Siloxane Linkages Research Articles

Synthesis and Characterization of Side-Chain Liquid Crystalline Polydienes and Their Hydrogenated Derivatives

Polydienes having mesogenic groups in the side chain and their hydrogenated derivatives were synthesized by the radical polymerization of diene derivatives with siloxane linkage in the spacer and benzoates as mesogenic groups, followed by hydrogenation of the double bond of the main chain. The stereochemistry of the main chain is principally (E)-1,4) elucidated by NOESY spectrum. The diene polymers take smectic liquid crystalline state, basically with fan like structure, irrespective of spacer length. The hydrogenated polymers did not take clear mesophase structures.

Synthesis and characterization of liquid crystalline polystyrenes with disiloxane linkage in the spacer

Novel polystyrenes with mesogenic groups as p-substituents connected through disiloxane-containing spacer are synthesized by anionic and radical polymerization and characterized. Some polymers are found to show smectic phases. Influences of the position of the siloxane linkage in the spacer, molecular weight and molecular weight distribution of the polymer on liquid crystallinity are observed.

Chemical Interaction between Chlorosulfonated Polyethylene and Silica—Effect of Surface Modifications of Silica

Abstract The surface of precipitated silica was modified by heat treatment (800°C, 4 h) and hexadecanol treatment. Diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements reveal that the modification of the silica surface reduces the silanol content. Heat treatment causes condensation of the silanol groups forming siloxane linkages, while hexadecanol treatment causes esterification, thereby, shielding the free silanol groups. As a result, the modified silicas exhibit much less interaction with polar molecules (e.g. water, chloroform), compared to the unreacted silica. Bound rubber formation in the chlorosulfonated polyethylene (CSM)/silica system is also adversely affected by the modification of the filler surface. CSM upon heat treatment (180°C, 1 h) loses -SO2Cl groups and the modified polymer lacks in its ability to form bound rubber. Accordingly, it is believed that the rubber-filler interaction occurs between the silanol groups of the silica and sulfonyl chloride groups of CSM.

Preparation and Evaluation of Two‐Dimensional Polymer Films by Chemical Modification of an Alkanethiol Self‐Assembled Monolayer for Protection of Copper Against Corrosion

Chemical modification of an 11‐mercapto‐1‐undecanol (MUO) self‐assembled monolayer chemisorbed on the copper surface with alkyltrichlorosilanes has improved the protective ability of the monolayers against corrosion of copper in aqueous and atmospheric environments. In this study, further improvements of the ability were investigated by modification of the MUO self‐assembled layer adsorbed on copper with tetrachlorosilane (TCS) and 1,2‐bis(trichlorosilyl)ethane (BTCSE) for constructing a two‐dimensional polymer structure in the assembly layer on the surface. The TCS or BTCSE‐modified MUO monolayer was further treated with coupling agents like octyldimethylchlorosilane, octylmethyldichlorosilane, and octyltrichlorosilane. The modified monolayers were characterized by Fourier transform infrared reflection spectroscopy and contact angle measurements. Although the protective abilities of the modified layers against the cathodic reaction of copper corrosion in aerated were not necessarily increased remarkably from those of the MUO monolayers, network structures arising from two‐dimensional polymerization with lateral siloxane linkages between molecules adsorbed on copper resulted in enhancement of the protective ability against the anodic process.

Multinuclear NMR study of aluminosilicate sol-gel synthesis using the prehydrolysis method

Tetraethoxysilane (TEOS), water and aluminum sec-butoxide (Al(OBu s) 3) are combined in several stages of prehydrolysis technique, and reaction intermediates at each stage were examined by means of both liquid and solid nuclear magnetic resonance of 13C, 29Si, 17O, and 27Al nuclei. The spectra indicate that when Al(OBu s) 3 is added to a prehydrolyzed TEOS solution an aluminosilicate precursor is formed in which the aluminum is tetrahedrally coordinated by four silicate ligands. When further water is added, gelation is accompanied by the expansion of aluminum coordination; the spectra indicate that this occurs by the nucleophilic attack of silanol groups. At water contents for which gels of low transparency result, this coordination expansion is accompanied by the formation of new siloxane linkages, but at water contents so high that opaque gels result, the coordination expansion proceeds much more quickly and no new siloxane linkages are observed.

