silanes in terms of maintaining the integrity of surface coatings, adhesive primers and composites in aqueous and aggressive environments. The improved durability of such dipodal silanes is associated with an increased crosslink density of the interphase and the inherent resistance to hydrolysis, as they can form six, rather than three, Si-O bonds to the substrate. This study examines dipodal silanes with hydrophobic alkyl functionality and compares them with similar functionality on conventional silane coupling agents. It also introduces new structural dipodal silanes containing “pendant” and “bridged” functionality and then examines their stability in aqueous environments. In strongly acidic and brine environments, dipodal silanes clearly demonstrate improved resistance to hydrolysis compared to conventional silane coupling agents.

An overview of silane and silicone chemistry in 15 full chapter reviews. A register of over 2500 silicon compounds with physical properties, chemical structures and application data is provided. 608 pages + inserts. Review Chapters: An Organosilicon Chemistry Primer; Naming Silicon Compound; Polysilanes; Silicon-Based Anion Relay Chemistry; Bioactive Organosilanes;Cross-Couling of Silanols and Silanolates; Silicon-Based Blocking Agents; Silanes and Surfaces; Bond Dissociation Energies of Organosilicon Compounds; Si NMR: Practical Aspects; Infrared Analysis of Organosilicon Compounds; Ring-Opening Polymerization of Cyclosiloxanes; Telechelic Siloxane Oligomers; Silicones: Stable, Inert Media; Reactive Silicones and Elastomer Formulation. Detailed and referenced properties for ~2500 Silicon Compounds are presented.

Additives for epoxy resin systems, both silane coupling agents and silicones and epoxy functional siloxanes are discussed.  Topics include: Silane Coupling Agents, Difunctional and Multifunctional Epoxy-Terminated Silicones, Silicone Resin Modifiers, Monofunctional Silicones, Cycloaliphatic Silanes and Silicones, Silane  and Silicone Hardeners.  Electrical, optical and thermal properties are considered.

This article provides an overview of the state-of-the-art chemistry and processing technologies for silicon nitride and silicon nitride-rich films, i.e., silicon nitride with C inclusion, both in hydrogenated (SiN x :H and SiN x :H(C)) and non-hydrogenated (SiN x and SiN x (C)) forms. The emphasis is on emerging trends and innovations in these SiN x material system technologies, with focus on Si and N source chemistries and thin film growth processes, including their primary effects on resulting film properties. It also illustrates that SiN x and its SiN x (C) derivative are the focus of an ever-growing research and manufacturing interest and that their potential usages are expanding into new technological areas.

Silylene Transfer Reactions for Synthesis of Strained Alkenes, Keith Woerpel; Methylsilicones Pushed in Several Directions, Thomas McCarthy; N-Heterocyclic Silylenes, Matthias Dreiss; Surface Modification of Silicon Nanostructures; Michael Sailor; Silicon-Hybrid Materials, Joseph Mabry; Silicon Nanocrystal Assemblies; Brian Korgel; New Materials Properties Through a Silicone Blend Strategy, Francois Ganachaud; New Methods for Tethered Carbonyl Silylations, Gregory O'Neil; Advances in Preparation of Organosilanes Using Palladium Catalysis, Donald Watson; Synthesis and Applications of Silicone Copolymers, Ramesh Kumar; Towards Controlled Synthesis and Characterization of Complex Silicone Architectures; Use of Nanocatalysis in the Direct Synthesis of Methylchlorosilanes and Alkoxysilanes; Kendrick Lewis; Material Behavior of Self-Aligned Silicon Carbide Nanowire Arrays; Spyros Gallis; Cyclohexasilane, A Source of Quantum Dots, Nanowires, Philip Boudjouk; Mechanism of Oligomerization of N-Heterocyclic Silylenes, Andrey Rogachev; The Addition of Isocyanides to Disilenes, Kim Baines; Oscilations in the mSR Spectra of Muionated Organosilyl Free Radicals, Kerim Samedov; Electrophilic Substitution on Phenylsilsesquioxanes, Richard Laine;  Synthesis and Reaction of Janus Prisms, Masafumi Unno

Evaluation of a GC-MS method using N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) as the silylating agent for GC-MS. Study of the stability of creatine and guanidinoacetate in urine. 22 urines were kept at RT, 4 degrees C and -30 degrees C for 15 days. MTBSTFA produces a single chromatographic peak in contrast with other derivatizing agents. Creatine concentration increases at room temperature (326% on average), and at 4 degrees C (75%). However, detection decreases after freezing (-37%). Guanidinoacetate is stable, but decreases after freezing (-37%). Sonication before analysis is crucial to obtain repetitive results. A modified GC-MS method has been validated and the conditions for preservation of the urine have been established.

