Silsesquioxane Research Articles

Crystallization behavior and thermal properties of octa-phenyl-substituted silsesquioxane-modified polylactide (PLA)

This study aims to understand the effects of adding octa-phenyl-substituted silsesquioxane (phSQ) on the crystallization process and thermal stability of polylactide (PLA). Nowadays, PLA is the most industrially used compostable polymer, but its uses are limited by its low crystallization and thermal degradation during processing. The possibility of introducing functionalized silsesquioxanes (SQs) to improve thermal stability and increase its crystallinity and ductility in a controlled way is desirable. The nanometric size of the Si-O-Si cage, coupled with the influence of the functional groups attached to its structure, enables it to function as a heterogeneous nucleating agent. In this work, a specially synthesized octa-phenyl-substituted SQ (phSQ) was added to the PLA in 0.5–5 wt%. Crystallization in non-isothermal and isothermal conditions was conducted and monitored using differential scanning calorimetry (DSC); the course of the spherulite formation under identical conditions to DSC was also assessed using optical microscopy in polarized light. The results showed that phSQ increases the degree of crystallinity of PLA by introducing additional sites of heterogeneous nucleation but does not increase the spherulite growth coefficient. Additionally, the analysis of thermal properties indicates that the presence of phSQ could not have a positive impact on thermal stability. The agglomeration of the nanometric particles and changes in the main structural features of the polymeric matrix could be present in the samples, affecting the obtained results.Graphical abstract

Organocatalytic synthetic route to esters and their application in hydrosilylation process

A facile esterification of α,β-unsaturated aldehydes with alcohols has been developed for the synthesis of esters by using bulky N-heterocyclic (NHC) carbene as a metal-free and eco-friendly organocatalyst. This new protocol has been proved to be effective with a wide substrate scope, giving selective esters in yields greater than 84% under mild conditions. Moreover, proposed synthetic strategy enables modification of various types of silsesquioxanes (SQ) which cannot or are technically difficult to be carried out with known protocols. For the first time, a one-pot sequential esterification/hydrosilylation has been successfully carried out.

Perylene diimide tethered with multi-POSS nanocages for polymer composite material with nonlinear optical property

A novel perylene diimide derivative tethered with three polyhedral oligosilsesquioxane nanocages (PDI-3POSS) was designed and synthesized as an organic-inorganic hybrid with donor-acceptor (D-A) conjugated structure. The experimental results reveal that the introduction of multi-POSS nanocages endows PDI-3POSS with inhibition of continuous PDI-stacking and subsequent good dispersivity in polymer matrix. Moreover, the molecular simulation indicates that PDI-3POSS can exhibit intense intramolecular charge transfer due to the electron-donating modification at the bay position. As a result, PMMA film doped with PDI-3POSS possesses unique reverse saturable absorption property and potential optical limiting application. It is hoped that the synergistic modification of multi-nanocages and D-A structure may be a new strategy to prepare composite materials with both good dispersivity and novel nonlinear optical property.

Functionalization of Siloxanes with Arynes Generated from o-Triazenylarylboronic Acids.

Herein, we report the functionalization of polyhedral oligosilsesquioxanes (POSS) and related siloxanes with arynes. Using o-triazenylarylboronic acids as aryne precursors and silica gel as the activator, the transformation of siloxane bearing various arynophilic moieties on the side chains was achieved with high yields without touching the siloxane core. This method was applied to the conjugation of POSS and pharmaceutical cores using an aryne derived from the synthetic intermediate of cabozantinib. Furthermore, orthogonal dual functionalization of POSS was realized by combining the aryne reaction with Huisgen cyclization.

Conjugation through Si-O-Si bonds, silsesquioxane (SQ) half cage copolymers, extended examples via SiO0.5/SiO1.5 units: multiple emissive states in violation of Kasha's rule.

