Synthesis of a novel benzoxazine monomer‐intercalated montmorillonite and the curing kinetics of polybenzoxazine/clay hybrid nanocomposites

Polybenzoxazine (PBZ), which has a structure similar to that of phenolic resin, is formed through the thermal self‐curing of benzoxazine, that is through a heterocyclic ring opening reaction that requires no catalyst and releases no condensation byproducts. We have used the solvent blending method to prepare PBZ/clay nanocomposites possessing various clay contents. We synthesized a monofunctional benzoxazine monomer (MBM) and then treated the clay with this intercalation agent. The results of X‐ray diffraction (XRD) analysis indicated that MBM intercalated into the galleries of the clay; the nanocomposite possessed an exfoliated structure at 3% clay content. To better understand the curing kinetics of the PBZ/clay nanocomposites, we performed dynamic and isothermal differential scanning calorimetry (DSC) measurements. We describe the thermodynamics of the curing process, using all three of the Kissinger, Ozawa, and Kamal models. The Kissinger and Ozawa methods gave fairly close results for the calculated activation energies, which decreased upon increasing the clay content. The Kamal method, based on an autocatalytic model, suggested a total reaction order of between 2.4 and 2.8. The glass transition temperature (T_g) decreased upon increasing the clay content. Thermogravimetric analysis (TGA) indicated that the nanocomposites have higher decomposition temperatures than does the pristine PBZ; this finding suggests an enhancement in their thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 347–358, 2006     

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.     

Preparation and characterization of polyimide/pure silica zeolite hybrid films

In this study, amino derivative of pure silica zeolite nanocrystal (A‐PSZN) was dispersed into polyimide (PI) matrix to prepare PI/A‐PSZN hybrid films, and their thermal and mechanical properties, as well as hydrophobicity, were characterized scientifically. The test results show that PI/A‐PSZN hybrid films possess higher glass transition temperature, higher thermal stability and lower in‐plane coefficient of thermal expansion than pristine PI. The mechanical property data suggest that the incorporation of A‐PSZN results in an increase in Young's modulus and tensile strength of the hybrid films, but as its content exceeds the critical value (maybe 5 wt%), its enhancement effect on the hybrid's strength and toughness gets weaker. Furthermore, liquid dripping imaging analysis results indicate that the film's hydrophobicity is clearly improved by the introduction of A‐PSZN. As compared with PSZN, A‐PSZN exhibits better effect on enhancing the overall performance of pristine PI films. A comparison with other studies suggests that PI/A‐PSZN is a hybrid film with superior comprehensive properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Polyacrylate/silica hybrid materials: A step towards multifunctional properties

