Oligomeric Silsesquioxane Nanocomposites Research Articles

Experimental study of UV induced tensile properties deterioration and chemical aging of polyurea–POSS composites

Ultraviolet (UV) radiation present in natural sunlight degrades the chemical and mechanical properties of polymeric matrices in composites. Polyurea possess a unique set of chemical and mechanical properties due to its complex microstructure comprising of hard and soft segments (phases). The primary objective of the work presented here is to characterize the chemical and mechanical degradation of pure polyurea and polyurea - polyhedral oligomeric silsesquioxane (POSS) nanocomposites subjected to UV radiation exposure for 45 days. Control specimen in as-received condition (reference specimen) and UV-aged tensile test specimen are tested in the study. Analysis of Fourier transformed infrared (FTIR) spectra for UV-aged polyurea and polyurea-POSS composites reveals that the addition of POSS nanoparticles accelerate the deterioration of polyurea matrix by breaking the hard phase network and altering the mechanism of degradation for the soft phase present in polyurea microstructure. The deterioration of hard and soft segments cause a significant reduction in tensile properties of polyurea-POSS composites.

Tetra functional epoxy/polyhedral oligomeric silsesquioxane (POSS) nanocomposites with enhanced mechanical, thermal, anticorrosion and dielectric properties

Tetra functional epoxy resin namely tetraglycidyl 1,4’-bis (4-amine-phenoxy) sulphone benzene epoxy (TGBAPSB) was developed via 1,4’-bis (4-amine-phenoxy) sulphone benzene (BAPSB) and epichlorohydrin. TGBAPSB was reinforced with polyhedral oligomeric silsesquioxane (POSS) nanomaterial in various weight percentages (1–2 wt%) and polyamidoimidazoline (Aradur 140) was used as curing agent. FT-IR results validated the molecular structure of the synthesized POSS. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) evaluated the thermo-mechanical and thermal behaviour of TGBAPSB epoxy matrix and its organic-inorganic hybrid epoxy nanocomposites (TGBAPSB/POSS). X-Ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) investigated the surface morphological behaviour of the organic-inorganic hybrid epoxy nanocomposites. TGBAPSB epoxy resin with optimized POSS reinforcement exhibited excellent thermo-mechanical, thermal, mechanical, dielectric, and water absorption properties, making it a suitable material for advanced high-performance applications.

Relating the Degree of Nanofiller Functionality to the Glass Transition Temperature and Structure in a Polymer–Polyhedral Oligomeric Silsesquioxane Nanocomposite

Relating the Degree of Nanofiller Functionality to the Glass Transition Temperature and Structure in a Polymer–Polyhedral Oligomeric Silsesquioxane Nanocomposite

Preparation of Bio‐Based Polybenzoxazine/Pyrogallol/Polyhedral Oligomeric Silsesquioxane Nanocomposites: Low Dielectric Constant and Low Curing Temperature

AbstractIn this work, a bio‐based benzoxazine monomer (C‐s) is synthesized from cardanol, stearylamine, and paraformaldehyde through solvent‐free method. Pyrogallol is used as a curing catalyst for the ring‐opening polymerization of benzoxazine. Differential scanning calorimeter (DSC) results reveal that doping with pyrogallol reduces the exothermic peak temperature (Tp) of C‐s from 256 to 174 °C. The polybenzoxazine/pyrogallol/polyhedral oligomeric silsesquioxane (PC‐s/py/POSS) nanocomposites are prepared via thermal curing. The doping of aminopropyl isobutyl POSS (POSS‐NH2) can reduce the dielectric constant of polybenzoxazine. The dielectric constant of PC‐s/py/POSS is 2.64 at 1 MHz when the doping amount of POSS‐NH2 is 10 wt%. The results of thermogravimetric analysis (TGA) and water absorption test indicate that the PC‐s/py/POSS nanocomposites possess good thermal stability and water resistance. In summary, the PC‐s/py/POSS nanocomposites with low curing temperature and low dielectric constant are expected to be applied to the low dielectric materials for microelectronic applications.