We previously reported that phenyl- and vinyl-silsesquioxanes (SQs), [RSiO1.5]8,10,12 (R = Ph or vinyl) functionalized with three or more conjugated moieties show red-shifted absorption- and emission features suggesting 3-D conjugation via a cage centered LUMOs. Corner missing [PhSiO1.5]7(OSiMe3)3 and edge opened, end capped [PhSiO1.5]8(OSiMe2)2 (double decker, DD) analogs also offer red shifted spectra again indicating 3-D conjugation and a cage centered LUMO. Copolymerization of DD [PhSiO1.5]8(OSiMevinyl)2 with multiple R-Ar-Br gives copolymers with emission red-shifts that change with degree of polymerization (DP), exhibit charge transfer to F4TNCQ and terpolymer averaged red-shifts suggesting through chain conjugation even with two (O-Si-O) end caps possibly via a cage centered LUMO. Surprisingly, ladder (LL) SQ, (vinylMeSiO2)[PhSiO1.5]4(O2SiMevinyl) copolymers offer emission red-shifts even greater for analogous copolymers requiring a different explanation. Here we assess the photophysical behavior of copolymers of a more extreme SQ form: the half cage [PhSiO1.5]4(OSiMe2Vinyl)4, Vy4HC SQs. We again see small red-shifted absorptions coupled with significant red-shifted emissions, even with just a half cage, thus further supporting the existence of pπ-dπ and/or σ*-π* conjugation through Si-O-Si bonds and contrary to most traditional views of Si-O-Si linked polymers. These same copolymers donate an electron to F4TCNQ generating the radical anion, F4TCNQ-. as further proof of conjugation. Column chromatographic separation of short from longer chain oligomers reveals a direct correlation between DP and emission λmax red-shifts as another indication of conjugation. Further, one- and two-photon absorption and emission spectroscopy reveals multiple excited fluorescence-emitting states in a violation of Kasha's rule wherein emission occurs only from the lowest excited state. Traditional modeling studies again find HOMO LUMO energy levels residing only on the aromatic co-monomers rather than through Si-O-Si bonds as recently found in related polymers.

Vinylhydridosilsesquioxne: Synthesis and characterization of a potential filler material for vinyl‐containing polysiloxanes

AbstractThis paper reports the synthesis and characterization of an organic silsesquioxane (SQ) containing Sivinyl and SiH groups named as vinylhydridosilsesquioxane (SQVH‐12). Detailed investigation of the structure of this organosilsesquioxane revealed that SQVH‐12 has a highly cross‐linked (polycyclic) SiO network of silsesquioxane with Sivinyl and SiH functional groups. Thermogravimetric analysis of the pyrolysis behavior of SQVH‐12 yielded a high percentage of ceramic residue (~92%) at 1200°C under an argon atmosphere. The presence of functional groups in SQVH‐12 and the high rate of ceramic residue highlights the potential usefulness of SQVH‐12 as a filler for vinyl‐containing polysiloxanes. Thus, further research of SQVH‐12 can find applications in a wide variety of areas such as additive manufacturing, protective coatings, and advanced composites.

Intercalation of silsesquioxane surfactant in layered double hydroxide for silicone rubber composites: Enhancing interfacial interactions toward improvement of mechanical, thermal, and gas barrier properties

AbstractThe incorporation of two‐dimensional layered metal hydroxides (LDHs) into nonpolar silicone rubber (SR) is not yet universal, mainly because of their originally hydrophilic surface and limited interlamellar galleries that make nanoparticle dispersion and intercalation of polymer segments more difficult. In this work, we develop a modified Ca‐Mg‐Al LDH form by conjugating the ternary Ca‐Mg‐Al LDH with silsesquioxane (SQ) surfactants containing benzoic acid moieties and polyethylene glycol chains via an in‐situ intercalation process. The bulky anions conjugation to the hydroxide layers dictated both the surface hydrophobicity and interlayer spacing of the modified Ca‐Mg‐Al LDH, enabling strong inter‐constituent interactions within the nanocomposites as well as extensive polymer penetration after incorporation into the SR matrix. The SR/modified LDH nanocomposites show excellent thermal stability and satisfactory mechanical properties due to the homogeneous dispersion and good compatibility of modified Ca‐Mg‐Al LDH. Moreover, we have observed that the shear‐induced orientation of the nano‐layered particles upon application of stress imparts a more notably decreased SR/LDH‐SQ‐40 gas transmission rate (reduced by 55% with respect to that in the unstretched composite films). This result also corroborates the better interfacial bonding and highly efficient load transfer between silsesquioxane‐modified LDH and polymer in melt extrusion mixing of such composites.Highlights Modified Ca‐Mg‐Al LDH with increased layer spacing and reduced hydrophilicity. Modifier enhanced the interfacial adhesion between Ca‐Mg‐Al LDH and SR matrix. SR/modified LDH showed excellent thermal stability and mechanical properties. Orientation and exfoliation enhanced gas barrier properties of SR/modified LDH.

