A Simple Method for the Reinforcement of UV‐Cured Coatings via Sol‐Gel Photopolymerization

A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using ²⁹Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.

     

Preparation of Hybrid Nanocomposite Particles via in situ Miniemulsion Polymerization and the Sol‐Gel Process

In this paper, the preparation of polymer/silica nanocomposite particles in a convenient one‐step process, via in situ miniemulsion polymerization and the sol‐gel technique, is described. The products were characterized using differential scanning calorimetry, transmission electron microscopy, and dynamic light scattering. Moreover, the effects of various reaction parameters, including the content of silica and the concentrations of sodium dodecyl sulfate and potassium persulfate, on the particle size and size distribution were also investigated. It is shown that polymer/silica hybrid nanocomposite particles were successfully synthesized in one step by this novel technique.

     

Preparation and Characterization of Hyperbranched Polymer/Silica Hybrid Nanocoatings by Dual‐Curing Process

Summary: Organic‐inorganic nanocomposite hybrid coatings were prepared through a dual‐cure process involving cationic photopolymerization of a hyperbranched epoxy functionalized resin and subsequent condensation of an alkoxysilane inorganic precursor. All the formulations investigated gave rise to photocured films characterized by high gel content values. An increase in glass transition temperature and an increase in storage modulus above T_g in the rubbery plateau is observed with increasing TEOS content in the photocurable formulation. The important role of GPTS on reducing the inorganic domain size and avoiding macroscopic phase separation was demonstrated by TEM analyses.

TEM obtained for one of the cured films in the presence of GPTS.     

Diffraction Gratings in Hybrid Sol‐Gel Films: On the Understanding of the Relief Generation Process

Hybrid organic‐inorganic materials based on the sol‐gel synthesis of an organically modified silicon alkoxide have demonstrated their great potential for optical applications. They offer a high versatility in terms of chemical, physical properties and macroscopic shape molding of the final component. Recently, a photolithographic process allowed the generation of relief optical elements without requiring a wet treatment to reveal the latent image. It enabled a low cost, simple and quick method for the fabrication of integrated optical components. The aim of the present paper is to give new insights into the mechanisms of surface self‐corrugation leading to gratings generation in hybrid sol‐gel films. A study of the relief formation was led by giving particular attention to the kinetic aspects of the polymerization of the organic component. The control of the C?C double bonds conversion of methacrylate functionalized alkoxides in case of photopolymerization is therefore an essential issue to tailor material properties. The study also focuses on the influence of physico‐chemical parameters that govern the relief generation and underlines the particular role of temperature. Kinetics of surface corrugation point out the importance of strain relaxation, mass‐transfer by flowing and organic network formation during the photolithographic process. Some illustrations of the generated diffraction gratings are given.

Interferogram of the diffraction grating obtained after 120 s exposure through a chromium mask.     

Characterization and properties of UV‐curable polyurethane‐acrylate/silica hybrid materials prepared by the sol‐gel process

UV‐curable, transparent hybrid material of urethane‐acrylate resin was prepared by the sol‐gel process using 3‐(trimethoxysilyl)propylmethacrylate (TMSPM) as a coupling agent between the organic and inorganic phases. The effects of the content of acid and silica on the morphology and mechanical properties of UV‐curable polyurethane‐acrylate/silica hybrid (UA‐TMSPM)/SiO₂ materials have been studied. The results of thermogravimetric analysis for the (UA‐TMSPM)/SiO₂ hybrid materials indicated that the thermal stability of the hybrids is greatly improved. It was found that with the increase of HCl content, the interfacial interaction between organic and inorganic phases had been strengthened, as demonstrated by field emission scanning electron microscopy. Without sacrificing flexibility, the hybrid materials showed improved hardness with increasing content of acid and silica. Compared with the pure organic counterpart UA/hexanediol diacrylate (UA/HDDA) system, abrasion resistance of the hybrids improved with increasing acid content, at low silica content. Copyright © 2004 Society of Chemical Industry     