Polyhedral oligomeric silsesquioxane (POSS)-based epoxy nanocomposite involving a reversible Diels–Alder-type network as a self-healing material

Epoxy-polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by incorporating POSS nanofiller into the epoxy-amine network. The monofunctional epoxy-POSS monomer or nonfunctional octaphenyl POSS unit were applied to reinforce the epoxy network by producing the nanocomposite with chemically bound pendant POSS or physically admixed POSS. The combination of reactive and unreactive POSS, leads to a synergistic effect and to the most efficient reinforcement of the epoxy network. Both polymer-POSS and POSS–POSS interactions are present in the system and lead to a strong physical crosslinking through the path polymer-bound POSS-unbound POSS domain. The nanocomposite was modified by incorporation of the thermoreversible Diels–Alder (DA) type network. The produced interpenetrating network composed of the irreversible reinforced epoxy and the reversible DA networks exhibits an efficient self-healing capability. This strong nanocomposite, showing a modulus of 800 MPa at room temperature, was healed with an efficiency of 61%. The developed stiff nanocomposite is shown to be a promising material because self-healing of strong thermosets is still a big challenge. With the increasing content of POSS nanofiller and heterogeneity of the nanocomposite, however, the healing efficiency diminishes. The insufficient contact of crack surfaces due to involved inhomogeneities results in a worse sealing of the material crack.

Enhanced Dielectric and Thermal Performance of Bio-polyamide Polyhedral Oligomeric SilseSquioxane (PA-POSS) Nanocomposites

Polyamide-polyhedral oligomeric silsesquioxane (PA-POSS) nanocomposites are prepared using eco-friendly surfactant-free dimer fatty acid polyamide with different wt% of POSS by a facile solvent casting method. The prepared biopolymer nanocomposites are investigated using transmission electron microscopy, scanning electron microscopy, atomic force microscopy to understand the structural orientation between POSS and polyamide. Thermogravimetric analysis indicates that the PA-POSS have better thermal stability as compared to that of pristine polymers. Differential scanning calorimetry shows a shift in glass transition temperature as the loadings of POSS increase in the polymer. Dielectric properties such as dielectric breakdown strength, dielectric permittivity, dielectric loss, and AC conductivity are performed on polymeric materials to investigate frequency dependent dielectric properties. Results showed that the thermal stability and dielectric permittivity of PA-POSS are 25% superior compared to pristine polyamides; such an enhancement may be due to the POSS being uniformly settled in nano-level by proper structural orientation of POSS with the polyamide throughout the polymer matrix. PA-POSS nanocomposites exhibiting improved dielectric properties can be explored for the fabrication of biocompatible polymeric film capacitors application.

C30‐45 long‐chain alkyls modified silsesquioxane: A promising additive for polyethylene

AbstractA novel commercial available and inexpensive long‐chain alkyl (C30‐45) modified silsesquioxane, namely (C30‐45 alkyl)dimethylsilyl polypropylsilsesquioxane (C30PSS), was applied as a functional filler for linear low density polyethylene (LLDPE). For comparison, LLDPE/octaisobutyl polyhedral oligomeric silsesquioxane (BuPOSS) nanocomposites were also prepared via melt blending. The chemical and crystalline structures of C30PSS and BuPOSS were first identified by Fourier transform infrared spectroscopy, solid 29Si NMR, and X‐ray diffraction. The dispersion of two fillers in the polymer matrix was analyzed via scanning electron microscopy and X‐ray energy dispersive spectroscopy. The rheological, tensile, and thermal properties of pristine LLDPE, LLDPE/C30PSS, and LLDPE/BuPOSS composites were systematically studied. Our results showed that C30PSS can serve as a promising and low‐priced filler for LLDPE with respect to its fine dispersion in LLDPE and its abilities to improve the rheological and mechanical properties of LLDPE.

Biomass/polyhedral oligomeric silsesquioxane nanocomposites: Advances in preparation strategies and performances

AbstractPolyhedral oligomeric silsesquioxane (POSS) as an organic–inorganic hybrid at a molecular level, has excellent mechanical properties, thermodynamic properties, dielectric properties and so on. In recent decades, POSS has been extensively used in modification of various polymers to prepare nanocomposites with enhanced comprehensive performances. Biomass materials such as chitosan, cellulose, silk protein, collagen fibers and gelatin have excellent biocompatibility and biodegradability, which have been widely used in the fields such as biomedical, innovative environmental protection and so on. However, deficiencies including insufficient mechanical properties and rapid rate of biodegradation hampered their application. This paper briefly introduced the principal methods to synthesize POSS nanoparticles, and then focused on technologies for preparing biomass‐based composites utilizing diverse functional POSSs. Finally, put forward the prospects of POSS modification technology and its future application direction. This article will have a positive guiding role for the further research and development of biomass/POSS nanocomposites.

