Effects of curing,washing, and pre-oxidation on the bonding of monofunctional silanes to polished copper surfaces

Polished Cu surfaces were silylated with trimethylmethoxysilane or trimethylchlorosilane and washed in water to determine the stability of the silane layers. The surfaces were analyzed using X-ray photoelectron spectroscopy (XPS). Methoxysilane was found to remain stably bound during washing, whereas chlorosilane was completely washed away. This confirmed that methoxysilanes were probably bound to surface oxides as hydrogen-bonded Si-O-R species or metal siloxanes, whereas chlorosilanes could only physisorb because they had removed surface oxides and hydroxyl groups. The silane layers were cured at high temperature in vacuum to promote the formation of metal siloxanes from hydrogen-bonded Si-O-R groups. For both silanes, the cured layers were almost completely washed away. The Si-O-R groups in methoxysilane layers were probably converted to less stably bound siloxane dimers during curing. The polished Cu samples were pre-oxidized in an attempt to increase the amount of oxides on the surface and thereby retain chlorosilane. Pre-oxidation converted Cu₂0 to CuO. This did not change the behavior of chlorosilane and reduced the uptake of methoxysilane. Solution and surface reactions are suggested for both silanes. For methoxysilane, silanes or silanols directly hydrogen-bonded to surface oxide or hydroxyl groups are proposed to be the primary species that lead to metal siloxanes.     

Novel materials based on silicone–acrylate copolymer networks

This article presents a broad class of materials made by copolymerization of a family of telechelic free radically polymerizable siloxanes with various acrylate monomers that polymerize to form high T_g polymers. Films with properties ranging from strong elastomers to plastics have been obtained by UV‐initiated bulk copolymerization of functional siloxanes dissolved in acrylate monomers (in the presence of a photoinitiator). The molecular weight of the functional siloxanes, the nature of functional endgroups, the choice of (meth)acrylate comonomer, and the siloxane/acrylate ratio all have a rather dramatic effect on the morphology, and thus, on the properties of the copolymeric networks. Physical properties of the materials, such as optical appearance and mechanical and transport properties are correlated with the unique morphologies observed by TEM studies. Unusual properties such as reversible whitening of some of the materials and low Poisson ratios have been attributed to the microcavitation observed when high T_g acrylate domains interfere with the network deformation. Networks composed of high T_g acrylates (major fraction) coreacted with elastomeric siloxanes can provide heat‐shrinkable materials when they are elongated at temperatures higher than the T_g of the corresponding polyacrylates and quenched. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 159–180, 2001     

Burning behaviors of selected chlorosilanes and SiH‐containing siloxanes

Chlorosilanes are silanes containing the Si‐Cl functional group and SiH‐containing siloxanes are siloxanes containing the Si‐H functional group. Some chlorosilanes and SiH‐containing siloxanes present potentially high fire or explosion hazards during handling, storage, transport and process operations. Cone calorimeter tests have been used to study the burning behaviors of selected chlorosilanes and SiH‐containing siloxanes at various incident heat fluxes to simulate pool fire burning. The peak heat release rate of a silicon intermediate obtained from the cone calorimeter at 15 kW/m² incident heat flux was very close to that measured by a relatively large‐scale field test. The flammability of monochlorosilanes was similar to that of organic hydrocarbons having comparable volatility. The flammability of chlorosilanes descends in the order of monochlorosilanes, dichlorosilanes and trichlorosilanes. SiH‐containing siloxanes ignited faster than non‐SiH‐containing siloxanes because of the reactive silicon‐hydrogen linkages. The ignition of SiH‐containing siloxanes was much more violent than the ignition of non‐SiH‐containing siloxanes. The SiH‐containing siloxanes exhibited a lower peak heat release rate, less total heat released and a lower peak smoke extinction coefficient compared with non‐SiH‐containing siloxanes having comparable volatility. Copyright © 2004 John Wiley & Sons, Ltd.     

