Preparation and properties of polyimide/silica hybrid nanocomposites

In this study, a commercially available nano‐sized silica (SiO₂) was surface‐modified via esterification with oleic acid (OA), a relatively inexpensive and hydrophobic modifier. The surface‐modified silica (SiO₂‐OA) nanoparticles were used to disperse in the poly(amic acid) solutions of a commercial polyimide (PI), used for two‐layer film, and thermally imidized to form a series of PI/silica nanocomposites. The effects of the addition of SiO₂‐OA nanoparticles on the properties of the as‐prepared PI/silica nanocomposites were studied. The results indicated that the as‐prepared PI/silica nanocomposites exhibited improvements in the dynamic mechanical property, thermal stability, water resistance, and thermal expansion. POLYM. COMPOS. 28:575–581, 2007. © 2007 Society of Plastics Engineers     

Preparation and characterization of silica/polyimide nanocomposite films based on water‐soluble poly(amic acid) ammonium salt

In this article, a series of new silica/polyimide (SiO₂/PI) nanocomposite films with high dielectric constant (>4.0), low dielectric loss (<0.0325), high breakdown strength (288.8 kV mm⁻¹), and high volume resistivity (2.498 × 10¹⁴ Ω m) were prepared by the hydrolysis of tetraethyl orthosilicate in water‐soluble poly(amic acid) ammonium salt (PAAS). The chemical structure of nanocomposite films compared with the traditional pure PI was confirmed by Fourier transform infrared spectroscopy and X‐ray diffraction patterns. The results indicated that both the PAAS and the polyamide acid (PAA) material were effectively converted into the corresponding PI material through the thermal imidization and the amorphous SiO₂ was embedded in the nanocomposite films without structural changes. Thermal stability of the nanocomposite films was increased though mechanical property was generally decreased with increasing the mass fraction of SiO₂. All the nanocomposite films exhibited an almost single‐step thermal decomposition behavior and the average decomposition temperature was about 615°C. It was concluded that the effective dispersion of SiO₂ particles in PI matrix vigorously improved the comprehensive performance of the SiO₂/PI nanocomposite films and expanded their applications in the electronic and environment‐friendly industries. POLYM. COMPOS., 38:774–781, 2017. © 2015 Society of Plastics Engineers     

Dielectric and conduction properties of polyimide/silica nano‐hybrid films

Dielectric and conduction properties of polyimide/silica nano‐hybrid films were investigated with the silica content and the testing frequency, using a small electrode system. The hybrid films were prepared through sol‐gel process and thermal imidization, by using pyromellitic dianhydride and 4,4′‐oxydianiline as polyimide precursors, and tetraethoxysilane and methyltriethoxysilane as silica precursors. The dielectric coefficient of PI/SiO₂ films was monotonically increased with increasing silica content, and decreased with increasing testing frequency. The dielectric loss of PI/SiO₂ films had no obvious changes with increasing silica content, but monotonically increased with increasing testing frequency. These can be contributed to the different quantity and migration chunnels of current carriers, which were mainly influenced by a few of complicated factors. There were remarkable differences between conduction property of PI/TEOS‐SiO₂ films and PI/MTEOS‐SiO₂ films because of the different size and dispersion status of silica particles in the polyimide matrix. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation and properties of polyimide/silica hybrid composites based on polymer‐modified colloidal silica

A new type of polyimide/silica (PI/SiO₂) hybrid composite films was prepared by blending polymer‐modified colloidal silica with the semiflexible polyimide. Polyimide was solution‐imidized at higher temperature than the glass transition temperature (T_g) using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organic–inorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both T_g and thermal stability of the resulting films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2053–2061, 2006     

Structure and dielectric properties of polyimide/silica nanocomposite nanofoam prepared by solid‐state foaming

