Poly Silsesquioxanes Research Articles

An integrated microreaction system for controllable continuous synthesis of polysilsesquioxane microspheres

The complexities in polysilsesquioxanes (PSQ) formation process is considerably challenging for large-scale production. There are both fast and slow reactions with solid generation in this process, and the coupling of the reactions makes it difficult to realize the uniform growth of particles in batch reactors. In this study, a novel continuous microreaction system integrating a microreactor with a Taylor-Couette reactor (TCR) was developed to synthesize PSQs. The preparation process can be decoupled into independent reactions in different reactors: the microreactor was employed to achieve rapid microdispersion or micromixing for fast reactions, TCR was used to form a nearly ideal plug flow to realize uniform growth and suspending of particles. The obtained PSQ particles exhibited high sphericity, dispersibility, and uniform composition. The reaction time was reduced nearly 10-fold compared to the batch process. The integrated continuous microreaction system displayed high process controllability, long-term operation stability, and the potential for reliable scaling-up. • An integrated microreaction system is developed to synthesize polysilsesquioxanes. • The complex formation process of PSQ is decoupled to proceed in exclusive reactors. • The particle size can be tuned from submicrons to microns. • The reaction time was reduced nearly 10-fold compared to the batch method. • The system shows high process controllability and potential for scaling-up.

Double-Decker Silsesquioxane-Grafted Polysilsesquioxane Hybrid Films as Thermal Insulation Materials

The development of thermal insulators possessing high thermal insulating properties and thermal stability is desired for realizing a sustainable society. In polysilsesquioxanes (PSQs), which are promising as next-generation thermal insulation materials, the introduction of cross-linking units allows improving the thermal insulating properties through formation of intramolecular void spaces. However, this is usually accompanied by a loss of transparency and stability. To circumvent this issue, the hydrosilylation reaction between hydrodimethylsilylated oligomethylsilsesquioxane and vinyl-functionalized double-decker silsesquioxane (vinyl-DDSQ), which is a highly thermally stable unit, was conducted to obtain aggregation-free DDSQ-grafted PSQ films. The high miscibility of the double-decker silsesquioxane (DDSQ) molecule allowed introducing a high amount of vinyl-DDSQ, and colorless and transparent DDSQ-grafted PSQ films were obtained without aggregation of DDSQ molecules. The thermal diffusivities of the DDSQ-grafted PSQ films decreased from 1.21 × 10–7 to 1.02 × 10–7 m2/s with increasing the DDSQ amount from 5 to 25 mol %. Although a similar trend was observed for the previously reported polyhedral oligomeric silsesquioxane-containing hybrid films, the hardness of the DDSQ-grafted PSQ films decreased with increases in the vinyl-DDSQ content, and their thermal stability was higher (over 400 °C), with higher 5% mass loss temperature and 10% mass loss temperature values of 438–463 °C and 495–523 °C, respectively. Therefore, the high thermal insulating properties and thermal stability of the DDSQ-grafted PSQ films render them promising materials for next-generation thermal insulators.

The role of β relaxations in determining the compressive properties of an epoxy amine network modified with POSS and mono-functional epoxy resins

Presented here is an investigation into the glassy state molecular mobility of modified epoxy amine networks using sub-ambient β relaxations measured from dynamic mechanical relaxations and their relationship to compressive properties. Two classes of additives are used to modify the epoxy amine network, the first are bulky inorganic siloxane caged epoxy functional polysilsesquioxanes (POSS) and the second are mono-functional epoxy diluents. Different pre-reaction methods between the POSS and amine were used to maximise dispersion or improved covalent attachment within the epoxy amine network while the mono-functional epoxy diluents easily react into the network via simple blending. Despite the wide structural variations in modifier and result effects upon final structure, microstructure and properties, the glassy state molecular mobility as measured by sub-ambient β relaxations correlates strongly with changes in modulus and yield strain.

SiO2/Ladder-Like Polysilsesquioxanes Nanocomposite Coatings: Playing with the Hybrid Interface for Tuning Thermal Properties and Wettability

The present study explores the exploitation of ladder-like polysilsesquioxanes (PSQs) bearing reactive functional groups in conjunction with SiO2 nanoparticles (NPs) to produce UV-curable nanocomposite coatings with increased hydrophobicity and good thermal resistance. In detail, a medium degree regular ladder-like structured poly (methacryloxypropyl) silsesquioxane (LPMASQ) and silica NPs, either naked or functionalized with a methacrylsilane (SiO2@TMMS), were blended and then irradiated in the form of a film. Material characterization evidenced significant modifications of the structural organization of the LPMASQ backbone and, in particular, a rearrangement of the silsesquioxane chains at the interface upon introduction of the functionalized silica NPs. This leads to remarkable thermal resistance and enhanced hydrophobic features in the final nanocomposite. The results suggest that the adopted strategy, in comparison with mostly difficult and expensive surface modification and structuring protocols, may provide tailored functional properties without modifying the surface roughness or the functionalities of silsesquioxanes, but simply tuning their interactions at the hybrid interface with silica fillers.

