POSS Structure Research Articles

Percolation network and piezoresistive properties of ultraductile cementitious monitoring coating with A-POSS modified carbon-based nanoconductors

Conventional cement-based sensors are large and often embedded in cast-in-place concrete structures, resulting in poor flexibility, low sensing accuracy, and inability to be replaced after damage. This paper reports a promising health monitoring technology, namely the composite coated sensor (sensing skin) prepared by anionic waterborne polyurethane (WPU)-modified cement, in which N-(2-aminoethyl)-3-amino propyl trime thoxy silane (NAEAPTMS) silsesquioxane modified ettringite (A-POSS) acts as a core modifier. The results showed that a continuous interpenetration polymer network was formed between the WPU and the cement, which greatly improved the crack resistance and balanced the polarisation reaction field. The agglomerated GO-CNT particles self-dispersed into micron/nanometer-sized particles under the co-precipitation of Ca2+/Al3+ and the semi-cage-like POSS structure formed by NAEAPTMS, using AFt as the supporting skeleton. The toughness and bond strength of the sensing skins were improved in the presence of A-POSS and, in particular, the maximum deflection angle exceeded 110°. Meanwhile, the electrical resistivity was reduced by more than 2 orders of magnitude. The effective conductivity inside and outside the interface can be precisely delineated when GO-CNT was perfectly arranged inside WPU-CEMENT. The agreement between the theoretical and experimental results of effective conductivity indicates that the sensing skin had a percolation network with imperfect and tunnel-assisted interfaces. The synergistic effect of WPU and A-POSS gave the sensing skin excellent performance of high sensitivity (80 times larger than strain gauges), low relaxation time (50 ms), and monitoring stability.

A Study of the Degradation Mechanism of Ladder-like Polyhedral Oligomeric Silsesquioxane via Fourier Transform Infrared Spectroscopy

As a result of global warming, fire outbreaks are becoming a common occurrence. There is, therefore, the need for an effective, low-cost and environmentally friendly fire-retardant material. Amine-terminated polyhedral oligomeric silsesquioxane, ATL-POSS, is a low-cost, water-soluble, fire-retardant material based on aminosilane coupling agents. Because of its solubility in water, it can serve as a general-purpose fire retardant. The ATL-POSS nanoparticles reported in this paper have high char retentions of about 75 and 54% in nitrogen and air atmospheres, respectively. Differential scanning calorimetry (DSC) was used to determine the phase transition temperatures. It was shown that ATL-POSS is an amorphous material. The thermal stability and rate of decomposition of POSS was determined by using thermogravimetric analysis (TGA). The TGA derivative curves (DTA) show that the degradation of ladder-like POSS occurred in multiple stages and that the rate of degradation is affected by the heating rate. The mechanism of decomposition of ATL-POSS was determined by using Fourier transform infrared spectroscopy, FTIR. The FTIR technique was chosen for this study because of its accessibility and ability to distinguish ladder-like POSS from the cage-type POSS structures. The FTIR spectra showed that the -Si-O-Si- cyclic structure was the predominant structure of POSS. By analyzing the FTIR spectra of the thermally treated POSS residues, obtained at the specified test temperatures, the detailed degradation mechanism of POSS was inferred. It was shown that the terminal silanol group was degraded at test temperatures below 400 °C. Silica was shown to be the final product of the pyrolysis of POSS. The presence of the FTIR transmission peaks at 1000 and 1100 cm−1, due to asymmetric vertical and horizontal stretching vibrations of the Si-O-Si, respectively, was the key evidence used to infer the ladder-like structure of POSS.

Resistance to space atomic oxygen radiation of MAC-based supramolecular gel lubricant containing POSS

This paper presents the synthesis of a POSS-based supramolecular gel with polyalkylcyclopentane (MAC) as the base oil through molecular design, which exhibits excellent resistance to space atomic oxygen (AO) irradiation. Herein, the reduce-friction (RF) and anti-wear (AW) properties and the resistance to space AO irradiation of the gel were first systematically investigated under atmospheric and simulated space environments. The results demonstrate that effectively improves the RF and AW of MAC in atmospheric or simulated space environments due to the POSS structure and high load-carrying capability of silicon-containing compounds generated by tribochemical reactions, as well as effectively separates the direct contact of the friction interface. POSS gel shows excellent promise in being used as a lubricant in the space environment.

