Polyhedral Oligomeric Silsesquioxane Core Research Articles

Exciplex Emission in the POSS Possessing Two Kinds of Luminophores

Here we report the synthesis and luminescent properties of the modified polyhedral oligomeric silsesquioxane (POSS) that possesses two types of luminophores, cyanobenzene and N,N‐diethylaniline for inducing significant emission not only from each dye but also from molecular interactions on the POSS core. From the optical measurements in the diluted solution, we observed both locally‐excited emission and excimer emission originating from intramolecular interactions assisted by POSS. Moreover, highly‐efficient exciplex emission was observed from the thin film, indicating that the interaction between luminophores easily occurs in the solid state by accumulating two kinds of molecules in the single POSS molecule. Finally, we also found that the modified POSS showed a unique acid responsiveness which can be caused by protonation at two types of amino moieties. In this manuscript, it is shown that POSS is able to play various roles at the same time: recruiting excited molecules to form exciplexes, suppressing concentration quenching in the solid state, and imparting stimulus responsiveness to exciplexes.

Hierarchical Nanostructures Constructed by Soft Epitaxial Self-Assembly of Organic-Inorganic Hybrid Giant Amphiphiles.

2D nanomaterials with ångström-scale thicknesses offer a unique platform for confining molecules at an unprecedentedly small scale, presenting novel opportunities for modulating material properties and probing microscopic phenomena. In this study, mesogen-tethered polyhedral oligomeric silsesquioxane (POSS) amphiphiles with varying numbers of mesogenic tails to systematically influence molecular self-assembly and the architecture of the ensuing supramolecular structures, are synthesized. These organic-inorganic hybrid amphiphiles facilitate precise spatial arrangement and directional alignment of the primary molecular units within highly ordered supramolecular structures. The correlation between molecular design and the formation of superlattices through comprehensive structural analyses, incorporating molecular thermodynamics and kinetics, is explored. The distinct intermolecular interactions of the POSS core and the mesogenic tails drive the preferential formation of a 2D inorganic sublattice while simultaneously guiding the hierarchical assembly of organic lamellae via soft epitaxy. The findings reveal the intricate balance between shape, size, and interaction strengths of the inorganic and organic components, and how these factors collectively influence the structural hierarchy of the superstructures, which consist of multiple sublattices. By controlling this unique molecular behavior, it is possible to modulate or maximize the anisotropy of optical, mechanical, and electrical properties at the sub-nanometer scale for nanotechnology applications.

Unlocking Synthesis of Polyhedral Oligomeric Silsesquioxane-Based Three-Dimensional Polycubane Covalent Organic Frameworks.

Reticular chemistry effectively yields porous structures with distinct topological lattices for a broad range of applications. Polyhedral oligomeric silsesquioxane (POSS)-based octatopic building blocks with a rare Oh symmetric configuration and attracting inorganic features have great potential for creating three-dimensional (3D) covalent organic frameworks (COFs) with new topologies. However, the intrinsic flexibility and intensive motion of cubane-type POSS molecules make the construction of 3D regular frameworks challenging. Herein, by fastening three or four POSS cores with per aromatic rigid linker from rational steric directions, we successfully developed serial crystalline 3D COFs with unpresented "the" and scu topologies. Both the experimental and theoretical results proved the formation of target 3D POSS-based COFs. The resultant hybrid networks with designable chemical skeletons and high surface areas maintain the superiorities of both the inorganic and organic components, such as their high compatibility with inorganic salts, abundant periodic electroactive sites, excellent thermal stability, and open multilevel nanochannels. Consequently, the polycubane COFs could serve as outstanding solid electrolytes with a high ionic conductivity of 1.23 × 10-4 S cm-1 and a lithium-ion transference number of 0.86 at room temperature. This work offers a pathway to generate ordered lattices with multiconnected flexible cube motifs and enrich the topologies of 3D COFs for potential applications.

Covalent Grafting of Dielectric Films on Cu(111) Surface via Electrochemical Reduction of Aryl Diazonium Salts.