Organic/Inorganic hybrid systems present a promising alternative for the creation of high-performance materials due to their biphasic structure that imparts multifunctional properties. The sol-gel process which initiated with the synthesis of inorganic glasses has now become a synthetic route for organic-inorganic assemblies due to several advantages such as mild processing conditions and the freedom to play with the structures of precursors. This versatility of the low-temperature sol-gel process provides an opportunity to engineer both the phases resulting in a synergistic combination or entirely new set of properties fruitful for different applications. This review highlights the several pathways for synthesis of silica particles, the interfacial modification and the classification of hybrid materials based on the method of incorporation of an inorganic moiety in the organic matrix along with the structure-property relationship, and the characterization to develop a fundamental understanding of the process. The nature of bonding between the two different species greatly affects the hybrid nanostructure and thus, the bulk properties of the system. In particular, acrylate/silica system has been focused due to its distinctive properties such as transparency, gloss, and strength that find large-scale application in the field of coatings, plastics and rubbers.Abbreviations: °: Degree; °C: Degree Celsius; ¹H NMR: Proton nuclear magnetic resonance; A°: Angstrom; AHAS: N-(3-acryloxy-2-hydroxyl propyl)-3-amino-propyltriethoxysilane; AIBA: 2,2′-Azobis(2-methylpropionamidine) dihydrochloride; AIBN: 2,2′-Azobis(2-methylpropionitrile); Al: Aluminium; APDMES: Aminopropyldimethylethoxysilane; APTES: 3-Aminopropyltriethoxysilane; ATRP: Atom transfer radical polymerization; CERAMERS: Ceramically Modified Monomers; CTAB: Cetyltrimethylammonium bromide; DFMA: Dodecafluoroheptyl methacrylate; DMF: Dimethylformamide; DPSD: Diphenylsilanediol; FESEM: Field Emission Scanning Electron Microscope; FTIR: Fourier-transform infrared spectroscopy; GPTMS: 3-Glycidoxypropyltrimethoxysilane; HDTMS: Hexadecyltrimethoxysilane; HEMA: 2-Hydroxyethyl methacrylate; HLB: Hydrophilic-Lyophilic Balance; HMDS: Hexamethyldisilazane; HPC: Hydroxypropyl Cellulose; IPN: Interpenetrating Network; KPS: Potassium persulfate; LCST: Lower critical solution temperature; McPTMS: 3-Mercaptopropyltrimethoxysilane; MOI: 2-(methacryloyloxy)ethyl isocyanate; MPEGMA: Monomethoxy-capped poly(ethylene glycol) methacrylate; MPTMS: 3-methacryloxypropyltrimethoxysilane; MTC: 2-(methacryloyl) ethyltrimethylammonium chloride; MTES: Methyltriethoxysilane; MTMS: Methyltrimethoxysilane; NMP: Nitroxide-Mediated Polymerization; ORMOCERs: Organically Modified Ceramics; ORMOSILs: Organically Modified Silica; OTES: Octyltriethoxysilane; OTMS: Octadecyltrimethoxysilane; PAA: Poly(acrylic acid); PDMS: Polydimethylsiloxane; PEO-PPO-PEO: Poly (ethylene oxides)-b-poly (propylene oxides)-b-poly (ethylene oxides); PHPS: Perhydropolysilazane; PMMA: Poly(methyl methacrylate); POSS: Polyhedral Oligomeric Silsesquioxane; PTMO: Poly(tetramethylene oxide); PTMS: Phenyltrimethoxysilane; PTMS: Phenyltrimethoxysilane; PVP: Poly (vinylpyrrolidone); RAFT: Reversible addition- fragmentation chain transfer; Si: Silicon; Sn: Tin; Ta: Tantalum; TBN: 4-(triethoxysilyl)butyronitrile; TEM: Transmission Electron Microscopy; TEMED: N,N,N′,N′-tetramethylethylenediamine; TEOS: Tetraethoxysilane; Tg: Glass-Transition Temperature; THF: Tetrahydrofuran; Ti: Titanium; TMOS: Tetramethoxysilane; UV: Ultraviolet; VTES: Vinyltriethoxysilane; VTMS: Vinyltrimethoxysilane; Zr: Zirconium

• Highlights

• Advantages of hybrid systems over the conventional materials

• Discusses the fundamental aspects of sol-gel chemistry

• Focusses on a detailed classification of hybrid polymers

• Covers different synthetic strategies, properties, and applications in diverse fields

     

Preparation and properties investigation of PMMA/silica composites derived from silicic acid

Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

Amphiphilic silica/fluoropolymer nanoparticles: Synthesis,tem‐responsive and surface properties as protein‐resistance coatings

