Effects of Segment Length and Crosslinking via POSS on the Calorimetric and Dynamic Glass Transition of Polyurethanes with Aliphatic Hard Segments

The glass transition in polyurethanes is a complicated phenomenon governed by a multitude of factors, including the microphase separation, which in turn depends strongly on the molar mass of the hard and soft segments, as well as the presence of additives. In this work, we study the effects of the segments' length on the microphase separation and consequently on the calorimetric and dynamic glass transition of a polyurethane with aliphatic, "flexible" hard segments. It is found that the dependence of the calorimetric glass transition follows the same principles as those in systems with aromatic hard segments. Strikingly, however, the dynamic glass transition, as studied by dielectric spectroscopy, shows a slowing down of its dynamics despite a decrease in Tg. This discrepancy is discussed in terms of the strong dielectric response of the flexible segments, especially those close to the interface between the hard domains and soft phase, as opposed to a weak thermal one. In addition, polyhedral oligomeric silsesquioxanes (POSS) are introduced in the soft phase of the three matrices as crosslinking centres. This modification has no visible effect on the calorimetric glass transition; nevertheless, it affects the microphase separation and the dielectric response in a non-monotonic manner.

New Janus Tricyclic Laddersiloxanes: Synthesis, Characterization, and Reactivity

The synthesis of four novel syn-type tricyclic laddersiloxanes bearing eight or six alkenyl groups is presented. These compounds possess reactive alkenyl groups on both the bridged and side silicon atoms, and their structures were determined through characterization using multinuclear 1D and 2D NMR spectroscopy, mass spectrometry, and elemental analysis techniques. To investigate their reactivity, the compounds were subjected to hydrosilylation using two different silanes, and the resulting fully hydrosilylated compounds were thoroughly analyzed. Remarkably, all the synthesized laddersiloxanes displayed high thermal stability, suggesting their potential as promising precursors for the development of new hybrid materials. Additionally, preliminary findings indicate the possibility of exploiting the reactivity difference between the alkenyl groups attached to the D- and T-unit silicon atoms for the synthesis of Janus molecules. These findings highlight the potential of the reported compounds as valuable building blocks in the construction of innovative materials.

Improvement of Heat Resistance of Fluorosilicone Rubber Employing Vinyl-Functionalized POSS as a Chemical Crosslinking Agent

Fluorosilicone rubber (F-LSR) is a promising material that can be applied in various cutting-edge industries. However, the slightly lower thermal resistance of F-LSR compared with that of conventional PDMS is difficult to overcome by applying nonreactive conventional fillers that readily agglomerate owing to their incompatible structure. Polyhedral oligomeric silsesquioxane with vinyl groups (POSS-V) is a suitable material that may satisfy this requirement. Herein, F-LSR-POSS was prepared using POSS-V as a chemical crosslinking agent chemically bonded with F-LSR through hydrosilylation. All F-LSR-POSSs were successfully prepared and most of the POSS-Vs were uniformly dispersed in the F-LSR-POSSs, as confirmed by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. The mechanical strength and crosslinking density of the F-LSR-POSSs were determined using a universal testing machine (UTM) and dynamic mechanical analysis (DMA), respectively. Finally, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements confirmed that the low-temperature thermal properties were maintained, and the heat resistance was significantly improved compared with conventional F-LSR. Eventually, the poor heat resistance of the F-LSR was overcome with three-dimensional high-density crosslinking by introducing POSS-V as a chemical crosslinking agent, thereby expanding the potential fluorosilicone applications.

Design Hybrid Porous Organic/Inorganic Polymers Containing Polyhedral Oligomeric Silsesquioxane/Pyrene/Anthracene Moieties as a High-Performance Electrode for Supercapacitor

We synthesized two hybrid organic-inorganic porous polymers (HPP) through the Heck reaction of 9,10 dibromoanthracene (A-Br₂) or 1,3,6,8-tetrabromopyrene (P-Br₄)/A-Br₂ as co-monomers with octavinylsilsesquioxane (OVS), in order to afford OVS-A HPP and OVS-P-A HPP, respectively. The chemical structures of these two hybrid porous polymers were validated through FTIR and solid-state ¹³C and ²⁹Si NMR spectroscopy. The thermal stability and porosity of these materials were measured by TGA and N₂ adsorption/desorption analyses, demonstrating that OVS-A HPP has higher thermal stability (T_d10: 579 °C) and surface area (433 m² g^-1) than OVS-P-A HPP (T_d10: 377 °C and 98 m² g^-1) due to its higher cross-linking density. Furthermore, the electrochemical analysis showed that OVS-P-A HPP has a higher specific capacitance (177 F g ^-1 at 0.5 A F g^-1) when compared to OVS-A HPP (120 F g ^-1 at 0.5 A F g^-1). The electron-rich phenyl rings and Faradaic reaction between the π-conjugated network and anthracene moiety may be attributed to their excellent electrochemical performance of OVS-P-A HPP.