Low‐Stress Hyperbranched Polymer/Silica Nanostructures Produced by UV Curing,Sol/Gel Processing and Nanoimprint Lithography

Nanocomposite materials based on a HBP and silica are produced using either a dual‐cure sol/gel and photopolymerization process or by mixing silica nanoparticles with the HBP. In both cases the conversion of the HBP is independent of composition and obeys a time‐intensity superposition with power‐law dependence on UV intensity. Optimization of the dual‐cure process leads to transparent sol/gel composites with ultrafine structures. These materials systematically outperform the particulate composites, including an increase of the glass transition temperature of 63 °C and a process‐induced internal stress as low as 2.5 MPa. Nano‐sized gratings are produced from the sol/gel composites by low‐pressure UV nanoimprint lithography.

     

Hybrid Organic‐Inorganic Materials Derived from a Monosilylated Hoveyda‐type Ligand as Recyclable Diene and Enyne Metathesis Catalysts

The synthesis of a monosilylated Hoveyda‐type monomer is described as well as the preparation of several organic‐inorganic hybrid materials derived from it by sol‐gel processes and by anchoring to commercial silica gel and MCM‐41. The resulting materials were treated with first and/or second generation Grubbs’ catalyst to generate Hoveyda–Grubbs’ type alkylidene ruthenium complexes covalently bonded to the silica matrix. These materials are efficient recyclable catalysts for the ring‐closing metathesis reaction of dienes and enynes, even for the formation of tri‐ and tetrasubstituted olefins.     

Development of Hybrid Polymeric Materials Based on Thiol‐Ene/Cationic Formulations

Novel materials were prepared from dual photo and thermal polymerization of hybrid thiol‐ene/cationic systems. In the first stage, the thiol‐ene system proceeded to high conversions, while the cationic photopolymerization was inhibited. The formation of sulfides during this stage was the main factor for the inhibition of the cationic photopolymerization of the epoxy monomers. Once those sulfides were formed, they reacted with the oxonium‐terminated growing polyether chains to form trialkylsulfonium salts. These salts promoted the thermal polymerization of the epoxy monomers in the second stage. The viscoelastic properties of the resulting polymers were measured by DMA.

     

Determination of Heat Treatment Temperature for Completing Polycondensation of Vinyl Substituted Silica Particles Prepared by Sol‐Gel Method

The completion of the polycondensation of sol‐gel derived organic‐inorganic hybrid silica by heat treatment was studied for powder samples prepared from vinyltrimethoxysilane and vinyltriethoxysilane. The appropriate temperature for the completion of the prepared submicron powdery samples from both starting compounds was determined through thermogravimetric analysis. The completion or incompletion of the polycondensation was elucidated by means of several instrumental methods in addition to a light scattering test. The lowest heat treatment conditions for the particles from vinyltrimethoxysilane and vinyltriethoxysilane are 170 °C and 180 °C, respectively, for 24 h. The morphologies of the heat treated samples were found to be slightly different depending on the starting material used.     

Preparation and Characterization of Nanostructured TiO2/Epoxy Polymeric Films

Summary: Titania‐containing coatings were prepared by cationic photopolymerization of an epoxy resin either by dispersion of preformed TiO₂ nanoparticles or by their in‐situ generation through a sol‐gel dual‐cure process. The kinetics of photopolymerization was evaluated by real‐time FT‐IR, studying the effect of the TiO₂ concentration. The properties of cured films were investigated, showing an increase of hydrophilicity on the surface of the coatings with increasing TiO₂ content. TEM analysis demonstrated that it is possible to achieve a significantly better control of the dispersion of the inorganic particles within the organic matrix by in‐situ generation of TiO₂, thus completely avoiding macroscopic phase separation and obtaining homogeneous, transparent coatings.

Bright‐field TEM micrograph for TIP20 dual‐cured film.     