Changes in optical properties of polymeric materials due to atomic oxygen in very low Earth orbit

Atomic oxygen (AO) is the dominant constituent of the residual atmosphere in low Earth orbit (LEO). AO collides with spacecraft at a velocity of 8 km/s, causing oxidation and erosion of polymeric materials. Particularly in very low Earth orbit (VLEO) at altitudes below 300 km, the AO density is at least ten times that at 500–700 km, and the concentration of molecular nitrogen (N2) is 10% or more. Such high-flux AO and N2 can cause nonlinear processes and mass losses for polymers. This study aims to clarify the optical property changes for polymeric materials exposed to LEO and VLEO in the Material Degradation Monitor (MDM) mission onboard the Super-Low-Altitude Test Satellite (SLATS). The AO and N2 fluences and the UV irradiances were estimated using the NRLMSISE-00 atmospheric and solar radiation models. The relationships were investigated between the changes in CCD images and the estimated fluences of the samples. For silsesquioxane (SQ)-coated polyimide film, the diffuse reflection of visible light increased noticeably with an AO fluence above 1 × 1021 atoms/cm2. The formation of a silica layer on the coating induces cracks. For silver-coated FEP films, the diffuse reflection increased entirely at AO fluences above 3 × 1021 atoms/cm2. The AO and N2 collisions would erode and roughen the FEP surfaces. Visible transmission through silver-coated FEP films also increased locally with increasing AO fluence, indicating that some AO oxidized the silver layer despite the presence of an Inconel (Ni alloy) layer. The visible reflection from Beta Cloth was decreased by its reaction with UV. Further, the competitive reactions with UV and AO resulted in two-step changes in the visible reflection from the ETFE polymer (cable covering).

Poly(cyclohexylsilsesquioxane)-Based Hydrophilic Thermoset-Resistant Deep-Ultraviolet-Transparent Glasses with Low Melting Temperatures.

Silsesquioxane (SQ)-based glasses with low melting temperatures were prepared by the cosolvent-free (solventless) hydrolytic polycondensation of organotrimethoxysilanes with cyclopentyl (c-Pe) and cyclohexyl (c-Hx) groups. Copolymers consisting of phenylsilsesquioxane (Ph-SQ) units and c-Pe-SQ units [poly(Ph-co-c-Pe-SQ)] or c-Hx-SQ units [poly(Ph-co-c-Hx-SQ)] were melted at 140 °C and formed clear glasses. The glasses prepared by this method contained many residual SiOH groups and exhibited high adhesive strength to microscope glass plates, metals, and several polymers. The glass-transition temperature of poly(c-Hx-SQ) was lower than that of poly(Ph-SQ) by only a small margin, whereas that of poly(c-Pe-SQ) was much lower. The poly(c-Hx-SQ)-based glasses were stiff at room temperature and transparent in the deep-ultraviolet spectral region (≲300 nm). They formed fragile melts with kinetic fragility parameters as high as ∼0.8. The melts of poly(c-Hx-SQ) and poly(c-Hx-co-Et-SQ) exhibited better resistance to thermal curing than that of poly(Ph-SQ) and maintained thermoplasticity even after heat treatment at 200 °C for 6 h.