Covalent grafting of dielectric films containing polyhedral oligomeric silsesquioxane (POSS) on the surface of Cu(111) is performed by a one-step electrochemical reduction of diazonium salts. This method is efficient and economic and performs in a proton-polar solvent of deionized water and tetrahydrofuran (THF), where the monomer employs an octavinylsilsesquioxane (OVS) containing a POSS core. The eight vinyl bonds contained in OVS are used to participate in aryl radical-initiated polymerization reactions to form films. The formed film is dense and covers the copper surface completely and uniformly. The thickness of the film can be controlled by adjusting the reaction time. The components of the films are mainly polynitrophenyl (PNP) or polyaminophenyl (PAP) as well as poly(octavinylsilsesquioxane) (POVS), and the POVS content could be adjusted by the applied voltage. The introduction of POSS prevents the copper surface from being oxidized and often gives the film good properties such as good dielectric properties, mechanical properties, and thermal properties. In addition, the presence of Cu-O-C and Cu-C bonds between the film and copper interface is confirmed at different film thicknesses by X-ray photoelectron spectroscopy (XPS), which allowed the construction of covalent bonds between metal and nonmetal, further enhancing the bonding between the film and copper. Organic films prepared by electrochemical reduction of diazonium salts using OVS as a monomer will have potential significance for the future development of the electronics industry.

Simultaneous removal of pollutants from sub-nanometric to nanometric scales by hierarchical dendrimers modified aerogels

The disposal of dyestuff wastewater containing metal ions and dyes is a tough challenge, due to the competition of adsorption sites. Here, aramid nanofiber (ANF) based aerogels are fabricated, which exhibit excellent adsorption performance for sub-nanometric and nanometric adsorbates, such as Cu2+ and Congo red (CR) in this work. Synthesized hierarchical polyhedral oligomeric silsesquioxanes (POSS) cored polyamide amine (PPAMAM) is used to modify ANF aerogels and molecular dynamics simulation results indicate that the POSS core endows synthesized PPAMAM with cavities and mobile terminal groups on ANF surface, compared to normal PAMAM. When prepared aerogels are applied to treat wastewater with co-adsorbate, small metal ions could enter the cavities and coordinate with internal tertiary amines. In contrast, CR molecules are too large to enter cavities and prefer interacting with external primary amines. In addition, blending PPAMAM also increases the specific surface area, which highly enhances the adsorption performance. As a result, simultaneous and effective removal of Cu2+ and CR is achieved, and in binary system, the adsorption capacities are 248.49 and 1502.95 mg/g, respectively. After five cycles, fabricated adsorbents still maintain excellent adsorption performance. Therefore, this work provides a new way to the preparation of effective adsorbents for simultaneous removal of different sized pollutants.

Tadpole‐like Copolymer for Fabrication of Silica‐encapsulated Polysulfide Microspheres

AbstractA novel giant surfactant, possessing a well‐defined hydrophilic tail and a hydrophobic head with rigid multiple conjugate chains, tadpole‐like copolymer with polyhedral oligomeric silsesquioxane core (P9‐1), had been designed and synthesized via aminolysis/addition, interfacial oxidation polymerization. It was used to form complex micelles with polysulfides (PSL) for constructing the silica microspheres with micrometer dimensions in a simplified one‐pot synthesis. The characterization results for the morphologies of the complex micelles and the resulting microspheres indicated that the introduction of conjugated segments and steric hindrance of hybrid cage contributes to promote the stability and provide larger core space of the self‐assembled micelle to accommodate more PSL. With increasing the PSL/P9‐1 feed ratio, the size of microspheres and the content of PSL in the resulting microsphere were increased due to the PSL droplets providing a soft‐template for silica particles to build larger‐sized silica microspheres with PSL cores. And the growth mechanism of microstructures was also proposed in evaporation synthetic procedures, especially for special hollow morphology.

Effects of hetero‐armed star‐shaped PCL‐PLA polymers with POSS core on thermal, mechanical, and morphological properties of PLA

AbstractIn this study, AB type‐heteroarm star‐shaped poly(ε‐caprolactone)‐poly(lactic acid) (PCL‐PLA) polymers with polyhedral oligomeric silsesquioxane (POSS) core ((PCL)4‐POSS‐(PLA)4, coded as SPLA) were synthesized successfully by using ring opening polymerization and click chemistry techniques together. The synthesized polymers were compounded with commercial PLA at different blending ratios (PLA/SPLA = 100/0, 95/5, 90/10, and 80/20% wt). The effects of heteroarm SPLA polymers having different arm lengths (n = 10, 20, 30, and 50) on morphological, mechanical, and thermal behaviors of PLA were investigated. It is determined that SPLA polymers with four PLA and four PCL arms on its structure enhanced mechanical properties of PLA. The tensile modulus decreased, and lowest modulus values were observed with blends prepared at 80/20 ratio. Elongation at break values increased in all blends, maximum increment was observed with 1,4‐phenylene diisocyanate (PDI) containing SPLA20 blends prepared at 90/10 ratio. This result showed that SPLA20 had optimum chain length for chain extension reactions of between PLA chains. Besides, a trade compatibilizer PDI was utilized to enhance the intercompatibility of binary polymer blends.

