Preparation and characterization of epoxy/polyhedral oligomeric silsesquioxane hybrid nanocomposites

We have prepared epoxy/polyhedral oligomeric silsesquioxane (POSS) nanocomposites by photopolymerization from octakis(glycidylsiloxy)octasilsesquioxane (OG) and diglycidyl ether of bisphenol A. We used nuclear magnetic resonance, Raman, and Fourier transform infrared spectroscopies to characterize the chemical structure of the synthetic OG. Differential scanning calorimetry and dynamic mechanical analysis (DMA) revealed that the nanocomposites possessed higher glass transition temperatures than that of the pristine epoxy resin. Furthermore, DMA indicated that all of the nanocomposites exhibited enhanced storage moduli in the rubbery state, a phenomenon that we ascribe to both the nano‐reinforcement effect of the POSS cages and the additional degree of crosslinking that resulted from the reactions between the epoxy and OG units. Thermogravimetric analysis revealed that the thermal stability of the nanocomposites was better than that of the pristine epoxy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1927–1934, 2009     

Crystallization behavior and morphological development of isotactic polypropylene blended with nanostructured polyhedral oligomeric silsesquioxane molecules

The thermal properties and morphological development of isothermally crystallized isotactic polypropylene (iPP) blended with nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules at very small loading of POSS were studied with differential scanning calorimeter (DSC), thermal gravimetric analysis, dynamic mechanical analysis, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The result of DSC indicated that the crystallization rate of iPP increases with the increase in POSS contents during crystallization; moreover, the melting temperature of iPP/POSS nanocomposites slightly decreases, while the heat of fusion increases with the addition of POSS molecules at melting and remelting traces. The storage modulus and thermal stability, respectively, remarkably decrease, while the glass transition temperature of isothermally crystallized iPP/POSS nanocomposites increases slightly with the increase in POSS contents. The morphologies results of WAXD and POM show that the POSS molecules form about 35 nm sized nanocrystals and aggregate to form thread‐like and network structure morphologies, respectively, in the molten state even when the POSS content is very small. These results, therefore, suggest that the interaction force between the POSS molecules should be larger than the force between POSS molecules and iPP matrix; however, those interactions depend on the chain length of functionalized substituents on the POSS cage. Therefore, the POSS molecules aggregate forming nanocrystals and act as an effective nucleating agent for iPP and influence the thermal properties of iPP/POSS nanocomposites due to the shorter chain length of functionalized substituents, methyl, on the POSS cage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2122–2134, 2006     

Synthesis of polyethylene hybrid copolymers containing polyhedral oligomeric silsesquioxane prepared with ring‐opening metathesis copolymerization

Ring‐opening metathesis copolymerizations of cyclooctene and the polyhedral oligomeric silsesquioxane (POSS) monomer 1‐[2‐(5‐norbornen‐2‐yl)ethyl]‐3,5,7,9,11,13,15‐heptacyclopentylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13] octasiloxane (POSS–norbornylene) were performed with Grubbs's catalyst, RuCl₂(?CHPh)(PCy₃)₂. Random copolymers were formed and fully characterized with POSS loadings as high as 55 wt %. Diimide reduction of these copolymers afforded polyethylene–POSS random copolymers. Thermogravimetric analysis of the polyethylene–POSS copolymers under air showed a 70 °C improvement, relative to a polyethylene control sample of similar molecular weight, in the onset of decomposition temperature based on 5% mass loss. The homopolymer of POSS–norbornylene was also synthesized. This polymer had a rigid backbone according to ¹H NMR evidence of broad olefinic signals. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2920–2928, 2001     

Nanocomposites of polyethylene with polyhedral oligomeric silsesquioxane: from thermoplastics to vitrimers through silyl ether metathesis

