Polyhedral Oligomeric Silsesquioxanes (POSS)-Containing Nanohybrid Polymers

Preparation and Characterization of Chloroprene Latexes Modified with Vinyl-POSS

Water-based chloroprene latex is a solvent-free, environmentally friendly adhesive. Currently, its market demand is growing rapidly. However, there are problems such as a lack of heat resistance and poor mechanical properties, which limit its application. The introduction of vinyl-POSS (OVS) into the resin structure can effectively improve the thermal stability of chloroprene adhesives. In this paper, modified waterborne chloroprene latex was prepared by copolymerization of methyl methacrylate and OVS with chloroprene latex. The results showed that vinyl-POSS was successfully grafted onto the main chain of the waterborne chloroprene latex, and the modified waterborne chloroprene latex had good storage stability. With the increase in vinyl-POSS, the tensile strength of the chloroprene latex firstly increased and then decreased, the tensile property (peel strength of 20.2 kgf) was maintained well at a high temperature (100 °C), and the thermal stability of the chloroprene latex was improved. When the addition amount was 4%, the comprehensive mechanical properties were their best. This study provides a new idea for the construction of a new and efficient waterborne chloroprene latex system and provides more fields for the practical application of waterborne chloroprene latex. This newly developed vinyl-POSS modified chloroprene latex has great application potential for use in home furniture, bags, and seat cushions.

Examining the Water-Polymer Interactions in Non-Isocyanate Polyurethane/Polyhedral Oligomeric Silsesquioxane Hybrid Hydrogels

Non-isocyanate polyurethane (NIPU) networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS, 0-10 wt%) were conditioned in environments of different relative humidities (up to 97%) to study water-polymer interactions. The equilibrium sorption isotherms are of Brunauer type III in a water activity range of 0-0.97 and are discussed in terms of the Guggenheim (GAB) sorption model. The study shows that the introduction of 8OHPOSS, even in a large amount (10 wt%), does not hinder the water affinity of the NIPU network despite the hydrophobic nature of POSS; this is attributable to the homogenous dispersion of POSS in the polymer matrix. The shift in the urethane-derived carbonyl bands toward lower wavenumbers with a simultaneous shift in the urethane N-H bending bands toward higher wavenumbers exposes the breakage of polymer-polymer hydrogen bonds upon water uptake due to the formation of stronger water-polymer hydrogen bonds. Upon water absorption, a notable decrease in the glass transition temperature (Tg) is observed for all studied materials. The progressive reduction in Tg with water uptake is driven by plasticization and slaving mechanisms. POSS moieties are thought to impact slaving indirectly by slightly affecting water uptake at very high hydration levels.

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.

Application of Silsesquioxanes in the Preparation of Polyolefin-Based Materials

This paper is a review of studies on the use of the polyhedral oligomeric silsesquioxanes (POSS) of various structures in the synthesis of polyolefins and the modification of their properties, namely: (1) components of organometallic catalytic systems for the polymerization of olefins, (2) comonomers in the copolymerization with ethylene, and (3) fillers in composites based on polyolefins. In addition, studies on the use of new silicon compounds, i.e., siloxane-silsesquioxane resins, as fillers for composites based on polyolefins are presented. The authors dedicate this paper to Professor Bogdan Marciniec on the occasion of his jubilee.

Synthesis of Multifunctional Oligomethylsilsesquioxanes by Catalyst-Free Hydrolytic Polycondensation of Methyltrimethoxysilane under Microwave Radiation

