In situ polyurethane/silica composite formation via a sol‐gel process

Polyurethane acrylate anionomer (PUAA)/silica composite gels were prepared by the sol‐gel reaction of tetraethoxysilane (TEOS) and methacryloxypropyl trimethoxysilane (MPTS) incorporated to PUAA gels by using a swelling method. The formation and structure of composites were confirmed by FTIR, X‐ray diffraction, and SEM. As a result, we found that silica components in composites are located within the ionic domains of their gels and interacted with PUAA via hydrogen bonding. This drastically enhanced the mechanical properties of the composites. Mechanical properties are also improved by MPTS, because MPTS improves the dispersibility and adhesion of silica components in PUAA/silica composite gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2327–2334, 2002     

Transparent photo‐curable co‐polyacrylate/silica nanocomposites prepared by sol‐gel process

This work prepared the highly transparent photo‐curable co‐polyacrylate/silica nanocomposites by using sol‐gel process. The FTIR and ¹³C NMR analyses indicated that during the sol‐gel process, the hybrid precursors transform into composites containing nanometer‐scale silica particles and crosslinked esters/anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt % of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 150°C and coefficient of thermal expansion (CTE) less than 35 ppm/°C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters/anhydrides might influence the thermal stability of nanocomposite samples. The UV‐visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano‐scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the ? OH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Hydrogenated rosin ester latexes/waterborne polyacrylate blends for pressure‐sensitive adhesives

Diethylene glycol ester of hydrogenated rosin (DGE‐HR) emulsion was prepared via phase inversion method and then blended with waterborne (wb) polyacrylate for pressure‐sensitive adhesives (PSAs). The preparation conditions of DGE‐HR emulsion were studied. DGE‐HR emulsion with an average particle size of about 220 nm was obtained. Furthermore, the thermal, adhesive, and viscoelastic properties and the morphology of DGE‐HR/polyacrylate composite were investigated. Thermal analysis indicated that glass transition temperatures (T_g) of the DGE‐HR/polyacrylate blends became higher as the DGE‐HR content increased and DGE‐HR did not have a significant influence on thermal stability of the blend films. Atomic Force Microscopy (AFM) observation revealed that the DGE‐HR particles added had a good miscibility with acrylic particles. Additionally, for these tackified acrylic PSAs, positive correlations between mechanical performance and viscoelastic response at bonding and debonding frequencies were also found. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42965.     

Sol–gel process of alkoxysilane in emulsifier‐involved aqueous emulsions: A one‐pot synthetic route to emulsions of core‐shell composite particles and their applications

In this work, a one‐pot route to prepare emulsions of silica/polymer core‐shell composite particles was developed through the direct sol–gel processing of alkoxysilane on the surface of newly synthesized template polymer particles in emulsifier‐involved aqueous emulsions. It included two continuous steps: first, the polymer emulsions were synthesized through emulsion polymerization, and second, the template particles in the emulsions were directly coated with silica via sol–gel reaction of precursors without adding ethanol or removing emulsifiers. The size and morphology of the composite particles were characterized, and the results showed that the silica/polymer composite particles with core‐shell structure could be prepared only on the basis of cationic template emulsions, and the in situ‐coating reaction of sol–gel precursors carried on easier with the increasing of the positive charge density on the surface of template particles. The films formed from the composite emulsions were found to have superior optical and flame‐retardant properties compared to polymer films, owing to the core‐shell composite microstructure of the particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of rigid‐rod polyimide/silica hybrid materials by sol–gel process

Polyimide (PI) materials with a low coefficient of thermal expansion (CTE) while still retaining high strength and toughness are desirable in various applications. In this study a sol–gel process was used to incorporate silica into homopolyimides and copolyimides with highly rigid structures in an attempt to pursue this aim. A number of highly rigid monomers were used, including pyromellitic dianhydride (PMDA), p‐phenylene diamine (PPA), m‐phenylene diamine (MPA), benzidine, 2,4‐diaminotoluene, and o‐toluidine. No homopolyimide flexible films were obtained. However, it was possible to obtain flexible films from the copolyimides. Therefore, a copolyimide based on PPA, MPA, and PMDA (PPA/MPA = 2/1 mol) was then chosen as the matrix to prepare the PI/silica hybrids. Flexible films were obtained when the silica content was below 40 wt %. The hybrid films possessed low in‐plane CTEs ranging from 14.9 to 31.1 ppm with the decrease of the silica content. The copolyimide film was strengthened and toughened with the introduction of an appropriate amount of silica. The thermal stability and the Young's modulus of the hybrid films increased with the increase of the silica content. The silica particle size was assessed by scanning electron microscopy and was about 100 nm for the hybrids containing 10 and 20 wt % silica and 200–500 nm for the hybrids containing 30 and 40 wt % silica. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 794–800, 2001     