Studies of cyclic and linear poly(dimethyl siloxanes): 6. Effect of heat

Cyclic and linear poly(dimethyl siloxanes) were heated under vacuum in the temperature range 623–693K for periods of hours or days in the absence of catalysts. The products were analysed by gas-liquid chromatography and gel permeation chromatography. The results for the linear poly(dimethyl siloxanes) were in full agreement with the published work of Thomas and Kendrick. The effect of heat on the cyclic poly(dimethyl siloxanes) was that predicted, assuming that similar siloxane bond interchange reactions take place to those believed to occur in the linear polymers. The cyclic poly(dimethyl siloxanes) produced mixtures of cyclic oligomers, together with polymeric products which have considerably higher molecular weights than the starting materials. It is proposed that these polymeric products consist of mixtures of ring molecules [(CH₃)₂SiO]_x. Some of these cyclic polymers are estimated to contain (on average) more than 10 000 skeletal bonds. Similar mixtures of cyclic oligomers and high molecular weight polymeric products were obtained by heating hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane.     

Methacrylate-capped fluoro side chain siloxanes: Synthesis,characterization, and their use in the design of oxygen-permeable hydrogels

Methacrylate end-capped 3-(2,2,3,3,-tetrafluoropropoxy)propyl, 3-(2,2,3,3,4,4,5,5-octafluoropentoxy)propyl, and 3-(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluorotridecoxy)propyl side chain siloxanes were evaluated for potential use in hydrogels for contact lens application. The preparation of the methacrylate end-capped perfluoro side chain siloxanes was accomplished in two relatively simple synthetic steps. The first step consisted of the acid-catalyzed co-ring opening polymerization of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and 1,3-bis-methacryloxybutyltetramethyldisiloxane, followed by a platinum-catalyzed hydrosilation with the tetrafluoro-, octafluoro-, and dodecafluoro-substituted allylic ethers. The incorporation of the terminal [—CF₂—H] functionality had a dramatic effect on the increased solubility of the fluoro siloxane with hydrophilic monomers. Radical bulk polymerization of the methacrylate-capped fluoro side chain siloxanes with hydrophilic monomers, such as dimethylacrylamide and N-vinyl pyrrolidinone, resulted in transparent hydrogels possessing a wide range of water contents, high oxygen permeability, and a low modulus of elasticity. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1081–1089, 1997     

Polymeric Routes to Silicon Carbide

Several classes of organosilicon polymers are effective precursors for silicon carbide ceramic compositions. These include polydimethylsilane (via a two-step process), ‘polysilastyrene’, polycarbosilazanes or polysilazanes, and certain siloxanes, plus the branched polycarbosilanes, branched polysilahydrocarbons, and vinylic polysilanes developed at Union Carbide. The latter three classes are prepared by active metal dechlorinations of appropriate chlorosilane blends, leading to recognition of branching at backbone silicon atoms (either as prepared or during processing) as a prerequisite for obtaining useful ceramic yields. Fundamental reactivity differences between the active metals (potassium and sodium) allow the preparation of sodium-derived vinylic polysilanes. The latter offer certain economic and performance advantages as ceramic precursors.     

Study on the mechanism of the formation of polyhedral oligomeric silsesquioxanes by the 2D correlation infrared spectral

Synthesis of polyhedral oligomeric silsesquioxanes (POSS) by the hydrolytic condensation reaction of trifunctional organosilanes [e.g., RSiCl₃ or RSi(OR)₃] may have achieved success. However, the exact formation mechanism of POSS, especially, an evolution process in the reaction still remains unclear. In this work, a real-time FTIR was carried out to trace the synthesis process of POSS. It was found that linear siloxanes, cyclic siloxanes, and cage-like polysiloxanes were formed during the reaction. With the help of generalized two-dimensional (2D) correlation analysis, we obtained exact sequential change among the three siolxanes, with the linear silicons formed initially. Following this was the emergence of cyclic siloxanes, and finally the cage-like polysiloxanes. Consequently, we not only proved the existence of the linear and cyclic siloxanes but also accurately detected the sequential change of the siloxanes in the process, which exhibited an intact and visual evolution process of POSS formation. Based on this, the reaction mechanism is presented. Finally, the chemical structure of cage-like products was further characterized by ²⁹Si-NMR and GPC measurements. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of mesoporous silica nanoparticles with controlled pore size,particle diameter,morphology, and structure by two-step process of chlorosilane residue