Preparation of CO2-adsorbable amine-functionalized polysilsesquioxanes containing cross-linked structures without using surfactants and strong acid or base catalysts

In this study, we prepared a series of amine-functionalized polysilsesquioxanes (PSQs) containing cross-linked structures via the hydrolytic condensation of mixtures of amino-group-containing organotrialkoxysilanes and bridged organoalkoxysilanes in water under CO2 gas bubbling, followed by lyophilization and heat treatment at 120 °C for 4 h. Among the resulting materials, the amine-functionalized PSQ (PSQ-Am-CL-0.67) prepared from a mixture of 3-aminopropyltrimethoxysilane and bis[3-(trimethoxysilyl)propyl]amine (molar ratio 1:1) as the starting materials in CO2-gas-bubbling water with a solution concentration of 0.67 mol/L exhibited relatively high CO2 adsorption capacity under dry conditions (2.30 mmol(CO2)/g(material)). Moreover, even after repeating the adsorption and desorption of CO2 10 times, the CO2 adsorption capacity of PSQ-Am-CL-0.67 did not noticeably reduce, indicating that it could be used repeatedly as a CO2 capture material.

Fabrication and properties of polysilsesquioxane-based trilayer core–shell structure latex coatings with fluorinated polyacrylate and silica nanocomposite as the shell layer

Polysilsesquioxanes (PSQ)-based core–shell fluorinated polyacrylate/silica hybrid latex coatings were synthesized with PSQ latex particles as the seeds, and methyl methacrylate, butyl acrylate, 3-(trimethoxysilyl) propyl methacrylate (MPS)-modified SiO2 nanoparticles (NPs), 1H,1H,2H,2H-perfluorooctyl methacrylate (PFOMA) as the shell monomers by emulsifier-free miniemulsion polymerization. The results of Fourier transform IR spectroscopy, transmission electron microscopy, and dynamic light scattering suggested the obtained hybrid particles emerged with trilayer core–shell pattern. Contact angle analysis, x-ray photoelectron spectroscopy, and atom force microscopy results indicated that the hybrid film containing SiO2 NPs showed higher hydrophobicity, lower surface free energy and water absorption, in comparison with the control system (without SiO2 NPs). Compared with the control system, the hybrid latex film containing SiO2 NPs in the fluorinated polyacrylate shell layer showed the higher content of fluorine atoms and a rougher morphology on the film surface. Additionally, thermogravimetric analysis demonstrated the enhanced thermostability of PSQ-based nanosilica composite fluorinated polyacrylate latex film.

Assignment of the vibrational spectra of the parent polysilsesquioxane (POSS): Octahydridosilasequioxane, H8Si8O12

Polysilsesquioxanes (POSS) are molecules with the empirical formula (RSiO1.5)n where R is a hydrogen atom or hydroxyl or an organic moiety such as an alkyl, alkene, acrylate or epoxide. The silicon atoms occupy the corners of a cube and oxygen atoms are located on the edges, the versatility of silsesquioxanes arises from the vacant fourth position of silicon. The choice of substituent enables a wide variety of properties to be engineered in a straightforward manner. The parent POSS is octasilsesquioxane, H8Si8O12, with R=H and n=8. The present work employs periodic density functional theory calculations in conjunction with all the available vibrational (infrared, Raman and inelastic neutron scattering) spectra to generate a complete assignment of all the modes of the parent POSS octasilsesquioxane and some of its isotopomers for both the free, (Oh), molecule and the solid state material (C3i site symmetry) including the forbidden and very weak modes. The latter are of interest because in less symmetrical silsesquioxanes, these modes will be activated.

Studies of Wear and Tear and Hydrogen Bonding in Dendrimeric Fluorinated Polysilsequioxanes Coatings on an Aluminum Surface

This paper explores the physicochemical and physicomechanical process occurring during the formation of dendrimeric fluorinated polysilsesquioxanes (PSSQ) coated over an active aluminum surface. The changes in chemical composition of PSSQ have been monitored as a function of time and investigated using FTIR 2D correlation spectroscopy. The percolation of water molecules, hydrogen bonding, and interference of several physicochemical processes occurring in curing and cross-linking reaction in PSSQ have been monitored. The changes in surface morphology as a function of time have been recorded with atomic force microscopy and correlated with the nanomechanical analyses through nanoindentation. Specifically, nanoscratch and wear resistances were recorded at various time intervals to understand the transformation in the surface characteristics of the material. The ultimate aim of this work was to understand the correlation between reacting ingredients, surface features, wear, and friction by applying a self-lubricated coating made of fluorinated PSSQ over an aluminum surface. Attempts have been made to understand how the quantity and interaction of water molecules control the hydrolysis, condensation, and subsequent cross-linking reactions. The degree of cross-linking eventually controls the hardness and adhesion characteristics of the molecules, which in turn control the surface topology, resulting friction, wear resistance, and consequent surface life span of the material.