Construction of Fluorescent Conjugated Polytriazole Containing Double-Decker Silsesquioxane: Click Polymerization and Thermal Stability

This study synthesized two azide-functionalized monomers through p-dichloro xylene and double-decker silsesquioxane (DDSQ) units with NaN₃ to form DB-N₃ and DDSQ-N₃ monomers, respectively. In addition, five different propargyl-functionalized monomers were also prepared from hydroquinone, bisphenol A, bis(4-hydroxyphenyl)methanone, 2,4-dihydroxybenzaldehyde (then reacted with hydrazine hydrate solution) and 1,2-bis(4-hydroxyphenyl)-1,2-diphenylethene with propargyl bromide to form P-B, P-BPA, P-CO, P-NP, and P-TPE monomers, respectively. As a result, various DDSQ-based main chain copolymers could be synthesized using Cu(I)-catalyzed click polymerization through DDSQ-N₃ with different propargyl-functionalized monomers, of which the chemical structure and molecular weight could be confirmed by using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) analyses. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy analyses also could characterize the thermal stability, morphology, and optical behaviors of these DDSQ-based copolymers. All results indicate that the incorporation of an inorganic DDSQ cage could improve the thermal stability such as thermal decomposition temperature and char yield, because of the DDSQ dispersion homogeneously in the copolymer matrix, and this would then affect the optical properties of NP and TPE units in this work.

ABC-Type, Bola-Form Giant Surfactants: Synthesis and Self-Assembly

Due to the fast phase separation kinetics and small feature size, the self-assembly of giant molecules has attracted lots of attention. However, there is not much study on multicomponent giant surfactants. In this work, through a modular synthetic strategy, different polyhedral oligomeric silsesquioxane (POSS)-based molecular nanoparticles are installed with diverse functionalities (hydrophobic octavinyl POSS (VPOSS), hydrophilic dihydroxyl-functionalized POSS (DPOSS), and omniphobic perfluoroalkyl-chain-functionalized POSS (FPOSS)) on the ends of one polystyrene (PS) chain to build up a series of triblock bola-form giant surfactants denoted as XPOSS-PS_n -FPOSS (X represents V or D). The target molecules are prepared by a combination of atom transfer radical polymerization (ATRP), esterification, as well as Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and thiol-ene "click" reactions. These macromolecules are thoroughly characterized by combined technologies including nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analyses. It is revealed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) that VPOSS-PS_n -FPOSS adopts a two-phase separation scenario where VPOSS and POSS are segregated in one phase. DPOSS-PS_n -FPOSS with a third hydrophilic DPOSS shows a three-phase separation scenario, where highly ordered phase structures are difficult to develop owing to the competition of mutual phase separation processes and may be trapped in kinetically metastable states.

Distinct insight into the use of difunctional double-decker silsesquioxanes as building blocks for alternating A–B type macromolecular frameworks

A distinct look at known, hydrosilylation reactions used for the formation of DDSQ-based linear A–B alternating macromolecular systems with DPn > 1000 is presented. Selected physicochemical properties of obtained hybrid co-polymers were determined.

The Use of the Thiol-Ene Addition Click Reaction in the Chemistry of Organosilicon Compounds: An Alternative or a Supplement to the Classical Hydrosilylation?

This review presents the main achievements in the use of the thiol-ene reaction in the chemistry of silicones. Works are considered, starting from monomers and ending with materials.The main advantages and disadvantages of this reaction are demonstrated using various examples. A critical analysis of the use of this reaction is made in comparison with the hydrosilylation reaction.

Design of Fluorescent Hybrid Materials Based on POSS for Sensing Applications

Polyhedral oligomeric silsesquioxane (POSS) has a nanoscale silicon core and eight organic functional groups on the surface, with sizes from 0.7 to 1.5 nm. The three-dimensional nanostructures of POSS can be used to build all types of hybrid materials with specific performance and controllable nanostructures. The applications of POSS-based fluorescent materials have spread across various fields. In particular, the employment of POSS-based fluorescent materials in sensing application can achieve high sensitivity, selectivity, and stability. As a result, POSS-based fluorescent materials are attracting increasing attention due to their fascinating vistas, including unique structural features, easy fabrication, and tunable optical properties by molecular design. Here, we summarize the current available POSS-based fluorescent materials from design to sensing applications. In the design section, we introduce synthetic strategies and structures of the functionalized POSS-based fluorescent materials, as well as photophysical properties. In the application section, the typical POSS-based fluorescent materials used for the detection of various target objects are summarized with selected examples to elaborate on their wide applications.