In this contribution, we reported the transformation of linear polyethylene-polyhedral oligomeric silsesquioxane (PE-POSS) copolymers into PE vitrimers through silyl ether metathesis. First, the PE-POSS copolymers were synthesized via the ring-opening metathesis polymerisation (ROMP) of cyclooctene with heptaisobutyl POSS-norbornene followed by subsequent hydrogenation reaction. The PE-POSS copolymers were microphase -separated, and the POSS cages were aggregated into the microdomains with the size of 10–20 nm. The thermoplastic PE-POSS nanocomposites were transformed into the PE vitrimers via direct silyl ether metathesis, which was catalyzed with zinc trifluoromethyl sulfonate [Zn(OTf)₂]. It was found that the cross-linking with the dynamic covalent bonds occurred within the POSS microdomains. The cross-linking significantly influenced the morphologies and thermal and mechanical properties of the materials. More importantly, the cross-linked PE products displayed the self-adaptivity at elevated temperature, that is, the PE-POSS thermoplastics were transformed into PE-polysilsesquioxane vitrimers. Because of the formation of cross-linked networks, the PE vitrimers were endowed with shape memory properties. In the meantime, the permanent shapes of the shape memory PEs can readily be reprogrammed by taking advantage of the self-adaptivity of the vitrimers.     

Poly(methyl methacrylate)/Methacryl-POSS Nanocomposites with Excellent Thermal Properties

Poly(methyl methacrylate) (PMMA) nanocomposites containing (methacryloxy)propyl polyhedral oligomeric silsesquioxane (methacryl‐POSS) were prepared by bulk‐polymerization process. The structures of the products were characterized by FTIR, solid‐state NMR, TEM, XRD, DSC, TGA, XPS and UV‐Vis spectra. The hybrid materials were found to be largely homogeneous. DSC and TGA results indicate that the thermal properties of PMMA nanocomposites are significantly improved. The glass transition temperature (T_g) and thermal decomposition temperature (T_dec) of the nanocomposites increased by 58 and 110°C, respectively. The bulk hybrid material maintains excellent optical transparency in visible region.     

Synthesis and thermal properties of hybrid copolymers of syndiotactic polystyrene and polyhedral oligomeric silsesquioxane

Copolymerizations of styrene and the polyhedral oligomeric silsesquioxane (POSS)–styryl macromonomer 1‐(4‐vinylphenyl)‐3,5,7,9,11,13,15‐heptacyclopentylpentacyclo [9.5.1.1^3,9.1^5,15.1^7,13] octasiloxane have been performed with CpTiCl₃ in conjunction with methylaluminoxane. Random copolymers of syndiotactic polystyrene (sPS) and POSS have been formed and fully characterized with ¹H and ¹³C NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. NMR data reveal a moderately high syndiotacticity of the polystyrene backbone consistent with this use of CpTiCl₃ as a catalyst and POSS loadings as high as 24 wt % and 3.2 mol %. Thermogravimetric analysis of the sPS–POSS copolymers under both nitrogen and air shows improved thermal stability with higher degradation temperatures and char yields, demonstrating that the inclusion of the inorganic POSS nanoparticles makes the organic polymer matrix more thermally robust. The polymerization activity and thermal stability are also compared with those of reported atactic polystyrene–POSS copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 885–891, 2002; DOI 10.1002/pola.10175     

Surface modification of gold nanoparticles with polyhedral oligomeric silsesquioxane and incorporation within polymer matrices

A new approach to achieve polymer‐mediated gold ferromagnetic nanocomposites in a polyhedral oligomeric silsesquioxane (POSS)‐containing random copolymer matrix has been developed. Stable and narrow distributed gold nanoparticles modified by 3‐mercaptopropylisobutyl POSS to form Au‐POSS nanoparticles are prepared by two‐phase liquid‐liquid method. These Au‐POSS nanoparticles form partial particle aggregation by blending with poly(n‐butyl methacrylate) (PnBMA) homopolymer because of poor miscibility between Au‐POSS and PnBMA polymer matrix. The incorporation the POSS moiety into the PnBMA main chain as a random copolymer matrix displays well‐dispersed gold nanoparticles because the POSS‐POSS interaction enhances miscibility between gold nanoparticles and the PnBMA‐POSS copolymer matrix. This gold‐containing nanocomposite exhibits ferromagnetic phenomenon at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 811–819, 2009     

