Silsesquioxane Core Research Articles

Single molecular hyperbranched nanoprobes for fluorescence and magnetic resonance dual modal imaging

We designed and synthesized a gadolinium(III)-decorated hyperbranched polyglycerol with a fluorescent polyhedral oligomeric silsesquioxane core (POSS–HPG–Gd), and demonstrated its application as a single-molecular nanoprobe for fluorescence and magnetic resonance dual imaging. The nanoprobe exhibited a uniform size with a mean diameter of 6 ± 1 nm revealed by transmission electron microscopy. POSS–HPG–Gd showed absorption and emission maxima at 405 and 570 nm in water, respectively, with a quantum yield of 41 ± 1%. Fluorescence cell imaging by confocal laser scanning microscopy using MCF-7 cancer cells as a model cell line revealed that the nanoprobe had been successfully internalized into the cytoplasm with high brightness, low cytotoxicity and good photostability. Further magnetic resonance imaging study demonstrated that POSS–HPG–Gd can serve as a promising probe for fluorescence and magnetic resonance dual modal imaging.

Temperature and pH Dual‐Responsive Behavior of Dendritic Poly(N‐isopropylacrylamide) with a Polyoligomeric Silsesquioxane Core and Poly(2‐hydroxyethyl methacrylate) Shell

AbstractNovel temperature and pH dual‐responsive dendritic polyoligomeric silsesquioxane (POSS)–poly(N‐isopropylacrylamide) (PNIPAm)–poly(2‐hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (Tc) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter‐molecular interactions and enhanced intra‐molecular hydrogen bonding, whereas the Tc exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated.

Synthesis and Reactivity of Nitrogen Nucleophiles-Induced Cage-Rearrangement Silsesquioxanes

Novel phthalimide and o-sulfobenzimide-functionalized silsesquioxanes were successfully synthesized via nucleophilic substitution reactions from octakis(3-chloropropyl)octasilsesquioxane. Surprisingly, the formation of deca- and dodecasilsesquioxanes cages was discovered during substitution with phthalimide, but only octasilsesquioxane maintained a cage in the o-sulfobenzimide substitution reaction. Moreover, we report the electronic effect of nitrogen nucleophiles to promote cage-rearrangement of inorganic silsesquioxane core for the first time. Structures of products were confirmed by (1)H, (13)C, and (29)Si NMR spectroscopy, ESI-MS analysis, and single-crystal X-ray diffraction.

Effects of 2 nm size added heterogeneity on non-exponential dielectric response, and the dynamic heterogeneity view of molecular liquids

To investigate how non-exponential response could vary under different conditions, we studied the effects of adding 2 nm size polyhedral oligomeric silsesquioxane (POSS) to diglycidyl ether of bisphenol-A, whose molecules have the same terminal (epoxide) dipoles as the tentacle-like side chains attached to the silsesquioxane core of the POSS molecule. Dielectric relaxation spectra show that, on initial addition, the POSS nano-heterogeneity decreases the non-exponential response parameter β, which is consistent with the dynamic heterogeneity view, but it also decreases the relaxation time τ(m), which is inconsistent with that view. The variations in β and τ(m) with the composition have a thermal equivalence. Despite the lack of translational diffusion required for dynamic heterogeneity, plastic crystals show non-exponential response and non-Arrhenius dynamics. Measurements of β and τ(m) seem more appropriate than using probe molecules or modeling nonlinear response data as a sum of linear responses for testing the dynamic heterogeneity view. Data on molecular liquid mixtures is not generally consistent with this view, and adding a solute does not always decrease β. Studies of mixtures of different size rigid molecules with identical dipolar groups, including polymers, may be useful for comparing the relative effects of temperature and molecular size on β and τ(m).

Formation of a crosslinked POSS network by an unusual hydrosilylation: Thermo-oxidative stabilization of the α-cristobalite phase in its amorphous regions

A semicrystalline inorganic–organic hybrid crosslinked network containing polyhedral oligomeric silsesquioxane (POSS) cores was constructed by the unusual hydrosilylation of the terminal vinyl groups of an internal acetylene-containing silane linker by a POSS monomer. Products from the thermal treatments of this network in either argon or air at 250, 550, and 1000 °C, respectively, were characterized by Fourier transform infrared, Solid-state 13C and 29Si magic angle spinning NMR, X-ray diffraction and XPS analyses. The highly symmetrically functionalized POSS silica clusters, in the fluorite silica phase, in the network were found to remain unchanged on thermal treatment possibly due to the shielding of the silica core by the functionalities and a cancellation of thermal stresses on the silica core. Stabilization of the metastable α-cristobalite phase, which is typically formed on cooling by a β- to α-transition of the β-cristobalite phase formed above 1400 °C, was observed in the amorphous regions in the network sample treated only to 1000 °C in air. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Organic/inorganic hybrid star-shaped block copolymers of poly(l-lactide) and poly(N-isopropylacrylamide) with a polyhedral oligomeric silsesquioxane core: Synthesis and self-assembly

