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1.
Epoxy/polyhedral oligometric silsesquioxane (POSS) hybrid materials, containing 50 wt % POSS and exhibiting good homogeneity, were obtained in a two‐step preparation. Monoamine‐functionalized POSS was first reacted with diglycidyl ether of bisphenol A to form an epoxy POSS precursor, which was then cured. Curing agents such as 4,4′‐diaminodiphenylmethane, dicyandiamide (DICY), and diethylphosphite (DEP) were used for the synthesis of the epoxy–POSS hybrid materials. The use of small‐molecule curing agents, such as DICY and DEP, efficiently avoided macrophase separations and enhanced the thermal properties of the hybrid materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1869–1876, 2006  相似文献   

2.
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  相似文献   

3.
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  相似文献   

4.
The soluble poly(methyl methacrylate‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved Tg 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 Tg and better thermal properties than the pure PMMA homopolymer. The Tg increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the Tg 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  相似文献   

5.
This study investigates the curing of epoxidized soybean oil (ESO) using dicyandiamide (DICY) and combinations of DICY with several accelerators as curing agents. The differential scanning calorimetry (DSC) results indicated that carbonyldiimidazole (CDI) is a highly efficient accelerator for the ESO‐DICY curing system. CDI accelerated ESO‐DICY curing system can gel within a short period of 13 min at 190 °C. The activation energies of the ESO‐DICY curing systems with and without CDI are 95 and 121 kJ mol?1, respectively. Similar acceleration effect was observed in the ESO‐diglycidyl ether of biphenyl A (DGEBA) blending formulations. When the molar part of the glycidyl epoxy groups of DGEBA was equal to the internal epoxy groups of ESO in the mixture, gelation of the DICY curing system accelerated by CDI was achieved in 3 min at 160 °C. Furthermore, the DSC results with FTIR analysis suggest that the stoichiometric curing molar ratio was 3 ESO epoxy units per 1 DICY molecule. Two epoxy units reacted with DICY to give secondary alcohols, while the other one linked to the nitrile group. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 375–382  相似文献   

6.
The mechanical properties and thermal stability of polymers can be enhanced through the formation of nanocomposites. Nanocomposites consisting of hybrid copolymers of methacrylcyclohexyl polyhedral oligomeric silsesquioxane (POSS‐1) and methyl methacrylate (MMA) with up to 92 wt % (51 mol %) POSS‐1 and with superior thermal properties were synthesized using solution polymerization. The POSS‐1 contents of the copolymers were similar to or slightly higher than those in the feeds, the polydispersity indices were relatively low, and the degree of polymerization decreased with increasing POSS‐1 content. POSS‐1 enhanced the thermal stability, increasing the degradation temperature, reducing the mass loss, and preventing PMMA‐like degradation from propagating along the chain. The mass loss was reduced in a high POSS‐1 content copolymer since the polymerization of POSS‐1 with itself reduced sublimation. Exposure to 450 °C produced cyclohexyl‐POSS‐like remnants in the POSS‐1 monomer and in all the copolymers. The degradation of these remnants, for the copolymers and for the POSS‐1 monomer, yielded 75% SiO2 and an oxidized carbonaceous residue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4264–4275, 2007  相似文献   

7.
Nanocomposites composed of a poly(vinylidene fluoride) (PVDF) matrix and 0, 3, 5, and 8 wt % fluoropropyl polyhedral oligomeric silsesquioxane (FP‐POSS) were prepared by using the solvent evaporation method. The morphology and the crystalline phase of the nanocomposites were investigated by digital microscopy, scanning probe microscopy, X‐ray diffractometer, and Fourier transform infrared spectroscopy. FP‐POSS acted as nucleating agent in PVDF matrix. A small content of FP‐POSS resulted in an incomplete nucleation of PVDF and generated bigger spherical particles, whereas higher contents led to a complete nucleation and formed more separate and less‐crosslinked particles. Nanoindentation, nanoscratch, and nanotensile tests were carried out to study the influence of different contents of FP‐POSS on the key static and dynamic mechanical properties of different systems. The nanocomposite with 3 wt % FP‐POSS was found to possess enhanced elastic properties and hardness. However, with the increase of the FP‐POSS content, the elastic modulus and hardness were found to decrease, and the improvement on stiffness was negative at contents of 5 and 8 wt %. Compared with neat PVDF, the scratch resistance of the PVDF/FP‐POSS nanocomposites was decreased due to a rougher surface derived from the bigger spherulites. Nanotensile testing results showed both the stiffness and toughness of PVDF‐FP3% were enhanced and further additions of FP‐POSS brought dramatic enhancements in toughness while associated with a decline in stiffness. Dynamical mechanical properties indicated the viscosity of the nanocomposites increased with the increasing FP‐POSS contents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012  相似文献   