The catalyst-free hydrolytic polycondensation of methyltrimethoxysilane under microwave radiation has been studied. The effect of molar ratios of the reagents (MTMS/H₂O = 1/0.5-1/9), radiation power (20-300 W), temperature (30-50 °C) and duration of exposure (2.5-90 min) on the course of the process is considered. It has been shown that the use of microwave radiation promotes the activation of the process, and almost complete conversion of the monomer can be achieved in 5 min at 30 °C, 20 W and an MTMS/H₂O ratio of 1/3. The optimal radiation power for the maximum conversion of the monomer and MeO-groups is in the range from 20 to 100 W. An increase in the water amount, the duration and temperature of the process contribute to an increase in the monomer conversion, a decrease in the content of residual MeO-groups and the yield of non-volatile oligomethylsilsesquioxanes. The limits of this approach using to the synthesis of multifunctional branched polyorganosilsesquioxanes are determined. Depending on the process conditions, homogeneous water-alcohol solutions of oligomethylsilsesquioxane with a concentration of 20 to 50 wt.% can be obtained. The OH-group content and the molecular weight of the obtained oligomers vary from 10 to 30 wt.% and from 1000 to 600 Da, respectively.

THE STUDY OF INTERMOLECULAR INTERACTIONS IN THE POSS-CONTAINING NANOCOMPOSITES BASED ON POLYURETHANE AND POLYURETHANE/POLY(HYDROXYPROPYL METHACRYLATE) MATRICES

The nanocomposites based on polyurethane matrix and multicomponent polymer matrices consisting of polyurethane and poly(hydroxypropyl methacrylate) with different contents of the last, and 1,2-propanediolisobutyl polyhedral oligomeric silsesquioxane (1,2-propanediolisobutyl-POSS), which was used as a functionalized nanofiller, were synthesized. The influence of the content of 1,2-propanediolisobutyl-POSS on intermolecular interactions and structural features of the nanocomposites was investigated by the method of IR-spectroscopy with Fourier transformation and attenuated total reflection (FTIR-ATR). The study of thermal curing of the model system, which consists of the adduct of trimethylolpropane with toluene diisocyanate and 1,2-propanediolisobutyl-POSS, made it possible to conclude that 1,2-propanediolisobutyl-POSS participates in the reaction of urethane formation using of one of the terminal hydroxyl groups, and it is incorporated into the polymer chain between cross-linking of polyurethane networks. The investigation of multicomponent polymer matrices by FTIR-ATR spectroscopy was done and was shown that photopolymerization of second polymer poly(hydroxypropyl methacrylate) in the matrix of polyurethane was completed by the opening of a double bond and the formation of a linear polymer in the composition of semi-IPN. Studies of nanocomposites based on multicomponent polymer matrices consisting of polyurethane and poly(hydroxypropyl methacrylate) with 15 and 30 % of the last by FTIR-ATR spectroscopy demonstrated the presence of POSS in the nanocomposites and the influence of POSS content on the structure of the studied systems and on the degree of phase separation. The POSS is "embedded" into the polymer chain between cross-linking of the polyurethane networks, with the additional formation of a complex system of intermolecular hydrogen bonds between the carboxyl and amine components of urethane groups in the nanocomposites.

Kinetic Analysis on the Stabilization Effects of Substituted POSS Powders Embedded in γ-Radiolyzed Polypropylene

The present paper proposes a reliable alternative for the increasing stability of polypropylene (PP) by modified polyhedral oligomeric silsesquioxanes (POSS). The chemiluminescence measurements and FTIR records point complementarily out the determinant influence of substituents on the progress of oxidation during the accelerated degradation caused by γ-irradiation. The main kinetic approach of oxidation acting in radiation-induced aging recommends some of the studied structures of modified POSS as appropriate compounds for improving stability of polypropylene at low additive concentration. The analysis of the present results is based on the implication of substituted POSS, whose contribution to the limitation of oxidation is conditioned by the influence of substituents. The delay of the oxidative degradation in studied γ-irradiated polypropylene is the consequence of the interaction between molecular PP fragments and the silanol moieties generated during radiolysis, which are the most vulnerable points of POSS structure.