The star-shaped organic/inorganic hybrid poly(l-lactide) (PLLA) based on polyhedral oligomeric silsesquioxane (POSS) was prepared using octa(3-hydroxypropyl) polyhedral oligomeric silsesquioxane as initiator via ring-opening polymerization (ROP) of l-lactide (LLA). The molecular weight of POSS-containing star-shaped hybrid PLLA (POSSPLLA) can be well controlled by the feed ratio of LLA to initiator. The POSSPLLA was further functionalized into the macromolecular reversible addition-fragmentation transfer (RAFT) agent for the polymerization of N-isopropylacrylamide (NIPAM), leading to the POSS-containing star-shaped organic/inorganic hybrid amphiphilic block copolymers, poly(l-lactide)–block–poly(N-isopropylacrylamide) (POSS(PLLA–b–PNIPAM)). The self-assembly behavior of POSS(PLLA–b–PNIPAM) block copolymers in aqueous solution was investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). DLS showed the PNIPAM block in the aggregates is temperature-responsive and its phase-transition is reversible. TEM proved that the star-shaped POSS(PLLA–b–PNIPAM) amphiphilic block copolymers can self-assemble into the vesicles in aqueous solution. The vesicular wall and coronas are composed of the hydrophobic POSS core and PLLA, and hydrophilic PNIPAM blocks, respectively. Therefore, POSSPLLA and POSS(PLLA–b–PNIPAM) block copolymers, as a class of novel organic–inorganic hybrid materials with the advantageous properties, can be potentially used in biological and medical fields.

Star-branched cationic light-emitting dot with silsesquioxane core, synthesis, and light scattering studies

Novel star-like hydrophobic (M) and hydrophilic (W) hybrid light-emitting dots were synthesized by grafting conjugated arms at eight vertexes of polyhedral oligomeric silsesquioxane (POSS) cage. The water-soluble cationic polymer W contains POSS as a core and two layers shell—an inner layer shell consists of the conjugated organic chain and a long chain of hydrophilic polymer as outer layer shell for solubilization in water. The 3D structure renders non-aggregation properties of W in solution as the wavelength for the absorption and luminescence spectra remains unchanged over different concentrations. The effects of ionic strength and pH on the properties of cationic polymer W were studied using UV, dynamic- and static-light scattering (DLS and SLS).

A new supramolecular POSS electroluminescent material

A new polyhedral oligomeric silsesquioxane (POSS) core star-like supramolecular blue-light electroluminescent material, 4-uracilbutyl-1-methylpyrene ether (U-PY)/octakis[dimethyl(N-(6-acetamidopyridin-2 yl))siloxy] silsesquioxane (ODAP-POSS) has been synthesized. This U-PY/ODAP-POSS contains eight pyrene chromophore arms formed through complementary uracil-diamidopyridine (U-DAP) pairs and exhibits high quantum efficiencies and good solution processing properties. The photoluminescence spectra of U-PY/ODAP-POSS (50/50) reveal that the color is stable after heating the sample at 150 °C for 1 h, in contrast, the pyrene/ODAP-POSS (50/50) shows significant thermal quenching. An electroluminescence (EL) device based on U-PY/ODAP-POSS exhibits higher maximum brightness and higher luminance efficiency relative to that of the U-PY. In addition, U-PY/ODAP-POSS also behaves as an effective dopant that enhances energy transfer from itself to MEH-PPV. The U-PY/ODAP-POSS-doped MEH-PPV blends exhibit high luminance efficiency, 1.45 times greater than MEH-PPV.

Solution processeable organic–inorganic hybrids based on pyrene functionalized mixed cubic silsesquioxanes as emitters in OLEDs

Traditional materials for application in organic light emitting diodes (OLEDs) are primarily based on small molecules and polymers, with much fewer examples of intermediate molecular weight materials. Our interest lies in this intermediate molecular weight range, specifically in hybrids based on 3-dimensional silsesquioxane (SSQ) cores that represents a new class of versatile materials for application in solution processable OLEDs. We report here various SSQ based hybrids that are easily prepared in one high-yield step from the Heck coupling of commercially available 1-bromopyrene, and 1-bromo-4-heptylbenzene with octavinyl-T8-SSQ, and a mixture of octavinyl-T8-, decavinyl-T10- and dodecavinyl-T12-SSQ. The resulting materials offer numerous advantages for OLEDs including amorphous properties, high-glass-transition temperatures (Tg), low polydispersity, solubility in common solvents, and high purity via column chromatography. Solution processed OLEDs prepared from the SSQ hybrids provide sky-blue emission with external quantum efficiencies and current efficiencies of 3.64% and 9.56 cd A−1 respectively.

