Studies on Polybenzoxazine/Capron PK4/octakis(dimethylsiloxypropylglycidylether) Silsesquioxane Nanocomposites for Radiation Resistant Applications

Polymeric materials can erode when exposed to the radiation environment that includes atomic oxygen (AO), ultraviolet (UV) ionizing radiation, and ultrahigh vacuum (UHV). Many studies have been devoted to develop polymeric materials that can withstand decades of exposure on radiation. In this connection an attempt has been made to develop polyhedral oligomeric silsesquioxane (POSS) reinforced capron PK₄ (CPL) modified polybenzoxazine nanocomposites in the present work and to assess their ability to resist radiation for a prolonged period. Varying weight percentages of (0, 1, 3, and 5 wt%) POSS were reinforced in to 1:1 (w/w) PBZ/CPL copolymerization through chemical ring opening polymerization. The POSS reinforced PBZ/CPL nanocomposites have been studied their tensile strength and morphological behavior before and after exposure of UV irradiation. Data resulted from the studies indicated that the neat PBZ-CPL has significantly eroded after UV exposure, whereas POSS reinforced PBZ/CPL composites have eroded only an insignificant extent and the value of tensile properties are reduced to a small extent. The POSS reinforced nanocomposites during exposure under UV radiation undergo changes on the surface and lead to the formation of silica (Si-O-Si) passivation layer. The formation of silica layer protects (act as inert layer) from further erosion of the composites and was ascertained from SEM images. Data obtained from thermal and dielectric studies indicate that thermal stability and dielectric behavior of composites were appreciably improved when compared with those of neat PBZ/CPL matrix.     

Preparation and characterization of styrene/styryl–polyhedral oligomeric silsesquioxane hybrid copolymers

BACKGROUND: Organic–inorganic nanocomposites were prepared by copolymerization of various monomers and polyhedral oligomeric silsesquioxane (POSS) derivatives. Preliminary results showed that styrene/styryl–POSS copolymers could be obtained using CpTiCl₃ catalyst. In the work reported here, the copolymerization of styrene and styryl‐substituted POSS was studied in detail for a more effective catalyst, Cp*TiCl₃. RESULTS: The glass transition temperature (T_g) of the copolymers prepared increased with increasing POSS content. The degradation temperature (T_d) of the copolymers was 60 °C higher than that of syndiotactic polystyrene under nitrogen. Although the thermal properties were improved by incorporation of POSS, the catalytic activity decreased with POSS content. The racemic triad and syndiotactic index of the copolymers decreased with increasing POSS content. Gel permeation chromatograms of the copolymers exhibited multimodal distribution due to the presence of multi‐active centres, which were formed by interaction of Ti with the POSS siloxane linkage. CONCLUSION: With the incorporation of POSS, the thermal properties of polystyrene were improved. The styrene/styryl–POSS copolymers are formed through the various active sites arising from the interactions of Ti with POSS. Copyright © 2008 Society of Chemical Industry     

Radiation damage behavior of carbon/carbon composite in Low Earth Orbit environment

To understand the degradation behavior of Carbon/Carbon(C/C) composite in LEO radiation environment, groups of 2D-C/C composites samples were exposed to ground-based Low Earth Orbit(LEO) simulating facilities. The LEO radiating environment covers part of Van Allen inner belt, which contains atomic oxygen(AO) and high-energy proton radiating regions. These two kinds of radiating sources were arranged for simulating the real LEO radiating conditions regarding to the first orbit movement speed of serving space shuttles. Changes of micro-structure, mass loss, surface roughness, chemical construction and thermal physical properties after environmental assessment were analyzed and compared to understand the damage behavior of LEO radiation on C/C composite. It was found that AO is the main factor of mass loss in LEO radiating particles. The charged high-energy protons have an aggravating damage ability with energetic AO, damage situations of degree in orbit down process is more serious than in orbit rising process. The LEO radiation damage mechanisms of C/C composite are revealed and expounded either.     