Soluble and film‐formable homopolymer tethering side‐opened cage silsesquioxane pendants

AbstractCage silsesquioxane, denoted as polyhedral oligomeric silsesquioxane (POSS) has high crystallinity to readily cause aggregation when it is induced into polymer side chain. In this work, side‐opened POSS was employed to construct a bifunctional monomer for cyclopolymerization. The collapsed symmetry of the POSS core effectively reduced the crystallinity to realize homogeneous films, while a traditional POSS homopolymer formed turbid and brittle films. The obtained film showed high transparency and thermal stability.

Facile preparation and properties of polyhedral oligomeric silsesquioxane (POSS) nano-hybrid materials with disaggregation effect

This work reports on a facile and efficient strategy for preparing a class of chromophores- including organic-inorganic functional hybrid materials. These hybrid materials are based on pyrene and octavinyl-polyhedral oligomeric silsesquioxane (OV-POSS), in which the positive vinyls in OV-POSS were heck coupling reacted with pyrenes. It was found that the incorporation of polyhedral oligomeric silsesquioxane (POSS) can significantly precluded aggregation of hybrid molecules due to the inhibition of π-π stacking between chromophore units, which were also further confirmed by theoretical simulation. Moreover, the fluorescence quantum efficient of H2 (Φsolid = 80%) is higher than H1 (Φsolid = 65%) and H3 (Φsolid = 68%), respectively. AFM and OM images showed the smooth surface structure of the hybrid film, which demonstrated that the incorporation of inorganic POSS could improve the film-forming property of organic chromophores. Simultaneously, thermogravimetric analysis (TGA) results also display inorganic POSS core leads to the good thermal stabilities (>250 °C) of the functional hybrids materials.

Molecular shape conversion of POSS-(PLLA)x with various arm lengths and its effect on the compatibility of PLLA/POSS-(PLLA)x as a nanofiller blended into PLLA matrix: From spiky ball to panel-like

As a nanofiller, the well-defined star POSS-(PLLA)x formed by introducing poly(l-lactide) arms onto an octa(3-hydroxypropyl) polyhedral oligomeric silsesquioxane (POSS) nanocage core was blended into the poly(l-lactide) (PLLA) matrix. Molecular models of the star POSS-(PLLA)x and PLLA hybrids were constructed to investigate the geometrical characteristics of nanofiller and its effect on the compatibility of hybrids by using molecular mechanics (MM) and molecular dynamics (MD). Geometric descriptors and dipole moments demonstrated that the molecular geometry of POSS-(PLLA)x nanofiller converted from a spiky ball to a panel-like shape as the number of l-lactide (LA) units in the arms attached to the POSS core increased from 9 to 12. The highest crystallinity was achieved in blends of PLLA with POSS-(PLLA)12 forming panel-like shape since the longest arms in POSS-(PLLA)12 tended to be parallel, leading to an improved compatibility in hybrid. When blended with the spiky ball-like shape of POSS-(PLLA)9, PLLA hybrid obtained the lowest crystallinity with an apparent plasticization in matrix, due to the steric barrier in adjacent chains resulting from mutually exclusive arms in POSS-(PLLA)9. Moreover, consistent with the experimental results, analysis of the mean square displacement (MSD) and radial distribution function (RDF) confirmed that POSS-(PLLA)x nanofiller acted as a nucleating core for crystallization due to its limited mobility compared to the PLLA chain.

A high-emissive and stable luminescent silafluorene hybrid constructed by hydrosilylation

Under Karstedt’s catalyst, an organic–inorganic hybrid fluorescent nano-molecular dendrimer has been synthesized by grafting silafluorene units onto the polyhedral oligomeric silsesquioxane core through hydrosilylation reaction. The new hybrid molecule exhibits high solid fluorescence quantum efficiency because of the nano-size and large steric hindrance of the polyhedral oligomeric silsesquioxane core. Thermogravimetric analysis shows that the thermal stability of the target compound is effectively improved by the presence of polyhedral oligomeric silsesquioxane.

A Diarylethene-Based Photoswitch and its Photomodulation of the Fluorescence of Conjugated Polymers.