Film‐forming behavior and mechanical properties of colloidal silica/polymer latex blends with high silica load

In this article, silica sol (diameter: 8–100 nm) and polymer latex (T_g < 25°C) were mixed and dried at room temperature to prepare nanocomposite films with high silica load (≥50 wt %). Effects of silica size, silica load, and the T_g of the polymer on the film‐forming behavior of the silica/polymer latex blend were investigated. The transparency, morphology, and mechanical properties of the nanocomposite films were examined by UV–Vis spectroscopy, SEM, and nanoindentation tests, respectively. Transparent and crack‐free films were produced with silica loads as high as 70 wt %. Thirty nanometers was found to be the critical silica size for the evolution of film‐forming behavior, surface morphology, and mechanical properties. Colloidal silica particles smaller than this critical size act as binders to form strong silica skeleton. This gives the final silica/polymer nanocomposite film its porous surface and high mechanical strength. However, silica particles with sizes of 30 nm or larger tend to work as nanofillers rather than binders, causing poor mechanical strength. We also determined the critical silica load appeared for the mechanical strength of silica/polymer film at high silica load. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of silica/poly(styrene‐co‐butyl acrylate) core/shell composite particles for absorption of toluene

An absorbent for benzene series with silica/poly(styrene‐co‐butyl acrylate) core/shell structure was prepared via emulsion polymerization. The effects of emulsifier dosage, monomer concentration, and crosslinker dosage on the absorption of the core/shell composite particles were investigated. The composite particles with good absorbency could be obtained when the emulsifier concentration was 2.5 g/L, monomer concentration was 40 g/L, crosslinker dosage was 2.0% (based on the total mass of the monomer), and the initiator dosage was 1.0%. The composite particles exhibited a rapid absorption and the absorption process conformed to the quasi‐second order kinetics. Fourier‐transform infrared spectroscopy, scanning electron microscope, and energy dispersive spectrometer (EDS) showed the presence of copolymer layer on the surface of silica. The work provided a new path to fabricate novel composite absorbent particles for a wide range of applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46172.     

Synthesis and characterization of polyacrylate composite with thiol‐modified nanosilica as chain transfer agent

Polyacrylate composites with thiol‐modified nanosilica as chain transfer agent were prepared. The FTIR results indicated that the chemical bond has formed between polyacrylate and modified nanosilica. The change of molecular weight distribution proved that the thiol group on the nanosilica surface played the chain transfer agent role just as common thiol. A possible mechanism of modified nanosilica in the polymerization was proposed and the core‐shell may be formed finally. In addition, the dispersion of nanosilica in the polyacrylate also improved as a result of the organic bridge structure between the nanosilica and polyacrylate. The thermal decomposition temperature increased as much as 10°C for polyacrylate with 10 wt % modified nanosilica composites compared to polyacrylate. The coatings hardness increased from 2 to 6 H and the abrasion resistance improved from 28 to 10 mg under the same conditions. Especially, the gloss change of coatings with different content of modified nanosilica indicated that the polyacrylate composites have obviously better aging resistance performance compared to polyacrylate. It may be ascribed to the property that nanosilica can absorb large UV light. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42756.     

Environmental aging of cold‐cured epoxy‐silica hybrids prepared by sol−gel process

The article investigates the effects of long term environmental aging on thermal and mechanical properties of epoxy‐silica hybrids. These nanostructured materials, prepared by non‐aqueous sol‐gel process and in situ generation of nanosilica during epoxy curing at room temperature, present the potential to be used as cold‐cured adhesives for civil engineering and Cultural Heritage applications. A specifically developed conditioning procedure for these cold‐cured nanostructured materials was applied before moisture/water absorption tests. The work evidenced the superior durability of the studied epoxy‐silica hybrid, which kept its performances in severe, but realistic, environmental conditions with respect to traditional epoxy adhesives. The reduction in the glass transition temperature and mechanical properties of the studied epoxy‐silica hybrid, observed in the first weeks of environmental aging, was followed by a significant recovery. This was attributed to two concomitant phenomena: the reactivation of the incomplete curing reactions in the epoxy domains and the continuation of the condensation reactions in the siloxane domains activated by the absorbed water. Finally, the Fickian behavior, presented by the studied epoxy‐silica hybrid, was used as an indirect indication of the homogeneity of achieved microstructure, with well dispersed silica nanostructures in the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40093.     