In this article, polyimide (PI)/silica nanocomposite nanofoams were prepared by solid‐state foaming using supercritical CO₂ as foaming agent. To control the cell size and morphology of the PI/silica foam, the silica nanoparticles as nucleating agent were in situ formation from TEOS via sol‐gel process, which make the silica nanoparticles homogeneously dispersed in PI matrix. The resulting PI/silica nanocomposite nanofoams were characterized by scanning electron microscopy (SEM), the image analysis system attached to the SEM and dielectric properties measurements. In PI/silica nanocomposite nanofoams, one type of novel morphology was shown that each cell contained one silica nanoparticle and many smaller holes about 20–50 nm uniformly located in the cell wall. This special structure could visually prove that the nucleation sites during foaming were formed on the surface of nucleating agents. Compared with those of neat PI foam, the cell size of PI/silica nanocomposite nanofoams was smaller and its distribution was narrower. The dielectric constant of PI/silica nanocomposite nanofoams was decreased because of the incorporation of the air voids into the PI/silica nanofoams. While the porosity of PI/silica nanocomposite nanofoam film was 0.45, the dielectric constant of the film (at 1 MHz) was reduced from 3.8 to about 2.6. Furthermore, the dielectric constant of PI/silica nanofoam films remained stable across the frequency range of 1×10²～1×10⁷ H_Z. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42355.     

Effects of water on the preparation,morphology, and properties of polyimide/silica nanocomposite films prepared by sol–gel process

Polyimide/silica (PI/SiO₂) nanocomposite films with 10 wt % of silica content were prepared by sol–gel process under the conditions with and without additional water. The presence of additional water has great effect on the silica particle size and thus on the properties of the prepared PI/SiO₂ films. The results indicated that with additional water, the silica particles formed before the imidization of poly(amic acid) (PAA) and aggregated with the increasing of temperature and degree of the proceeding imidization process. For the nonaqueous process, the hydrolysis condensation reaction of tetraethoxysilane (TEOS) did not occur until the imidization of PAA took place, and no silica particles were found in the unimidized PAA films. The hydrolysis–condensation reaction of TEOS was initiated simultaneously by the trace water released from the imidization reaction, the self‐catalysis mechanism of the approach provide a means of achieving uniformly dispersed silica particles formed in the PI matrix with particle size in the range of 30–70 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1579–1586, 2007     

Preparation of poly(acrylamide‐co‐acrylic acid)/silica nanocomposite microspheres and their performance as a plugging material for deep profile control

In this work, poly(acrylamide‐co‐acrylic acid)/silica [poly(AM‐co‐AA)/SiO₂] microspheres were prepared by inverse phase suspension polymerization in the presence of γ‐3‐(trimethoxysilyl) propyl methacrylate (or 3‐methacryloxypropyltrimethoxysilane) modified SiO₂. The effects of SiO₂ nanoparticles on tuning morphology and properties of the nanocomposite microspheres were studied. Plugging ability and oil displacement performance were also systematically investigated by single‐ and double‐tube sand pack models. The results showed that SiO₂ nanoparticles can effectively adjust surface smoothness, swelling behavior, and thermal stability of the nanocomposite microspheres. Compared with pure copolymer microspheres, these nanocomposite microspheres also displayed better salt tolerance and shear resistance. Such multifunctional nanocomposite microspheres can provide effective plugging in the high‐permeability channels and can also achieve deep profile control. The highest plugging rate can be 86.11% and the oil recovery for low‐permeability tube was enhanced by 19.69%. This research will provide a candidate material for the further enhanced oil recovery (EOR) research and supply the theoretical support for profile control system in field application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45502.     

