Siloxane Chain Research Articles

Influence of liquid phase on nanoparticle-based giant electrorheological fluid

We show that the chemical structures of silicone oils can have an important rolein the giant electrorheological (GER) effect. The interaction between siliconeoils and solid nanoparticles is found to significantly influence the ER effect. Byincreasing the kinematic viscosity of silicone oils, which is a function of siloxane chainlength, sol-like, gel-like and clay-like appearances of the constituted ER fluids wereobserved. Different functional-group-terminated silicone oils were also employed as thedispersing media. Significant differences of yield stress were found. We systematicallystudy the effect of siloxane chain lengths on the permeability of oils travelingthrough the porous spaces between the particles (using the Washburn method), oilsadsorbed on the particles’ surface (using FT-IR spectra), as well as their particle sizedistribution (using dynamic light scattering). Our results indicate the hydrogenbonds are instrumental in linking the silicone oil to GER solid particles, and longchain lengths can enhance the agglomeration of the GER nanoparticles to formlarge clusters. An optimal oil structure, with hydroxyl-terminated silicone oiland a suitable viscosity, was chosen which can create the highest yield stress of∼300 kPaunder a 5 kV mm−1 DC electric field.

シリカ粒子充てんイソプレンゴムの力学特性におよぼすメルカプト基含有シランカップリング剤による表面処理の影響

The surface treatment of spherical silica particles with Silane coupling agent (SCA) having mercapto group was carried out. The treated silica particles were incorporated with polyisoprene, and then vulcanized. Effects of loading amount and alkoxy group number of SCA on the stress-strain curve of the filled composite were investigated. For this purpose, the SCAs with dialkoxy and trialkoxy structures were used. The loading amount of SCA on the silica surface was varied from one to thirteen times of the amount required for monolayer coverage. The stress increased by the SCA-treatment of silica, and it was higher in the dialkoxy structure than in the trialkoxy structure. There was no significant influence of loading amount on the stress for the trialkoxy structure. The stress was influenced strongly by the loading amount for the dialkoxy structure, and the maximum stress was observed at four times of the loading amount required for monolayer coverage. The stress had the good relation with the crosslinking density of silica-filled isoprene rubber measured by a swelling test. It was found that the reinforcement effect by the SCA treatment of silica is affected strongly both by the entanglement of siloxane chain formed by the condensation of SCA and isoprene rubber matrix and the crosslinking reaction between mercapto group of silane and isoprene rubber at the interfacial region.

Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol–gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si–O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol–gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS–2Si) was firstly synthesized using direct nucleophilic addition between –OH groups of polydiol and –NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS–2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS–2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5°C for the composite containing 50–60% (wt%) PCS–2Si, over 150°C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS–2Si and epoxy, the forming of Si–O–Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.

Polyrotaxanes composed of β-cyclodextrin and polydimethylsiloxanes: synthesis, morphology and thermal behavior

Epoxy-terminated polydimethylsiloxanes (E-PDMSs) of different molecular weight Mn were proved to undergo inclusion complexation into the inner cavity of β-cyclodextrin (β-CD), resulting in polyrotaxanes (PRots). The dethreading of the macrocycle was prevented by blocking the siloxane chain with a bulky substituent derived from 4-aminophenyltriphenyl methane (APhTPhM). As revealed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), wide-angle X-ray diffraction and statistical analysis of SEM images, the thermal properties and the morphology of polyrotoxanes are dependent upon Mn, β-CD/E-PDMS molar ratio and the presence of free β-CD in the complexes.

Synthesis, characterization, and comparison of properties of novel fluorinated poly(imide siloxane) copolymers

AbstractFour new poly(imide siloxane) copolymers were prepared by a one‐pot solution imidization method at a reaction temperature of 180°C in ortho‐dichlorobenzene as a solvent. The polymers were made through the reaction of o‐diphthaleic anhydride with four different diamines—4,4′‐bis(p‐aminophenoxy‐3,3″‐trifluoromethyl) terphenyl, 4,4′‐bis(3″‐trifluoromethyl‐p‐aminobiphenyl ether)biphenyl, 2,6‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)pyridine, and 2,5‐bis(3′‐trifluoromethyl‐p‐aminobiphenylether)thiopene—and aminopropyl‐terminated poly dimethylsiloxane as a comonomer. The polymers were named 1a, 1b, 1c, and 1d, respectively. The synthesized polymers showed good solubility in different organic solvents. The resulting polymers were well characterized with gel permeation chromatography, IR, and NMR techniques. 1H‐NMR indicated that the siloxane loading was about 36%, although 40 wt % was attempted. 29Si‐NMR confirmed that the low siloxane incorporation was due to a disproportionation reaction of the siloxane chain that resulted in a lowering of the siloxane block length. The films of these polymers showed low water absorption of 0.02% and a low dielectric constant of 2.38 at 1 MHz. These polyimides showed good thermal stability with decomposition temperatures (5% weight loss) up to 460°C in nitrogen. Transparent, thin films of these poly(imide siloxane)s exhibited tensile strengths up to 30 MPa and elongations at break up to 103%, which depended on the structure of the repeating unit. The rheological properties showed ease of processability for these polymers with no change in the melt viscosity with the temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Quasielastic neutron scattering of poly(methyl phenyl siloxane) in the bulk and under severe confinement