Contact lenses are one of the most successful biomaterials in history with a global market estimated to be worth over $17 billion in 2025. Silicone hydrogel contact lenses dominate the market and are complex biphasic biomaterials with several critical material properties needed for clinical use. Careful consideration of composition and chemistry is needed to identify formulations of lenses meeting all commercial standards with the potential for improved manufacturability, cost, and/or next generation use. Four silicone macromers were investigated in this work with varying symmetry of siloxane units and macromer structure, number of siloxane groups, branching, length, and concentration. Novel silicone hydrogel lenses were produced and evaluated for optical transmittance, elastic modulus, oxygen transmissibility, water content, and surface wettability. Several lenses met commercial standards and demonstrated an increase in oxygen permeability (Dk) and inverse relationship with elastic modulus and siloxane concentration, respectively. A hydrophobic/hydrophilic ratio below 1.4 was needed for a co‐continuous water phase. Substitution of methoxypropyl groups for butyl groups increased hydrophobic microdomains leading to decreased optical quality and mechanical properties. Generally, fluorine‐containing silicone macromers allowed for a wider range of successful compositions, and above a certain hydrophilic composition, the presence of trifluoropropyl groups resulted in improved solubility and optically clear lenses. Data also showed asymmetric siloxane macromers have potential to meet critical lens properties at lower overall siloxane content. New lens materials with wider composition ranges meeting all clinical lens properties is a significant challenge and may significantly expand the field.

The need for tighter control over film uniformity, conformality, and properties at decreasing thicknesses was met by a gradual evolution from physical vapor deposition (PVD), to chemical vapor deposition (CVD), and eventually atomic layer deposition (ALD) processes.  Of all manufacturing-worthy thin-film deposition processes, ALD has the greatest potential to satisfy these requirements.  However, the intrinsic constraints of recurrent two atom reactivity and associated byproducts have kindled tremendous interest in other self-limiting deposition processes such as Molecular Layer Deposition (MLD), Self-Assembled Monolayer (SAM), and “Click” Chemistry Deposition (CCD)  processes, either as alternatives to or in conjunction with ALD.  This overview provides definitions, illustrations and examples of these processes.

Cyclic azasilanes have been synthesized for the purpose of developing coupling agents appropriate for a variety of nanotechnologies including surface modification of nanoparticles, nanocrystals, mesoporous materials and substrates. N-Methyl-aza-2,2,4-trimethylsilacyclopen-tane is representative of this class of compounds. Preliminary data for the treatment of inorganic surfaces, including nanoparticles and oxidized silicon wafers, with cyclic azasilanes suggest high-density monolayer deposition by a ring-opening reaction. Cyclic azasilanes contain a cryptic amine functionality that can perform a subsequent tandem coupling reaction with functional molecules after the surface-triggered ring-opening reaction, allowing for a one-pot self-assembly route on nanostructures. Tandem coupling reactions are demonstrated via addition reactions of the cryptic amine with epoxy and acrylate systems .

Bis(tert-butyldimethylsiloxy)- (7), bis(dimethylthexylsiloxy)- (8), bis(tri-n-hexylsiloxy)- (9), and bis(dimethyloctadecylsiloxy)silicon 2,3-naphthalocyanines (10) were prepared via substitution of the bis(hydroxy) precursor with the corresponding chlorosilane ligands and characterized by spectroscopic and combustion analyses. They show strong absorption around 780 nm where tissues exhibit optimal transparency. Compounds 7-10 are capable of producing singlet oxygen. They are relatively photostable although less stable than the analogous phthalocyanine, i.e., the bis-(dimethylthexylsiloxy)silicon phthalocyanine (12). They were evaluated as potential photosensitizers for the photodynamic therapy (PDT) of cancer in vitro against V-79 cells and in vivo against the EMT-6 tumor in Balb/c mice. In vitro all four dyes showed limited phototoxicity combined with substantial dark toxicity. Surprisingly, in vivo (i.v., 0.1 mumol/kg, 24 h prior to the photoirradiation of the tumor with 780-nm light, 190 mW/cm2, 400 J/cm2) all dyes induced tumor regression in at least 50% of mice whereas compound 8 gave a complete tumor response in 80% of mice without apparent systemic toxicity at doses as high as 10 mumol/kg. At 24 h postinjection, compound 8 showed a favorable tumor to muscle ratio of 7, assuring minimal damage to the healthy tissue surrounding the tumor during PDT. Our data confirm the potential of silicon naphthalocyanines as far-red-shifted photosensitizers for the PDT of cancer and indicate the importance of the selection of the two axial silicon ligands for optimal photodynamic efficacy.