Determination of characterization, antibacterial and drug release properties of POSS-based film synthesized with sol-gel technique.

In the study, antibacterial film synthesis was aimed using sol-gel technique from POSS structure with various functional groups. For this purpose, antibacterial properties have been acquired by metronidazole to the films to be synthesized. The films obtained were coated on glass surface samples by dip coating method. Antibacterial activities of surface coated glass samples were observed in E.coli and S. aureus bacteria. Metronidazole release studies in the film samples were followed by UV spectrophotometer. It was observed that drug release reached 68.90% at the end of the 24th h. As a result, it is thought that the synthesized film will be a good candidate especially for biomedical surface coating areas.

Supramolecular organogel of polyureas containing POSS units in the main chain: dependence on the POSS and comonomer structures

Supramolecular organogel of polyureas containing POSS units in the main chain: dependence on the POSS and comonomer structures

Study of the kinetics of gas evolution of a polymer composite under the influence of vacuum and VUV

The paper presents data on the effect of high vacuum and vacuum ultraviolet (VUV) on a polymer composite based on polyimide track membranes. Polyimide track membranes were filled with POSS structures. For comparison, we also used pure polyimide films without filler. Exposure in high vacuum and surface treatment of the developed VUV composite were carried out in the imitation chamber of near-Earth space, located in the Space Materials Science Laboratory of BSTU named after V.G. Shukhov (Russia, Belgorod). The high resistance of the composite to high vacuum and VUV has been established. The total weight loss of the composite by 24 hours was 0.26 wt. % (after holding in vacuum) and 0.28 wt. % (after VUV).

Supramolecular organogel formation behaviors of beads-on-string shaped poly(azomethine)s dependent on POSS structures in the main chains

Organogel formation was observed for isobutyl-substituted cage octasilsesquioxane (T8) in the main-chain type polyazomethines, while precipitates instead of gel formation were observed for phenyl-substituted double-decker-shaped silsesquioxanes (DDSQ)-poly(azomethine)s.

Synthesis of PI/POSS nanocomposite films based on track nuclear membranes and assessment of their resistance to oxygen plasma flow

This work presents, for the first time, data on the possibility of synthesizing polyimide nanocomposite films based on track nuclear membranes and organosiloxane (polyhedral oligomeric silsesquioxanes) POSS structures. The synthesis of the nanocomposite films was carried out by filling the tracks of a polyimide membrane with POSS structures under hydrothermal conditions in a high-pressure reactor. The surface and mechanical characteristics of the developed nanocomposite films were studied, and the results of their resistance to the flow of oxygen plasma are presented. It was found that the introduction of POSS structures significantly increased the resistance of polyimide to the flow of oxygen plasma. The PI/POSS composite exhibited an insignificant change in weight, the weight loss reached 0.92 ± 0.05 mg/cm2 in 24 h after the start of the experiment, which is almost two orders of magnitude lower than that of the polyimide film.

Synthesis of polyhedral oligomeric silsesquioxane-n-acetylcysteine conjugate with click chemistry and ıts antioxidant response and biocompatibility

In this study, polyhedral oligomeric silsesquioxane-N-acetylcysteine (POSS-NAC) conjugate as a potential antioxidant molecule was synthesized from N-acetylcysteine (NAC) and amino-functional POSS structure by click chemistry. The chemical structures and thermal properties of the synthesised POSS-NAC conjugate was characterized by spectroscopic and thermal analysis techniques. The antioxidant capacity of the POSS-NAC conjugate was also determined by the 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity and reducing power methods. According to the reducing power method, POSS-NAC structure has lower reducing activity than standard ascorbic acid and trolox (p<0.001). It was found from the ABTS radical scavenging activity results that the synthesized POSS-NAC conjugate had a significantly higher radical scavenging effect than the standards (p <0.001). Biocompatibility properties of the POSS-NAC structure were detected in vitro cell culture system with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test on L-929 mouse fibroblast cells. The synthesized POSS-NAC conjugate exhibits high antioxidant activity and good biocompatibility.