Surface chemistry and moisture sorption properties of wood coated with multifunctional alkoxysilanes by sol‐gel process

Sol‐gel surface deposition of a hydrophobic polysiloxane coating on wood was accomplished by using a mixture of a low molecular weight multifunctional alkoxysilane, methyltrimethoxysilane (MTMOS), and a high molecular weight multifunctional alkoxysilane, hexadecyltrimethoxysilane (HDTMOS). Investigation of the surface chemistry and morphology of the wood specimens by means of ATR–FTIR, energy‐dispersive X‐ray analysis, X‐ray photoelectron spectroscopy, SEM, and atomic force microscopy indicated that the sol‐gel process results in deposition of polysiloxane networks that are bonded to the wood by polycondensation with surface hydroxyl groups. The surface hydroxyl groups involved in the bonds appear to be located predominantly on the cellulose component of the wood. The sol‐gel deposit on the wood substrates lowered the rates of water and water vapor sorption. The low molecular weight MTMOS apparently penetrated the outer surface layers of the wood and condensed with hydroxyls that may not be readily accessible to the high molecular weight HDTMOS. Once attached to such sites, it is reasonable to assume that some of these surface derivatives of MTMOS condensed with other molecules of MTMOS and HDTMOS with a long hydrocarbon chain to form a polysiloxane network that is hydrophobic. The ultimate effect of the sol‐gel deposit can therefore be regarded as not only to decrease the surface concentration of hydrogen‐bonding sites, but also to stereochemically hinder the formation of hydrogen bonds between such sites and water molecules. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2828–2841, 2003     

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     

Modification of polyurethane‐coated fabrics by sol–gel thin films

Sol–gel derived silica and hybrid films from tetraethoxysilane (TEOS) and 3‐glycidyloxypropyltrimethoxysilane (GLYMO) were deposited by dip‐coating, in order to find the best treatment. GLYMO‐based treatments preserved textile feel of the material. The coatings were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and water contact angle measurement. IR spectra confirmed the existence of silicate network and successfully conducted modification for both precursors. DSC and TGA showed that the conditions of hydrolysis had greater influence on TEOS than GLYMO‐based treatments. Both treatments shifted the degradation onset to higher temperatures. SEM images showed that polyurethane surface and pores were completely covered and filled by silica or hybrid thin films forming a composite organic–inorganic coating. Hydrophobic effect was preserved for all the samples, except for a single treatment of the GLYMO, due to its polar epoxy group. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39914.     

Preparation and properties of organosoluble polyimide/silica hybrid materials by sol–gel process

Organosoluble polyimide/silica hybrid materials were prepared using the sol–gel process. The organosoluble polyimide was based on pyromellitic anhydride (PMDA) and 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane (MMDA). The silica particle size in the hybrid is increased from 100–200 nm for the hybrid containing 5 wt % silica to 1–2 µm for the hybrid containing 20 wt % silica. The strength and the toughness of the hybrids are improved simultaneously when the silica content is below 10 wt %. As the silica content is increased, the glass transition temperature (T_g) of the hybrids is increased slightly. The thermal stability of the hybrids is improved obviously and their coefficients of thermal expansion are reduced. The hybrids are soluble in strong polar aprotic organic solvents when the silica content is below 5 wt %. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2977–2984, 1999     

Molecular characterization of alkyd/acrylic latexes prepared by miniemulsion polymerization

The molecular characterization of alkyd/acrylic hybrid latexes produced by miniemulsion polymerization was characterized in terms of the resin degree of grafting, acrylic degree of grafting, reacted double bonds in the alkyd, gel content, and molecular weight distribution of the sol part. A simple method based on conventional size exclusion chromatography measurements was developed to estimate the fraction of alkyd resin grafted to the acrylic polymer. The method could be applied to completely soluble hybrids and to hybrids containing gel. Also, the limits of the extraction method used in the literature to estimate the fraction of acrylic polymer grafted to the alkyd was investigated; we found that this technique only provided accurate results at high values of the acrylic degree of grafting. The combination of this information with the reacted double bonds of the alkyd (determined by iodine titration) and the molecular weight distribution of the sol polymer provided a detailed characterization of the alkyd–acrylic hybrid polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of polychloroprene–silica composites by sol‐gel method in the presence of modified polychloroprene containing triethoxysilyl group

Triethoxysilyl‐modified polychloroprene (CR) latex was synthesized by the emulsion copolymerization of 2‐(3‐triethoxysilylpropyl)‐1,3‐butadiene with chloroprene. This latex was mixed with unmodified CR latex and tetraethoxysilane to obtain CR–silica composites by sol‐gel reaction in the latex. SEM observation showed that the silica particles in unvulcanized composites have various diameters ranging from 0.1 to 0.6 μ m, and their size became larger with the decrease of the silica content. Vulcanized CR–silica composites showed that the tensile modulus and tear strength improved with an increase of the amount of modified CR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1545–1552, 2005     