Quasielastic neutron scattering was utilized to investigate the influence of confinement on polymer dynamics. Poly(methyl phenyl siloxane) chains were studied in the bulk as well as severely confined within the approximately 1-2 nm interlayer spacing of intercalated polymer/layered organosilicate nanohybrids. The temperature dependence of the energy resolved elastic scattering measurements for the homopolymer and the nanocomposites exhibit two distinct relaxation steps: one due to the methyl group rotation and one that corresponds to the phenyl ring flip and the segmental motion. Quasielastic incoherent measurements show that the very local process of methyl rotation is insensitive to the polymer glass transition temperature and exhibits a wave-vector independent relaxation time and a low activation energy, whereas it is not affected at all by the confinement. At temperatures just above the calorimetric glass transition temperature, the observed motion is the phenyl ring motion, whereas the segmental motion is clearly identified for temperatures about 60 K higher than the glass transition temperature. For the nanohybrid, the segmental motion is found to be strongly coupled to the motion of the surfactant chains for temperatures above the calorimetric glass transition temperature of the bulk polymer. However, the mean square displacement data show that the segmental motion in confinement is faster than that of the bulk polymer even after the contribution of the surfactant chains is taken into consideration.

Hydrophobic zeolite–silicone rubber mixed matrix membranes for ethanol–water separation: Effect of zeolite and silicone component selection on pervaporation performance

High-silica ZSM-5 zeolites were incorporated into poly(dimethyl siloxane) (PDMS) polymers to form mixed matrix membranes for ethanol removal from water via pervaporation. Membrane formulation and preparation parameters were varied to determine the effect on pervaporation performance including siloxane chain length, crosslinking agent concentration and density of reactive groups, catalyst level, solvent type, zeolite type and loading, mixing method, and presence of a porous support membrane. Uniform dispersion of zeolite was critical to the achievement of reproducible results and ultrasonication with a probe-type device was found to be effective at particle dispersal. Properties of the vinyl-terminated PDMS and methyl-hydride crosslinking agents in the polymer system had a limited effect on performance while zeolite loading had the greatest effect. The highest observed selectivity of 3.0 was observed with 65 wt% zeolite loading, the highest practicable loading for the polymer system studied. The current results are placed in the context of ZSM-5/PDMS mixed matrix membranes previously reported in the literature for ethanol–water separation.

Influence of Chemical Structure on Processing and Thermotropic Properties of Poly(siloxane-azomethine)s

A disiloxane dialdehyde was obtained from bis (chloromethyl)disiloxane and p-hydroxybenzal-dehyde and it was used in an equilibration (redistribution) reaction to synthesize an oligomeric dialdehyde. By solution polycondensation, starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines, poly(azomethine)s were obtained. In the case of aromatic diamines with high rigidity, which gave insoluble polymers, different approaches were tested in order to improve the solubility: the use of the dialdehyde having longer siloxane chain, or of a siloxane diamine in a copoly-condensation reaction. The polymers’ structures were confirmed by IR and 1H NMR spectroscopy and by elemental analysis. The structure-properties relationship was studied in terms of solubility, thermal and thermotropic behavior. Most of the obtained poly(azomethine)s has mesomorphic properties, which were studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The influence of aromatic diamines’ chemical structure on the processability of the siloxane-organic poly(azomethine)s was emphasized.