Mechanical and flame‐retardant properties and thermal decomposition of vinyl ester resin modified by different phenyl silsesquioxanes

The mechanical properties and fire resistance of vinyl ester resin (VER) composites containing cage‐shaped octaphenyl silsesquioxane (OPS), incompletely cage‐shaped phenyl silsesquioxane (PhT7POSS), and ladder‐shaped phenyl silsesquioxane (PPSQ) were investigated. The POSS structure and dispersion have a great influence on the mechanical properties, thermal stability, and decomposition process of VER composites. The bending strength at break and modulus of the VER‐POSS composites were enhanced obviously, especially for VER‐PPSQ composite and VER‐OPS composite, respectively. In addition, PhT7POSS‐based VER composites revealed the lower values of the peak heat release rate, total heat release, and total smoke release in cone calorimetry tests due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. Moreover, the flame‐retardant mechanisms of condensed phase and gas phase were also investigated in detail. These results illustrate VERs modified by OPS, PhT7POSS, and PPSQ are providing an applicable method to fabricate the composites with excellent flame‐retardant and mechanical properties.

Self-assembly of polyhedral oligomeric silsesquioxane structures through ion exchange

In this study, we synthesized 3-chloroammoniumpropyl polyhedral oligomeric silsesquioxanes (CAP-POSS) by acid hydrolysis and condensation. Partial ion exchange resulted in the formation of supramolecular structures through electrostatic interactions. The interactions between POSS macroions were led by multiple hydrogen bonds that form supramolecular structures. After ion exchange, the structures of the CAP-POSS reduce the symmetry by the exchange of counterions and associate to form rigid transparent films at room temperature. The amount of chloride modulated the size and structure of macroions aggregates in the supramolecular films. Regardless of the amount of chloride removed, the films were formed of mass-fractal like structures with sizes ranging from 80 to 28 nm. The surface energy was proportional to the free amine content, and UV–vis was a light transmission characteristic. Therefore, the use of partial ion exchange represents an alternative to design of supramolecular POSS structures with properties tunable through multiple hydrogen bonds.

Synthesis of Zirconium-Containing Polyhedral Oligometallasilsesquioxane as an Efficient Thermal Stabilizer for Silicone Rubber.

Free radicals play a negative role during the thermal degradation of silicone rubber (SR). Quenching free radicals is proposed to be an efficient way to improve the thermal-oxidative stability of SR. In this work, a novel zirconium-containing polyhedral oligometallasilsesquioxane (Zr-POSS) with free-radical quenching capability was synthesized and characterized. The incorporation of Zr-POSS effectively improved the thermal-oxidative stability of SR. The T5 (temperature at 5% weight loss) of SR/Zr-POSS significantly increased by 31.7 °C when compared to the unmodified SR. Notably, after aging 12 h at 280 °C, SR/Zr-POSS was still retaining about 65%, 60%, 75%, and 100% of the tensile strength, tear strength, elongation at break, and hardness before aging, respectively, while the mechanical properties of the unmodified SR were significantly decreased. The possible mechanism of Zr-POSS for improving the thermal-oxidative stability of SR was intensively studied and it was revealed that the POSS structure could act as a limiting point to suppress the random scission reaction of backbone. Furthermore, Zr could quench the free radicals by its empty orbital and transformation of valence states. Therefore, it effectively suppressed the thermal-oxidative degradation and crosslinking reaction of the side chains.