Mechanochemical modification of silica with poly(1‐vinyl‐2‐pyrrolidone) by grinding in a stirred media mill

The polymerization of 1‐vinyl‐2‐pyrrolidone (VP) mechanochemically initiated by grinding silica was investigated in a wet stirred media mill. The polymerization itself proceeds from the silica grinding without any additional initiator. We have found that the amount of grafted polymer increases with an increase in total ground silica surface. The suspension of polymer‐modified silica nanoparticles showed high colloidal stability in water because of the appearance of grafted hydrophilic PVP on the surface during the reactive grinding. Because the nanoparticles SiO₂‐graft‐PVP are biocompatible, the developed polymer nanocomposite material can be of particular interest for the performance of membranes and for the fabrication of biocompatible hydrogels with enhanced mechanical properties and porosity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3708–3714, 2007     

Synthesis and characterization of core‐shell SiO2 nanoparticles/poly(3‐aminophenylboronic acid) composites

SiO₂/Poly(3‐aminophenylboronic acid) (PAPBA) composites were synthesized under different experimental conditions, using ultrasonic irradiation method. Polymerization was carried out in the presence of sodium fluoride and D ‐fructose to anchor 3‐aminophenylboronic acid groups on to SiO₂ surface. The SiO₂/PAPBA nanocomposite prepared by NaF and D ‐fructose in the polymerization medium was found to show different morphology, electrical properties, thermal behavior and structural characterization in comparison to the nanocomposites prepared under other conditions. Ultrasonic irradiation minimizes the aggregation of nanosilica and promotes anchoring of PAPBA units over SiO₂ surface. The morphology of PAPBA/ SiO₂ nanocomposite was investigated by using transmission electron microscopy, UV‐visible spectroscopy; thermogravimetric analysis, Fourier transform infrared spectroscopy, and X‐ray diffraction analysis were used for characterization. Transmission electron microscope of the nanocomposites observation shows that SiO₂/PAPBA composite, prepared with D ‐fructose and NaF under ultrasonication has a core–shell morphology. The thermal and crystalline properties of core‐shell SiO₂/PAPBA nanocomposite was prepared via ultrasonication method is different from the SiO₂/PAPBA nanocomposite prepared via conventional stirring method, in which SiO₂ nanoparticles are submerged in PAPBA. Conductivity of the composite prepared via ultrasonication shows around 0.2 S/cm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2743–2750, 2007     

PMMA‐grafted‐silica/PVC nanocomposites: Mechanical performance and barrier properties

Poly(vinyl chloride) (PVC)/SiO₂ nanocomposites were prepared via melt mixture using a twin‐screw mixing method. To improve the dispersion degree of the nanoparticles and endow the compatibility between polymeric matrix and nanosilica, SiO₂ surface was grafted with polymethyl methacrylate (PMMA). The interfacial adhesion was enhanced with filling the resulting PMMA‐grafted‐SiO₂ hybrid nanoparticles characterized by scanning electron microscopy. Both storage modulus and glass transition temperature of prepared nanocomposites measured by dynamic mechanical thermal analysis were increased compared with untreated nanosilica‐treated PVC composite. A much more efficient transfer of stresses was permitted from the polymer matrix to the hybrid silica nanoparticles. The filling of the hybrid nanoparticles caused the improved mechanical properties (tensile strength, notched impact strength, and rigidity) when the filler content was not more than 3 wt %. Permeability rates of O₂ and H₂O through films of PMMA‐grafted‐SiO₂/PVC were also measured. Lower rates were observed when compared with that of neat PVC. This was attributed to the more tortuous path which must be covered by the gas molecules, since SiO₂ nanoparticles are considered impenetrable by gas molecules. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of polyimide/silica hybrid nanocomposites