Hybrid‐Bridged Silsesquioxane as Recyclable Metathesis Catalyst Derived from a Bis‐Silylated Hoveyda‐Type Ligand

The synthesis of a bis‐silylated Hoveyda‐type monomer is described as well as the preparation of several organic‐inorganic hybrid materials derived from it by a sol‐gel process (with and without tetraethyl orthosilicate) and by anchoring to MCM‐41. The resulting materials were treated with second generation Grubbs' catalyst to generate second generation Hoveyda–Grubbs‐type alkylideneruthenium complexes covalently bonded to the silica matrix. These materials are recyclable catalysts for the ring‐closing metathesis reaction of dienes and enynes.     

Fabrication of High‐Performance Cationic UV Curable Cycloaliphatic Epoxy/Silicone Hybrid Coatings

A series of cycloaliphatic epoxy acrylate prepolymer poly (METHB‐co‐MMA‐co‐BA) (MMB) and an epoxycyclohexyl‐modified polydimethylsiloxane (PDMS‐VCH) are prepared to fabricate hybrid coatings. The curing process, surface performance, mechanical properties, and thermal behavior are investigated by real‐time Fourier transform infrared (FT‐IR), contact angle measurements, tensile test, thermogravimetric analyzer (TGA), and differential scanning calorimeter (DSC). For the same photoinitiator (PI) concentration, both the epoxy value and the amount of PDMS‐VCH negatively affect the UV‐curing process. The contact angle of hybrid coatings increases by almost 12° with 4 wt% PDMS‐VCH's addition. The increasing ratio of soft acrylate segment can strengthen the toughness of materials markedly. Besides, thermal stability is enhanced with the increasing of epoxy value, while slight changes are found with the addition of PDMS‐VCH. Based on these properties, the hybrid coatings can be applied in various fields, including protection, decoration, and other displayed fields.     

Preparation and Properties of an AP/RDX/SiO2 Nanocomposite Energetic Material by the Sol‐Gel Method

A nanocomposite energetic material was prepared using sol‐gel processing. It was incorporated into the nano or submicrometer‐sized pores of the gel skeleton with a content up to 95 %. AP, RDX, and silica were chosen as the energetic crystal and gel skeleton, respectively. The structure and its properties were characterized by SEM, BET methods, XRD, TG/DSC, and impact sensitivity measurements. The structure of the AP/RDX/SiO₂ cryogel is of micrometer scale powder with numerous pores of nanometer scale and the mean crystal size of AP and RDX is approx. 200 nm. The specific surface area of the AP/RDX/SiO₂ cryogel is 36.6 m² g⁻¹. TG/DSC analyses indicate that SiO₂ cryogel can boost the decomposition of AP and enhance the interaction between AP and RDX. By comparison of the decomposition heats of AP/RDX/SiO₂ at different mass ratios, the optimal mass ratio was estimated to be 6.5/10/1 with a maximum decomposition heat of 2160.8 J g⁻¹. According to impact sensitivity tests, the sensitivity of the AP/RDX/SiO₂ cryogel is lower than that of the pure energetic ingredients and their mixture.     

Recoverable Palladium Catalysts for Suzuki–Miyaura Cross‐ Coupling Reactions Based on Organic‐Inorganic Hybrid Silica Materials Containing Imidazolium and Dihydroimidazolium Salts

The systems formed by palladium acetate [Pd(OAc)₂] and hybrid silica materials prepared by sol‐gel from monosilylated imidazolium and disilylated dihydroimidazolium salts show catalytic activity in Suzuki–Miyaura cross‐couplings with challenging aryl bromides and chlorides. They are very efficient as recoverable catalysts with aryl bromides. Recycling is also possible with aryl chlorides, although with lower conversions. In situ formation of palladium nanoparticles has been observed in recycling experiments.     