8.
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  相似文献   

9.
We report on the structures and electro‐optical properties of epoxy/acrylic polymer‐dispersed liquid‐crystal (PDLC) films. A thermal stimulated current (TSC) analysis was used to investigate the physical structures of PDLC. In the TSC spectrum of PDLC, three relaxation peaks were observed: the glass transition of the liquid crystal, the glass transition of the polymer matrix, and the ρ transition. The ρ transition represents the discharge behavior of space charges, and its intensity increased as the curing time and content of the curing agent dicyandiamide (DICY) increased. The pre‐UV‐cured films with different DICY contents were thermally cured at 130 °C for various periods. The electro‐optical properties of PDLC, such as the contrast ratio and switching voltage, increased as the curing time of DICY, the content of DICY, or both increased. As the ambient temperature increased from 10 to 40 °C, the contrast ratio and switching voltage of PDLC gradually decreased. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 507–514, 2001  相似文献   

10.
Polyhedral oligosilsequioxane (POSS) tethered aromatic polyamide nanocomposites with various POSS fractions were prepared through Michael addition between maleimide‐containing polyamides and amino‐functionalized POSS. The chemical structures of the polyamide–POSS nanocomposites were characterized with Fourier transform infrared and 1H NMR. The polyamide–POSS nanocomposites exhibited good homogeneity in scanning electron microscopy and transmission electron microscopy observations. POSS modification increased the storage modulus and Young's modulus of the polyamides, slightly decreased their glass‐transition temperatures from 312 to 305 °C, and significantly lowered their dielectric constants from 4.45 to 3.35. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4632–4643, 2006  相似文献   

11.
Novel poly(butylene terephthalate) (PBT)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by ring‐opening polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS with various feed ratios. The impact of POSS incorporation on melting and crystallization behaviors of PBT/POSS nanocomposites was investigated by means of X‐ray diffraction and differential scanning calorimetry. It was found that the novel organic–inorganic association result in the significant alterations in the melting and crystallization behavior of PBT. Thermal studies confirmed that the incorporation of POSS can enhance the thermal stability of the polymers, and the copolymer glass transition temperature increased with the increasing of POSS macromonomer content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1853–1859, 2010  相似文献   

12.
We have synthesized a polyhedral oligomeric silisesquioxane (POSS) derivative containing eight acetoxystyryl functional groups [octa(acetoxystyryl)octasilsesquioxane (AS‐POSS)] and then blended it with phenolic resin to form nanocomposites stabilized through hydrogen bonding interactions between the phenolic resin's hydroxyl group and the AS‐POSS derivative's carbonyl and siloxane groups. One‐ and two‐dimensional infrared spectroscopy analyses provided positive evidence for these types of hydrogen bonding interactions. In addition, we calculated the interassociation equilibrium constant, based on the Painter–Coleman association model (PCAM), between phenolic resin and POSS indirectly from the fraction of hydrogen‐bonded carbonyl groups; quantitative analyses indicate that the hydroxyl–siloxane interassociation from the PCAM is entirely consistent with the classical Coggesthall and Saier (C and S) methodology. From a thermal analysis, we observed that the miscibility between phenolic and AS‐POSS occurs at a relatively low AS‐POSS content, which characterizes this mixture as a polymer nanocomposite system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 673–686, 2006  相似文献   

13.
The IPI‐POSS‐modified epoxy resin (IPEP) was prepared from isocyanato‐propyldinethylsilyl‐isobutyl‐POSS (IPI‐POSS) and diglycidyl ether of bisphenol A epoxy resin. The steric hindrance of the IPEP bulky POSS side chain improved the curing activation energies. The POSS particles sizes were about 2–3 nm and dispersed uniformly. At lower IPEP concentration (POSS < 12 wt %), the glass transition temperatures (Tgs) of the IPEP nanocomposites increased from 118 to 170 °C. The char yield increased from 15 to 20 wt %, and the LOI values increased from 22 to 28. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 643–652, 2010  相似文献   

14.
A high‐performance, low‐dielectric‐constant polyimide (PI) nanocomposite from poly(amic acid) (PAA) cured with a reactive fluorine polyhedral oligomeric silsesquioxane (POSS) isomer was successfully synthesized. The features of this reactive fluorine POSS isomer [octakis(dimethylsiloxyhexafluoropropylglycidyl ether)silsesquioxane (OFG)] provided two important approaches (containing fluorine or being porous in the polymer matrix) of reducing the dielectric constant of PI. This reactive POSS isomer had an average of four epoxy groups and four fluorine groups on the POSS cage, and the epoxy groups could be cured with PAA to form a network framework of a PI/POSS nanocomposite. The PI/OFG nanocomposite had a high crosslinking density, high porosity (24.3%), high hydrophobicity, and low polarizability. These properties enhanced the thermal (glass‐transition temperature ~ 362 °C) and dielectric (dielectric constant ~2.30) properties of PI more than other POSS derivatives introduced into the PI backbone. A large number of small POSS particles (<10 nm) were embedded inside the PI matrix when the OFG content was low, whereas interconnected POSS aggregation domains were observed when the OFG content was high. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5391–5402, 2006  相似文献   