Pyrolysis study of a hydride-sol-gel silica

A homogeneous silica gel sample bearing ≡Si-H groups was prepared, via sol-gel method, by hydrolysis of trimethoxysilane under acid condition in tetrahydrofuran. Preliminary NMR experiments in liquid phase indicated an immediate and complete hydrolysis of Si-OCH3, followed by a slower condensation of the Si-OH groups, with maintenance of Si-H bonds. The crude-gel, and samples heated to various temperatures, were characterized by different instrumental methods, including FTIR, density, porosity, and specific surface area. These data indicate that the crude-gel was a dense material which, on heating, increases porosity and surface area up to ca 500°C. The thermal behavior was studied in inert atmosphere by means of coupled thermogravimetric, gas chromatographic, mass spectrometric analyses. The pyrolysis process was described by the fundamental chemical reactions occurring among the siloxane chains of the gel network and by the qualitative and semiquantitative chemical analysis of the compounds released in gas-phase. The proposed pyrolysis mechanism was discussed and interpreted in agreement with the change of the morphological properties of the gel. The pyrolysis data and the mass balance between the compounds released in gas-phase and the solid residue at 1000°C allowed the determination of a nominal chemical formula to describe the crude-gel composition.

A novel approach for the preparation of organic-siloxane oligomers and the creation of hydrophobic surface

In this paper, poly(acrylate- g-siloxane) with novel comb-like structure was designed and prepared so as to create a strongly hydrophobic polymer surface. In order to achieve this goal, a series of organic-siloxane oligomers with different chain lengths and a double bond were firstly synthesized through the catalytic reforming and hydrosilylation reaction. Then, poly(acrylate- g-siloxane) was prepared by the copolymerization of the resulting oligomers with acrylate via emulsion polymerization. The as-synthesized oligomers were characterized by 1H NMR and UV spectrometry, and the morphologies and surface chemical compositions of the dried membrane were investigated by FT-IR, XPS, as well as AFM. XPS analysis result shows that the chemical composition of the membrane's surface was rich in polysiloxane segments, which could be responsible for an increase of surface water repellency (the contact angle could reach 115° at a lower content of polysiloxane). A further investigation suggest that the side chain length of siloxane in the poly(acrylate- g-siloxane) was the dominant factor in influencing the hydrophobicity of the membrane’ surface. When the siloxane chain length reaches to eight, the membrane's surface could exhibit the strongest hydrophobicity.

Fluorosiloxane sealants for aviation industry

Properties of sealants based on fluorosiloxane oligomers are considered. It is shown that polysibxanes containing the γ-trifluoropropyl radical can be applied in practice as the base for sealants. It is established that the flexibility of the siloxane chain is responsible for high freeze resistance, while large values of the energy of polar-Si-O-bond allow us to obtain materials with high thermal stability. Mechanical and technological properties of fluorosiloxane sealants are reported, and their advantages relative to materials on the basis of organofluoric rubbers are shown. The domains of the applicability of sealants for surface and interjoint sealing are discussed. It is shown that sealants based on fluorosiloxane oligomers are characterized by adequate stability to prolonged action of different fuels and are widely used in the aircraft construction.

Dipolar orientation stabilities of hybrid films for second-order nonlinear optical applications

Organic–inorganic hybrid films containing nonlinear optical (NLO) active chromophores were prepared through the polyaddition of methacrylate and hydrolytic polycondensation of sila-functional alkoxy groups of 3-(trimethoxysilyl)propyl methacrylate (TSPM) which is capable of forming carbon–carbon and siloxane chains, respectively. The NLO-active chromophores are designed and synthesized to be covalently grafted to the carbon–carbon or the siloxane chains. The comparative study of the two different incorporation methods reveals that the poled hybrid film with NLO-active chromophores bonded to siloxane chains would possess a more stable dipolar orientation.

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

AbstractSiloxane‐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.

Alkoxysilane Functionalized Polyurethane/Polysiloxane Copolymers: Synthesis and the Effect of End-Capping Agent

A series of moisture curable polyurethane/polysiloxane (PUSR) copolymers with different end-capping agents were prepared based on amine terminated polysiloxane (PDMS), poly-1,4-butylene adipate glycol (PBA), 4,4′-diphenylmethane diisocyanate (MDI). The copolymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogarvimetric (TGA), X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA), X-ray photoelectron spectroscopy (XPS), surface contact angle and stress–strain measurement. Compared with conventional moisture curable PU the PUSR copolymer showed the better thermal stability and surface properties due to the forming of Si-O-Si crosslinking network and the enrichment of siloxane chains on the surface of films , and the tensile strength was not obviously damaged. DMTA results suggested that micro-phase separation was formed in the PUSR copolymer. It was found that the PUSR copolymer with mixed alkoxysilanes as end-capping agents showed better compromised properties than that with single alkoxysilane.