Synthesis of silsesquioxanes with methacryloyloxy and phenyl groups using corn stover ash as the major precursor

To address the challenges associated with corn stover utilization and the synthesis of phenyl- and methacryloyloxy-based silsesquioxanes (SQs) with difficulty and poor controllability, the authors present a novel approach that combines advanced biorefining techniques and innovative chemical synthesis methods. Spirocyclic alkoxysilane synthesized from corn stover ash was subsequently utilized for the synthesis of phenylSQs. The resulting phenylSQs were then subjected to fluorine ion-catalyzed rearrangement with 3-(trimethoxysilyl)propyl methacrylate (KH570) to yield SQs containing phenyl and methacryloyloxy functional groups. Through manipulating the ratio of phenylSQs and KH570, the authors successfully achieved a desired ratio of functional groups on individual SQ cages. Optimization of the ratio significantly impacted product collection, with a range of 5.5:1 to 8.5:1 recommended for efficient and effective synthesis. This study represents an important advancement in the field of high-value conversion of biomass, offering an easy means of tailoring the structure of phenyl- and methacryloyloxy-based cage SQs.

A Prediction Method of Effective Modulus of POSS Modified Quartz Fiber Reinforced Silicone Matrix Unidirectional Composites

In the manufacturing process of Polyhedral oligosilsesquioxane(POSS) modified quartz fiber reinforced silicone resin composite, if the POSS content ratio and the combination performance of POSS and silicone resin can be effectively controlled, the comprehensive performance of the material can be significantly improved, and many weaknesses of the composite can be improved. At the same time, the substantial problems such as the stiffness and strength of the wave transmitting composite still need to be greatly improved can be solved, and the new wave transmitting composite can be widely used in the main bearing parts of aerospace. When POSS modified quartz fiber reinforced silicone resin matrix composites are used as structural materials, their mechanical properties, such as modulus, are one of the most important macro mechanical material parameters in engineering applications. However, there is no effective prediction method in engineering to give practical guidance. Therefore, this paper establishes a prediction method of effective modulus of POSS modified quartz fiber reinforced silicone resin matrix composites based on micromechanics, The system can accurately understand the relationship between material structure and properties, thus making it possible to predict properties and design materials, and quickly guiding the practical application of engineering.

Transparent Superhydrophobic Coatings with Mechanical and Chemical Stability Prepared by Modified Polyhedral Oligosilsesquioxanes via UV-Curable Method

Superhydrophobic coating with applicable transmittance was synthesized by simple UV-curable method which was likely suitable for large-scale production. The super-hydrophobicity was derived from the component containing modified polyhedral oligomeric silsesquioxanes which was chosen for low free energy and the potential to form hierarchical structure. The coating adhesion could reach the highest level by strip tape peel test. Compared to the UV-cured commercial coatings, the coating adhesion is enhanced by at least two levels. Super-hydrophobicity was preserved after long duration of water droplet impact, while water contact angle decreased slightly after sand impact due to partial damage of hierarchical structure. The coating can resist chemical corrosion by acid solution (HCl), base solution (NaOH) and salt solution (NaCl). The coating with water repellence function, adequate transmittance, and good mechanical and chemical stability is of great interest for practical outdoor applications.

Tricky but repeatable synthetic approach to branched, multifunctional silsesquioxane dendrimer derivatives

The efficient one-pot procedure based on a sequence of hydrosilylation and reduction reactions was applied to obtain carbosilane dendrimers with different silsesquioxane (SQ) cores,i.e.from mono-T8SQ, octa-T8SQ to di- and tetrafunctional double-decker silsesquioxanes.

Slick Synthetic Approach to Various Fluoroalkyl Silsesquioxanes-Assessment of their Dielectric Properties.

We present a smart and efficient methodology for the synthesis of a variety of fluorinated silsesquioxanes (SQs) with diverse Si-O-Si core architecture. The protocol is based on an easy-to-handle and selective hydrosilylation reaction. An investigation on the placement of the reactive Si-HC=CH2 vs. Si-H in the silsesquioxane, as well as silane vs. olefin structure, respectively, on the progress and selectivity of the hydrosilylation process, was studied. Two alternative synthetic pathways for obtaining a variety of fluorine-functionalized silsesquioxanes were developed. As a result, a series of mono- and octa- T8 SQs, tri- 'open-cage' T7 SQs, in addition to di- and tetrafunctionalized double-decker silsesquioxane (DDSQ) derivatives, were obtained selectively with high yields. All products were characterized by spectroscopic (NMR, FTIR) techniques. Selected samples were subjected to the measurements revealing their dielectric permittivity in a wide range of temperatures (from -100 °C to 100 °C) and electric field frequencies (100-106 Hz).