Evaluation of two new white silicone thermal control paints under atomic oxygen

The exterior optical surfaces of satellites are directly exposed to the harsh space environment. Thermal control paints are resistant to the conditions encountered at low earth orbit (LEO): vacuum, atomic oxygen, thermal cycling, and ultraviolet radiation. In this paper two white paints were prepared by ultrasonic dispersing method for application to space structures. The white paints include zinc-oxide-pigmented silicone elastomer SilGel 612 (U1) and a zinc-oxide-pigmented silicone elastomer RT604 (U2). These coatings are electrically non-conductive. We present the behavior of thermal control paints under atomic oxygen (AO). The effects of AO exposure were studied by the mass loss of paint specimens and complementary techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM). Also the optical degradation in the reflectance spectra, solar absorptance and thermal emittance for U1 and U2 samples before and after AO exposure were investigated. The paints have promising AO resistance properties that could be suitable for space applications.     

Effect of polyhedral oligomeric silsesquioxane on water sorption and surface property of Bis‐GMA/TEGDMa composites

2,2‐Bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy)phenyl]propane (Bis‐GMA), one of the most important light‐curable dimethacrylate resins, is widely used as dental restorative material. However, one problem of Bis‐GMA is the high water sorption due to the hydrophilic hydroxyl (–OH) group, resulting in a short life in actual application. In this study, to overcome the drawback stated above, novel organic–inorganic dimethacrylate monomer containing polyhedral oligomeric silsesquioxanes (POSS), Bis‐GMA‐graft‐POSS, is synthesized via the nucleophilic addition reaction of isocyanate functionalized POSS (IPOSS) and pendent hydroxyl group of Bis‐GMA. Then the as‐synthesized Bis‐GMA‐graft‐POSS, of which hydroxyl group was substituted by hydrophobic POSS, is also introduced into the Bis‐GMA/TEGDMA matrix to prepare a series of methacrylate‐based hybrids for dental materials under visible light with camphorquinone and ethyl‐4N,N‐dimethy‐laminobenzoae (EDMAB) as initiator and coinitiator, respectively. Compared to Bis‐GMA/TEGDMA composites, water sorption of modified composites can be significantly reduced with the addition of Bis‐GMA‐graft‐POSS. Moreover, the Bis‐GMA/TEGDMA/POSS hybrids show hydrophobic surfaces, leading to much higher water contact angles than that of Bis‐GMA/TEGDMA composites. The morphology of hybrids containing POSS was furthermore studied by X‐ray diffraction (XRD) analysis and X‐ray photoelectron spectroscopy (XPS). The results show that POSS disperses in the matrix in noncrystalline form and tend to migrate to the surface of the modified composites that lead to the lower water sorption and higher water contact angles. These results are very useful for design of novel methacrylate monomers and clinical application. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

New composites of spherical bridged polysilsesquioxanes and aggregates of Pd nanoparticles with POSS via ionic interactions

Spherical bridged polysilsesquioxane (BPS) particles with sulfonic groups (BPS–SO₃ ^?) were prepared by the subsequent reduction and oxidation of BPS with disulfide groups (BPS–S–S) after the hydrolysis and condensation reaction of silane monomers with disulfide groups under ammonia and alcoholic solutions. Spherical aggregates of Pd nanoparticles (Pd–polyhedral oligomeric silsesquioxanes, Pd–POSS) were produced by the mixing of POSS and palladium (II) acetate in methanol solution. The average size of BPS–SO₃ ^? and Pd–POSS was about 200–400 and 30–50 nm, respectively. New BPS–SO₃ ^?/Pd–POSS composites with the shape of BPS–SO₃ ^? covered with Pd–POSS nanoparticles were fabricated by ionic interactions between negatively charged BPS–SO₃ ^? and positively charged Pd–POSS. Pd–POSS nanoparticles were more effectively attached to BPS–SO₃ ^? than BPS–S–S, which resulted from the difference of zeta potential between BPS–SO₃ ^? and BPS–S–S. That is, ionic interactions in BPS–SO₃ ^?/Pd–POSS composites were stronger than those in BPS–S–S/Pd–POSS composites. As the storage time was increased, the precipitation of BPS–SO₃ ^?/Pd–POSS composites in methanol solution resulted from the strong complex between BPS–SO₃ ^? and Pd–POSS unlike BPS–S–S/Pd–POSS composites. New particle composites were characterized by Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy.     