Self-Healing Silsesquioxane-Based Materials

This review is devoted to self-healing materials (SHM) containing polyhedral oligomeric silsesquioxanes (POSS) as building blocks. The synthetic approach can vary depending on the role POSS are expected to play in a given system. POSS (especially double-decker silsesquioxanes) can be grafted in side chains of a polymer backbone or used as segments of the main chain. Appropriate functionalization allows the formation of dynamic bonds with POSS molecules and makes them an active component of SHM, both as crosslinking agents and as factors that enhance the dynamics of macromolecules in the polymer matrix. The latter effect can be achieved by reversible release of bulky POSS cages or by the formation of separated inclusions in the polymer matrix through hydrophobic interactions and POSS aggregation. The unique properties of POSS-based self-healing systems make them interesting and versatile materials for various applications (e.g., repairable coatings, sealants, sensors, soft materials for tissue engineering, drug delivery, and wound healing).

Recent advances in poly(ionic liquid)s for biomedical application

Poly(ionic liquid)s (PILs) are polymers containing ions in their side-chain or backbone, and the designability and outstanding physicochemical properties of PILs have attracted widespread attention from researchers. PILs have specific characteristics, including negligible vapor pressure, high thermal and chemical stability, non-flammability, and self-assembly capabilities. PILs can be well combined with advanced analytical instruments and technology and have made outstanding contributions to the development of biomedicine aiding in the continuous advancement of science and technology. Here we reviewed the advances of PILs in the biomedical field in the past five years with a focus on applications in proteomics, drug delivery, and development. This paper aims to engage pharmaceutical and biomedical scientists to full understand PILs and accelerate the progress from laboratory research to industrialization.

Well-defined cyclic silanol derivatives

Cyclic silanol derivatives (CSDs), possessing siloxane rings consisting of T-unit silicon and oxygen atoms, are considered efficient precursors for the preparation of versatile well-defined building blocks of hybrid materials such as cyclic, cage- or ladder-type SQs. This review provides an outline of the main synthetic routes to numerous stereoregular CSDs with different sizes of siloxane rings since the first example of CSDs reported by Brown et al. in 1965. The typical reaction conditions and chemical shifts of ²⁹Si NMR of all mentioned CSDs in this review are summarized in tables and schemes to recapitulate the state of the art. The synthesis of all-cis-cyclotetrasiloxanes (T₄), the most investigated CSDs, and their functionalization by different organic reactions to access various all-cis-T₄ with functional groups are methodically presented. Moreover, the potential of CSDs in multiple application fields is discussed to show the possible research directions of this family of compounds in the future.

Effectiveness of an ocular adhesive polyhedral oligomeric silsesquioxane hybrid thermo-responsive FK506 hydrogel in a murine model of dry eye

Dry eye is a common ocular disease that results in discomfort and impaired vision, impacting an individual's quality of life. A great number of drugs administered in eye drops to treat dry eye are poorly soluble in water and are rapidly eliminated from the ocular surface, which limits their therapeutic effects. Therefore, it is imperative to design a novel drug delivery system that not only improves the water solubility of the drug but also prolongs its retention time on the ocular surface. Herein, we develop a copolymer from mono-functional POSS, PEG, and PPG (MPOSS-PEG-PPG, MPEP) that exhibits temperature-sensitive sol-gel transition behavior. This thermo-responsive hydrogel improves the water solubility of FK506 and simultaneously provides a mucoadhesive, long-acting ocular delivery system. In addition, the FK506-loaded POSS hydrogel possesses good biocompatibility and significantly improves adhesion to the ocular surface. In comparison with other FK506 formulations and the PEG-PPG-FK506 (F127-FK506) hydrogel, this novel MPOSS-PEG-PPG-FK506 (MPEP-FK506) hydrogel is a more effective treatment of dry eye in the murine dry eye model. Therefore, delivery of FK506 in this POSS hydrogel has the potential to prolong drug retention time on the ocular surface, which will improve its therapeutic efficacy in the management of dry eye.

Synthesis of Octachloro- and Octaazido-Functionalized T8-Cages and Application to Recyclable Palladium Catalyst

Unprecedented T₈-cages bearing eight chloromethyldimethylsilylethyl substituents were obtained in excellent yield from the readily and commercially available octavinylsilsesquioxane. The chloro groups can be quantitatively substituted by azido ones to yield the corresponding octaazido T₈ without rearrangement of the cage. The syntheses of both functionalizable POSSs are scalable (gram-scale). The azido-functionalized T₈ compound constitutes a versatile building block able to undergo copper-catalyzed azide-alkyne [3 + 2] cycloaddition. As a proof of concept, it was allowed to react with 2-ethynylpyridine to give rise to a multidentate ligand bearing eight 2-pyridyl-triazole moieties (N,N-pincers). The coordination of the eight N,N-bidentate ligands to palladium(II) led to the corresponding octa-palladium complex shown to successfully promote the coupling reaction between anisole and phenylboronic acid. The low solubility of this catalytic complex in the reaction medium enabled (or facilitated or made possible) its straightforward recovery and recycling with four cycles with no loss of activity.