Rigid POSS Nanofiller Regulated the Interfacial Self‐assembly of Particles into 2D Monolayer Superlattice with Fixed Interparticle Spacing†

Comprehensive SummaryPlasmonic superlattices of nanoparticles (NPs) possess unique “surface lattice resonances” properties that facilitates their wide applications in plasmonic sensing, photocatalysis, and nanoscale light manipulation. However, it is still challenging to manufacture superlattices with precisely controllable NPs distance and break the size limitation of NPs. Herein, we provided an effective strategy to construct NPs superlattices via shape‐persistent polyhedral oligosilsesquioxane (POSS) molecular nanoparticles govern interfacial assembly. As a nanoscale molecule with diameter of 1.5 nm, the POSS‐SH molecule provides sufficient rigid steric hindrance and hydrophobic effect for tailoring the uniformity and controllable distance between NPs in superlattices. Interestingly, synergistically with hydrophilic ligands of polyethylene glycol (PEG‐SH) with optimized ratio, the rigid POSS ligands can effectively regulate the distance between NPs in a fixed range of 2.3—2.8 nm, which is independent of ligands molecular weight and particle size. Furthermore, the effective approach can be universal to anisotropic NPs for manufacturing monolayer films with high NPs density. We believe this nanoscale molecule tailored interfacial self‐assembly strategy can effectively break the size of NPs and assembly obstacles for superlattice monolayer film. Additionally, the definite distance between NPs in superlattices can minimize optical energy attenuation and facilitates the applications such as surface‐enhanced Raman spectroscopy and photocatalysis.

Au Nanoparticles in Silsesquioxane-Based Hybrid Networks by Simultaneous Recovery and Reduction of Au(III) in Wastewater

The recovery of gold from wastewater or electronic waste is significant due to its enormous value in a variety of fields. An amine-functionalized silsesquioxane (SQ)-based hybrid network (PCS-PAA) was successfully synthesized through the cost-effective, mild amine–ene reaction of acrylate-functionalized SQ with triaminoethylamine (TAA). Hydrophilic PCS-PAA helps to adsorb Au(III) via the coordination with abundant heteroatoms (N and O). The adsorption capacity of PCS-PAA for Au(III) reaches 647 mg/g within 30 min at room temperature and 1235 mg/g at 323 K, respectively. The Langmuir model is more suitable to describe the adsorption process, and the pseudo-second-order model well fits the adsorption kinetic. Surprisingly, most Au(III) ions are in situ reduced to Au(0) particles, which are uniformly distributed on the surface of PCS-PAA. PCS-PAA-Au (PCS-PAA loaded with Au) can reduce 4-nitrophenol to 4-aminophenol with high catalytic activity. More interestingly, PCS-PAA can selectively adsorb Au(III) from e-waste. This work provides a convenient and mild method to recover Au(III) from wastewater or e-waste for multiple purposes.

Flame retardancy of carboxylated polyhedral oligosilsesquioxane modified layered double hydroxide in the process of leather fatliquoring

AbstractCarboxyl polyhedral oligomeric silsesquioxane(P[POSS‐MAA]) modified layered double hydroxides (LDHs) (P[POSS‐MAA]‐LDHs) was prepared by exfoliating and recombination method, which used P(POSS‐MAA) and LDHs attracted each other through electrostatic force and hydrogen bond. The structure and morphology of P(POSS‐MAA)‐LDHs were characterized by X‐ray diffraction and transmission electron microscope, which showed that LDHs was exfoliated and P(POSS‐MAA) was on the surface of LDHs. Then it was introduced into the modified zanthoxylum bungeanum seed oil(MZBMSO) to obtain MZBMSO/P(POSS‐MAA)‐LDHs and applied it in leather fatliquoring process. The effect of the introduction of P(POSS‐MAA)‐LDHs on the flame retardancy, thermal stability, thermal insulation and smoke suppression of leather was investigated. Compared to the MZBMSO treated leather, the after flame time of MZBMSO/P(POSS‐MAA)‐LDHs treated leather decreased from 84 s to 32 s, and the limiting oxygen index increased from 23.1% to 27.5%, which exhibited improvement on flame retardancy of the leather. The temperature at 50% mass loss of MZBMSO/P(POSS‐MAA)‐LDHs treated leather increased from 375.1 to 408.3°C, which showed improvement on thermal stability of the leather. And the leather treated by MZBMSO/P(POSS‐MAA)‐LDHs had reduction of the total heat release and the total smoke production around 26.8% and 65.7%, respectively, which showed that MZBMSO/P(POSS‐MAA)‐LDHs treated leather had heat insulation and smoke suppression. Flame retardant mechanism of MZBMSO/(P(POSS‐MAA)‐LDHs) treated leather involved a combination of the gaseous phase and condensed phase flame retardancy. This work provided a new material for the flame retardant field and expanded the application range of polyhedral oligomeric silsesquioxane(POSS).