Polytriazole resins toughened by an azide-terminated polyhedral oligomeric silsesquioxane (OADTP)

An azido-terminated polyhedral oligomeric silsesquioxane (POSS) compound, octakis(azidopropyl-3-oxycarbonyl-1-decyl-10-thiopropyl-3-)POSS (OADTP), is synthesized and characterized. POSS-polytriazole (PTA) resins are prepared from an azide, an alkyne monomer, and OADTP. The toughening effect of OADTP on PTA resins is analyzed by impact performance test and electronic microscope characterization, and the thermal performance of resins is measured by thermogravimetric analysis and dynamic mechanical analysis. The results show that the addition of the POSS can improve the mechanical properties of PTA resins. The impact strength of POSS-PTA resins first increases and then decreases with the increase in the POSS compound, and the maximum one arrives at 54.8 kJ m−2 which increases by 44.2% as compared to 38 kJ m−2 of the PTA resin. A good thermal stability remains in POSS-PTA resins.

Synergistic Effects of Ladder and Cage Structured Phosphorus-Containing POSS with Tetrabutyl Titanate on Flame Retardancy of Vinyl Epoxy Resins

The cage and ladder structured phosphorus-containing polyhedral oligomeric silsesquioxanes (DOPO-POSS) have been synthesized through the hydrolytic condensation of 9,10-dihydro-9-oxa-10-phosphenanthrene-10-oxide (DOPO)-vinyl triethoxysilane (VTES). The unique ladder and cage–ladder structured components in DOPO-POSS endowed it with good solubility in vinyl epoxy resin (VE), and it was used with tetrabutyl titanate (TBT) to construct a phosphorus-silicon-titanium synergy system for the flame retardation of VE. Thermal stabilities, mechanical properties, and flame retardancy of the resultant VE composites were investigated by thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), three-point bending tests, limiting oxygen index (LOI) measurement, and cone calorimetry. The experimental results showed that with the addition of only 4 wt% DOPO-POSS and 0.5 wt% TBT, the limiting oxygen index value (LOI) increased from 19.5 of pure VE to 24.2. With the addition of DOPO-POSS and TBT, the peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) were decreased significantly compared to VE-0. In addition, the VE composites showed improved thermal stabilities and mechanical properties comparable to that of the VE-0. The investigations on pyrolysis volatiles of cured VE further revealed that DOPO-POSS and TBT exerted flame retardant effects in gas phase. The results of char residue of the VE composites by SEM and XPS showed that TBT and DOPO-POSS can accelerate the char formation during the combustion, forming an interior char layer with the honeycomb cavity structure and dense exterior char layer, making the char strong with the formation of Si-O-Ti and Ti-O-P structures.

POSS nanostructures in catalysis

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

Anchor Effect in Polymerization Kinetics: Case of Monofunctionalized POSS

The effect of the anchoring group on the detailed polymerization kinetics was investigated using monomethacryloxy-heptaisobutyl POSS (1M-POSS). This compound was copolymerized with lauryl methacrylate (LM) as the base monomer, at various molar ratios. The process was initiated photochemically. The polymerization kinetics were followed by photo-DSC and photorheology while the polymers were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). For comparison, a methacrylate containing the branched siloxy-silane group (TSM) was also studied. It was found that the modifiers with a bulky substituent have a dual effect on the termination process: (i) At low concentrations, they increase the molecular mobility by increasing the free volume fraction, which leads to an acceleration of the termination and slows the polymerization; while (ii) at higher concentrations, they retard molecular motions due to the “anchor effect” that suppresses the termination, leading to acceleration of the polymerization. The anchor effect can also be considered from a different point of view: The possibility of anchoring a monomer with a long substituent (LM) around the POSS cage, which can further enhance propagation. These conclusions were derived based on kinetic results, determination of polymerization rate coefficients, and copolymer analysis.

Application of olefin metathesis in the synthesis of functionalized polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials

This mini-review summarizes the applications of olefin metathesis in synthesis and functionalization of polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials. Three types of processes, i.e., cross metathesis (CM) of vinyl-substituted POSS with terminal olefins, acyclic diene metathesis (ADMET) copolymerization of divinyl-substituted POSS with α,ω-dienes and ring-opening metathesis polymerization (ROMP) of POSS-substituted norbornene (or other ROMP susceptible cycloolefins) are discussed. Emphasis was put on the synthetic and catalytic aspects rather than on the properties and applications of synthesized materials.