Star‐shaped POSS–methacrylate copolymers with phenyl–triazole as terminal groups,synthesis, and the pyrolysis analysis

Star‐shaped polyhedral oligomeric silsesquioxane (POSS)–methacrylate hybrid copolymers with phenyl–triazole as terminal groups had been designed and synthesized via sequential atom transfer radical polymerization (ATRP), azidation, and phenylacetylene‐terminated procedures, and the hybrid copolymers here could be denoted as POSS–(PXMA‐Pytl)₈, where X can be M, B, L, and S, represented four different methacrylate monomers, such as methacrylate (MMA), butyl methacrylate (BMA), lauryl methacrylate (LMA), and stearyl methacrylate (SMA), respectively. Thermal gravimetric analysis (TGA) and in situ Fourier transform infrared spectroscopy (FTIR) were applied for studying the thermal stability and degradation mechanism, and it was found that all of the POSS–(PXMA‐Cl)₈ and POSS–(PXMA‐Pytl)₈ copolymers exhibited excellent thermal stabilities, which had great potential in heat‐resistant material application. Different tendencies of decomposition temperatures at 5% and 10% weight loss (T₅ and T₁₀) dependent on the side‐chain length and terminal group species were investigated respectively. The longer alkyl side chains of the monomers, the lower thermal stabilities, and enhanced T₅ and T₁₀ were also shown with the introduction of phenyl–triazole groups instead of chlorine groups. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40652.     

Effect of weathering cycle and manufacturing method on performance of wood flour and high‐density polyethylene composites

Wood–plastic lumber is promoted as a low‐maintenance high‐durability product. When exposed to accelerated weathering, however, wood–plastic composites may experience a color change and loss in mechanical properties. Differences in weathering cycle and composite surface characteristics can affect the rate and amount of change caused by weathering. In this study, 50% wood flour filled high‐density polyethylene composite samples were injection molded, extruded, or extruded and then planed to remove the manufacturing surface characteristics. Composites were exposed to two accelerated weathering cycles in a xenon arc weathering apparatus. This apparatus exposed the samples to xenon arc radiation, which is a combination of UV, visible, and IR radiation that is similar to solar radiation. Composites were exposed to radiation with or without water spray. After exposure to radiation and water spray, composites with more wood component at the surface (i.e., planed samples) experienced a larger percentage of total loss in flexural modulus of elasticity and strength after weathering compared with the other composites. Composites exposed to radiation only did not experience as much change in properties as those exposed to radiation with water spray. The results of this study demonstrate that exposing wood–plastic composites to water spray in combination with radiation is more severe than exposing wood–plastic composites to radiation only. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3131–3140, 2006     

Covalent functionalization of carbon nanotubes with polyhedral oligomeric silsequioxane for superhydrophobicity and flame retardancy

Multiwalled carbon nanotubes (MWCNTs) were covalently functionalized with polyhedral oligomeric silsequioxane (POSS). The results of Fourier Transform Infrared Spectroscopy, Raman spectroscopy and Transmission Electron Microscopy indicated that POSS particles were grafted onto MWCNTs. The POSS content determined by thermo‐gravimetric analysis (TGA) was estimated to be ～25 wt%. A stable and superhydrophobic surface characteristic was observed for the film made of MWCNTs grafted with POSS (MWCNT‐g‐POSS) even after an exposure to a high‐humidity environment for three weeks. The water contact angle of the sample was measured to be 160.5 ± 1.1°. Buckypapers were made from both pristine MWCNTs and chemically converted to MWCNT‐g‐POSS. The pore structures of the buckypapers were characterized by mercury intrusion porosimetry and scanning electron microscopy. The flame‐retardant performance of the buckypaper‐based composites was evaluated by TGA and microscale combustion calorimetry (MCC) test. The TGA test results indicated that the MWCNT‐g‐POSS dramatically increased the char residues of the composite. Approximately 72% reduction in peak heat release rate was achieved for the MWCNT‐g‐POSS /resin composite from the MCC testing. The fire‐retardant mechanism was discussed. POLYM. ENG. SCI., 2013. © Society of Plastics Engineers     