Enhancement of affinity in molecular recognition viahydrogen bonds by POSS-core dendrimer and its application for selective complex formation between guanosine triphosphate and 1,8-naphthyridine derivatives

We report that a polyhedral oligomeric silsesquioxane (POSS) core in a dendrimer can enhance the affinity of the molecular recognition via hydrogen bonds between 1,8-naphthyridine and guanosine nucleotides. The complexation of the naphthyridine ligands with a series of guanosine nucleotides was investigated, and it is shown that the POSS core should play a significant role in the stabilization of the complexes via hydrogen bonds. Finally, we demonstrate that the 1,8-naphthyridine ligand can selectively recognize guanosine triphosphate by assisting with the POSS-core dendrimer.

Synthesis and Evaluation of Nanoglobular Macrocyclic Mn(II) Chelate Conjugates as Non-Gadolinium(III) MRI Contrast Agents

Because of the recent observation of the toxic side effects of Gd(III) based MRI contrast agents in patients with impaired renal function, there is strong interest on developing alternative contrast agents for MRI. In this study, macrocyclic Mn(II) chelates were conjugated to nanoglobular carriers, lysine dendrimers with a silsesquioxane core, to synthesize non-Gd(III) based MRI contrast agents. A generation 3 nanoglobular conjugate of Mn(II)-1,4,7-triaazacyclononane-1,4,7-triacetate-GA amide (G3-NOTA-Mn) was also synthesized and evaluated. The per ion T(1) and T(2) relaxivities of G2, G3, G4 nanoglobular Mn(II)-DOTA monoamide conjugates decreased with increasing generation of the carriers. The T(1) relaxivities of G2, G3, and G4 nanoglobular Mn(II)-DOTA conjugates were 3.3, 2.8, and 2.4 mM(-1) s(-1) per Mn(II) chelate at 3 T, respectively. The T(1) relaxivity of G3-NOTA-Mn was 3.80 mM(-1) s(-1) per Mn(II) chelate at 3 T. The nanoglobular macrocyclic Mn(II) chelate conjugates showed good in vivo stability and were readily excreted via renal filtration. The conjugates resulted in much less nonspecific liver enhancement than MnCl(2) and were effective for contrast-enhanced tumor imaging in nude mice bearing MDA-MB-231 breast tumor xenografts at a dose of 0.03 mmol Mn/kg. The nanoglobular macrocyclic Mn(II) chelate conjugates are promising nongadolinium based MRI contrast agents.

Versatile grafting approaches to star-shaped POSS-containing hybrid polymers using RAFT polymerization and click chemistry

An alkyne-bearing polyhedral oligomeric silsesquioxane (POSS) core was used to prepare POSS-containing polymer hybrids using 'grafting to' or 'grafting from' strategies in combination with reversible chain transfer and click chemistry.

Co-cross-linking Silk Matrices with Silica Nanostructures for Robust Ultrathin Nanocomposites

We report on a novel assembly approach to fabricate ultrathin robust freely standing nanocomposite membranes. The materials are composed of a pre-cross-linked silk fibroin matrix with incorporated silica nanoparticles with silsesquioxane cores (POSS) or clay nanoplatelets. These reinforced silk membranes have enhanced mechanical properties as compared to traditional silk-based nanocomposites reported previously. Up to 6-fold and 8-fold increase in elastic modulus and toughness, respectively, were found for these nanocomposites. In contrast, traditional LbL-assembled nanocomposites showed only a 3-fold increase in mechanical strength. The silk nanocomposites obtained also revealed excellent optical transparency in the visible region especially if reinforced with POSS nanoparticles, which suggests their utility as low cost, nontoxic, and easily scalable reinforced biomaterials for mechanically demanding applications.