Preparation of polymer/silica nanoscale hybrids through sol‐gel method involving emulsion polymers. II. Poly(ethyl acrylate)/SiO2

Poly(ethyl acrylate) (PEA)/SiO₂ hybrids with different compositions were prepared under different casting temperatures and pH values. Their morphology as investigated by transmission electron microscopy (TEM) shows that samples with different compositions have different morphologies. When the SiO₂ content is lower, PEA is the continuous phase and SiO₂ is the dispersed phase. At higher SiO₂ content, the change in phase morphology takes place, nd PEA gradually dispersing in the form of latex particles in SiO₂ matrix. Change in phase morphology depends mainly on the time the sol‐gel transition occurs. At suitable casting temperature and pH value, PEA/SiO₂ in 95/5 and 50/50 hybrids with even dispersion was obtained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3532–3536, 2002     

Preparation and characterization of UV‐curable organic/inorganic hybrid composites for NIR cutoff and antistatic coatings

In this study, UV‐curable organic/inorganic hybrid composite coatings with near infrared (NIR) cutoff and antistatic properties were prepared by high‐shear mixing of two kinds of polymer matrices and coated on plastic and glass substrates by the doctor‐blade method. This study also investigated the morphology, stability, optical properties, electrical resistivity, and durability of the UV‐cured composite coats. It was found that the composite coatings were very stable under centrifugation. Moreover, the films with transmittance of above 80% in a visible light region (400–800 nm) and of ～ 40% to 50% in the NIR region (1000–1600 nm) showed low haze of 6.9%, electrical resistivity of around 2.3 × 10⁷ Ω/square. Thus, excellent adhesion, scratch, and weathering durability can be produced on polycarbonate substrate at room temperature. The experimental results reveal that UV‐curable organic/inorganic hybrid composites can be used effectively to fabricate films with NIR cutoff as well as antistatic properties, indicating a high potential for practical application in architectural, automotives, and optoelectronics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High‐Temperature Capture of CO2 on Lithium‐Based Sorbents Prepared by a Water‐Based Sol‐Gel Technique

A convenient water‐based sol‐gel technique was used to prepare a highly efficient lithium orthosilicate‐based sorbent (Li₄SiO₄‐G) for CO₂ capture at high temperature. The Li₄SiO₄‐G sorbent was systematically studied and compared with the Li₄SiO₄‐S sorbent prepared by solid‐state reaction. Both sorbents were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The CO₂ sorption stability was investigated in a dual fixed‐bed reactor. Li₄SiO₄‐G exhibited a special Li₄SiO₄ structure with smaller crystalline nanoparticles, larger surface area, and higher CO₂ adsorption properties as compared with Li₄SiO₄‐S. The Li₄SiO₄‐G sorbent also maintained higher capacities during multiple cycles.     

Sol‐Gel Materials, 1. Synthesis and Hydrolytic Condensation of New Cross‐Linking Alkoxysilane Methacrylates and Light‐Curing Composites Based upon the Condensates

New methacryloyloxyalkylaminoalkylalkoxysilanes have been synthesised by Michael addition of the corresponding acryloyloxyalkyl methacrylates with (3‐aminopropyl)triethoxysilane (APTES). Low‐viscosity polycondensates have been formed by hydrolysis and condensation of these silanes in the presence of ammonium fluoride (NH₄F). The reaction of APTES with the addition product of succinic or glutaric anhydride with glycerol dimethacrylate results in the formation of new dimethacrylate‐functionalised 3‐amidopropyltriethoxysilanes. The hydrolytic condensation of these silanes was carried out in the presence of 0.5 M HCl. The hydrolysis and condensation of the silanes have been studied by ²⁹Si NMR spectroscopy. Cross‐linked inorganic‐organic materials have been obtained by free‐radical photopolymerisation of the polycondensates and their mixtures in the presence of camphorquinone and ethyl 4‐(dimethylamino)benzoate with visible light (VL). The synthesised polycondensates enable the preparation of diluent‐free composites. The mechanical properties of VL‐cured polycondensates and composites have been investigated.