Organic trihydridosilanes can be grafted to hydrogen terminated porous Si nanostructures with no catalyst. The reaction proceeds efficiently at 80 8C, and it shows little sensitivity to air or water impurities. The modified surfaces are stable to corrosive aqueous solutions and common organic solvents. Octadecylsilane H 3 Si(CH 2) 17 CH 3 , and functional silanes H 3 Si(CH 2) 11 Br, H 3 Si(CH 2) 9 CH = CH 2 , and H 3 Si(CH 2) 2-(CF 2) 5 CF 3 are readily grafted. When performed on a mesopo-rous Si wafer, the perfluoro reagent yields a superhydrophobic surface (contact angle 1518). The bromo-derivative is converted to azide, amine, or alkyne functional surfaces via standard transformations, and the utility of the method is demonstrated by loading of the antibiotic ciprofloxaxin (35 % by mass). When intrinsically photoluminescent porous Si films or nanoparticles are used, photoluminescence is retained in the grafted products, indicating that the chemistry does not introduce substantial nonradiative surface traps.

A method for the preparation of inorganic superhydrophobic silica coatings using sol–gel processing with tetramethoxysilane and isobutyltrimethoxysilane as precursors is described. Incorporation of isobutyltrimethoxysilane into silica layers resulted in the existence of hydrophobic isobutyl surface groups, thereby generating surface hydrophobicity. When combined with the surface roughness that resulted from sol–gel processing, a superhydrophobic surface was achieved. This surface showed improved UV and thermal stability compared to superhydrophobic surfaces generated from polybutadiene by plasma etching. Under prolonged UV tests (ASTM D 4329), these surfaces gradually lost superhydrophobic character. However, when the as-prepared superhydrophobic surface was treated at 500 °C to remove the organic moieties and covered with a fluoroalkyl layer by a perfluorooctylsilane treatment, the surface regained superhydrophobicity. The UV and thermal stability of these surfaces was maintained upon exposure to temperatures up to 400 °C and UV testing times of 5500 h. Contact angles remained >160° with contact angle hysteresis ∼2°.The UV stability was significantly improved after the hydrophobic surface groups (isobutyl) were replaced by fluoroalkyl groups.

Silicon nitride (SiN x , x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO 2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C 9 H 27 N 3 Si 3) with a continuous ammonia (NH 3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70°C) and could act as a single source for SiN x with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350°C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH 3 plasma at a NH 3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiN x growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiN x average refractive index of ∼1.75.

Silsesquioxane polymers that are useful for preparing SiO2 -rich ceramic coatings are obtained as the polymeric reaction products from the hydrolysis and condensation of organosilanes having a β-substituted alkyl group. A preferred silsesquioxane polymer is the polymeric reaction product obtained from β-chloroethyltrichlorosilane. More preferred silsesquioxones are those with non-halogenated alkyl groups, such as the β.-acetoxyethyl- and β-hydroxyethyl-silsesquioxones. Coating compositions containing such silsesquioxane polymers dissolved in organic solvent may be applied to a substrate and converted to SiO2 -rich ceramic thin layers by evaporating the solvent and heating the coated substrate at moderate temperatures.

Parameters controlling intrinsic stability and reactivity of organosilanols generated from alkoxysilanes in aqueous environments have been elucidated in several experiments. Data involving kinetics, equilibrium, phase separation, and bonding studies of alkyl and organofunctional alkoxysilanes are presented. The studies indicate that the rates of hydrolysis of alkoxysilanes are generally related to their steric bulk, but demonstrate that after rate-limiting hydrolysis of the first alkoxy group steric effects are much less important. Aqueous hydrolysis of alkylalkoxysilanes was studied to determine equilibrium constants and the extent of oligomerization up to phase separation. In the case of propyltrialkoxysilane, phase separation is coincident with the formation of tetramer. The equilibrium constant for esterification of silanols is Also, the performance properties of new water-borne silanes were evaluated and in most cases, their performance equalled or exceeded their traditional silane counterparts. keywords: silanol; coupling agents; organosilicon chemistry.