A series of amphiphilic silica/fluoropolymer nanoparticles of SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) were prepared by silica surface‐initiating atom transfer radical polymerization (SI‐ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and poly dodecafluoroheptyl methacrylate (P12FMA). Their amphiphilic behavior, lower critical solution temperature (LCST), and surface properties as protein‐resistance coatings were characterized. The introduction of hydrophobic P(12FMA) block leads SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) to form individual spherical nanoparticles (～150 nm in water and ～170 nm in THF solution) as P(PEGMA)‐b‐P(12FMA) shell grafted on SiO₂ core (～130 nm), to gain obvious lower LCST at 36–52 °C and higher thermostability at 290–320 °C than SiO₂‐g‐P(PEGMA) (LCST = 78–90 °C, T_d = 220 °C). The water‐casted SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) films obtain much rougher surface (125.3–178.4 nm) than THF‐casted films (11.5–16.9 nm) and all SiO₂‐g‐P(PEGMA) films (26.8–31.3 nm). Therefore, the water‐casted surfaces exhibit obvious higher water adsorption amount (Δf = ?494 ～ ?426 Hz) and harder adsorbed layer (viscoelasticity of ΔD/Δf = ?0.28 ～ ?0.36 × 10^?6/Hz) than SiO₂‐g‐P(PEGMA) films, but present loser adsorbed layer than THF‐casted films (ΔD/Δf = ?0.29 ～ ?0.63 × 10^?6/Hz). While, the introduction of P(12FMA) segments does not show obviously reduce in the protein‐repelling adsorption of SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) films (△f = ?15.7 ～ ?22.3 Hz) compared with SiO₂‐g‐P(PEGMA) films (△f = ?8.3 ～ ?11.3 Hz) and no obvious influence on water adsorption of ancient stone. Therefore, SiO₂‐g‐P(PEGMA)‐b‐P(12FMA) is suggested to be used as protein‐resistance coatings. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 381–393     

Rice husk silica as a sustainable filler in the tire industry

In this paper, we studied commercially available precipitated rice husk silica (RHS) with conventional precipitated silica, which has nearly the same surface area, and replaced part of the carbon black with RHS and conventional silica in a basic tread formulation. All formulations were mixed with the same amount of filler during the study. Silica was used at 15, 30 and 50 phr loading, and part of the carbon black was replaced by silica. Compound curing characteristics, physical properties, rebound resilience, heat generation, abrasion loss, dynamic properties and morphology were analyzed. The results indicated that RHS demonstrated compound properties comparable to those of conventional silica. As part of the carbon black was replaced with conventional silica, a slower cure rate, higher rebound resilience, lower heat generation, lower abrasion loss, and lower tan delta were observed with no significant change in physical properties, but some changes in physical properties were observed using one way ANOVA analysis. We found the same trend when replacing part of the carbon black with RHS, such as a slower cure rate, higher rebound resilience, lower heat generation, lower abrasion loss, and lower tan delta with no significant change in physical properties, but some changes in physical properties were observed using one way ANOVA. This sustainable material could be used to replace conventional silica in tire compounding, as well as to replace a portion of carbon black with RHS for improved heat build-up, rolling resistance, and abrasion loss.     

Effects of incorporation of modified silica nanoparticles on the mechanical and thermal properties of PMMA

Silica nanoparticles of various sizes have been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA) matrix to enhance its thermal and mechanical properties. In order to improve nanoparticles dispersion, PMMA grafted particles have been prepared by atom transfer radical polymerization (ATRP) from well-defined silica nanoparticles. This strategy was expected to ensure compatibility between both components of the PMMA nanocomposites. TEM analysis have been performed to evaluate the nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites thermal stability and mechanical properties have been investigated by both thermogravimetric and dynamical mechanical analysis.     

Thermooxidative stability of polymethyl methacrylate containing nanoparticles of silica/titania and silica/zirconia

The influence of silica/titania and silica/zirconia nanoparticles on thermooxidative degradation of PMMA was studied by non-isothermal thermogravimetry. Kinetic parameters describing the length of the oxidation induction periods were obtained from the treatment of the dependence of oxidation onset temperature on heating rate. Using these parameters, the protection factors of nanoparticles have been calculated. It was found that SiO₂/TiO₂ nanoparticles increase the thermooxidation stability of PMMA where the stabilizing effect, expressed as the protection factor, depends on temperature only slightly. The stabilizing effect of SiO₂/ZrO₂ is much stronger than that of SiO₂/TiO₂ and decreases with increasing temperature.     