Polyimide/silica (PI/SiO₂) hybrid nanocomposites were prepared by the sol‐gel process directly from a soluble polyimide. This soluble PI was synthesized from a diamine with a pendant phenyl hydroxyl group, 4,4′‐diamino‐4″‐hydroxy triphenyl methane (DHTM) and a dianhydride, pyromellitic dianhydride (PMDA), followed by cyclodehydration. Three ways of preparing PI/SiO₂ hybrid nanocomposites were investigated in this study. Two of them used the coupling agent 3‐glycidyloxy propyl trimethoxysilane (GPTMOS) to enhance the compatibility between PI and silica. The coupling agent can react with the PI to form covalent bonds. The structures of the modified hybrid nanocomposites were identified with a FTIR, whereas the size of the silica in polyimides was characterized with a scanning electron microscope. The size of silica particles in the modified system was <100 nm. The covalently bonded PI/SiO₂ hybrid nanocomposites prepared by the novel third approach exhibited good transparency when the silica content was <15%. Moreover, their thermal and mechanical properties exhibited a significant improvement. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 382–393, 2004     

Thermal properties and morphology of a poly(vinyl alcohol)/silica nanocomposite prepared with a self‐assembled monolayer technique

A poly(vinyl alcohol) (PVA)/silica (SiO₂) nanocomposite was prepared with a novel self‐assembled monolayer technique, and its morphology and thermal properties were studied with different material characterization instruments. The treated SiO₂ nanoparticles were dispersed in the PVA matrix homogeneously, and the thermal properties of the nanocomposite were markedly improved in comparison with those of pure PVA. Under the same isothermal heating conditions, the decomposition of the nanocomposite was delayed significantly in comparison with that of PVA. The thermal degradation of the nanocomposite was a two‐step reaction, including the degradation of the side chain and main chain. The products of side‐chain degradation were mainly carboxylic acid, whereas main‐chain degradation primarily produced carbon dioxide and low‐molecular‐weight conjugated polyene. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1436–1442, 2005     

Synthesis and characterization of nanocomposite of polyimide–silica hybrid from nonaqueous sol–gel process

Polyimide–silica (PI–SiO₂) hybrids with a nanostructure was obtained using the nonaqueous sol–gel process by polycondensation of phenyltriethoxysilane in a polyamic acid solution. Self‐catalyzed hydrolysis of phenyl‐substituted akoxysilane and modification on the polyimide structure are applied and result in highly compatible PI–SiO₂ hybrids. Transparent PI–SiO₂ with a high silica content of about 45% was thus obtained. The prepared PI–SiO₂ films were characterized by infrared spectrometry, ²⁹Si‐NMR, thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. These characterizations showed the silica influence on the properties of the hybrid. The thermal expansion coefficient of the PI–SiO₂ and the temperature correlation were also established for probing the potential for application. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1609–1618, 2000     

Preparation and properties of poly[styrene‐co‐(butyl acrylate)‐co‐(acrylic acid)]/silica nanocomposite latex prepared using an acidic silica sol

BACKGROUND: Polyacrylate/silica nanocomposite latexes have been fabricated using blending methods with silica nanopowder, in situ polymerization with surface‐functionalized silica nanoparticles or sol–gel processes with silica precursors. But these approaches have the disadvantages of limited silica load, poor emulsion stability or poor film‐forming ability. RESULTS: In this work, poly[styrene‐co‐(butyl acrylate)‐co‐(acrylic acid)] [P(St‐BA‐AA)]/silica nanocomposite latexes and their dried films were prepared by adding an acidic silica sol to the emulsion polymerization stage. Morphological and rheological characterization shows that the silica nanoparticles are not encapsulated within polymer latex particles, but interact partially with polymer latex particles via hydrogen bonds between the silanol groups and the ? COOH groups at the surface of the polymer particles. The dried nanocomposite films have a better UV‐blocking ability than the pure polymer film, and retain their transparency even with a silica content up to 9.1 wt%. More interestingly, the hardness of the nanocomposite films increases markedly with increasing silica content, and the toughness of the films is not reduced at silica contents up to 33.3 wt%. An unexpected improvement of the solvent resistance of the nanocomposite films is also observed. CONCLUSION: Highly stable P(St‐BA‐AA)/silica nanocomposite latexes can be prepared with a wide range of silica content using an acidic silica sol. The dried nanocomposite films of these latexes exhibit simultaneous improvement of hardness and toughness even at high silica load, and enhanced solvent resistance, presumably resulting from hydrogen bond interactions between polymer chains and silica particles as well as silica aggregate/particle networks. Copyright © 2009 Society of Chemical Industry     