Damage behavior of atomic oxygen on zirconium carbide coating modified carbon/carbon composite

Zirconium carbide (ZrC) components were induced as coating modification on carbon/carbon (C/C). These ZrC–C/C specimens were investigated after atomic oxygen (AO) exposure for different assessment times, low earth orbit (LEO) ground-based environmental simulator was employed. The results indicate that ZrO₂ is the major production generated by the AO chemical reaction with the ZrC coating. Upon further exposure to AO, the production of ZrO₂ would drop off, then exfoliate easily, due to the mechanical impacting effect. Then the exposed graphite matrix and carbon fiber get corroded. Amorphous diamond-like carbon (DLC) is detected by X-ray photoelectron spectroscopy during AO exposure. Bending strength performance increased by 25% under AO exposure at first 10 h, then dropped by 52.1% from 10 h to 30 h of AO exposure. The AO damage mechanisms of ZrC–C/C composites are revealed.     

Synthesis of POSS-containing fluorosilicone block copolymers via RAFT polymerization for application as non-wetting coating materials

By using a polydimethylsiloxane (PDMS) macro-chain transfer agent with trithiocarbonate groups at both ends, fluorosilicone block copolymers containing polyhedral oligomeric silsesquioxane (POSS) were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. Acryloisobutyl POSS (APOSS) and 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) were sequentially introduced into the copolymers. The obtained triblock copolymers PDMS-b-(PAPOSS)₂ exhibited a low polydispersity index (PDI) of less than 1.42 in the first 6 h of polymerization, but the PDI value became broader later because of the steric hindrance of the POSS macromer. The POSS-containing fluorosilicone pentablock copolymers with a PDI of about 2.0, which were prepared by the further RAFT polymerization of HFBA, showed clear microphase separation. The average roughness values of the copolymer films were enhanced by introducing POSS, and a certain POSS content led to a significant decrease of the receding contact angle. Measurements of water contact angles and ice shear strengths demonstrated that the non-wetting properties of the copolymer films were improved by the incorporation of both POSS and fluorine blocks. The block copolymers combine the advantages of POSS, PDMS and fluoropolymers, and can be potentially applied as non-wetting coating materials for anti-icing or anti-frosting.     

Preparation of POSS/Quartz fibers/cyanate ester resins laminated composites

Quartz fibers (QFs) and two polyhedral oligomeric silsesquioxane (POSS) (epoxy‐POSS and hydroxy‐POSS) are performed to regulate the dielectric properties, heat resistance, and mechanical properties of cyanate ester (CE) resins. With the introduction of POSS, the dielectric constant and dielectric loss tangent values of the POSS/QFs/CE laminated composites are decreased obviously. The heat resistance properties and flexural strength values of the laminated composites are increased, but the interlaminar shear strength values of the laminated composites are decreased slightly. The EP‐POSS/QFs/CE laminated composites have relatively better dielectric, heat resistance, and mechanical properties than those of HO‐POSS/QFs/CE laminated composites. POLYM. COMPOS., 36:2017–2021, 2015. © 2014 Society of Plastics Engineer     

Morphology and rheological behaviors of poly(ethylene terephthalate) nanocomposites containing polyhedral oligomeric silsesquioxanes

Poly(ethylene terephthalate) (PET)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by in situ polymerization. Light scattering measurement suggested that there is significant change in molecular weight arising from gel formation by chemical crosslinking during polymerization. The thermal decomposition temperatures of the composites measured at 5 wt % weight loss were 5–10°C higher than that of PET. There is no significant change in other thermal properties. Scanning electron microscopy observations suggest that there is obvious phase separation in PET/POSS composites, composites containing 1 wt % of disilanolisobutyl and trisilanolisobytyl‐POSS show fine dispersions of POSS (30–40 nm in diameter), which arise from strong interfacial interactions between POSS and PET during polymerization. The viscosity of the composites increased with the addition of POSS. The observation of a plateau region of composites containing 1 wt % of POSS in the plot of log G′ vs. log G″ indicates strong interfacial interactions between POSS and PET. Sixty‐three percent and 41% increase in tensile strength and 300 and 380% increase in modulus were achieved in the composites containing 1 wt % of disilanol‐ and trisilanol‐POSS, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Epoxy/POSS organic–inorganic hybrids: Viscoelastic,mechanical properties and micromorphologies