Polymethacrylates containing cage-silsesquioxanes in the side chains: effects of cage and linker structures on film properties

Polymers in which cage-silsesquioxanes were tethered through urethane linkers, were newly synthesized. The free-standing films were supported by the hydrogen bonding networks. Their properties were dependent on the cage structure.

Use of Polyhedral Oligomeric Silsesquioxane (POSS) in Drug Delivery, Photodynamic Therapy and Bioimaging

Polyhedral oligomeric silsesquioxanes (POSS) have attracted considerable attention in the design of novel organic-inorganic hybrid materials with high performance capabilities. Features such as their well-defined nanoscale structure, chemical tunability, and biocompatibility make POSS an ideal building block to fabricate hybrid materials for biomedical applications. This review highlights recent advances in the application of POSS-based hybrid materials, with particular emphasis on drug delivery, photodynamic therapy and bioimaging. The design and synthesis of POSS-based materials is described, along with the current methods for controlling their chemical functionalization for biomedical applications. We summarize the advantages of using POSS for several drug delivery applications. We also describe the current progress on using POSS-based materials to improve photodynamic therapies. The use of POSS for delivery of contrast agents or as a passivating agent for nanoprobes is also summarized. We envision that POSS-based hybrid materials have great potential for a variety of biomedical applications including drug delivery, photodynamic therapy and bioimaging.

Synthesis and characterization of tetrathiol-substituted double-decker or ladder silsesquioxane nano-cores

Tetra(3-mercaptopropyl)-silsesquioxanes with double-decker (DDSQ) or ladder nano-cores were easily prepared from the corresponding tetraallyl derivatives through fast and convenient thiol-ene reactions. An additional tetrathiol-DDSQ with more flexible arms was also synthesized in high yield from the corresponding tetrachloro-DDSQ derivative. The three novel tetrathiol silsesquioxanes described represent versatile building blocks for the preparation of hybrid organic-inorganic materials.

The synthesis of thermoresponsive POSS-based eight-arm star poly(N-isopropylacrylamide): A comparison between Z-RAFT and R-RAFT strategies

Z-Type POSS-based eight-arm star poly(N-isopropylacrylamide), POSS-(PNIPAM)₈-Z, is synthesized and demonstrated to be a thermoresponsive switchable emulsifier.

Polysiloxanes Grafted with Mono(alkenyl)Silsesquioxanes-Particular Concept for Their Connection

Herein, a facile and efficient synthetic route to unique hybrid materials containing polysiloxanes and mono(alkyl)silsesquioxanes as their pendant modifiers (T₈@PS) was demonstrated. The idea of this work was to apply the hydrosilylation reaction as a tool for the efficient and selective attachment of mono(alkenyl)substituted silsesquioxanes (differing in the alkenyl chain length, from -vinyl to -dec-9-enyl and types of inert groups iBu, Ph at the inorganic core) onto two polysiloxanes containing various amount of Si-H units. The synthetic protocol, determined and confirmed by FT-IR in situ and NMR analyses, was optimized to ensure complete Si-H consumption along with the avoidance of side-products. A series of 20 new compounds with high yields and complete β-addition selectivity was obtained and characterized by spectroscopic methods.

Formation of Bifunctional Octasilsesquioxanes via Silylative Coupling and Cross-Metathesis Reaction

Bifunctional silsesquioxanes create an attractive group of compounds with a wide range of potential applications, and recently they have gained much interest. They are known to be obtained mainly via hydrosilylation, but we disclose novel synthetic protocols based on different but complementary reactions, i.e., cross-metathesis (CM) and silylative coupling (SC). A series of cubic T₈ type silsesquioxane derivatives with a broad scope of styryl substituents were synthesized in a one-pot procedure and characterized by spectroscopic and spectrometric methods. All of the new compounds can be obtained in a one-pot manner, which has an attractive impact on the synthetic procedure, as it is economic in terms of the isolation of intermediate products. Additionally, the methodology disclosed here enables the (E)-stereoselective introduction of styrenes derivative to the cubic T₈ type core. The presented compounds can be interesting precursors for a further functionalization that may significantly increase the possibility of their application in the design and synthesis of new functional materials.

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

POSS nanostructures in catalysis

In this review we highlight the use of appealing POSS-based nanostructures for both homogeneous and heterogeneous catalytic applications.