Fabrication of highly refractive barium‐titanate‐incorporated polyimide nanocomposite films with high permittivity and thermal stability

Crystalline nanoparticles of barium titanate (BT) are incorporated into polyimide (PI) to fabricate highly refractive, anti‐UV‐degradable nanocomposite films with high permittivity and thermal stability. For homogeneous incorporation of BT nanoparticles into the PI matrix, the BT nanoparticles are surface modified by phthalimide with the aid of a silane coupling agent as a scaffold. The PI nanocomposites are prepared by in situ polymerization in which a diphthalic anhydride and a diamine are used to form the PI matrix in the presence of the surface‐modified nanoparticles. The refractive index of the transparent nanocomposite films reaches 1.85 at a nanoparticle content of 59 vol% with a high dielectric constant of ε = 37 and thermal stability up to 460 °C. Copyright © 2012 Society of Chemical Industry     

Synthesis and physicochemical investigation of imide-functionalized silica nanocomposites

The incorporation of inorganic nanoparticles into polymers have gained significant attention to improving functional properties. The ultimate nanocomposite behaviors are influenced by many parameters, such as microstructural distribution that are produced during the treatment process. Herein, a hybrid material integrating a modified network into a polyimide PI matrix was produced via the sol–gel method by the reaction of pyromellitic dianhydride, 4, 4-oxydianaline, and 1, 5-diaminonaphthalene to synthesize copolyimides nanocomposite. The modified polyimide and unmodified polyimide silica (SiO₂) nanoparticles were incorporated in the polyimide matrix to have polyimide silica nanocomposite. In modified silica nanoparticles, 3-aminopropyltriethosilane was introduced to have better compatibility among inorganic–organic hybrid with similar chemical contact due to their flexible alkyl group. The surface morphology or structure of silica and polyimide was affirmed by scanning electron microscopy, Fourier transforms infrared spectroscopy confirmed the synthesis of pure polyimide, unmodified polyimide, and modified polyimide silica via presence and absence of certain peaks. Thermogravimetric analysis (TGA) results showed high thermal stability of nanocomposites as silica content increases. In contrast to unmodified silica, the modified silica provides more thermal stability to the nanocomposites. Dynamic mechanical analysis was used to investigate the tensile stress of pure polyimide, unmodified, and modified silica nanocomposites. Thermal stability, storage modulus, and moisture absorption of these hybrid materials were improved with silica nanoparticles. The TG mass spectrum confirms the successful synthesis of modified silica networks. The substituted silica nanoparticles show higher mechanical toughness and storage in modified compared to unmodified silica nanocomposite, which exhibits stronger binding attraction between silica nanoparticles and polyimide matrix.     

Preparation of poly(methyl methacrylate)‐Silica nanoparticles via differential microemulsion polymerization and physical properties of NR/PMMA‐SiO2 hybrid membranes

Poly(methy methacrylate) (PMMA)‐SiO₂ nanoparticles were prepared via differential microemulsion polymerization. The effects of silica loading, surfactant concentration, and initiator concentration on monomer conversion, particle size, particle size distribution, grafting efficiency, and silica encapsulation efficiency were investigated. A high monomer conversion of 99.9% and PMMA‐SiO₂ nanoparticles with a size range of 30 to 50 nm were obtained at a low surfactant concentration of 5.34 wt% based on monomer. PMMA‐SiO₂ nanoparticles showed spherical particles with a core‐shell morphology by TEM micrographs. A nanocomposite membrane from natural rubber (NR) and PMMA‐SiO₂ emulsion was studied for mechanical and thermal properties and pervaporation of water‐ethanol mixtures. PMMA‐SiO₂ nanoparticles which were uniformly dispersed in NR matrix, significantly enhanced mechanical properties and showed high water selectivity in permeate flux. Thus, the NR/PMMA‐SiO₂ hybrid membranes have great potential for pervaporation process in membrane applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