In this study, mesoporous silica nanoparticles (MSNs) were successfully prepared in two steps using chlorosilane residue. First, chlorosilane residue was subjected to alcoholysis with n-propanol to synthesize tetrapropoxysilane (TPOS), followed by the synthesis of MSNs using TPOS as silicon source. Alcoholysis experiment was designed and optimized using orthogonal experimental method. In addition, effects of four factors (i.e., molar ratio of n-propanol to chlorosilane residue; feed rate of n-propanol; reaction temperature; and molar ratio of n-hexane to chlorosilane residue) on the yield of TPOS were investigated. The optimum alcoholysis conditions were determined. Yield of TPOS was 56% under the optimum alcoholysis conditions. Results obtained from single factor analysis of variance revealed that molar ratio of n-propanol to chlorosilane residue was the most significant factor affecting TPOS yield. Next, a series of spherical MSNs with dendritic structure and irregular mesoporous/microporous silica nanoparticles with non-dendritic structure were successfully synthesized via precise regulation of various experimental parameters in emulsion systems. In this regard, the adjustment of n-hexanol/1,3,5-triisopropylbenzene (TIPB) molar ratio or n-octane/n-hexanol/TIPB molar ratio was found to be effective for achieving controllable regulation of morphology (spherical or irregular); structure (dendritic or non-dendritic); pore size (mesoporous (4.6–9.2?nm) or microporous (1.6–1.7?nm)); and particle diameter (60–134?nm) of silica nanoparticles. However, the adjustment of n-octane/TIPB molar ratio marginally affected spherical morphology, dendritic structure, and pore size (4.0–4.6?nm) of synthesized MSNs, with considerable effect on particle diameter (61–151?nm). In addition, as-synthesized MSNs exhibited large specific surface area (708–857?m²/g) and large pore volume (1.5–3.6 cm³/g).     

Synthesis and characterization of silicon-containing graft copolymers

Poly(4-t-butoxycarbonyloxystyrene)-g-poly(dimethylsiloxane) and poly(t-butylmethacrylate)-g-poly(dimethylsiloxane) with various chemical compositions were synthesized via free radical polymerization of 4-t-butoxycarbonyloxystyrene (TBCS) or t-butylmethacrylate (TBMA) with silicone macromers. These macromers were prepared by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D₃) and subsequent termination with a chlorosilane compound having a methacrylate functionality. The morphology of the graft copolymer systems was investigated by DSC and TEM.     

Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.     

Surface enrichment of siloxanes with covalent bound ultraviolet (UV) absorber groups

The ability of siloxanes with UV absorber groups to enrich at the surface of cast polystyrene films was studied. Model compounds were siloxanes of the type Me₃SiO(SiMe₂O) _n (SiMeRO) _m SiMe₃, withR representing a 2-hydroxy-benzophenone-4-oxypropyl group. Surface studies were carried out by contactangle measurements and ESCA (Electron Spectroscopy for Chemical Application) investigations. UV absorbers with a high content of dimethylsiloxane units strongly enrich at the surface of polystyrene, forming a thin surface layer with a high siloxane content. UV absorbers with few or no dimethylsiloxane units pe hydroxybenzophenone group are evenly distributed in the polymer matrix. ESCA sputter depth profiles are also given. Migration studies show that the siloxanes are delivered from the bulk to the surface subsequently after sputtering.Dedicated to Prof. Dr. Dr. h.c. R. Müller on the occasion of his 90th birthday, in recognition of his pioneering contributions to organosilicon chemistry.Siloxanes with Functional Groups, XIV. For communication XIII, see Ref. 1. Long-Term Stabilization of Polymers, VIII. For communication VII, see Ref. 1.     

Synthesis and thermoelastic characterization of PDMSM networks

Summary The synthesis of poly(dimethyl silmethylenes) with two hydroxyl endgroups is described. Networks produced by endlinking with tetraethoxysilane were characterized, and thermoelastic data were estimated. f_e/f and dln2>_o/dT of these networks are much smaller than those of poly(dimethyl siloxanes).     