P(VPBA-DMAEA) as a pH-sensitive nanovalve for mesoporous silica nanoparticles based controlled release

A pH-sensitive controlled release system was proposed in this work, which consists of mesoporous silica nanoparticles(MSNs) functionalized on the pore outlets with poly(4-vinylphenybronic acid-co-2-(dimethylamino)ethyl acrylate) [P(VPBA-DMAEA)]. Four kinds of P(VPBA-DMAEA)-gated MSNs were synthesized and applied for the p H-sensitive controlled release. The results showed that P(VPBADMAEA) can work as a p H-sensitive nanovalve. The release behavior of the hybrid nanoparticles could be adjusted by changing the mole ratio of VPBA and DMAEA. With the increasing of the mole ratio of VPBA,the leakage of the entrapped molecules in the pores of MSNs could be decreased at neutral and alkaline conditions. By altering the p H of buffer from 4.0 to 8.0, the valve could be switched ‘‘on' and ‘‘off'reversibly. In addition, cells viability results indicated that these P(VPBA-DMAEA)-gated MSNs had good biocompatibility. We believe that these MSNs based p H-sensitive controlled release system will provide a promising nanodevice for sited release of drug delivery.     

Thermoresponsive PNIPAM/silica nanoparticles by direct photopolymerization in aqueous media

This article presents a simple and facile method to fabricate thermoresponsive polymer‐grafted silica particles by direct surface‐initiated photopolymerization of N‐isopropylacrylamide (NIPAM). This method is based on silica particles bearing thiol functionalities, which are transformed into thiyl radicals by irradiation with UV light to initiate the polymerization of NIPAM in aqueous media at room temperature. The photopolymerization of NIPAM could be applied to smaller thiol‐functionalized particles (～48 nm) as well as to larger particles (～692 nm). Hollow poly(NIPAM) capsules could be formed after etching away the silica cores from the composite particles. It is possible to produce tailor‐made composite particles or capsules for particular applications by extending this approach to other vinyl monomers. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015 , 53, 1260–1267     

Palladium nanoparticles supported on poly (N-vinylpyrrolidone)-grafted silica as new recyclable catalyst for Heck cross-coupling reactions

Novel catalytic system based on palladium nanoparticles supported on poly (N-vinylpyrrolidone) (PVP) grafted silica was prepared. Aminopropylsilica was reacted with acryloyl chloride to form acrylamidopropylsilica, and onto this functionalized silica vinylpyrrolidone monomer was polymerized by free-radical polymerization. The complexation of PVP-grafted silica with PdCl₂ was carried out to obtain the heterogeneous catalytic system. X-ray diffraction (XRD) technique and transmission electron microscopy (TEM) image showed that palladium dispersed through the support in nanometer size. This catalytic system exhibited excellent activity in cross-coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck-Mizoraki reactions in short reaction time and high yields. Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hot filtration test showed low leaching of the metal into solution from the supported catalyst. The catalyst can be reused several times in repeating Heck reaction cycles without considerable loss in its activity.     

Effect of silica nanoparticles/poly（vinylidene fluoride-hexafluoropropylene） coated layers on the performance of polypropylene separator for lithium-ion batteries

In an effort to reduce thermal shrinkage and improve electrochemical performance of porous polypropylene （PP） separators for lithium-ion batteries, a new composite separator is developed by introducing ceramic coated layers on both sides of PP separator through a dip-coating process. The coated layers are comprised of heat-resistant and hydrophilic silica nanoparticles and polyvinylidene fluoride-hexafluoropropylene （PVDF-HFP） binders. Highly porous honeycomb structure is formed and the thickness of the layer is only about 700 nm. In comparison to the pristine PP separator, the composite separator shows significant reduction in thermal shrinkage and improvement in liquid electrolyte uptake and ionic conduction, which play an important role in improving cell performance such as discharge capacity, C-rate capability, cycle performance and coulombic efficiency.     

Novel inorganic morphologies formed in polyimide/silica hybrid films

2-(4-Aminophenyl)-5-aminobenzimidazole was used to prepare polyimide/silica hybrid films via sol-gel process. At 40 wt.% silica content, hybrid films were still translucent. No noticeable silica particle has been observed. Unexpectedly, after treating at 800 °C, novel morphologies of silica were observed on the surface of inorganic films, which changed from homogeneous to sea-island and to co-continuous structure with increasing silica content in the matrix. Hydrogen bonding between NH in imidazole and silanol group results that silica tends to linear structures, which is considered as the main reason for this morphological change.     