15.
A novel flame‐retardant epoxy resin, (4‐diethoxyphosphoryloxyphenoxy)(4‐glycidoxyphenoxy)cyclotriphosphazene (PPCTP), was prepared by the reaction of epichlorohydrin with (4‐diethoxyphosphoryloxyphenoxy)(4‐hydroxyphenoxy)cyclotriphosphazene and was characterized by Fourier transform infrared, 31P NMR, and 1H NMR analyses. The epoxy resin was further cured with diamine curing agents, 4,4′‐diaminodiphenylmethane (DDM), 4,4′‐diaminodiphenylsulfone (DDS), dicyanodiamide (DICY), and 3,4′‐oxydianiline (ODA), to obtain the corresponding epoxy polymers. The curing reactions of the PPCTP resin with the diamines were studied by differential scanning calorimetry. The reactivities of the four curing agents toward PPCTP were in the following order: DDM > ODA > DICY > DDS. In addition, the thermal properties of the cured epoxy polymers were studied by thermogravimetric analysis, and the flame retardancies were estimated by measurement of the limiting oxygen index (LOI). Compared to a corresponding Epon 828‐based epoxy polymer, the PPCTP‐based epoxy polymers showed lower weight‐loss temperatures, higher char yields, and higher LOI values, indicating that the epoxy resin prepared could be useful as a flame retardant. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 972–981, 2000  相似文献   

16.
We report the synthesis and characterization of novel elastomeric nanocomposites containing polyhedral oligomeric silsesquioxanes (POSS) as both the cross‐linker and filler within a polydimethylsiloxane (PDMS) polymer matrix. These polymer composites were prepared through the reaction of octasilane‐POSS (OS‐POSS) with vinyl‐terminated PDMS chains using hydrosilylation chemistry. In addition, larger super‐POSS cross‐linkers, consisting of two pendant hepta(isobutyl)POSS molecules attached to a central octasilane‐POSS core, were also used in the fabrication of the PDMS composites. The chemical incorporation of these POSS cross‐linkers into the PDMS network was verified by solid‐state 1H magic angle spinning NMR. Based on dynamic mechanical analysis, the PDMS nanocomposites prepared with the octafunctional OS‐POSS cross‐linker exhibited enhanced mechanical properties relative to polymer systems prepared with the tetrafunctional TDSS cross‐linker at equivalent loading levels. The observed improvements in mechanical properties can be attributed to the increased dimensionality of the POSS cross‐linker. The PDMS elastomers synthesized from the larger super‐POSS molecule showed improved mechanical properties relative to both the TDSS and OS‐POSS composites due to the increased volume‐fraction of POSS filler in the polymer matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2589–2596, 2009  相似文献   

17.
Polymers having polyhedral oligomeric silsesquioxane (POSS) in the main chains are an important class of organic–inorganic hybrid materials. Despite the increasing attention to the POSS polymers, variation of the monomers is still limited. Herein, we have proposed side‐opening POSS (SO‐POSS) monomers. Platinum‐catalyzed hydrosilylation polymerization proceeded to produce polysiloxanes having SO‐POSS in the main chains. The obtained polysiloxanes showed good solubility, high thermal stability, high transparency, and tunable reflective index. In addition, cyclic compounds were obtained during the investigation of the polymerization, and were synthesized with high selectivity under the slightly diluted conditions. The obtained cyclic compounds showed high thermal stability due to the silsesquioxane backbone, and the high dispersibility as a filler in poly(methyl methacrylate) was demonstrated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2243–2250  相似文献   

18.
Thermally induced polymerization of multifunctional methylmethacrylate POSS (MMA‐POSS) was studied in this work for preparation of polymer/POSS nanocomposites. The polymerization of MMA‐POSS could be promoted with benzoyl peroxide (BPO). Self‐assembly of POSS into a layer‐by‐layer structure in the MMA‐POSS polymer (TP‐MMA‐POSS) is observed with a transmission electron microscopy. An ultra‐low‐k value of about 1.85 is measured with TP‐MMA‐POSS. In addition, polyimide‐POSS nanocomposites are also prepared. These nanocomposites demonstrate good homogeneity and enhanced mechanical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5157–5166, 2008  相似文献   

19.
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 (Tg) 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  相似文献   

20.
Copolymerization of ethylene with iso‐butyl substituted monoalkenyl(siloxy)‐ or monoalkenylsilsesquioxane (POSS) comonomers over bis(phenoxy‐imine) and salen‐type titanium and zirconium catalysts was studied. It was found that the polyreaction performance was significantly depended by the kind of the catalyst and by the structure and concentration of POSS in the feed. The POSS comonomer was efficiently incorporated into the polymer chain at up to 0.2 mol %. The differences in the copolymer compositions as the functions of the catalyst kind and the POSS comonomer were observed, including the varied number‐average sequence length of ethylene and unsaturated end groups, as determined by 1H NMR and FT‐IR. The presence of POSS comonomers affected also the melting and crystallization behavior of the copolymers, as evidenced by DSC, because of influence on the polymer chain arrangement. The POSS units could act as the nucleating agents. Moreover, the crystal and structural parameters of ethylene/POSS copolymers were evaluated on the basis of X‐ray results, and the limited self‐aggregation of POSS incorporated into the polymer chain, the small number and size of POSS aggregates, and the increased crystallinity degree of copolymers were demonstrated. The ethylene/POSS copolymers produced by postmetallocenes offered also high thermal stability and interesting morphological properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3918–3934  相似文献   

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