Interfacial regions and network dynamics in epoxy/POSS nanocomposites unravelling through their effects on the motion of molecular chains

Interfacial regions formed by incorporating a certain percentage of nanofillers into a polymer matrix can impact on the motion of molecular groups, chain units or chain segments, and alter molecular chain network dynamics, which is regarded as a key factor to achieve a finer degree control of dielectric properties of polymer nanocomposites. It is of interest to investigate the molecular chain motion behavior at interfacial regions with the incorporation of nanofillers. Epoxy resin/polyhedral oligomeric silsesquioxane (EP/POSS) nanocomposites are fabricated and the observations of morphology structure and chemical elements indicate that POSS nanofillers are well dispersed in the matrix. Differential scanning calorimeter, dynamic thermomechanical analysis, and dielectric relaxation spectroscopy are measured to analyze the effect of nanodoping on the motion properties of molecular chain units and chain segments that satisfy the Arrhenius and Vogel-Fulcher-Tammann equations respectively. The thicknesses of interfacial regions between POSS nanofillers and EP matrix are estimated from dielectric spectra and effective relative permittivity simulations, which are around several nanometers and decrease with the increment in the nanofiller content. In addition, the dielectric spectra scaling analysis indicates that the motion of small chain units can be hindered in interfacial regions and be tuned simultaneously by the variations of molecular chain network structure and dynamics. Nevertheless, the thin interfacial regions cannot effectively restrict the orientation of long molecular chain segments during the glass transition process. The variation of chain segment orientation behavior is ascribed to the interactions among molecular chains tuned by the binding effect of POSS nanofillers.

Improving nanoparticle dispersion and polymer crystallinity in polyvinylidene fluoride/POSS coatings using tetrahydrofuran as co-solvent

Dispersion quality of nanoparticles has always limited the performance of polymer nanocomposites and coatings. Herein, the main purpose is to improve the dispersion quality of nanoparticles and overall properties in polyvinylidene fluoride (PVDF)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites fabricated through spray-coating technique. POSS was added to PVDF/DMF solution at varying concentrations. Based on morphological analysis, low to moderate contents (1 and 3 wt%) of POSS exhibited a good dispersion quality but the high contents (5 and 10 wt%) of POSS led to the formation of large aggregates. To improve the dispersion quality of POSS, tetrahydrofuran (THF) was used as co-solvent. The improved dispersion of POSS caused a significant enhancement in the crystallinity of PVDF from 29.8–59.5% according to the differential scanning calorimetry (DSC) results. X-ray diffraction results revealed that the majority of PVDF crystals from the α-type and addition of co-solvent led to the formation of a slight amount of γ phase which was confirmed by the multiple endotherms based on DSC results. The co-solvent addition also led to higher hydrophobicity due to the increased crystallinity. Overall, the use of a proper co-solvent led to better dispersion of nanoparticles which can result in improved performance of nanocomposite coatings.

Superhydrophobic membrane by hierarchically structured PDMS-POSS electrospray coating with cauliflower-shaped beads for enhanced MD performance

The construction of superhydrophobic surfaces for improving the anti-wetting performance of membrane distillation (MD) is still an on-going challenge. In this study, we fabricated a hierarchically structured electrospray coating with cauliflower-shaped beads by adjusting polymer chain entanglement. A series of poly(dimethylsiloxane)-polyhedral oligomeric silsesquioxane (PDMS-POSS) nanocomposites were synthesised by the chemical incorporation of rigid V-POSS into a flexible PDMS matrix. With the optimal incorporation content, we successfully obtained a homogeneous molecular-level dispersion of V-POSS into PDMS matrix, forming a more branched yet looser network, leading to the appearance of cauliflower-shaped beads when electrosprayed with polyvinylidene fluoride (PVDF). Moreover, the integrated V-POSS and its self-crosslinked clusters contributed to the formation of convexities and protrusion on the beads. This optimal coated membrane with PVDF as substrate exhibited superhydrophobicity, as evidenced by a water contact angle of ~166°; which resulted from the rough surface with well-defined ridges and valleys, composed of irregular beads. Once applied in direct contact MD (DCMD) processes, it demonstrated stable performance and high salt rejection (>99.9%) during the 200 h treatment of synthetic seawater containing 0.1 mM sodium dodecyl sulfate (SDS), along with great robustness under harsh feed condition containing 0.3 mM SDS, showing good applicability for preventing wetting.

