Star-shaped Polyhedral Oligomeric Silsesquioxane Research Articles

Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of 3Ph-C3 at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Facile fabrication and SERS performance of polymer/Ag core-shell microspheres via the reverse breath figure accompanied by in situ reduction

A new facile fabrication process of the polymer/Ag core-shell microspheres is demonstrated via the reverse breath figure method accompanied by in situ reduction. In contrast to traditional approaches, which require the prior preparation of polymer microspheres, the star-shaped polyhedral oligomeric silsesquioxane (POSS) amphiphilic block copolymers solution containing AgNO3 is cast under ethanol vapor for the formation of polymer/AgNO3 core-shell microspheres in one step. The influence of polymer molecular structures, solvent, non-solvent and metal salt on the morphology of polymer microspheres was analyzed. Then the AgNO3 can be reduced in situ to form Ag nanoparticles on the surface of polymer microspheres, which resulted in the formation of polymer/Ag core-shell microspheres. The reduced Ag nanoparticles were homogeneously deposited on the surfaces of polymer microspheres, which can exhibit good performance in the surface-enhanced Raman scattering (SERS). The polymer/Ag core-shell microspheres substrate showed a high detection sensitivity (enhancement factor 2.49 × 106) with excellent uniformity and reproducibility for Rhodamine 6G (R6G) (relative standard deviation of the intensity at 612 cm−1 was 6.19%＜20%). The proposed strategy is facile to implement and thus a promising new method for the preparation of polymer/metal core-shell microspheres.

Surface Segregation of a Star-Shaped Polyhedral Oligomeric Silsesquioxane in a Polymer Matrix.

A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt % s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.

Tuning the surface hydrophobicity of honeycomb porous films fabricated by star-shaped POSS-fluorinated acrylates polymer via breath-figure-templated self-assembly

Porous films with tunable surface morphology and hydrophobicity were prepared via breath figure employing star-shaped polyhedral oligomeric silsesquioxane (POSS)-fluorinated polyacrylates, which were synthesized by atom transfer radical polymerization (ATRP) to ensure controlled polymer structure and molar mass. The influence of polymer architecture, solution concentration and the type of solvent on the surface morphology of the resulted porous films were evaluated. The optimized porous films with a broad range of pore diameter (D) and rim width (W) were characterized revealing in significant increasing of the surface hydrophobicity. Moreover, the surface morphology of the porous films, characterized by the D/W values (defined as fa), and surface hydrophobicity were found to have a notable positive correlation. Furthermore, the stripped films from above mentioned porous films were investigated revealing superhydrophobic surface due to the pincushion-like structure. Higher fa values for stripped films than the related porous film was found.

Star-shaped polyhedral oligomeric silsesquioxane-polycaprolactone-polyurethane as biomaterials for tissue engineering application

Polyhedral oligomeric silsesquioxane (POSS) is a unique molecule that is composed of an inorganic silica core with eight organic functional arms, which can be used as a nucleus for covalent bonding to create star-shaped block copolymers with improved mechanical and biological properties. In this work, highly porous star-shaped POSS-polycaprolactone-polyurethane (POSS-PCL-PU) films were synthesized as scaffold biomaterials for tissue engineering. These films have an interesting morphology consisting of rough spherulites with filamentous structures spreading out from their centers; the unique nanotopography was shown to be suitable for cell growth. In vitro degradation was monitored for 52 weeks in terms of the weight loss and morphology changes of the films. The degradation profile exhibited a slow initial weight loss of <1% during the first 24 weeks, followed by a rapid weight loss of ~18% in the following 28 weeks. The films demonstrated excellent biocompatibility and cell-substrate affinity, with a high cell viability of >95% and rapid cell proliferation. The high porosity, unique surface nanotopography and excellent biocompatibility of the star-shaped POSS-PCL-PU film make it a great candidate as a tissue engineering scaffold biomaterial. Researchers in Singapore have prepared highly porous films that are very promising as scaffold biomaterials for tissue engineering. They synthesized the films by using star-shaped polyhedral oligomeric silsesquioxane as the starting inorganic core and incorporating polycaprolactone (PCL) and polyurethane (PU). The researchers, who are from the Institute of Materials Research and Engineering and the National University of Singapore, demonstrate that the inorganic-organic nanocomposite films satisfy all the key criteria for a biodegradable scaffold biomaterial — they have an excellent biocompatibility, a high porosity and a controlled and slow degradability. In addition, the scientists show that the material's unique nanotopography, which is produced by filamentous structures branching out from the centres of rough spherulites, promotes cell growth. The combination of organic and inorganic functionalities makes these films superior to conventional PCL-PU films. Highly porous star-shaped polyhedral oligomeric silsesquioxane (POSS) hybrid films were synthesized using POSS as the starting core followed by polycaprolactone (PCL) extension and polyurethane (PU) cross-linking. The unique three-dimensional nanotopography of these films is conducive for cell growth. The combination of favorable factors such as high porosity, reactive surface topography, excellent biocompatibility and biphasic degradation makes the star-shaped POSS-PCL-PU film a great candidate as a tissue engineering scaffold biomaterial.