A series of epoxy resin (EP)/octa(aminpropyl)silsesquioxane (POSS‐NH₂) organic–inorganic hybrid composites (EP/POSS‐NH₂ 100/0, 95/5, 90/10, and 80/20 wt/wt) were prepared by melt casting and then curing. Viscoelastic and mechanical properties of these composites were studied by dynamic mechanical analysis and mechanical testing, respectively. Scanning electron microscopy was used to study of the micromorphologies of the composites and to elucidate the toughening mechanisms of POSS‐NH₂. POSS units incorporated into the epoxy network showed good compatibility with the resin matrix. Phase separation was not observed even at high POSS content (20 wt%). Incorporation of POSS macromer into the epoxy network after curing increased the glass transition temperature, slightly narrowed the temperature range widths of the glass transition, and lowered the intensities of their loss moduli peaks of the resultant composites. The glass transition temperature of EP/POSS‐NH₂ composites increased significantly with increasing POSS content at lower POSS content (<10 wt%), while increased slightly at higher POSS content. Both impact and flexural strengths of the hybrids reached their optimum values when 10 wt% content of POSS was introduced. POLYM. COMPOS., 28:175–179, 2007. © 2007 Society of Plastics Engineers.     

Zirconium-Embedded Polyhedral Oligomeric Silsesquioxane Containing Phosphaphenanthrene-Substituent Group Used as Flame Retardants for Epoxy Resin Composites

A zirconium hybrid polyhedral oligomeric silsesquioxane derivative (Zr–POSS–bisDOPO) is synthesized by the corner-capping and Kabachnik–Fields reactions. It is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR), and then used as a flame retardant in diglycidyl ether of bisphenol A (DGEBA) to endow epoxy resin (EP) with flame retardancy. The flame retardancy, thermal stability, and mechanical properties of the cured EP/Zr–POSS–bisDOPO composites are investigated. The results show that when Zr–POSS–bisDOPO is added by 5–7 wt%, the EP/Zr–POSS–bisDOPO composites pass the UL-94 V-0 rating test. In addition, they have a better flame-retardant effect than pure EP. The combination of Zr atom embedded in the Si O cubic cage and the two phosphaphenanthrene substituent groups in one corner of cubic cage is expected to realize the Zr/Si/P ternary intramolecular hybrid synergistic effect and achieve the possibility of dispersing metal–POSS cages at a sub-micrometer-scale level into polymer matrix. It also proves that Zr–POSS–bisDOPO produces phosphorus-containing free radicals and terminates the chain reactions in gas phase. Meanwhile the Si O Si and Zr O units are retained in the solid phase, which promote the char formation and enhance the flame retardancy. This kind of Zr-doped POSS will be helpful for developing the new metal–POSS hybrid flame-retardant and polymer composites.     

Synthesis,pH sensitivity,and drug‐release behavior of acrylic acid and polyhedral oligomeric silsesquioxane copolymer

pH‐Sensitive organic–inorganic copolymers of hydrogels were developed as drug delivery systems (DDS) to improve the swelling behavior of polyacrylic acid (PAA). They were represented through FTIR, TGA and XRD characterization which revealed that the functional groups of methacryl‐phenyl polyhedral oligomeric silsesquioxane (POSS) were successfully added to the acrylic acid (AA) molecular chains through radical solution polymerization. The DSC test results indicate that the addition of POSS could improve the thermal properties of the copolymers. The swelling properties at the pH range of 1.25–8.01 exhibited the pH sensitivity of POSS/AA copolymers (POSS‐co‐AA) and the lower swelling ratio in acidic conditions indicated that the DDS had low amount of release in SGF; this phenomenon suggested that the copolymer was available as DDS of theophylline. And it was proved by drug release curve and scanning electron microscopy. Since the addition of POSS reduced the release rate of theophylline and prolonged the release time of the drug, the concentration range of theophylline could remain low for an extended duration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of polyhedral oligomeric silsesquioxane coatings on the interface and impact properties of carbon‐fiber/polyarylacetylene composites