Morphology, dynamics, and order development in a thermoplastic polyurethane with melt blended POSS

ABSTRACTA top‐down approach is applied for the production of polyurethane (PU)–polyhedral oligomeric silsesquioxane (POSS) nanocomposites, namely melt blending. As opposed to the typical chemical incorporation during synthesis, a POSS moiety with two hydroxyl groups is melt blended into a commercial thermoplastic polyurethane with mass fraction up to 2 wt %. POSS disperses in the matrix in submicrometer‐sized crystals, as well as in length scale of few tens of nanometers, in the bulk. Phase separation of the produced composites was studied by both standard dynamic and isothermal annealing experiments. In an approach rare in the literature, the dynamics of phase separation is discussed based on isothermal differential scanning calorimetry curves recorded during annealing. The blended‐in nanoparticles affect the micromorphology in a complicated manner, dependent on the intrinsically complex phase separation mechanism of PU. At higher temperatures, POSS slows down the phase separation, whereas at lower ones, it enhances and accelerates it. POSS decreases the mechanical modulus of the final material, presumably as a result of changes in the microphase separation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1133–1142

Interfacial interactions in PTT\u2013PTMO/polyhedral oligomeric silsesquioxane (POSS) nanocomposites and their impact on mechanical, thermal, and dielectric properties

Poly(trimethylene terephthalate–block–tetramethylene oxide) (PTT–PTMO)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites, synthesized by in situ polymerization, are characterized in detail in terms of interfacial interactions between functional groups on the surface of POSS and polymer chains. The impact of POSS incorporation on the molecular mobility is investigated by means of dielectric spectroscopy. It is found that PTT–PTMO/POSS nanocomposites exhibit higher values of stress at strain of 100% that in comparison with neat PTT–PTMO might result from the influence of POSS particles on the molecular mobility of polymer chains, which is probably due to the interfacial interactions between functional groups on the surface of POSS particles with the polymer matrix. Moreover, it is found that there is no variation of the segmental relaxation for the nanocomposite investigated and there is an increase in the interfacial polarization induced by the presence of POSS as seen in the increment of the real part of the dielectric permittivity.

Effect of polyhedral oligomeric silsesquioxane nanoparticles on thermal decomposition of cyanate ester resin

A series of cyanate ester resin (CY)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared successfully. Morphology and thermal stability of the CY and its nanocomposites with POSS were studied by means of scanning electron microscopy (SEM) and Thermogravimetric Analysis (TGA). With the addition of POSS, the thermal stability of CY is dramatically improved. Under air atmosphere, the full decomposition temperature increased by 146°C, with incorporation of only 1wt% POSS. The heat generated by the thermal degradation of the CY/POSS nanocomposites is around 4 times less than that of the neat CY. Under nitrogen atmosphere, the char yield of the CY increased up to 15wt% with addition of the POSS. Besides, the heat required for the degradation of the CY/POSS nanocomposites was much higher than that of the neat CY. These results reveal that the incorporation of the POSS resulted in change of the degradation mechanism of CY. The breakdown of POSS/CY network retarded the breakdown of the triazine rings of CY hence the thermal stability of POSS/CY nanocomposites were improved comparing to that of pristine CY. Furthermore, the formation of char retarded the degradation of benzene rings as well.

Influence of low octavinyl-polyhedral oligomeric silsesquioxanes loadings on the crystallization kinetics and morphology of poly(ethylene suberate)

Through a solution and casting method, we successfully prepared poly(ethylene suberate) (PESub)/octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) nanocomposites at low ovi-POSS loadings. Ovi-POSS dispersed homogeneously in PESub matrix, showing regular crystalline morphology. Both PESub and ovi-POSS crystallized separately in the nanocomposites. Ovi-POSS did not obviously affect the thermal stability of the nanocomposites. The influence of low ovi-POSS loadings on the crystallization kinetics and morphology of PESub was investigated in detail under different crystallization conditions. On the basis of the crystalline morphology study, the influence of low ovi-POSS loadings on the crystallization behavior of PESub was attributed to the different nucleation density values of PESub spherulites induced by ovi-POSS in the nanocomposites, which was further related to the influence of ovi-POSS loading on the dispersion of ovi-POSS in PESub matrix.

Preparation and properties of UV-cured epoxy acrylate/glycidyl-POSS coatings

Epoxy acrylate (EA)/glycidyl-polyhedral oligomeric silsesquioxane (G-POSS) nanocomposites were synthesized via in situ ultraviolet initiated polymerization. XRD analysis indicates that G-POSS and EA are miscible and can form uniform composites. SEM micrographs show that the G-POSS particles (<500 nm in diameter) disperse uniformly in the polymer matrix. The EA/G-POSS nanocomposites exhibit heterogeneous morphology. FTIR analysis confirms the curing reaction is quite complete, and there are no chemical reactions between G-POSS and EA during the UV-curing process. The carbon–carbon double-bond conversion vs time profiles confirm that the addition of G-POSS improves the UV-curing rates of nanocomposites. The glass transition temperature (T g) of nanocomposites were obtained by DMA. T g reaches to the maximum at the loading of 1 wt% and then decreases with the increasing G-POSS loadings. The thermal stability, impact resistance, and flexibility of nanocomposites are all enhanced by the incorporation of G-POSS.