Density functional theory study of interactions between carbon dioxide and functionalized polyhedral oligomeric silsesquioxanes

AbstractPolyhedral Oligomeric Silsesquioxanes (POSS) are cage‐structured inorganic–organic hybrid materials which can be used in various industrial applications. It is recently discovered that POSS structures with certain functional groups can be solubilized in supercritical CO2 allowing their applications in environmentally benign supercritical processing of materials. In this theoretical study, nature and energetics of the interactions of octatrifluoropropyl POSS, octatrifluoromethyl POSS, and octamethyl POSS with CO2 are investigated according to the principles of density functional theory (DFT) by use of Gaussian 09 software. Simulations show that CO2‐octamethyl POSS pair has hydrogen bonding between the O atom of CO2 and the H atom of the methyl group, and CO2‐octatrifluoromethyl POSS pair has interactions between the C atom of CO2 and the F atom of the trifluoromethyl group. CO2‐octatrifluoropropyl POSS pair is found to have both interaction types. The octamethyl, the octatrifluoromethyl and the octatrifluoropropyl POSS structures have interaction energies of −2.18 kcal/mol, −3.10 kcal/mol, and −3.77 kcal/mol, respectively. This shows that the presence of Lewis acid–Lewis base interaction between C and F instead of hydrogen bonding between O and H atoms enhances the interaction of the molecule with CO2, while the presence of both interactions between the octatrifluoropropyl POSS‐CO2 pair makes the intermolecular interaction even stronger.

Copolymers of ethylene with monoalkenyl- and monoalkenyl(siloxy)silsesquioxane (POSS) comonomers – Synthesis and characterization

The hybrid ethylene/POSS copolymers were obtained using the rac-Et(Ind)2ZrCl2 catalyst activated by MAO. A series of monoalkenyl- and monoalkenyl(siloxy)silsesquioxanes derivatives with different structures of reactive alkenyl substituent and types of non-reactive groups attached to the T8 POSS cage was used as comonomers. The kind and concentration of the POSS comonomer in the reaction feed as well as extended reaction time were found to strongly influence the catalyst efficiency and incorporation of POSS units into polymer chains. The comonomer reactivity was significantly dependent on the length of the alkenyl reactive substituent in the POSS molecule and it was highest for the POSS structures with medium-length of the alkenyl substituent due to their steric and inductive effects of the silicon-oxygen cage. The molecular weight as well as the kind and the content of unsaturated end groups in copolymers were dependent on the kind and amount of POSS comonomer in the reaction feed. The change in melting temperature, crystallinity degree, crystallization temperature and morphology of copolymers was observed as compared to neat polyethylene (PE).

Study of thermal properties of polyethylene and polypropylene nanocomposites with long alkyl chain-substituted POSS fillers

The effect of incorporation of octakis({alkyl}dimethylsiloxy)octasilsesquioxanes molecules with n-octyl, n-octadecyl and 4-methyl-hexyl substituents on thermal properties of polypropylene (PP), low-density polyethylene (LDPE) and high-density polyethylene (HDPE) was investigated. Thermal properties of those composite materials were evaluated by means of the differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The type and mass% content of POSS nanofillers influenced the crystallization and melting properties as well as thermal stability of the obtained polyolefin nanocomposites. The incorporated POSS particles—acting as nucleating agents—improved the crystallization process of those polyolefin materials. The POSS nanofiller with n-octyl substituents turned out the most effective nucleating agent. The addition of POSS nanofiller particles into the polyolefin matrix affected the melting behavior of the nanocomposites obtained, decreasing their melting temperatures. Thermal stability under nitrogen as well as in air atmosphere was most significantly enhanced for polyolefin nanocomposites contained the POSS with n-octadecyl substituents. That may result from improved compatibility of the POSS structure with long n-alkyl chain substituents at the silicon–oxygen core. The uniform dispersion of the long n-alkyl chain-substituted POSS was confirmed by SEM analysis.

Proximity Effect using a Nanocage Structure: Polyhedral Oligomeric Silsesquioxane‐Imidazolium Tetrachloro‐ palladate Salt as a Precatalyst for the Suzuki–Miyaura Reaction in Water

AbstractA polyhedral oligomeric silsesquioxane‐imidazolium tetrachloropalladate salt (POSS‐Imi‐PdCl4) was prepared by the reaction of a polyhedral oligomeric silsesquioxane‐imidazolium chloride salt (POSS‐Imi‐Cl) with PdCl2 and used as a pre‐catalyst for the Suzuki–Miyaura reaction in water at 100 °C at a low loading (0.08–0.16 mol %). Biphenyl compounds were isolated in high to excellent yields. A comparison of the POSS‐based catalyst with the corresponding catalyst without the nanocage structure (i.e., 1‐butyl‐3‐methylimidazolium tetrachloropalladate) highlighted the role of the POSS structure to reach higher yields in the Suzuki–Miyaura reaction. This result is ascribed to a proximity effect of the imidazolium moieties linked to the nanocage structure. Fresh and used catalytic materials were characterised by using X‐ray photoelectron spectroscopy and TEM.