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane-reinforced epoxy matrices

Fiber-filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the β-relaxation to the α-relaxation, or glass transition temperature, (i.e., from −100 to 180 °C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the α-relaxation region, increasing in the vicinity of the β-relaxation, and then decreasing below the temperature associated with the peak in the β-relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the α-relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the β-relaxation peak. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2719–2732, 2008     

Synthesis and characterization of luminescent organic-inorganic hybrid nanocomposite from polyhedral oligomeric silsesquioxane

<正>A novel polyhedral oligomeric silsesquioxane(POSS)-based organic-inorganic hybrid nanocomposite(EF-POSS) was prepared by Pt-catalyzed hydrosilylation reaction of octahydridosilsesquioxane(T_8H_8,POSS) with a luminescent substituted acetylene(2- ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene(EF)) in high yield.The hybrid nanocomposite was soluble in common solvents such as CH_2Cl_2,CHCl_3,THF and 1,4-dioxane.Its structure and property were characterized by FTIR, NMR,TGA,UV and PL,respectively.The results show that the hybrid nanocomposite with high thermal stability emits stable blue light as a result of photo excitation and possesses high photoluminescence quantum efficiency(φ_(FL)).     

Preparation,characterization, and properties of nanofibers based on poly(vinylidene fluoride) and polyhedral oligomeric silsesquioxane

Nanostructered nanofibers based on poly(vinylidene fluoride) (PVDF) and polyhedral oligomeric silsesquioxane (POSS) have been prepared by electrospinning process. The starting solutions were prepared by dissolving both the system components in the mixture N,N‐dimethylacetamide/acetone. The characteristics of the fiber prepared, studied by scanning electron microscopy, atomic force microscopy, and wide angle X‐ray diffraction, have been compared with those of PVDF fibers. Morphological characterization has demonstrated the possibility to obtain defect‐free PVDF/POSS nanofibers by properly choosing the electrospinning conditions, such as voltage, polymer concentration, humidity, etc. Conversely, in the case of fibers based on the neat polymer, it was not possible to attain the complete elimination of beads in the electrospun nanofibers. The different behavior of the two types of solutions has been ascribed to silsesquioxane molecules, which, without influencing the solution viscosity or conductivity, favor the formation of uniform structures by decreasing the system surface tension. Concerning POSS distribution in the fibers, the morphological characterization of the electrospun films has shown a submicrometric dispersion of the silsesquioxane. It is relevant to underline that cast films, prepared by the same solutions, have been found to be characterized by POSS aggregation, thus demonstrating a scarce affinity between the two‐system components. Indeed, the peculiar solvent evaporation of the electrospun solution, which is much faster than that occurring during the cast process, prevents POSS aggregation, thus leading to the formation of nanofibers characterized by a silsesquioxane dispersion similar to that present in solution. Finally, the presence of POSS improves the electrospun film mechanical properties. Copyright © 2011 John Wiley & Sons, Ltd.     

Self‐assembly and secondary structures of linear polypeptides tethered to polyhedral oligomeric silsesquioxane nanoparticles through click chemistry

In this study, we used click chemistry to synthesize a new macromolecular self‐assembling building blocks, linear polypeptide‐b‐polyhedral oligomeric silsesquioxane (POSS) copolymers, from a mono‐azido–functionalized POSS (N₃‐POSS) and several alkyne‐poly(γ‐benzyl‐L ‐glutamate) (alkyne‐PBLG) systems. The incorporation of the POSS unit at the chain end of the PBLG moiety allowed intramolecular hydrogen bonding to occur between the POSS and PBLG units, thereby enhancing the α‐helical conformation in the solid state, as determined through Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction analyses. POSS‐b‐PBLG underwent hierarchical self‐assembly, characterized using small‐angle X‐ray scattering, to form a bilayer‐like nanostructure featuring α‐helical or β‐sheet conformations and POSS aggregates. Thermogravimetric analysis indicated that the thermal degradation temperature increased significantly after incorporation of the POSS moiety, which presumably formed an inorganic protection layer on the nanocomposite's surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Bridged polyhedral oligomeric silsesquioxane (POSS): A potential member of silsequioxanes