In situ sol‐gel process of polystyrene/silica hybrid materials: Effect of silane‐coupling agents

The polystyrene–silica hybrid materials have been successfully prepared from styrene and tetraethoxysilane in the presence of silane‐coupling agents by an in situ sol‐gel process. Triethoxysilyl group can be incorporated into polystyrene as side chains by the free‐radical copolymerization of polystyrene with silane‐coupling agents, and simultaneously polystyrene–silica hybrid materials with covalent bonds between two phases were formed via the sol‐gel reaction. The 3‐(trimethoxysilyl)‐propyl‐methacrylate (MPS) systems were found to be more homogeneous than the corresponding allytrimethoxysilane hybrid system of equal molar content. In the MPS‐introduced system, the thermal properties of the materials were greatly affected by the presence of MPS. FTIR results indicate successful formation of the silica networks and covalent bonding formation of coupling agents with styrene. The homogeneity of polystyrene–silica systems was examined by scanning electron microscope and atomic force microscope. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2074–2083, 2002     

Formation and structure of polyacrylamide–silica nanocomposites by sol–gel process

The formation of nanocomposites by the sol–gel reaction of tetraethoxysilane (TEOS) in polyacrylamide (PAAm) is studied. The nanocomposites are prepared in aqueous solution. Fourier transform IR spectroscopy shows that substantial hydrogen bonding occurs in the nanocomposites. The fracture surfaces of the nanocomposites are observed by atomic force microscopy (AFM) as a function of the TEOS content. The AFM images reveal that the PAAm–silica nanocomposite exhibits particle–matrix morphology. It is also found that aggregate formation is more dominant than the particle growth with the TEOS contents. The solution of composite precursor is also applied to spin coating. Furthermore, during the calcination there is an observable change in the silica networks, and then a microinterconnected structure is generated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1817–1823, 2002     

Preparation and characterization of acrylic resin/titania hybrid nanocomposite coatings by photopolymerization and sol–gel process

Titania‐containing coatings were prepared through a dual‐cure process involving radical photopolymerization of a polysiloxane diacrylate and subsequent condensation of alkyltitanate groups. The kinetics of photopolymerization and condensation reaction was investigated as a function of the inorganic phase precursor (titanium tetraisopropoxide) content. AFM analysis gave evidence of a strong interaction between the organic and inorganic phase with the formation of titania domains in the nanoscale region. An increase of hydrophilicity in the coatings surface with increasing TiO₂ content was evidenced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4659–4664, 2006     

硅溶胶／聚丙烯酸酯乳液型压敏胶的制备与性能

采用半连续加料乳液聚合方法制备了硅溶胶／聚丙烯酸酯核／壳结构聚合物,采用动态光散射方法跟踪了复合乳胶粒的粒径随反应进程的变化,其理论粒径与实测值基本一致,说明该聚合过程没有明显的二次成核过程。考查了壳层硬单体-甲基丙烯酸甲酯（MMA）含量对乳液聚合的影响,通过动态热机械分析仪（DMA）对聚合物的黏弹性能进行了表征,对制成的胶粘剂进行了压敏特性的测定,并与复合粒子的分子结构进行了关联。研究表明,随着MMA含量的增加,压敏胶的初粘性略有下降,而持粘性显著提高,剥离强度呈先升后降的趋势。     

Light‐curable composite of siloxane/hydroxyapatite prepared by the sol–gel process for bone defect treatment

The light‐curable composite of siloxane/hydroxyapatite (HA) had been successfully achieved by photopolymerization of a kind of gel combined tetraethoxyorthosilicate (TEOS) and 3‐methacryloxypropyltrimethoxysilane (MAPS) with siloxane‐modified nano‐HA (HA‐g‐Si). HA‐g‐Si was prepared by grafting reaction of 3‐isocyanatopropyltrimethoxysilane (IPS) onto the surface of HA. Then, TEOS and MAPS were mixed as precursor, and photoinitiator 2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone (Irgacure 2959) and as‐prepared HA‐g‐Si were added into the precursor to form a homogenous and sticky gel. The movable gel that could be cured with UV light resulted in various sharp immovable composites of siloxane/HA in different mold. The HA, HA‐g‐Si nanoparticles, and composites were analyzed by Fourier transformed infrared spectroscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, mechanical testing, and water contact angles. It could be a promising bone repairing material for orthopedic application. POLYM. COMPOS., © 2011 Society of Plastics Engineers.