New Polydiene Side-Chain Liquid Crystalline Polymers. Synthesis and Microstructure

Novel side-chain liquid crystalline polymers were synthesized based on the molecular design of the chemical structures of main-chain, spacer, and mesogenic groups. The main-chain structure is polydiene by the radical polymerization of diene derivatives with a mesogenic group. Spacer groups are not only oligomethylene but also those containing a siloxane or ether linkage. The stereochemistry of the main chain, elucidated by 1 H NMR, 13 C NMR, DEPT, and NOESY spectroscopies, is principally (E)-1,4 (cis concerning the carbon-carbon main chain). The polymers take the smectic liquid crystalline state with cyanobiphenyl, fluorobiphenyl, or alkoxybiphenyl as a mesogen. The transition temperatures of polymers with a spacer having a siloxane linkage are lower than those with hexamethylene as a spacer. Cooling the polymer with 4-(hexyloxy)biphenyl as a mesogen and siloxane linkage in the spacer seems to result in the change of the phase which is evidenced by the change in the optical polarization micrograph.

Hydrogen-bonded multilayers of self-assembling silanes: structure elucidation by combined Fourier transform infra-red spectroscopy and X-ray scattering techniques

Hydrogen-bonded multilayer stacks of laterally interconnected long-chain silanes are a new class of synthetic self-assembling thin film organizates endowed with a somewhat unusual combination of structural and dynamic characteristics. In this paper we present experimental results obtained from a combined Fourier transform infra-red (FTIR) spectroscopic and X-ray scattering study, on the basis of which it is possible to derive a rather detailed picture of some of the main features of the microstructure of these novel multilayer films and their monolayer precursors. The films are shown to be composed of discrete monolayers, coupled to each other in a flexible, non-epitaxial manner, via interlayer multiple hydrogen bonds. The hydrocarbon tails assume a perpendicular average orientation on the layer planes and form a ‘rotator phase’-like hexagonal lattice with a lateral packing density of ca. 21 Å 2 per molecule and a positional coherence length of ca.70 Å. Extensive lateral coupling of the silane head groups appears to be responsible for the high structural robustness and defect self-healing capability of these films, while the interlayer hydrogen bonding accounts for the facile post-assembly intercalation of various polar guest species into their vertically expandable interlayer polar regions. As the SiO bond is too short to permit extensive intralayer polymerization under the steric constraints imposed by the compact packing of the perpendicularly oriented hydrocarbon tails, the observed high interconnectivity of the silane head groups is rationalized in terms of a dynamic equilibrium model involving continuous redistribution of the SiO bonds within a two-dimensional network of oligomeric siloxane and silanol species. This model of dynamic equilibriation of siloxane linkages can also help to explain other intriguing properties of such silane monolayers.

Chloromethylation of poly(methylphenylsilane)

The chloromethylation of poly(methylsilane) is readily achieved using chloromethyl methyl ether in a tin(IV) chloride-catalysed reaction in chloroform solution at 0 °C. A convenient, less hazardous reaction, in which chloromethyl methyl ether is prepared in situ, is also reported. The accompanying variations of the polymer molecular-weight parameters are recorded for chloromethylations extending to 95% of the substituent phenyl groups, and discussed in terms of chain scissions arising at isolated siloxane linkages formed adventitiously during the isolation of the parent polymer.

Side-Chain Liquid-Crystalline Polymers Containing the Siloxane Spacer V. Syntheses and Thermal Properties of Copolymethacrylates with Different Spacer Structures

Copolymerizations of the methacrylate-type monomers whose spacer consisted of only alkylene unit with the comonomers containing a disiloxane unit in the spacer component were carried out by radical polymerization. The effects of copolymer composition and structure of mesogen on the mesomorphic properties of the obtained copolymers were investigated, using DSC, optical polarizing microscope and X-ray diffractometry. Tg and Ti of the copolymers decreased with increase in comonomer component reflecting the flexibility of the siloxane linkage. The introduction of the comonomer containing a siloxane spacer and a laterally attached mesogen was effective to lower the temperature range of the mesophase. The copolymers, of which the comonomer content was about 50 mol%, exhibited an enantiotropic nematic phase, whereas the parent homopolymers exhibited a smectic phase. Consequently, the mesophase and temperature range of liquid crystalline state could be controlled by the introduction of a comonomer unit containing a siloxane spacer.

Silane-modified poly(vinylimidazole) corrosion inhibitors for copper

Fourier-transform infra-red spectroscopy was used to study the thermal stability of silane-modified vinylimidazole copolymers on both KBr plates and copper coupons. The copolymers were synthesized by free-radical polymerization of γ-methacryloxypropyltrimethoxysilane and N-vinylimidazole. The ability of these copolymers to inhibit the oxidation of copper at elevated temperatures was compared to that of poly( N-vinylimidazole). The silane acted as a scavenger for the water released by the imidazole ring during heating. Upon heating, the silane methoxy groups hydrolysed and condensed to form siloxane linkages.