Surface-Modified Approach to Fabricate Nafion Membranes Covalently Bonded with Polyhedral Oligosilsesquioxane for Vanadium Redox Flow Batteries.

An aminopropyl isobutyl polyhedral oligosilsesquioxane (NH2-POSS) surface-modified Nafion membrane has been designed by chemical grafting for vanadium redox flow batteries (VRFBs). NH2-POSS is a cage-like macromer consisting of an inorganic Si8O12 core surrounded by seven inert isobutyl groups and one active aminopropyl group. The sulfonic acid groups on the surface of Nafion can be activated by 1,1-carbonyldiimidazole for further modification with NH2-POSS. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) prove that NH2-POSS has been successfully grafted on the surface of a Nafion 115 membrane. Although the proton conductivity decreases slightly, the organic-inorganic hybrid membranes display enhanced ion selectivity and excellent dimensional stability with lower water uptake and swelling ratio than Nafion 115. Moreover, two-dimensional-grazing incidence X-ray diffraction (2D-GIXRD) reveals that the introduction of NH2-POSS forms a POSS layer on the surface of the membrane and narrows the space of Nafion clusters, which helps to block VO2+ permeation. A VRFB with the surface-modified Nafion membrane displays an outstanding performance with an average Coulombic efficiency (CE) of 98.7% and energy efficiency (EE) of 84.5% at a current density of 80 mA cm-2, superior to those of the Nafion 115 membrane (CE = 95.7%, EE = 81.7%). Furthermore, the cell holds a high capacity retention of 49.2% after 1000 charge-discharge cycles, in contrast to that of 41.9% for the cell with Nafion 115 after only 200 cycles. The results suggest that the surface-modified hybrid membrane is a promising strategy to overcome the vanadium ion crossover in VRFBs.

Silsesquioxanes in the Cosmetics Industry-Applications and Perspectives.

The rising demand for innovative and sophisticated personal care products is a driving factor for manufacturers to obtain new formulations that will fulfill the customers’ preferences. In recent years, silsesquioxanes have attracted the attention of the cosmetics industry. These compounds have been proposed to be used in novel cosmetic formulations as emollient, dispersant, and viscosity modifiers. Therefore, this publication aims to review the main important aspects of polyhedral oligosilsesquioxanes as ingredients of personal care formulations, taking into consideration different types of products. The methods of obtaining these compounds were also presented. Additionally, the detailed analysis of patents dedicated to the application of silsesquioxanes in cosmetic formulations was also performed.

Sub-10-nm ordered structure and mechanochromism property of polyhedral oligosilsesquioxane tethered tetraphenylethylene

The construction of highly ordered nanostructure plays an important role in realizing the specific functions of organic materials. However, it remains challenging to design photoelectric materials with sub-10-nm nanostructures. Herein, a novel tetraphenylethylene derivative tethered with polyhedral oligosilsesquioxane nanocages (TPE-BPOSS) was designed and synthesized. The experimental results reveal that the introduction of POSS nanocages endows TPE-BPOSS with a hierarchically sub-10-nm ordered structure composed of columnar phase of non-planar TPE cores and crystalline phase of POSS moieties. Moreover, due to the transition between the ordered and disordered structure, TPE-BPOSS can exhibit reversible mechanochromism property. It is speculated that incorporating POSS nanocages into different non-planar fluorophores may be a new strategy to prepare functional materials with sub-10-nm nanostructure and luminescent property.