Effect of heat‐treatment on the performance of gas barrier layers applied by atomic layer deposition onto polymer‐coated paperboard

The effect of heat treatment on the gas barrier of the polymer‐coated board further coated with an Al₂O₃ layer by atomic layer deposition (ALD) was studied. Heat treatment below the melting point of the polymer followed by quenching at room temperature was used for the polylactide‐coated board [B(PLA)], while over‐the‐melting‐point treatment was utilized for the low‐density polyethylene‐coated board [B(PE)] followed by quenching at room temperature or in liquid nitrogen. Heat treatment of B(PLA) and B(PE) followed by quenching at room temperature improved the water vapor barrier. However, because of the changes in the polymer morphology, quenching of B(PE) with liquid nitrogen impaired the same barrier. No improvement in oxygen barrier was observed explained by, e.g., the spherulitic structure of PLA and the discontinuities and possible short‐chain amorphous material around the spherulites forming passages for oxygen molecules. This work emphasizes the importance of a homogeneous surface prior to the ALD growth Al₂O₃ barrier layer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrolysis and Condensation of Hydrophilic Alkoxysilanes Under Acidic Conditions

A hydrophilic silane was obtained from the reaction of ethylene carbonate and 3-aminopropyldiethoxymethylsilane. This silane undergoes rearrangement to yield an AB₂-type hyperbranched polymer under anhydrous conditions but hydrolyzes and condenses to produce linear siloxanes under acid hydrolysis. The hydrolysis and condensation reactions as a function of time, HCl concentration and water content were studied by ²⁹Si NMR. The compositions of the silanol containing hydrolysis intermediates and the siloxanes condensation products were identified under different conditions. The instantaneous composition was found to depend on the specific combination of the acid and the water. Under certain conditions the intermediate silane-diols were stable and did not condense even under mild acidic conditions.     

Preparation of poly(IPDI‐PTMO‐siloxanes) and influence of siloxane structure on reactivity and mechanical properties

Siloxane‐modified polyurethanes were prepared through isophorone diisocyanates (IPDI), poly(tetramethylene oxide) (PTMO), and siloxanes. IPDI served as the hard segment in the structure. Both PTMO and siloxanes were diols and served as the soft segments. In addition, different chemical structures of siloxanes were used, in which siloxane chains would remain in the main chain of polyurethanes (PU) or become the side chain of PU. First, the reactivities of PTMO and siloxanes to react with IPDI in bulk system were studied through DSC, in which the reaction heat was related to their reactivities. Copolymerization of IPDI, PTMO, and siloxanes in bulk were also studied. The results showed that hydrophobicity and steric hindrance of siloxane diols led to their low reactivities. Next, a series of siloxane‐modified PU in toluene solvent were synthesized, and the conversion of NCO groups was determined by the method of chemical titration. In the synthesis of PU copolymers in a solution polymerization, because of low reactivity of siloxanes, a two‐step procedure was adopted. The siloxane diol was first reacted with IPDI in toluene to form NCO‐terminated prepolymer. Then PTMO was added to form final PUcopolymers. The addition of side‐chain siloxanes resulted in PU copolymers with higher molecular weight than main‐chain siloxanes. Both main‐chain and side‐chain siloxanes increased the elongation at break and tensile strength of final PU copolymers. The microphase‐separation of siloxane segments was observed by SEM, which was the main cause for the improved mechanical properties. POLYM. ENG. SCI., 47:625–632, 2007. © 2007 Society of Plastics Engineers.     

Hydrogels based on hydrophilic side-chain siloxanes

Methacrylate end-capped diethylene glycol propyl methyl ether, 5-hexyl-1,2-diol, and 3-propyloxy-1,2-propane diol side-chain siloxanes were evaluated for potential use as hydrogels for contact lens application. The preparation of the methacrylate end-capped ether, hexane diol, and propane diol side-chain siloxanes was accomplished in two relatively simple synthetic steps: The first step consisted of the acid-catalyzed co-ring opening polymerization of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and 1-3-bis-methacryloyl-butyltetramethyldisiloxane, followed by a platinum-catalyzed hydrosilation with (in separate experiments) diethylene glycol allyl methyl ether, trimethylsilyl protected 3-allyloxy-1,2-propane diol, and trimethylsilyl protected 5-hexene-1,2-diol. The trimethylsilyl protecting groups was removed using a 10% 0.1N HCl solution in 2-propanol. Radical polymerization of the methacrylate end-capped ether, hexane, and propane diol side-chain siloxanes with hydrophilic monomers, such as dimethylacrylamide, and a strengthening agent, isobornylmethacrylate, resulted in transparent hydrogels possessing a wide range of water contents, high oxygen permeability, and a low modulus of elasticity and, for the propane diol side-chain siloxanes, excellent hydrolytic stability. The ether side-chain siloxane-based hydrogels exhibited poor hydrolytic stability. © 1995 John Wiley & Sons, Inc.     