Two novel and well-defined polyhedral oligomeric silsesquioxanes（POSS） with two same Si₈O₁₂ cores and a reactive NH group, namely bridged-POSS（2a and 2b）,have been prepared by the traditional ’corner-capping’ reaction.X-ray diffraction demonstrates that those two POSS have the similar T₈ structure.From the thermo-gravimetric analysis,bridged-POSS shows the belter thermal degradation stability than the contrastive POSS.     

Inorganic–organic nanocomposites of polybenzoxazine with octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane

Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) was used to prepare the polybenzoxazine (PBA‐a) nanocomposites containing polyhedral oligomeric silsesquioxane (POSS). The crosslinking reactions involved with the formation of the organic–inorganic networks can be divided into the two types: (1) the ring‐opening polymerization of benzoxazine and (2) the subsequent reaction between the in situ formed phenolic hydroxyls of PBA‐a and the epoxide groups of OpePOSS. The morphology of the nanocomposites was investigated by means of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Differential scanning calorimetry and dynamic mechanical analysis showed that the nanocomposites displayed higher glass‐transition temperatures than the control PBA‐a. In the glassy state, the nanocomposites containing less than 30 wt % POSS displayed an enhanced storage modulus, whereas the storage moduli of the nanocomposites containing more than 30 wt % POSS were lower than that of the control PBA‐a. The dynamic mechanical analysis results showed that all the nanocomposites exhibited enhanced storage moduli in the rubbery states, which was ascribed to the two major factors, that is, the nanoreinforcement effect of POSS cages and the additional crosslinking degree resulting from the intercomponent reactions between PBA‐a and OpePOSS. Thermogravimetric analysis indicated that the nanocomposites displayed improved thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1168–1181, 2006     

Synthesis and characterization of waterborne polyurethane/polyhedral oligomeric silsesquioxane composites with low dielectric constants

A facile method was developed to synthesize a new type of polyhedral oligomeric silsesquioxane (POSS). It contained a single amine group and seven aliphatic moieties on its corners. FT‐IR, ¹H‐NMR, ¹³C‐NMR, ¹³C‐¹H COSY, and ¹H‐¹H COSY confirmed that cages with eight corners were the main part of the product. This new POSS was used to modify the structure of hexamethylene diisocyanate trimer and then copolymerized with hexamethylene diisocyanate and poly (tetramethylene glycol) to get a serious of waterborne polyurethane (WPU)/POSS hybrid materials with low dielectric constants for microelectronics applications. The results showed that POSS particles were uniformly dispersed in the WPU dispersions. The WPU/POSS films did not show any macrophase separation, even when the POSS content was as high as 16%. As the POSS content increased from 0% to 16%, the tensile strength was increased from 2.3 to 7.3 MPa, the dielectric constant was decreased from about 2.9 to 2.0, and the thermal stability of the WPU/POSS was also improved.     

Synthesis,morphology, and viscoelastic properties of cyanate ester/polyhedral oligomeric silsesquioxane nanocomposites