Thiol-radical-mediated polymerization for preparation of POSS-containing polyacrylate monoliths in capillary liquid chromatography

Through introducing octakis (3-mercaptopropyl) octasilsesquioxane (POSS-SH) synthesized in our lab to the prepolymerization solution containing stearyl acrylate (SA), 1,6-hexanediol ethoxylate diacrylate (HEDA) in the existence of porogenic solvents (tetrahydrofuran, 1,4-butanediol and 1-propanol), a POSS-containing hybrid monolithic column was fabricated via photo-initiated thiol-acrylate polymerization within 7 min. The resulting poly(SA-co-HEDA-co-POSS) monoliths were investigated by physical characterization and chromatographic evaluation. It was found that both the additive amount of thiol group and the proportion of porogenic solvents played vital effect on column efficiency, pore morphology and hydrophobicity of monolithic columns. Consequently, the poly(SA-co-HEDA-co-POSS) monolith possessed superior thermal stability, suitable permeability and homogeneous microstructure. The highest column efficiency was ∼111,000 N m^-1 for butylbenzene at the linear velocity of 0.71 mm s^-1 in reversed-phase liquid chromatography. Subsequently, baseline separations of 9 phenolic compounds, 5 anilines and 5 antibiotics were achieved, indicating the monolithic poly(SA-co-HEDA-co-POSS) column had great ability for separation of small molecules. The analytic results of the tryptic digest of BSA and HeLa were also proved that the hybrid monolith had potential for the analysis of complicated biological samples.

Hyperbranched Polysiloxanes Based on Polyhedral Oligomeric Silsesquioxane Cages with Ultra-High Molecular Weight and Structural Tuneability

Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain energy of isolated small molecule in which all eight silane groups close into rings on the sides of a single cubic cage. The structural tuneability was further demonstrated by use of methyl(3-chloropropyl)diethoxysilane, which generates a polymer with similar ultra-high molecular weight. Introduction of phosphonate groups through the chloropropyl sites later leads to functionalized polymers which can encapsulate various transition metal nanoparticles.

Preparation and Characterization of Organic-Inorganic Hybrid Macrocyclic Compounds: Cyclic Ladder-like Polyphenylsilsesquioxanes

Organic-inorganic hybrid macrocyclic compounds, cyclic polyphenylsilsesquioxanes (cyc-PSQs), have been synthesized through hydrolysis and condensation reactions of phenyltrichlorosilane. Structural characterization has revealed that cyc-PSQs consist of a closed-ring double-chain siloxane inorganic backbone bearing organic phenyl groups. The cyc-PSQ molecules have been simulated and structurally optimized using the Forcite tool as implemented in Materials Studio. Structurally optimized cyc-PSQs are highly symmetrical and regular with high stereoregularity, consistent with the dimensions of their experimentally derived structures. Thermogravimetric analysis showed that these macrocyclic compounds have excellent thermal stability. In addition to these perfectly structured compounds, macrocyclic compounds with the same ring ladder structure but bearing an additional Si-OH group, cyc-PSQs-OH, have also been synthesized. A possible mechanism for the formation of the closed-ring molecular structures of cyc-PSQs and cyc-PSQs-OH is proposed.

Novel poss reinforced chitosan composite membranes for guided bone tissue regeneration

In this study, novel composites membranes composed of chitosan matrix and polyhedral oligomeric silsesquioxanes (POSS) were fabricated by solvent casting method. The effect of POSS loading on the mechanical, morphological, chemical, thermal and surface properties, and cytocompatibility of composite membranes were investigated and observed by tensile test, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), protein adsorption assay, air/water contact angle analysis and WST-1 respectively. Swelling studies were also performed by water absorption capacity determination. Results showed that incorporation of Octa-TMA POSS^® nanofiller to the chitosan matrix increased the surface roughness, protein adsorption and swelling capacity of membranes. The addition of POSS enhanced significantly the ultimate tensile strength and strain at break of the composite membranes up to 3 wt% POSS loaded samples. An increase of about 76% in tensile strength and of strain at break 1.28% was achieved for 3 wt% POSS loaded nanocomposite membranes compared with chitosan membranes. The presence of POSS filler into polymer matrix increased the plasma protein adsorption on the surface. Maximum protein capacity and swelling was obtained for 10 wt% loaded samples. High cell viability results were obtained with indirect extraction of chitosan/POSS composites. Besides, cell proliferation and ALP activity results showed that POSS incorporation significantly increased the ALP activity of Saos-2 cells cultured on chitosan membranes. This novel composite membranes with tunable properties could be considered as a potential candidate for guided bone regeneration applications.

Cage and linear structured polysiloxane/epoxy hybrids for coatings: Surface property and film permeability

Three polysiloxane/epoxy hybrids obtained by evolving cage- or linear-structured polysiloxane into poly glycidyl methacrylate (PGMA) matrix are compared used as coatings. One is the cage-structured hybrid of P(GMA/MA-POSS) copolymer obtained by GMA and methacrylisobutyl polyhedral oligomeric silsesquioxane (MA-POSS) via free radical polymerization, the other two are PGMA/NH₂-POSS and PGMA/NH₂-PDMS hybrids by cage-structured aminopropyllsobutyl POSS (NH₂-POSS) or linear-structured diamino terminated poly(dimethylsiloxane) (NH₂-PDMS) to cure PGMA. The effect of MA-POSS, NH₂-POSS and NH₂-PDMS on polysiloxane/epoxy hybrid films is characterized according to their surface morphology, transparency, permeability, adhesive strength and thermo-mechanical properties. Due to caged POSS tending to agglomerate onto the film surface, P(GMA/MA-POSS) and PGMA/NH₂-POSS films exhibit much more heterogeneous surfaces than PGMA/NH₂-PDMS film, but the well-compatibility between epoxy matrix and MA-POSS has provided P(GMA/MA-POSS) film with much higher transmittance (98%) than PGMA/NH₂-POSS film (24%), PGMA/NH₂-PDMS film (27%) and traditional epoxy resin film (5%). The introduction of polysiloxane into epoxy matrix is confirmed to create hybrids with strong adhesive strength (526-1113N) and high thermos-stability (T_g=262-282°C), especially the cage-structured P(GMA/MA-POSS) hybrid (1113N and 282°C), but the flexible PDMS improves PGMA/NH₂-PDMS hybrid with much higher storage modulus (519MPa) than PGMA/NH₂-POSS (271MPa), which suggests that PDMS is advantage in improving the film stiffness than POSS cages. However, cage-structured P(GMA/MA-POSS) and PGMA/NH₂-POSS indicate higher permeability than PGMA/NH₂-PDMS and traditional epoxy resin. Comparatively, the cage-structured P(GMA/MA-POSS) hybrid is the best coating in transparency, permeability, adhesive strength and thermostability, but linear-structured PGMA/NH₂-PDMS hybrid behaviors the best coating in mechanical property.

Organosilica hybrid nanomaterials with a high organic content: syntheses and applications of silsesquioxanes

Organic-inorganic hybrid materials garner properties from their organic and inorganic matrices as well as synergistic features, and therefore have recently attracted much attention at the nanoscale. Non-porous organosilica hybrid nanomaterials with a high organic content such as silsesquioxanes (R-SiO_1.5, with R organic groups) and bridged silsesquioxanes (O_1.5Si-R-SiO_1.5) are especially attractive hybrids since they provide 20 to 80 weight percent of organic functional groups in addition to the known chemistry and stability of silica. In the organosilica family, silsesquioxanes (R-SiO_1.5) stand between silicas (SiO₂) and silicones (R₂SiO), and are variously called organosilicas, ormosil (organically-modified silica), polysilsesquioxanes and silica hybrids. Herein, we comprehensively review non-porous silsesquioxane and bridged silsesquioxane nanomaterials and their applications in nanomedicine, electro-optics, and catalysis.