Synthesis of star-shaped polyhedral oligomeric silsesquioxane (POSS) fluorinated acrylates for hydrophobic honeycomb porous film application

Two different eight-arm star-shaped polyhedral oligomeric silsesquioxane (POSS) fluorinated acrylates were synthesized through atom transfer radical polymerization (ATRP) and applied for hydrophobic honeycomb-patterned porous films through the breath figure (BF) method. The structure of polymers was characterized by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC), and surface analysis was featured by X-ray photoelectron spectroscopy (XPS). Depending on the influences of polymer architectures, solvents utilized, and solution concentrations, honeycomb-patterned porous films were obtained. It could be found that the introduction of fluorine components was a favorable condition for BF formation and chloroform (CHCl3) utilized as solvent with an appropriate concentration of 30 mg/mL was the best condition for these hydrophobic honeycomb-patterned porous films. Meanwhile, the obtained honeycomb films could be retained after long-time preservation in an acid-base condition, which shows a great potential in filtration, cell culture, tissue engineering, and marine antifouling applications.

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.

Syntheses and properties of star- and dumbbell-shaped POSS derivatives containing isobutyl groups

Dumbbell-shaped isobutyl-substituted C2-linked polyhedral oligomeric silsesquioxane (POSS) ((1,2-bis(heptaisobutyl-T8-silsesquioxy)ethane) IBDE), C3-linked POSS ((1,3-bis(heptaisobutyl-T8-silsesquioxy)propane) IBDP) and C6-linked POSS ((1,6-bis(heptaisobutyl-T8-silsesquioxy)hexane) IBDH) were prepared by corner capping of heptaisobutyltricycloheptasiloxane trisilanol (IB7-OH) with 1,2-bis(trichlorosilyl)ethane, 1,3-bis(trichlorosilyl)propane and 1,6-bis(trichlorosilyl)hexane, respectively. The star-shaped POSS derivative ((octakis[3-(heptaisobutyl-T8-silsesquioxy) propyldimethylsiloxy]-Q8-silsesquioxane) 9POSIB) was prepared by hydrosilylation of heptaisobutylallyl-T8-silsesquioxane (IB7A1) and octadimethylsiloxy-Q8-silsesquioxane using Karstedt’s catalyst. The star and dumbbell structures of the obtained compounds were confirmed by 1H-, 13C- and 29Si-nuclear magnetic resonance and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses. With spin coating and subsequent baking at 120 °C, the star-shaped POSS compound formed an optical transparent film, but all of the dumbbell-shaped POSS compounds formed opaque whitish films. The refractive index of the transparent film was 1.4567, which was higher than that of a corresponding random silsesquioxane. 9POSIB showed significantly higher thermal stability than did the dumbbell-shaped POSS compounds. Thermogravimetric analysis of the star-shaped POSS derivative showed a clear baseline shift at 24 °C, indicative of the glass-transition temperature. However, IBDE, IBDP and IBDH showed no clear baseline shift. The melting points of IBDE, IBDP, IBDH and 9POSIB were observed at 231, 231, 239 and 96 °C, respectively. The lower melting point and appearance of the glass-transition point in 9POSIB suggested its lower crystallinity, which promotes the formation of a transparent film. The star- and dumbbell-shaped isobutyl-substituted POSS derivatives were synthesized. The star and dumbbell structures of the obtained compounds were confirmed by 1H-, 13C-, and 29Si-NMR and MALDI-TOF-MS analysis. The star-shaped POSS compound formed the optical transparent film, and showed Tg and Tm at 24 and 96 °C, respectively. All the dumbbell-shaped POSS compounds, however, formed opaque whitish films, and showed no Tg and high Tm over 230 °C. The lower Tm and appearenace of Tg in the star-shaped POSS suggested its lower crystallinity, which promoted formation of the transparent film.

Topology Controlled Supramolecular Self-Assembly of Octa Triphenylene-Substituted Polyhedral Oligomeric Silsesquioxane Hybrid Supermolecules

A series of liquid crystalline star supermolecules with polyhedral oligomeric silsesquioxane (POSS) as the central scaffold and eight triphenylenes (Tp) as the peripheral arms were synthesized via amidization reactions. The supermolecules were denoted as POSS(Tp)(8). Six POSS(Tp)(8) samples were prepared with two alkyl chain lengths in the Tp (C(5) and C(12)) and three spacer lengths (C(2), C(6), and C(10)) between the POSS core and the Tp arms. Three samples with C(5)-Tp were amorphous because of too short alkyl chains in the Tp, while the other three samples with C(12)-Tp self-assembled into hierarchical liquid crystalline mesophases, as studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). When the spacer length was C(2), a column-within-column super hexagonal columnar phase was observed, because the POSS core and the Tp arms were intimately coupled together. With increasing the spacer length to C(6) and C(10), respectively, the POSS core and Tp arms became gradually decoupled. Alternating POSS-Tp lamellar morphology with a rectangular columnar symmetry (by XRD) was observed by TEM for the POSS(Tp)(8) sample with a C(6)-spacer. For the POSS(Tp)(8) sample with a C(10)-spacer, an oblique columnar phase was determined by XRD, and inverted columnar morphology with four Tp columns forming a super column within the POSS/alkyl chain matrix was observed by TEM. This study suggested that molecular topology played an important role in the supramolecular self-assembly of star-shaped POSS(Tp)(8) supermolecules.