High-performance capillary electrophoresis of SDS-proteins using pullulan solution as separation matrix

Sodium dodecyl sulphate (SDS) capillary electrophoresis using pullulan solution as a separation matrix was developed for the separation and molecular mass determination of proteins. The silanol functions on the inner surface of a fused-silica capillary were deactivated by coating with linear polyacrylamide through SiC linkages, into which the pullulan solution was filled. The stability of the coating was examined by exposure to an alkaline buffer solution (pH 9.2) for up to 30 days. Compared with conventional coatings with linear polyacrylamide through siloxane linkages, the present capillary was more stable even under alkaline conditions and markedly reduced electroosmotic flow. Thus, polymer solutions of low viscosity such as pullulan solution could be stabilized in the capillary, resulting in a prolonged life-span of the capillary and improved reproducibility of separations. An excellent linear relationship was obtained between the mobility and the logarithm of the molecular mass of SDS-proteins. The relative standard deviation of migration times was below 0.5% when the pullulan solution was refilled in each analysis ( n = 10). The calibration plots of the integrated peak areas at 214 nm vs. concentration of standard proteins were linear in the range 5 μg/ml-0.1 mg/ml.

Siloxane bond formation by heterofunctional condensation of alkoxysilane and halogenosilane. Application to the preparation of copoly(tetramethyl- p-silphenylenesiloxane-dimethylsiloxane)

Siloxane linkages are formed non-hydrolytically by the reaction of dihalogenosilanes with either dibenzylether, or dibenzyloxysilanes and dibenzhydryloxysilanes. The heterocondensation reaction is activated in the presence of NaI (in acetonitrile) or fluoride anions. This offers an alternative copolymerization route to the usual dehydrocondensation of SiOH-terminated species. Thus, the title copolymer was prepared by reaction of equimolar amounts of Me 2Si(OCHPh 2) 2 and 1,4-bis(chlorodimethylsilyl)benzene at 100°C. The 29Si NMR spectrum supports a quasi-random sequence in the copolymer. Thermal stability is similar to that reported for an alternating microstructure, as inferred from thermogravimetric analysis.

Preparation and characterization of a stable polyacrylamide sieving matrix-filled capillary for high-performance capillary electrophoresis

A stable sieving matrix of polyacrylamide filled in a capillary was developed. The inner wall of a fused-silica capillary was covalently bonded with a linear polyacrylamide through SiC linkages, in which cross-linked polyacrylamide gel or linear polyacrylamide solution was filled. The stability of the coating was examined by exposure of the capillaries to alkaline buffer (pH 8) for up to 30 days. Compared with the coatings with linear polyacrylamide bonded through siloxane linkages, the present capillary markedly reduced the electroosmotic flow. Thus, the sieving matrix in the capillary was stabilized, resulting in a prolonged lifetime of the capillary and good reproducibility of separations. The migration behaviours of oligonucleotides were compared for the cross-linked gel and linear polyacrylamide solution at the same concentration.

Molecular recognition on acoustic wave devices: Zeolite thin films coated with organosilane gate layers

Microporous thin films composed of a molecular coupling layer, zeolite crystals, and a porous silica overlayer, were formed on the gold electrodes of quartz crystal microbalances (QCMs). The silica overlayer enhances the mechanical stability of the zeolite films, and results in additional surface area and porosity as characterized by the sorption isotherms and transient sorption of vapors with different molecular diameters and different polarities. The protecting silica layer is gas permeable such that the regular zeolite micropores with molecular sieving capability are still accessible in the composite film. A novel surface tailoring technique for the microporous thin films was developed, in which organosilane molecules were chemisorbed on the silica overlayer via siloxane linkages, forming a molecular “gate” at the gas thin film interface. The adsorption of vapors into the microporous zeolite films is therefore controlled by the permeability of the gate layer. Selective adsorption based on kinetic or equilibrium exclusion from the microporous films could be achieved, as demonstrated by discrimination of molecules with similar polarity but different molecular diameters (water vs. ethanol), and effective exclusion of larger molecules such as n-hexane. As a result of the increase in the vapor sorption selectivity and reduction of the external surface area of the thin films, the modified QCMs show high selectivity towards water over other molecules.

Polysiloxane‐Containing triblock copolymers via cationic ring‐opening polymerization of cyclic siloxanes

AbstractA novel original method allowing the synthesis of polydimethylsiloxane (PDMS)‐containing triblock copolymers is described. The synthetical procedure is based on the use of ω‐silyl triflate‐terminated polymers serving as macroinitiators for cyclic siloxane polymerization. Due to the continous interchange reactions between the siloxane linkages and the reactive cationic sites, triblock copolymers are obtained. This method was applied to the synthesis of triblock copolymers with a central PDMS block and either two polystyrene or two poly(ε‐caprolactam) rigid external blocks. Another method, the well‐known “end‐blocker” technique, was unsuccessful for obtaining block copolymers.

Sodium dodecyl sulfate-polyacrylamide solution-filled capillary electrophoresis of proteins using stable linear polyacrylamide-coated capillary.