Cyanate ester (PT‐15, Lonza Corp) composites containing the inorganic–organic hybrid polyhedral oligomeric silsesquioxane (POSS) octaaminophenyl(T₈)POSS [ 1 ; (C₆H₄NH₂)₈(SiO_1.5)₈] were synthesized. These PT‐15/POSS‐ 1 composites (99/1, 97/3, and 95/5 w/w) were characterized by X‐ray diffraction (XRD), transmission election microscopy (TEM), dynamic mechanical thermal analysis, solvent extraction, and Fourier transform infrared. The glass‐transition temperatures (T_g's) of the composite with 1 wt % 1 increased sharply versus the neat PT‐15, but 3 and 5 wt % 1 in these cyanate ester composites depressed T_g. All the PT‐15/POSS composites exhibited higher storage modulus (E′) values (temperature > T_g) than the parent resin, but these values decreased from 1 to 5 wt % POSS. The loss factor peak intensities decreased and their widths broadened upon the incorporation of POSS. XRD, TEM, and IR data were all consistent with the molecular dispersion of 1 due to the chemical bonding of the octaamino POSS‐ 1 macromer into the continuous cyanate ester network phase. The amino groups of 1 reacted with cyanate ester functions at lower temperatures than those at which cyanate ester curing by cyclotrimerization occurred. In contrast to 1 , 3‐cyanopropylheptacyclopentyl(T₈)POSS [ 2 ; (C₅H₉)₇(SiO_1.5)₈CH₂CH₂CH₂CN] had low solubility in PT‐15 and did not react with the resin below or at the cure temperature. Thus, phase‐separated aggregates of 2 were found in samples containing 1–10 wt % 2 . Nevertheless, the T_g and E′ values (temperature > 285 °C) of these composites increased regularly with an increase in 2 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3887–3898, 2005     

Preparation,Tg improvement,and thermal stability enhancement mechanism of soluble poly(methyl methacrylate) nanocomposites by incorporating octavinyl polyhedral oligomeric silsesquioxanes

The soluble poly(methyl methacrylate‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved T_g and high thermal stability were synthesized by common free radical polymerization and characterized using FTIR, high‐resolution ¹H NMR, ²⁹Si NMR, GPC, DSC, and TGA. The POSS contents in the nanocomposites were determined based on FTIR spectrum, revealing that it can be effectively adjusted by varying the feed ratio of POSS in the hybrid composites. On the basis of the ¹H NMR analysis, the number of the reacted vinyl groups on each POSS molecules was determined to be about 6–8. The DSC and TGA measurements indicated that the hybrid nanocomposites had higher T_g and better thermal properties than the pure PMMA homopolymer. The T_g increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the T_g improvement besides the molecular motion hindrance from the hybrid structure. The thermal stability enhances with increase of POSS content, which is mainly attributed to the incorporation of nanoscale inorganic POSS uniformly dispersed at molecular level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5308–5317, 2007     

Synthesis and characterization of fillers of controlled structure based on polyhedral oligomeric silsesquioxane cages and their use in reinforcing siloxane elastomers

Four polyhedral oligomeric silsesquioxane (POSS) cages with vinyl groups were linked to a central siloxane core by hydrosilylation. The goal was to obtain filler particles of sizes between those of the POSS cages themselves and the much larger silica particles typically used to reinforce elastomers. The hydrosilylation reaction was monitored with Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the resulting structure was confirmed by mass spectrometry. Simply blending these POSS-based fillers into silanol-terminated poly(dimethylsiloxane) (PDMS) had little effect on the mechanical properties, but bonding them to PDMS provided considerable reinforcement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3314–3323, 2003     

Synthesis and properties of thermoplastic and dissolvable polysiloxanes containing polyhedral oligomeric silsesquioxane

There are many benefits associated with thermoplastic silicones, but very few examples exist: silicone resins or rubbers are normally thermosets. In this article, a facile and efficient approach was reported to prepare thermoplastic silicone by introducing a bulky side siloxane group. Monofunctional polyhedral oligomeric silsesquioxane (POSS), as the bulky siloxane group, was grafted onto the linear polysiloxane backbone via thiol–ene click reaction, endowing the liquid polysiloxane with thermoplastic nature. The POSS-grafted polysiloxane could be remolded by a hot-melting or solution casting process. It was worth noting that the novel thermoplastic silicone was composed of both linear siloxane main chains and siloxane side groups, which was distinctly different from previous researches on thermoplastic silicones consisted of siloxane main chains and organic side groups. Thermal analysis, rheological characterization and molecular dynamics simulation results revealed the thermoplastic properties of POSS-grafted polysiloxane depended on the bulky POSS's hindrance to the movement of the polymer backbone rather than the interaction between the organic side groups.     

Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m² generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer.