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 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     

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     

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.     

Preparation and properties of polyhedral oligomeric silsesquioxane polymers

Polyhedral oligomeric silsesquioxane (POSS) polymers were synthesized by the dehydrogenative condensation of (HSiO_3/2)₈ with water in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by spin‐coating of the coating solution prepared by the dehydrogenative condensation of POSS. The hardness of the coating films was evaluated using a pencil‐hardness test and was found to increase up to 8H with increases in the curing temperature. Free‐standing film and silica gel powder were prepared by aging the coating solution at room temperature. The silica gel powder was subjected to heat treatment under air atmosphere to show a specific surface area of 440 m² g⁻¹ at 100 °C, which showed a maximum at 400 °C as 550 m² g⁻¹. Copyright © 2011 John Wiley & Sons, Ltd.     

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     

Novel,tadpole-shaped,polyhedral oligomeric silsesquioxane containing sulfonated block copolymer for humidity sensing

Due to the “trade-off” effect between the high water adsorption and low stability under high Relative Humidity of polymer matrix, fabrication of resistive-type polymer-based humidity sensors with a wide impedance response and excellent stability in high relative humidity remains a great challenge. Aim at solving that, a novel polymeric humidity sensing matrix, specifically a tadpole-shaped, polyhedral oligomeric silsesquioxane (POSS) containing block copolymers (BCPs) of POSS-poly(methyl methacrylate)-polystyrene (POSS-PMMA-SPS) were proposed. This novel BCP was synthesized using atom transfer radical polymerization (ATRP) employing a two-step approach, and following post sulfonation, a series of sulfonated BCPs (POSS-PMMA-SPS) with different sulfonation degree was obtained. The subject humidity sensors were produced using different sulfonated BCPs employing a dip-coating technique, and three wide-impedance response humidity sensors were produced. Each of these sensors exhibited an excellent humidity-sensing response of more than 10⁴ within the humidity range from 11% to 95% RH. In particular, the humidity sensor S-6 that had a proper degree of sulfonation presented a relatively fast response (t_90% of 11 s and 80 s in both the water adsorption and desorption processes), and superior repeatability for more than 30 days.     

Synthesis,characterization, and temperature‐responsive behaviors of novel hybrid amphiphilic block copolymers containing polyhedral oligomeric silsesquioxane

Organic/inorganic hybrid amphiphilic block copolymer poly(methacrylate isobutyl POSS)‐b‐poly(N‐isopropylacrylamide‐co‐oligo(ethylene glycol) methyl ether methacrylate) (PMAPOSS‐b‐P(NIPAM‐co‐OEGMA)) was synthesized via reversible addition–fragmentation chain transfer polymerization. The self‐assembly behavior of this block copolymer in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy. The results indicate that the novel block copolymer can self‐assemble into spherical micelles with PMAPOSS segment as the hydrophobic part and P(NIPAM‐co‐OEGMA) segment as the hydrophilic part. The temperature‐responsive characteristics of the assemblies were tested by UV–Vis spectra and DLS. Some factors such as the concentration, molecular weight, and copolymer generation that may affect the cloud point were studied systematically. The results reveal that this copolymer exhibits a sharp and intensive lower critical solution temperature (LCST). The essentially predetermined LCST can be conveniently achieved by adjusting the content of NIPAM or OEGMA domain. In addition, these novel hybrid micelles can undergo an association/disassociation cycle with the heating and cooling of solution and the degree of reversibility displaying a tremendous concentration dependence, as a novel organic/inorganic hybrid material with distinctive virtues can be potentially used in biological and medical fields, especially in drug nanocarriers for targeted therapy. Copyright © 2014 John Wiley & Sons, Ltd.     

The mechanical properties of crystalline cyclopentyl polyhedral oligomeric silsesquioxane

The anisotropic elastic constants of crystalline octacyclopentyl polyhedral oligomeric silsesquioxane (CpPOSS) were determined using molecular dynamics. The force field used for these calculations was shown to model accurately the rhombohedral and triclinic crystal structures of octasilsesquioxane and CpPOSS, respectively, as well as the vibrational frequencies of octasilsesquioxane. The moduli for CpPOSS are anisotropic, with a Reuss-averaged bulk modulus of 7.5 GPa, an isotropic averaged Young's modulus of 11.78 GPa, and an isotropic averaged shear modulus of 4.75 GPa. These isotropic averages or, alternatively, the full anisotropic stiffness tensor of the crystal can be used with micromechanical composite models to calculate the effective elastic properties of polymer nanocomposites that contain crystalline aggregates of CpPOSS.     

Cross-linking of carboxyl-terminated nitrile rubber with polyhedral oligomeric silsesquioxane

Glycidyl polyhedral oligomeric silsesquioxane (POSS) was used as a cross-linking agent to prepare a new organic–inorganic hybrid material from carboxyl-terminated poly(acrylonitrile-co-butadiene) (CTBN). The structure of the reacted material was characterized by Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) at different heating rates in the presence and absence of catalyst, triphenyl phosphine (TPP), was conducted to investigate the curing kinetics. The reaction is catalyzed by the addition of TPP, and rate is maximum at higher catalyst concentrations. Different kinetic models were used to analyze the kinetic parameters. The effect of catalyst on curing process was determined by calculating the activation energy (E _a) using Kissinger method. Dependency of E _a with extent of conversion was monitored by different isoconversional methods. The curing mechanism of POSS–CTBN system followed autocatalytic model. Moreover, the predicted curves from the kinetic models fit well with the non-isothermal DSC curve. The E _a of gelation obtained from rheological studies matched with that from DSC study, in league with the Flory’s theory of cross-linking.     

Miscibility and hydrogen-bonding behavior in organic/inorganic polymer hybrids containing octaphenol polyhedral oligomeric silsesquioxane

In this study, we investigated the miscibility behavior and mechanism of interaction of poly(methyl mechacrylate) (PMMA), poly(vinyl pyrrolidone) PVP, and PMMA- co-PVP blends with octa(phenol)octasilsequioxane (OP-POSS). For the PMMA/OP-POSS binary blend, the value of the association constant ( K A = 29) was smaller than that in the poly(vinyl phenol) (PVPh)/PMMA ( K A = 37.4) and ethyl phenol (EPh)/PMMA ( K A = 101) blend systems, implying that the phenol groups of the OP-POSS units in the PMMA/OP-POSS blends interacted to a lesser degree with the CO groups of PMMA than they did in the other two systems. In addition, the ionic conductivity of a LiClO4/PMMA- co-PVP polymer electrolyte was increased after blending with OP-POSS.     

A novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane and its nanocomposite with polybenzoxazine

The novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane macromonomer (BZ-POSS), containing 7.6 benzoxazine groups per molecule on average was synthesized from octaaminophenylsilsesquioxane, p-cresol and paraformaldehyde. BZ-POSS was well miscible with bisphenol A-based benzoxazine (BBZ) melt. By ring-opening copolymerization of BBZ and BZ-POSS under condition similar to that used for polymerizing neat BBZ, the transparent and uniform BBZ/BZ-POSS organic-inorganic hybrid nanocomposites were prepared. The nano-scale dispersion of POSS cores in the nanocomposite was verified by powder X-ray diffraction and transmission electron microscopy studies. Dynamic mechanical analyses and thermal gravimetric analysis indicated that thermal stabilities, cross-link densities and the flame retardance of the nanocomposites were increased in comparison with neat PBBZ resin, although only small amounts of inorganic POSS cores were incorporated into the systems. Structural analyses of BZ-POSS and BBZ/BZ-POSS nanocomposites are discussed herein.     

New organic-inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane

The synthesis of new organic-inorganic materials were investigated. Poly(ε-caprolactone) and poly(l, l-lactide) covalently end-capped by a polyhedral oligomeric silsesquioxane (POSS) moiety, leading to new nanohybrid materials, were successfully prepared by coordination-insertion ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and l,l-lactide (l,l-LA) respectively. The reaction was initiated from the primary amine available on aminopropylheptakis(isobutyl)POSS nanoparticles and catalyzed by tin(II) 2-ethylhexanoate (tin octoate, Sn(oct)₂). The covalent grafting of the polyester chains onto the POSS “nanocages” was assessed by selective fractionation experiment, Fourier transform infrared spectroscopy (FTIR) and further confirmed by proton nuclear magnetic resonance (¹H NMR). The polymerization proved to be well controlled as attested by the quite narrow polydispersity indices as determined by size exclusion chromatography (SEC). Furthermore, well-defined semi-crystalline poly(ε-caprolactone)-b-polylactide block copolymer carrying such POSS nanoparticle at one end was successfully synthesized attesting for the very efficient control over the polymerization reaction.     

Unique rodlike surface morphologies in trisilanolcyclohexyl polyhedral oligomeric silsesquioxane films

A trisilanol derivative of polyhedral oligomeric silsesquioxane (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. This paper explores the mono- and multilayer properties of another POSS derivative, trisilanolcyclohexyl-POSS, with pi-A isotherm and Brewster angle microscopy measurements. Results show that with continuously increasing surface concentration via symmetrical compression, trisilanolcyclohexyl-POSS amphiphiles at the air/water interface undergo a series of phase transitions from traditional Langmuir monolayers (one-POSS-molecule thick) to unique rodlike hydrophobic aggregates in multilayer films (approximately eight-POSS-molecules thick) that are dramatically different from "collapsed" morphologies seen in other systems. Stable and hydrophobic rodlike structure formation on water is presumably due to trisilanolcyclohexyl-POSS' unique molecular structure and strong tendency to form intermolecular hydrogen bonds in the solid state. This result is consistent with existing POSS/polymer composite research, which shows that POSS molecules tend to aggregate and crystallize into lamellar nanocrystals.     

Crystallization studies of isotactic polypropylene containing nanostructured polyhedral oligomeric silsesquioxane molecules under quiescent and shear conditions

Crystallization studies at quiescent and shear states in isotactic polypropylene (iPP) containing nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules were performed with in situ small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC was used to characterize the quiescent crystallization behavior. It was observed that the addition of POSS molecules increased the crystallization rate of iPP under both isothermal and nonisothermal conditions, which suggests that POSS crystals act as nucleating agents. Furthermore, the crystallization rate was significantly reduced at a POSS concentration of 30 wt %, which suggests a retarded growth mechanism due to the molecular dispersion of POSS in the matrix. In situ SAXS was used to study the behavior of shear‐induced crystallization at temperatures of 140, 145, and 150 °C in samples with POSS concentrations of 10, 20, and 30 wt %. The SAXS patterns showed scattering maxima along the shear direction, which corresponded to a lamellar structure developed perpendicularly to the flow direction. The crystallization half‐time was calculated from the total scattered intensity of the SAXS image. The oriented fraction, defined as the fraction of scattered intensity from the oriented component to the total scattered intensity, was also calculated. The addition of POSS significantly increased the crystallization rate during shear compared with the rate for the neat polymer without POSS. We postulate that although POSS crystals have a limited role in shear‐induced crystallization, molecularly dispersed POSS molecules behave as weak crosslinkers in polymer melts and increase the relaxation time of iPP chains after shear. Therefore, the overall orientation of the polymer chains is improved and a faster crystallization rate is obtained with the addition of POSS. Moreover, higher POSS concentrations resulted in faster crystallization rates during shear. The addition of POSS decreased the average long‐period value of crystallized iPP after shear, which indicates that iPP nuclei are probably initiated in large numbers near molecularly dispersed POSS molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2727–2739, 2001     

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

The reactive blending composites of isotactic polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) were prepared in the presence of dicumyl peroxide. Comparison of the rheological behavior of physical and reactive blending composites was made by oscillatory rheological measurements. It was found that the viscosity of physical blending composites drops at lower POSS content (0.5–1 wt %) and thereafter increases with increasing POSS content; that of reactive blending composites increases with increasing POSS content and displays a solid‐like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′–log G″ of linear polymer in Han plot, upturning at high viscosity in Cole–Cole plot, and from van Gurp–Palmen plot are related to the gelation behavior reactively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 526–533, 2008     

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.