Sodium dodecyl sulfate (SDS)-linear polyacrylamide solution-filled capillary electrophoresis using a stable coated fused silica capillary has been developed for the separation and molecular weight determination of proteins. A fused silica capillary was coated with linear polyacrylamide through Si-C bond which suppressed the electro-osmotic flow and reduced the adsorption of proteins. Acrylamide solution containing SDS was filled into the coated capillary and polymerized. Compared with a conventional fused silica capillary coated with 3-methacryloxypropyltrimethoxysilane through siloxane linkage (Si-O-Si-C), the developed capillary was much more stable, even in the alkaline condition. Consequently, the durability of the polymer matrices and the reproducibility of separation were markedly improved. An excellent linear relationship was obtained between the mobility and the logarithm of the protein molecular weight. The relative standard deviation of migration times was below 1%.

Molecular recognition on acoustic wave devices

Microporous thin films composed of a molecular coupling layer, zeolite crystals, and a porous silica overlayer, were formed on the gold electrodes of quartz crystal microbalances (QCMs). The silica overlayer enhances the mechanical stability of the zeolite films, and results in additional surface area and porosity as characterized by the sorption isotherms and transient sorption of vapors with different molecular diameters and different polarities. The protecting silica glass layer is gas permeable such that the regular zeolite micropores with molecular sieving capability are still accessible in the composite film. A novel surface tailoring technique for the microporous thin films was developed, in which organosilane molecules were chemisorbed on the silica overlayer via siloxane linkages, forming a molecular at the gas thin film interface. The adsorption of vapors into the microporous zeolite films is therefore controlled by the permeability of the gate layer. Selective adsorption based on kinetic or equilibrium exclusion from the microporous films could be achieved, as demonstrated by discrimination of molecules with similar polarity but different molecular diameters (water vs. ethanol), and effective exclusion of larger molecules such as rt-hexane. As a result of the increase in the vapor sorption selectivity and reduction of the external surface area of the thin films, the modified QCMs show high selectivity towards water over other molecules. Keywords: acoustic wave device; sensor; zeolite film; organosilane coating; humidity sensing

Molecular recognition on acoustic wave devices: sorption in chemically anchored zeolite monolayers

Zeolite crystals were attached to the gold electrodes of quartz crystal microbalances (QCM). Monolayers of thiol-alkoxysilanes on the gold surface served as interfacial layers for the subsequent adhesion of the zeolite crystals to the QCM. The process of anchoring the zeolite crystals via the thiol-silane monolayers was studied by reflection adsorption infrared (IR) spectroscopy, contact angle, and scanning electron microscopy (SEM). The siloxane linkages between the microporous zeolite crystals and the terminal cross-linked polysiloxane groups of the interfacial monolayer play an important role in enhancing the packing density of microporous crystals and the thermal stability (up to at least 350 {degrees}C) of the film on the gold surface. Dynamic sorption isotherms of organic vapors and nitrogen as well as the transient sorption behavior of organic vapor pulses were studied to characterize the zeolite-coated QCMs. The resonance frequency response of zeolite-coated QCMs to vapor pulses could be increased up to 500-fold compared to the bare sensor. The regular micropores (0.3-0.75 nm) of the QCM-attached zeolite crystals were found to efficiently control molecular access into the coating. Selectivity of the frequency response in excess of 100:1 toward molecules of different size and/or shape could be demonstrated. The kinetics of vapor desorption frommore » the zeolite layers are strongly dependent on the adsorbate/zeolite combination, thus providing an additional capability for molecular recognition. 33 refs., 11 figs., 2 tabs.« less

Convergent synthesis of siloxane starburst dendrons and dendrimers via hydrosilylation

New highly branched starburst dendrons and dendrimers containing siloxane linkages were convergently synthetized via hydrosilylation. Allyl cyanide all allybis[4-(hydroxydimethylsilyl)phenyl]-methylsilane were used as the starting material and building block, respectively. The allyl group was a synthon of (N,N-diethylamino)silane, which was a suitable electrophilic silicon species. The starburst dendrons and dendrimers were constructed starting at the point which became the periphery of the molecule

Relationships between structure, permeability and glass transition temperature of oligodimethylsiloxanyl substituted polymers

Structurally isomeric oligodimethylsiloxanyl substituted polymers were synthesized, and relationships between the structure of the substituent and the glass transition temperature of the polymer and the permeability of oxygen and nitrogen through the film were studied. p]Polymers with branched substituents showed higher glass transition temperatures than those with straight substituents. Trimethylsiloxyl groups and siloxane linkages in the substituents played an essential role in determining the permeability and glass transition temperature of the polymer. However, permeability could not be explained only by the glass transition temperature of the polymer. The role of the substituents is discussed based on the spin-spin relaxation behavior of the polymers in the solid state.