Stöber silica particle size effect on the hardness and brittleness of silica monoliths

Micro-indentation experiments were performed on monoliths prepared by drying dispersions of Stöber silica nano-sized particles in the 15–115 nm diameter range. Monolith hardness and resistance to fracture change gradually: the monoliths made with the smaller particles have smoother surfaces and resist to higher indentation forces while the monoliths made out of the larger particles are very brittle. These differences are assigned to changes in particle microchemistry associated to the differences in particle sizes, evidenced in a previous work from this group: larger particles are more extensively cross-linked and thus less plastic than smaller particles. This is in turn due to a larger amount of non-hydrolyzed ethoxy groups in the smaller particles, which limits the extent of cross-linking and creates domains containing linear siloxane chains that contribute to mechanical energy dissipation and thus to increased monolith tenacity and decreased hardness. Optical and electron microscopy examination of monolith surfaces show a large number of defects at different scales on the monoliths formed by larger particles. Under high magnification in a field-emission scanning electron microscope, larger particles appear less deformed and less densely packed than the smaller particles, thus contributing to lower cohesion energy. These results show a clear connection between the conditions for particle formation, their chemical and morphological features and the resulting mechanical properties of macroscopic solids.

Synthesis and characterization of polydimethylsiloxane-cured organically modified silicate hybrid coatings

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol–gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different chain lengths of siloxane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked, dense and adhered to the aluminum alloy substrates. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the siloxane chain length. Potentiodynamic analysis revealed that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Synthesis of hybrid methacrylate-silicone-cyclohexanepoxide monomers and the study of their UV induced polymerization

The synthesis of two hybrid methacrylate-silicone-epoxycyclohexane monomers is described. These monomers were prepared by sequential hydrosilation reactions attaching first the 4-vinyl-1-cyclohexene 1,2-epoxide, using the Wilkinson catalyst, and then the allyl methacrylate in the presence of chloroplatinic acid as catalyst for the hydrosilation reaction. The reactivity of these monomers was evaluated by RT-FT-IR finding that the methacrylate groups can be photopolymerized concomitantly with the epoxide groups using only a diaryliodonium salt as photoinitiator, in air-free conditions. The addition of a free radical photoinitiator helps to overcome the oxygen inhibition when the radical photopolymerization is performed in air. The films obtained from these monomers were almost totally crosslinked with T g's of 54 and 31 °C for EM2Si and EM4Si, respectively. It was found that the film made with the monomer with a longer siloxane chain exhibited a higher contact angle as a direct result of the higher hydrophobic surface.

Thermally initiated cationic polymerization and properties of epoxy siloxane

AbstractDifunctional epoxy siloxane monomers containing disiloxane, trisiloxane, and tetrasiloxane were prepared by hydrosilylation of an α,ω‐difunctional SiH‐terminated siloxane with a vinyl‐functional epoxide. Cationic polymerization of these monomers using 3‐methyl‐2‐butenyltetramethylenesulfonium hexafluoroantimonate and their reactivities were examined. The reactivity order was disiloxane > trisiloxane > tetrasiloxane. Thermal discoloration of these polymers increased with catalyst concentration and also with the length of dimethyl siloxane. UV discoloration was also accelerated by catalyst. From the thermo gravimetric analysis, it was found that the thermal stabilities of polymers increased with increasing the length of dimethyl siloxane chain. Mechanical properties of polymers were also tested by thermal mechanical analysis and dynamic mechanical analysis, and it was found that the flexibility of polymers was increased with increasing siloxane chain length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2010–2019, 2006

Is energy transfer through the siloxane chain (-Si-O-) possible?

Is energy transfer through the siloxane chain (-Si-O-) possible?

Transmission holographic gratings using (siloxane and mesogen)-containing compounds

(Siloxane and mesogen)-containing compounds were found effective in the formation of holographic gratings, over a wide concentration range from 3 wt% to 30 wt%. A fine grating with 40% diffractive efficiency was formed with 10 wt% 1-(4′-methoxyphenyloxycarbonylphenoxy)butyl-1,1,3,3,3-pentamethyldisiloxane. The diffraction efficiency and angle selectivity of the grating were also significantly affected by the structure of siloxane chain. 3-(4′-Methoxyphenyloxycarbonylphenoxy)butyl-1,1,1,3,5,5,5-heptamethyltrisiloxane gave high (approx. 90%) diffraction efficiency and showed very narrow angular selectivity of about 5°.