A new mechanism for the low dielectric property of POSS nanocomposites: the key role of interfacial effect.

The low dielectric constant (ε) of polyhedral oligomeric silsesquioxanes (POSS) was generally attributed to its porous structure. In this work, we propose a new mechanism for the low ε of the POSS-based nanocomposites from the interfacial effect point of view. The investigation on a typical nanocomposite, polystyrene/POSS, found that POSS molecules take crystallization to form crystalline nanoplatelets (PCPs) in PS. Correspondingly, the dielectric constant can be reduced to around 2.30. A detailed investigation excluded the possible influence of the chain stacking and chain mobility of the polymers on ε. It was demonstrated, for the first time, that the ε shows a high correlation with interface area which is reflected by a rigid amorphous fraction (RAF), thus revealing the key role of the interfacial effect on reducing the low dielectric constant.

Improvement in mechanical properties of NBR/LiClO4/POSS nanocomposites by constructing a novel network structure

The mechanical properties and the possible micro-structure of nitrile-butadiene rubber/lithium perchlorate/polyhedral oligomeric silsesquioxane (NBR/LiClO4/POSS) nanocomposites have been investigated thoroughly. The interactions among Li+ cations, CN groups and COC groups bring in a novel network structure consisting of several kinds of effective crosslinks, causing an increase in the glass transition temperature of POSS, as well as in the crosslink contribution (Gc) and the constraint contribution (Ge), which facilitates strong interface cohesion between POSS and NBR matrix and a well dispersion of POSS. The addition of POSS not only increases the crosslinking density of NBR/LiClO4/POSS nanocomposites, but also improves the 300% modulus and tensile strength greatly. Therefore, a possible micro-structure has been proposed to express the experimental observation.

Effect of poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes on the crystallization kinetics and morphology of biodegradable poly(ethylene succinate)

Biodegradable poly(ethylene succinate) (PES)/poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes (PEG-POSS) nanocomposites were prepared via a solution and casting method in this work. The distribution of PEG-POSS, miscibility between PES and PEG-POSS, and crystallization behavior of PES/PEG-POSS nanocomposites were fully investigated. PEG-POSS particles were homogeneously dispersed in the PES matrix. PEG-POSS was miscible with PES to some degree, because the samples displayed a single composition dependent glass transition temperature and a depression of equilibrium melting point of PES in the nanocomposites. PEG-POSS increased the chain mobility of PES, thereby improving the nonisothermal cold and melt crystallization processes, accelerating the isothermal melt crystallization rate, and increasing the spherulitic growth rate of the nanocomposites. However, the isothermal crystallization mechanism and the crystal structure of PES were not modified by PEG-POSS. PEG-POSS enhanced the crystallization behavior of PES by acting as a plasticizer.

Enhanced nonisothermal and isothermal cold crystallization kinetics of biodegradable poly(l‐lactide) by trisilanolisobutyl‐polyhedral oligomeric silsesquioxanes in their nanocomposites

ABSTRACTIn this work, the nonisothermal and isothermal cold crystallization behaviors of poly(l‐lactide) (PLLA)/trisilanolisobutyl‐polyhedral oligomeric silsesquioxanes (tsib‐POSS) nanocomposites with low tsib‐POSS contents were fully investigated. For all the samples, the variations of heating rate and the tsib‐POSS loading may influence the nonisothermal cold crystallization of PLLA. During the nonisothermal crystallization kinetics study, the Ozawa equation failed to fit the nonisothermal crystallization process of PLLA, while the Tobin equation could fit it well. For the isothermal crystallization kinetics study, the crystallization rates of all the samples increased with increasing crystallization temperature. The cold crystallization activation energy of PLLA was increased with 1 wt % tsib‐POSS. Moreover, the addition of tsib‐POSS and the increment of tsib‐POSS loading could increase the crystallization rate of PLLA, indicating the nucleating agent effect of tsib‐POSS. However, the crystallization mechanism and crystal structure of PLLA remained unchanged in the nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43896.