Photochromic diarylethene derivatives, which can reversibly switch the fluorescence of adjacent fluorophores between the ON and OFF states under light irradiation, have been widely used to construct photoswitchable materials. Herein, eight dithienylethene (DTE) groups are integrated onto one polyhedral oligomeric silsesquioxane (POSS) core, obtaining a novel super molecular photoswitch. After being doped into conjugated polymer nanoparticles, the POSS-DTE8 molecules show a higher contrast on/off photoswitching performance and a quicker responsive speed than free DTE molecules at same molar concentration of photochromic units. This enhanced photoswitching efficiency is attributed to the increased molecular interaction of the ring-open form and lowered energy of the ring-closed form of the DTE units on the POSS core, which is beneficial for the ring-closing reaction and subsequent energy transfer between photoswitch and fluorophores. In addition, POSS-DTE8 also exhibits good photomodulation behavior in the conjugated polymer film, giving it potential applications in optical devices.

Synthesis of Janus POSS star polymer and exploring its compatibilization behavior for PLLA/PCL polymer blends

Synthesis of hybrid hetero-arms star polymer with precisely defined arms distribution in three dimensional (3D) space is still a challenge. Herein, we have employed cubic polyhedral oligomeric silsesquioxane (POSS) nanoparticle as a scaffold to synthesize a biodegradable Janus POSS star polymer (oom-T8PLLA5PCL3), which contains an inorganic rigid POSS core, three poly(ε-caprolactone) (PCL) arms and five poly(l-lactide) (PLLA) arms on the POSS cage two sides, respectively. The chemical structure of oom-T8PLLA5PCL3 was confirmed by NMR, SEC, and FTIR spectra. As an example of application for the Janus POSS star polymer, oom-T8PLLA5PCL3 was used for the compatibilization of biodegradable PLLA/PCL (w/w = 70/30) blends. It was found that oom-T8PLLA5PCL3 could reduce the dispersed PCL phase size in PLLA matrix and enhance the properties of PLLA/PCL polymer blends, which was reflected in the increase of Izod impact strength and tensile performance of the polymer blends.

Preparation and Properties of Additive Polysiloxane/POSS Hybrid Composites

Octavinyl polyhedral oligomeric silsesquioxane (POSS) were used to hybrid with polysiloxane matrix by two methods, physical blending (PB) and chemical modification (CM). Mechanical, thermal and morphological properties of composites were studied by changing the percentage of POSS and investigated by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and wide angle X-ray diffraction (XRD) measurements. The results show that the hybrid composites have better mechanical and thermal property than the parent polymer matrix, and CM-prepared composites show better reinforcing role compared with PB-prepared samples. The CM method was hydrosilylation reaction of octavinyl-POSS with hydrogen terminated poly(methylphenylsiloxane) (HPMPS) and the FTIR and NMR results of modified POSS revealed that hydrosilylation reaction took place successfully but was not complete. The modified POSS consisting partial segments of HPMPS attached to the central POSS core showed better distribution in matrix than PB-prepared POSS hybrid composites.

Synthesis, characterization and surface properties of star-shaped polymeric surfactants with polyhedral oligomeric silsesquioxane core

Star-shaped amphiphilic polymeric surfactants comprising a hydrophobic polyhedral oligomeric silsesquioxane (POSS) core and hydrophilic poly(ethylene glycol) (PEG) arms with various chain lengths are successfully synthesized using copper(I)-catalysed azide–alkyne cycloaddition (CuAAC) click reaction. Their chemical structures and molecular characteristics are clearly confirmed using Fourier transform infrared and 1H NMR spectroscopies and gel permeation chromatography, and no homopolymer is found after CuAAC click reaction. Aqueous solutions of these star-shaped polymers have been investigated using atomic force and transmission electron microscopies and dynamic light scattering studies and it is found that they can self-assemble into micelles. The sizes of the micelles can be adjusted by the length of the PEG arms, where longer chains not only lead to increased micelle sizes, but also reduce the contact angle values. Moreover, the melting points and root mean square roughness of the obtained star-shaped polymers are slightly increased on increasing the chain length of the PEG arms. © 2017 Society of Chemical Industry

Subcellular co-delivery of two different site-oriented payloads for tumor therapy.

Co-delivery of multiple agents via nanocarriers is of great interest in cancer therapy, but subcellular delivery to the corresponding site of action remains challenging. Here we report a smart nanovehicle which enables two different site-oriented payloads to reach their targeted organelles based on stimulus-responsive release and nucleus-targeted modification. First, all trans retinoic acid (RA) conjugated camptothecin (RA-CPT) was loaded in a polyhedral oligomericsilsesquioxane (POSS)-based core; docetaxel (DTX) was grafted on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. The POSS core grafted with semitelechelic HPMA copolymers then self-assembled into micelles. Once internalized into the cell, the two drugs were unleashed environment-responsively, and nuclear targeted RA remarkably facilitated the nuclear transport of CPT. Compared with single drug-loaded micelles, the dual drug-loaded platform showed superior synergic cytotoxicity, which was further strengthened by the involvement of RA. The ability to induce DNA damage and apoptosis was also enhanced by nucleus-targeted modification. Finally, dual drug-loaded micelles exhibited much better in vivo tumor inhibition (87.1%) and less systemic toxicity than the combination of single drug-loaded systems or the dual drug-loaded micelles without RA. Therefore, our study provides a novel "one platform, two targets" strategy in combinatory anti-cancer therapy.