Synthesis and characterization of positively charged,alumina‐coated silica/polystyrene hybrid nanoparticles via pickering miniemulsion polymerization

Positively charged, raspberry‐like hybrid nanoparticles, consisting of a polystyrene core and an alumina‐coated silica shell were successfully prepared in a surfactant free system via the radical copolymerization of styrene (St) and different comonomers (acrylic acid, methacrylic acid, and acrylamide) by using a cationic silica sol as the sole emulsifier in Pickering miniemulsion polymerization. The influence of different parameters like pH of the dispersion, comonomer content, and the amount and size of silica nanoparticles on the colloidal stability of the systems, prepared with different comonomers, was examined. The particles' morphology was observed via high‐resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The removal of free silica particles via centrifugation was proved by TEM and SEM, and the content of free and adsorbed silica was quantified via thermogravimetric analysis (TGA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

POSS nanoparticles as a potential compatibilizer for natural rubber/butadiene rubber blends

In this study, it was aimed to investigate octavinyl‐polyhedral oligomeric silsesquioxane (OV‐POSS) incorporation into natural rubber (NR)/butadiene rubber (BR) elastomer blends as a potential compatibilizer. The effects of OV‐POSS loading levels on the thermal, mechanical, morphological, and dynamic‐mechanical properties of elastomer blends were explored. Fourier‐Transform Infrared Spectrometer (FTIR), Temperature Scanning Stress Relaxation (TSSR), and Differential Scanning Calorimetry (DSC) results revealed the conceivable effect of OV‐POSS nanoparticles in the vulcanization through reacting with sulfur and/or elastomers. Scanning Electron Microscope (SEM), X‐Ray Diffraction (XRD), and tensile test measurements supported the improvement of mechanical properties due to homogeneous dispersion at low loading levels. On the other hand, high amount of OV‐POSS incorporation (7 and 10 phr) resulted in a decrease in mechanical properties, owing to the agglomeration of nanoparticles. According to contact angle and Dynamic mechanical analysis (DMA) results, it could be concluded that OV‐POSS nanoparticles were localized at the interface of the elastomers and enabled the compatibilization of immiscible NR/BR blends.     

Polymer–filler interactions in sol–gel derived polymer/silica hybrid nanocomposites

The effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a₁ϕ, where a₁ was a constant and b₁ was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a₂ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005     

The flow-through silica as the matrix to immobilize gold nanoparticles for HPLC applications

In the present study, the flow-through silica, featured with hierarchical pores, i.e., tunable mesopores and penetrable macropores, was attempted as the chromatographic stationary phase matrix to immobilize gold nanoparticles (AuNPs). It was first modified by mercapto groups (named as SiO₂-SH), and then by AuNPs (named as SiO₂-S-Au). Thanks to the characteristic macropores, the column backpressure of SiO₂-S-Au was comparable to SiO₂-SH, which effectively overcame the difficulty of high column backpressure upon the nanoparticles were introduced to the chromatographic matrix. Both the reversed-phase and hydrophilic interaction liquid chromatographic performance were observed on these two columns but with different selectivities. Hydrophobic, hydrophilic, hydrogen bond and electrostatic interactions between the SiO₂-S-Au stationary phase and analytes could contribute to the retention. The SiO₂-S-Au column showed excellent aqueous compatibility by “Stop-flow” test with the relative standard deviations (RSD) of analyte’s k (capacity factor) values from 0.59% to 2.88%. The reproducibility of SiO₂-S-Au was acceptable with RSDs of analyte’s k values in the range of 3.13%-5.03%. In addition, compared with the SiO₂-SH column, the SiO₂-S-Au column had better separation performance and selectivity. The results demonstrated that the flow-through silica was a promising matrix for nanoparticles with low backpressure and different selectivities.