In vivo tissue responses to thermal-responsive shape memory polymer nanocomposites

To explore the safe use of thermal-responsive shape memory polymers (SMPs) as minimally invasive tissue scaffolds, we recently developed a class of biodegradable POSS-SMP nanocomposites exhibiting stable temporary shape fixing and facile shape recovery within a narrow window of physiological temperatures. The materials were covalently crosslinked from star-branched building blocks consisting a bioinert polyhedral oligomeric silsesquioxane (POSS) core and 8 degradable poly( d, l-lactide) (PLA) arms. Here we examine the degradation profiles and immunogenicity of POSS-SMPs as a function of the PLA arm lengths using a rat subcutaneous implantation model. We show that POSS-SMPs elicited a mild foreign body type immune response upon implantation. The degradation rates of POSS-SMPs, both in vitro and in vivo, inversely correlated with the length of the PLA chains within the crosslinked amorphous network. Upon in vivo degradation of POSS-SMPs, a second acute inflammatory response was elicited locally, and the inflammation was able to resolve over time without medical interventions. One year after the implantation of POSS-SMPs, no pathologic abnormities were detected from the vital/scavenger organs examined. These minimally immunogenic and biodegradable SMPs are promising candidates for scaffold-assisted tissue repair where both facile surgical delivery and controlled degradation of the scaffold are desired for achieving optimal short-term and long-term clinical outcomes.

High‐Performance Polybenzoxazine Nanocomposites Containing Multifunctional POSS Cores Presenting Vinyl‐Terminated Benzoxazine Groups

AbstractWe have prepared a new class of polybenzoxazine/POSS nanocomposites through the reactions of a multifunctional vinyl‐terminated VBa‐POSS with a VBa monomer at various compositional ratios. The incorporation of the silsesquioxane core units into the polybenzoxazine matrix significantly hindered the mobility of the polymer chains and enhanced the thermal stability of these hybrid materials. Increasing the POSS content in these hybrids improved their thermal and mechanical properties, relative to those of the neat polybenzoxazine, because of hydrogen bonding between the siloxane groups of the POSS core units and the OH groups of the polybenzoxazine moieties, as adjudged using FTIR spectroscopy. magnified image

Efficient Light-Emitting Devices Based on Platinum-Complexes-Anchored Polyhedral Oligomeric Silsesquioxane Materials

The synthesis, photophysical, and electrochemical characterization of macromolecules, consisting of an emissive platinum complex and carbazole moieties covalently attached to a polyhedral oligomeric silsesquioxane (POSS) core, is reported. Organic light-emitting devices based on these POSS materials exhibit a peak external quantum efficiency of ca. 8%, which is significantly higher than that of the analogous devices with a physical blend of the platinum complexes and a polymer matrix, and they represent noticeable improvement in the device efficiency of solution-processable phosphorescent excimer devices. Furthermore, the ratio of monomer and excimer/aggregate electroluminescent emission intensity, as well as the device efficiency, increases as the platinum complex moiety presence on the POSS macromolecules decreases.

Synthesis and characterization of polyhedral oligomeric silsesquioxane (POSS) with multifunctional benzoxazine groups through click chemistry

We prepared a new class of polybenzoxazine-POSS nanocomposites with network structures through thermal curing of multifunctional benzoxazine groups of POSS (OBZ-POSS), which was synthesized from octa-azido functionalized POSS (OVBN3-POSS) with 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine (P-pa) via a click reaction. Incorporation of the silsesquioxane core into the polybenzoxazine matrix could significantly enhance the thermal stability of these hybrid materials. For these nanocomposites, the POSS nanoparticles in the hybrids were improved their thermal properties with 2,2-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazine)propane (BA-m) and P-pa polybenzoxazine, analyzed via TGA analyses. In addition, the incorporation of the POSS led to the formation of an inorganic protective layer on the nanocomposite’s surface. Contact angle data provided positive evidence to back up this hypothesis that the incorporation of the POSS units would decrease the surface energy property. In addition, the low glass transition temperature of poly(4-vinyl pyridine) and polycarbonate thin films, which lack liquid resistance, could possess low surface free energy after modification with OBZ-POSS due to low temperature curing of this new compound.

Star Block Copolymers Through Nitroxide‐Mediated Radical Polymerization From Polyhedral Oligomeric Silsesquioxane (POSS) Core

AbstractA series of star block copolymers were prepared through nitroxide‐mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core‐first polymerization. Eight N‐alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q8M POSS) with 1‐(2‐(allyloxy)‐1‐phenylethoxy)‐2,2,6,6‐tetramethylpiperidine (allyl‐TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa‐N‐alkoxyamines POSS (OT‐POSS) were used as platform to synthesize star polystyrene‐POSS ((PS)8‐POSS) homopolymer and diblock copolymers of poly(styrene‐block‐4‐vinylpyridine)‐POSS ((PS‐b‐P4VP)8‐POSS) and poly(styrene‐block‐acetoxystyrene) ((PS‐b‐PAS)8‐POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS‐b‐PAS)8‐POSS, the poly(styrene‐block‐vinyl phenol) ((PS‐b‐PVPh)8‐POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self‐assembled structures of these star block copolymers based on POSS were characterized by 1H NMR, FTIR, SEC, TEM, and SAXS analyses.magnified image