Two kinds of polyhedral oligomeric silsesquioxane (POSS) coatings were used for the modification of the interface in carbon fiber (CF) reinforced polyarylacetylene (PAA) matrix composites. The effects of the organic–inorganic hybrid POSS coatings on the properties of the composites were studied with short‐beam‐bending, microdebonding, and impact tests. The interlaminar shear strength and interfacial shear strength showed that the POSS coatings resulted in an interfacial property improvement for the CF/PAA composites in comparison with the untreated ones. The impact‐test results implied that the impact properties of the POSS‐coating‐treated composites were improved. The stiffness of the interface created by the POSS coatings was larger than that of the fiber and matrix in the CF/PAA composites according to the force‐modulation‐mode atomic force microscopy test results. The rigid POSS interlayer in the composites enhanced the interfacial mechanical properties with a simultaneous improvement of the impact properties; this was an interesting phenomenon in the composite‐interface modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5202–5211, 2006     

Reaction of poly(vinyl butyral) with tetraethyl orthosilicate: grafting of siloxane chains and new composites

New graft copolymers with side polysiloxane chains were synthesized by sol–gel reaction of acid‐catalyzed hydrolysis of tetraethyl orthosilicate in the presence of poly(vinyl butyral). The grafting is realized by exchange reaction of the alkoxyl moieties in siloxane and acetal groups. When the reaction is carried out in non‐hydroxylic solvent (1,1‐dimethoxyethane) inter‐etherification with participation of the residual hydroxyl groups of poly(vinyl butyral) is also important. The copolymers obtained contain free silanol groups which are active in complexing with polymeric bases by hydrogen bonds, with formation of new composites. Copyright © 2004 Society of Chemical Industry     

复合材料POSS/TX-10/Bent的制备及其吸附性能

以多面齐聚倍半硅氧烷(POSS)、TX-10型非离子表面活性剂为改性剂对膨润土(Bent)进行复合改性制备了复合材料(POSS/TX-10/Bent),并利用亚甲基蓝研究了其吸附性能。采用XRD、XPS、EA、FTIR、SEM对POSS/TX-10/Bent进行了组成与结构表征。结果表明,POSS和TX-10型非离子表面活性剂都成功插入到膨润土层间,使得复合材料层间距增大,疏水性增强。吸附实验表明,在30℃、pH为6.52(原始值)的条件下,复合材料投加量5 g/L、吸附180 min时效果最佳。在同等吸附条件下,复合改性膨润土对亚甲基蓝的吸附能力远大于未改性的膨润土。吸附过程更符合准二级动力学模型,平衡吸附数据与Langmuir等温吸附曲线吻合较好,吸附是一个自发的吸热过程,POSS/TX-10/Bent对亚甲基蓝的理论最大吸附量为253.81 mg/g。     

Synthesis and characterization of poly(dimethyl siloxane) containing poly(vinyl pyrrolidinone) block copolymers

ABA‐type block copolymers containing segments of poly(dimethyl siloxane) and poly(vinyl pyrrolidinone) were synthesized. Dihydroxyl‐terminated poly(dimethyl siloxane) was reacted with isophorone diisocyanate and then with t‐butyl hydroperoxide to obtain macroinitiators having siloxane units. The peroxidic diradical macroinitiators were used to polymerize vinyl pyrrolidinone monomer to synthesize ABA‐type block copolymers. By use of physicochemical methods, the structure was confirmed, and its characterization was accomplished. Mechanical and thermal characterizations of copolymers were made by stress–strain tests and differential scanning calorimetric measurements. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1915–1922, 1999