Diazoketo-functionalized POSS resists for high performance replica molds of ultraviolet-nanoimprint lithography

Novel polyhedral oligomeric silsesquioxane (POSS) resists, which are based on a new photo-crosslinking system via Wolff rearrangement, are developed as ideal replica mold materials for ultraviolet-nanoimprint lithography. These POSS resist materials are synthesized by incorporating diazoketo and hydroxyl groups into the POSS core. The resist materials have exhibited a variety of desirable properties as replica molds, such as high modulus, low shrinkage ratio, high transparency, low surface energy, and resistance to organic solvents. The resultant replica molds exhibit a high resolution patterning capacity. These economic fabrication methods of replica molds with high mechanical durability and good releasing properties are potentially useful for versatile applications in the area of mold-based lithography.

Polystyrene–Polyhedral Oligomeric Silsesquioxane Core–Shell Element-block Polymer Particles Fabricated via Heterocoagulation Method

Colloidally stable polystyrene (PS)–polyhedral oligomeric silsesquioxane (POSS) element-block polymer particles were fabricated by heterocoagulation method using negatively charged POSS and positively charged PS seed particles in water. POSS was adsorbed to the PS particle surface via electrostatic interaction and the resulting particles had PS core and POSS shell morphology.

Novel polypropyleneβ‐nucleating agent with polyhedral oligomeric silsesquioxane core: synthesis and application

AbstractSynthesis and nucleation ability of a novel silsesquioxane‐basedβ‐nucleating agent for isotactic polypropylene (iPP) are presented. A silsesquioxane cage (POSS) was octa‐functionalized with a commercially used nucleating agent, namelyN2,N6‐dicyclohexylnaphthalene‐2,6‐dicarboxamide (NU‐100), and used as a carrier with the ability to promote crystallization ofβ‐phase in polypropylene matrix. Presented results include the synthesis route of theβ‐nucleating agent (SF‐B01) and a description of its nucleation ability in iPP. The influence of SF‐B01 on iPP matrix was examined using differential scanning calorimetry, wide‐angle X‐ray scattering and static tensile tests. Investigations were complemented with polarized light optical microscopy upon non‐isothermal crystallization of composites as well as scanning electron microscopy to qualitatively assess the filler distribution. Polypropylene samples modified with different amounts of NU‐100 were used as reference. Modification carried out with both nucleating agents reveals their comparable efficiency, i.e. a structure rich inβ‐phase is obtained in both cases. © 2016 Society of Chemical Industry

Dual Stimuli-Responsive Hybrid Polymeric Nanoparticles Self-Assembled from POSS-Based Starlike Copolymer-Drug Conjugates for Efficient Intracellular Delivery of Hydrophobic Drugs.

To further fine tune drug release and enhance therapeutic effects of polyhedral oligomericsilsesquioxane (POSS)-based nanomedicine, a starlike organic-inorganic conjugate was synthesized by grafting semitelechelic N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers to a POSS rigid core through reductively degradable disulfide bonds. The hydrophobic docetaxel (DTX) was attached to the grafts by pH-sensitive hydrazone bonds and also encapsulated into the POSS core (SP-DTX). Thus, the final amphiphilic star-shaped conjugates could self-assemble into nanoparticles and exhibited conspicuous drug-loading capacity (20.1 wt %) based on the covalently conjugated accompanied by physically encapsulated DTX. The stimuli-responsive DTX release under acidic lysosomal and reducing cytoplasmic environments was verified, leading to enhanced cytotoxicity against PC-3 human prostate carcinoma cells. To evaluate the in vivo therapeutic effects of the DTX-loaded nanovehicles objectively, a stroma-rich, prostate xenograft tumor model was generated. SP-DTX displayed uniform tumor distribution and suppressed tumor growth to a more pronounced level (tumor inhibition of 78.9%) than nonredox-sensitive SP-DTX-A (67.4%), SP-DTX-C contained DTX only in the core (65.5%) or linear P-DTX (60.7%) through enhanced depletion of cancer-associated fibroblasts and induction of apoptosis. The hybrid POSS-based polymeric nanoparticles offer an efficient approach to transport hydrophobic drugs for cancer therapy.