PES/SiO2 nanocomposite by in situ polymerization: Synthesis,structure, properties,and new applications

SiO₂ nanoparticles of a quantum size (15 nm or less) were prepared via sol–gel method using tetraethylorthosilicate as a precursor. SiO₂ nanoparticles were characterized by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) analyses. Polyethersulfone/silica (PES/SiO₂) crystal structure nanocomposite was prepared by in situ polymerization using silica nanoparticles as reinforcement filler. The polymerization reaction was done at 160°C in paraffin bath in the presence of diphenolic monomers. XRD and FESEM analyses were used to study the morphology of the synthesized nanocomposite. The purity and thermal property of the PES/SiO₂ nanocomposite were studied by energy dispersion of X‐ray analysis and differential scanning calorimetry, respectively. The effect of silica particles on the hydrophilicity of PES/SiO₂ nanocomposite was also investigated. It was showed that the PES/SiO₂ nanocomposite had a higher swelling degree when compared with the pure PES. The synthesized PES/SiO₂ powder was used to remove Cu(II) ions from its aqueous solution. The effect of experimental conditions such as pH, shaking time, and sorbent mass on adsorption capacity of PES/SiO₂ nanocomposite were investigated. It was found that incorporation of a low amount of silica (2 wt%) into the polymer matrix caused the increase of the Cu(II) ions adsorption capacity of PES. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Preparation and properties of polylactide–silica nanocomposites

Poly(lactic acid) (PLA)/SiO₂ nanocomposites were prepared via melt mixing with a Haake mixing method. To improve the dispersion of nanoparticles and endow compatibility between the polymer matrix and nanosilica, SiO₂ was surface‐modified with oleic acid (OA). The interfacial adhesion of the PLA nanocomposites was characterized by field‐emission scanning electron microscopy. The storage modulus and glass‐transition temperature values of the prepared nanocomposites were measured by dynamic mechanical thermal analysis. The linear and nonlinear dynamic rheological properties of the PLA nanocomposites were measured with a parallel‐plate rheometer. The effects of the filling content on the dispersability of the OA–SiO₂ nanoparticles in the PLA matrix, the interface adhesion, the thermomechanical properties, the rheological properties, and the mechanical properties were investigated. Moreover, the proper representation of the oscillatory viscometry results provided an alternative sensitive method to detect whether aggregation formed in the polymeric nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphologies and properties of epoxy resin/layered silicate–silica nanocomposites

A new nanofiller containing layered organo‐modified montmorillonite (oMMT) and spherical silica (SiO₂) was prepared by an in situ deposition method and coupling agent modification. Fourier transform infrared spectrometry, X‐ray diffraction and transmission electron microscopy show that there are interactions between oMMT and SiO₂, and the spherical SiO₂ particles are self‐assembled on the edge of oMMT layers, forming a novel layered–spherical nanostructure. An epoxy resin (EP)/oMMT–SiO₂ nanocomposite was obtained by adding oMMT–SiO₂ to EP matrix. Morphologies and mechanical and thermal properties of the new ternary nanocomposite were investigated. For purposes of comparison, the corresponding binary nanocomposites, i.e., EP modified with either oMMT or SiO₂, were also tested. The results for the mechanical properties show that oMMT obviously improves the strength of EP, and SiO₂ enhances the toughness of EP, but oMMT–SiO₂ exhibits a synergistic effect on toughening and reinforcing of EP. The toughening and reinforcing mechanism is explained by scanning electron microscopy. In addition, the thermal resistance of EP/oMMT–SiO₂ is better than that of EP/SiO₂, but it is worse than that of EP/oMMT. Copyright © 2006 Society of Chemical Industry