Oxygen transport and surface active properties of silicone containing copolymers of methyl methacrylate II

New organofunctional siloxanes from γ-methacryloxypropyltrimethoxysilane (MPTMS) were synthesized by transesterification of methoxy groups with linear high alcohols, ether alcohols, and α-hydroxyacids. The factors affecting the substitution ratios were determined. These siloxanes were copolymerized with methyl methacrylate (MMA), crosslinked with ethylene glycol dimethacrylate (EGDM) in order to examine the effect of substituted groups to the oxygen permeability coefficient (P_d) and surface free energy properties of the resultant copolymers. The substitution of the oxygen containing polar groups decreased the oxygen permeability due to the interactions between polar groups decreasing the free volume. However, these groups increased the polar component of surface free energy (γ) and thus total surface free energy (γ_S). The hydrophilicity of the carbitol and 2-ethoxyethanol containing siloxane-MMA copolymers was found to be suitable for biomedical applications.     

有机硅氧烷改性VAE乳液的研究

在醋酸乙烯-乙烯共聚乳液（vAE乳液）聚合过程中添加有机硅氧烷单体制备改性VAE乳液。对比分析了不同种类、不同用量的有机硅氧烷对改性vAE乳液性能的影响。确定了有机硅氧烷单体在vAE乳液聚合过程中的最佳添加方式，筛选了聚合引发体系。研究表明，在反应过程中以H2O2--ZFS作为氧化-还原引发体系，选用长链的含水解阻碍官能团的硅氧烷，有机硅氧烷采用后添加的方式，能够合理而有效地控制反应节奏。制备出性能优异的改性VAE乳液。     

Singlet oxygen quenching ability of naturally occurring carotenoids

The singlet oxygen quenching ability of various naturally occurring carotenoids was examined by measuring toluidine blue-sensitized photooxidation of linoleic acid. To assess quenching, the oxidation of linoleic acid was followed by measuring oxygen consumption and ultraviolet absorbance at 235 nm. We found that oxygen quenching increased as the number of conjugated double bonds in the carotenoids increased, but quenching varied with chain structure and functional groups. Acyclic carotenoids enhanced quenching more than did cyclic carotenoids. Conjugated keto groups and the presence of a cyclopentane ring stimulated quenching, while hydroxy, epoxy and methoxy groups showed lesser effects. The photosynthetic bacterial carotenoids, spirilloxanthin and rhodopin, were found to be most effective as quenchers, followed by the cayenne carotenoid, capsorbin.     

Silyl Peroxide-Some Chemical and Physical Effects on Adhesion Promotion

Silyl peroxides have previously been shown to promote the adhesion in a broad range of polymer/substrate and polymer/polymer systems. A correlation between the chemical composition of silyl peroxides and their ability to bond clearly exists. Their effectiveness is usually enhanced with increasing number of reactive sites. Whilemany reactive functional groups are useful, the presence of at least one peroxy group appears to be a necessity. Silyl peroxides are heat-activated. Strength of joints made of silyl peroxides are shown to depend on the extent of their dissociation which can be accelerated or retarded with known radical accelerators or retarders, respectively. Adhesion is believed to result from a sequence of silyl peroxide initiated, free radical reactions taking place during the curing step. This hypothesis is consistent with the kinetic behavior of the silyl peroxides. Internal reflection infrared study reveals that the areas immediately surrounding the interface are diffused layers of siloxanes and the substrate molecules. The possibility of chemical linking of the silyl peroxide fragments to the polymeric phase(s) is suggested. Silyl peroxide promoted joints exhibit good hydrolytic and thermal stabilities. However, the measured adhesive strength is also affected by the morphology of the polymer employed in the system. Results of a quenching study are presented.