Macrocyclic Gd3+ Chelates Attached to a Silsesquioxane Core as Potential Magnetic Resonance Imaging Contrast Agents: Synthesis, Physicochemical Characterization, and Stability Studies

Two macrocyclic ligands, 1,4,7,10-tetraazacyclododecane-1-glutaric-4,7,10-triacetic acid (H(5)DOTAGA) and the novel 1,4,7,10-tetraazacyclododecane-1-(4-(carboxymethyl)benzoic)-4,7,10-triacetic acid (H(5)DOTABA), were prepared and their lanthanide complexes (Ln = Gd(3+), Y(3+)) attached to an amino-functionalized T(8)-silsesquioxane. The novel compounds Gadoxane G (GG) and Gadoxane B (GB) possess eight monohydrated lanthanide complexes each, as evidenced by multinuclear ((1)H, (13)C, (29)Si) NMR spectroscopy and high resolution mass spectrometry (HR-MS). Pulsed-field gradient spin echo (PGSE) diffusion (1)H NMR measurements revealed hydrodynamic radii of 1.44 nm and global rotational correlation times of about 3.35 ns for both compounds. With regard to potential MRI contrast agent applications, a variable-temperature (17)O NMR and (1)H nuclear magnetic relaxation dispersion (NMRD) study was carried out on aqueous solutions of the gadolinium(III) complexes of the Gadoxanes and the corresponding monomeric ligands to yield relevant physicochemical properties. The water exchange rates of the inner-sphere water molecules are all very similar (k(ex)(298) between (5.3 +/- 0.5) x 10(6) s(-1) and (5.9 +/- 0.3) x 10(6) s(-1)) and only slightly higher than that reported for the gadolinium(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (H(4)DOTA) (k(ex)(298) = 4.1 x 10(6) s(-1)). Despite their almost identical size and their similar water exchange rates, GB shows a significantly higher longitudinal relaxivity than GG over nearly the whole range of magnetic fields (e.g., 17.1 mM(-1) s(-1) for GB and 12.1 mM(-1) s(-1) for GG at 20 MHz and 25 degrees C). This difference arises from their different local rotational correlation times (tau(lR)(298) = 240 +/- 10 ps and 380 +/- 20 ps, respectively), because of the higher rigidity of the phenyl ring of GB as compared to the ethylene spacer of GG. A crucial feature of these novel compounds is the lability of the silsesquioxane core in aqueous media. The hydrolysis of the Si-O-Si moieties was investigated by (29)Si NMR and PGSE diffusion (1)H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), as well as by relaxivity measurements. Although frozen aqueous solutions (pH 7.0) of GG and GB can be stored at -28 degrees C for at least 10 months without any decomposition, with increasing temperature and pH the hydrolysis of the silsesquioxane core was observed (e.g., t(1/2) = 15 h at pH 7.4 and 55 min at pH 8.1 for GG at 37 degrees C). No change in relaxivity was detected within the first 3 h, since the hydrolysis of the initial Si-O-Si moieties has no influence on the rotational correlation time. However, the further hydrolysis of the silsesquioxane core leads to smaller fragments and therefore to a decrease in relaxivity.

Synthesis and Characterization of Inorganic-Organic Hybrid Materials Derived from Polysilsesquioxanes (POSS)

This article describes two synthetic strategies of biodegradable multi-arm star polymers with a polyhedral oligomeric silsesquioxane (POSS) core. The goal is to develop synthetic strategies towards reinforced biodegradable polymers that can potentially be used in hard tissue engineering. The polymers were characterized including a preliminary evaluation of the cytotoxicity of the POSS-hybrid polymers and the POSS core. A core first strategy employed the ring opening polymerization of ϵ–caprolactone and/or L-lactide using Sn(Oct)2 as the catalyst and octa hydroxy silsequioxane as the initiating core. The arm first strategy utilized an esterification reaction between octaanhydride functionalized POSS (POSS-SA) molecule and hydroxyl functionalized polyesters. The hybrid polymers were characterized with FTIR, 1H, 13C, 29Si NMR, GPC and thermal analysis. The POSS-polymer ratio can be tailored to obtain polymers with different handling properties, from a solid to a viscous liquid. Preliminary cell toxicology studies of octakis hydroxy POSS and hybrid polymers were evaluated using Myoblast (C2C12 cells) and human osteoblast cells (MG63). The studies indicated that there is no significant cell toxicity exhibited by these POSS derived materials demonstrating their potential use as biomaterials.