Crystalline, Thermal, and Biodegradable Properties of Poly(L-Lactic Acid)/Poly(D-Lactic Acid)/POSS Melt Blends

ABSTRACTA ternary nanocomposite consisting of poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), and epoxy cyclohexyl polyhedral oligomeric silsesquioxane (e-POSS) was prepared by reactive blending method. Scanning electron microscopy revealed that the feeding of three compositions in batches, i.e., PDLA incorporation at different times, was more beneficial for the even dispersion of POSS in matrix. POSS introduction improved the homocrystallinity and stereocomplex of the blends. Rheological properties and heat resistance were enhanced, which indicated potential extensive application of PLLA-based materials. The optimization of degradation stability in saline buffer was attributed to the various hydrophobic properties of blends caused by POSS structure.

Star-Shaped and Linear POSS-Polylactide Hybrid Copolymers.

Novel octakis-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (POSS-S-OH) as well as heptaisobutyl-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (iBu-POSS-S-OH) were synthesized. POSS structures, bearing both types of groups i.e., 2[(6-hydroxyhexyl)thio]ethyl and the vinyl ones, pendant from the octahedral cage are also described. The synthetic pathway involved thiol-ene click reaction of 6-mercapto-1-hexanol (MCH) to octavinyloctasilsesquioxane (POSS-Vi), and heptaisobutylvinyloctasilsesquioxane (iBu-POSS-Vi), in the presence of 2,2′-azobisisobutyronitrile. The functionalized silsesquioxane cages of regular octahedral structure were used further as initiators for ring opening polymerization of l,l-dilactide, catalyzed by tin (II) 2-ethylhexanoate. The polymerization afforded biodegradable hybrid star shape and linear systems with an octasilsesquioxane cage as a core, bearing polylactide arm(s).

Sub-10-nm patterning process using directed self-assembly with high χ block copolymers

The perpendicularly orientated lamellar structure of the self-organized diblock copolymer is an attractive template for sub-10-nm line-and-space pattern formation. We propose a method of evaluating the neutral layer (NL) whose performance has an important bearing on the perpendicular orientation of the lamellar structure. The random copolymer of methyl methacrylate and i-butyl POSS methacrylate (MAIBPOSS) has been investigated as an NL for a polymethylmethacrylate-b-polymethacrylethylPOSS (PMMA-b-PMAIBPOSS) lamellar structure. PMMA-b-PMAIBPOSS material has the potential to form sub-10 nm line-and-space pattern, in addition to high etch selectivity due to its POSS structure. Under the free surface, PMMA-b-PMAIBPOSS film on the random copolymer layer showed horizontal orientation. However, a half-pitch of a 7-nm finger pattern structure was observed by peeling off the horizontally oriented layer. The upper portion of the PMMA-b-PMAIBPOSS film was eliminated till proximity of the random copolymer layer by CF4 gas etching. From the result, it was revealed that the PMMA-r-PMAIBPOSS works as an NL. It was confirmed that the contact angle analysis using an appropriate polymer is a suitable method for evaluation of the surface energy performance of the copolymer with the attribute of high segregation energy.

Thermal conductivity and thermal properties of POSS/polytriazole organic–inorganic hybrid material

ABSTRACTTo decrease the thermal conductivity of polytriazole‐based fiber reinforced composites, an organic–inorganic POSS/polytriazole hybrid resin was obtained. The influences of various proportions of POSS on thermal conductivity and the thermal properties of hybrid materials were emphatically investigated. The results show that POSS incorporation resulted in not only decreased thermal conductivity but also increased Tg and thermal decomposition temperature. The enhancement was ascribed to the nanoscale effect of POSS structure and the fact that the POSS framework has a high heat resistance property. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41967.