Preparation and thermal properties of soluble polysilsesquioxanes containing hydrophobic side-chain groups and their hybridization with organic polymers

In this study, a series of soluble polysilsesquioxanes (PSQs) containing hydrophobic side-chain groups (PSQ-Ph, PSQ-CyC6, PSQ-C6, and PSQ-C11) were prepared by the facile reaction of a ladder-like PSQ containing ammonium groups with the corresponding hydrophobic carboxylic acid chlorides (i.e., benzoyl, cyclohexanecarbonyl, heptanoyl, and dodecanoyl chlorides, respectively) in the presence of triethylamine in a mixed solvent of water and N,N-dimethylformamide. The resulting hydrophobic PSQs were soluble in chloroform. The weight-average molecular weights of the hydrophobic PSQs estimated by gel permeation chromatography with chloroform as the eluent and polystyrene standards ranged from 1.92 × 104 to 6.49 × 104. The pyrolysis temperatures of PSQ-Ph estimated by thermogravimetric analyses were relatively high (Td5 = 391 °C and Td10 = 425 °C) due to the presence of the thermally stable phenyl side-chain groups and SiOSi main-chain. Moreover, hybrid films of the hydrophobic PSQs and two organic polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), were prepared by drying the chloroform solutions of the mixtures of these polymers. The PMMA/PSQ-C6, PMMA/PSQ-C11, and PS/PSQ-Ph hybrids were highly transparent. For PS/PSQ-Ph hybrid films, the thermal stability increased with increasing amount of PSQ-Ph.

Free-standing, polysilsesquioxane-based inorganic/organic hybrid membranes for gas separations

Polysilsesquioxanes (PSSQs) are composite materials consisting of inorganic framework and organic functional groups. Their inherent dual characteristics offer various applications including microelectronics, optics and biosciences. For the first time, free standing ladder-like PSSQ films were successfully prepared for gas separations, allowing practical applications in the membrane area. In order to fabricate a free-standing PSSQ film, a novel ladder-like poly(phenyl-co-glycidoxypropyl) silsesquioxanes with phenyl:glycidoxypropyl copolymer ratio of 6:4 (LPG64) were synthesized by a base-catalyzed sol–gel reaction. Moreover, the LPG64 films were thermally crosslinked with octa(aminophenyl)-T8-silsesquioxane (OAPS) with different concentrations of OAPS. Single gas (i.e. He, H2, CO2, O2, N2, and CH4) transport measurements were performed for the LPG64 as well as LPG64/OAPS composite membranes. The LPG64 membrane exhibited a relatively high CO2 permeability of 47.88Barrer compared to other gases with CO2/N2 permselectivity of 30.5. The annealing effect on the transport results of the LPG64 membrane was negligible due to its rigid inorganic framework. Combination of our transport analysis and XRD characterization demonstrated that the addition of OAPS led to more dense chain packing, reducing permeability for all the gases tested in this work with increase in permselectivities. Especially, the LPG64/OAPS (80/20wt/wt) membrane improved He/N2 and H2/N2 permselectivities by 98% and 80%, respectively, compared to those for neat LPG64 membranes.

Ultra-thin films of polysilsesquioxanes possessing 3-methacryloxypropyl groups as gate insulator for organic field-effect transistors

Polysilsesquioxanes (PSQs) possessing 3-methacryloxypropyl groups as an organic moiety of the side chain were synthesized by sol–gel condensation copolymerization of the corresponding trialkoxysilanes. The ultra-thin PSQ film with a radical initiator and a cross-linking agent was prepared by a spin-coating method, and the film was cured integrally at low temperatures of less than 120°C through two different kinds of polymeric reactions, which were radical polymerization of vinyl groups and sol–gel condensation polymerization of terminated silanol and alkoxy groups. The obtained PSQ film showed the almost perfect solubilization resistance to acetone, which is a good solvent of PSQ before polymerization. It became clear by atomic force microscopy observation that the surface of the PSQ film was very smooth at a nano-meter level. Furthermore, pentacene-based organic field-effect transistor (OFET) with the PSQ film as a gate insulator showed typical p-channel enhancement mode operation characteristics and therefore the ultra-thin PSQ film has the potential to be applicable for solution-processed OFET systems.

Silseskwioksany jako nanonapelniacze. Cz. I. NANOKOMPOZYTY Z OSNOWA SILIKONOWA

The paper is the first of a series of review articles on the use of polysilsesquioxanes (POSS) for the modification of various polymers in order to prepare nanocomposites with specific physico-chemical properties. It has been the aim of the authors, in this and the following parts, to present the current state of knowledge and directions for further investigation in this area of chemistry. This opening paper reports on the synthesis, properties and use of nanocomposites based on POSS and silicone matrix.

Graft polymerization of acrylamide monomers from polysilsesquioxane containing xanthate groups

Polysilsesquioxanes (PSQs) containing 4-chloromethylphenyl groups were prepared and used for introducing ethylxanthate groups. The obtained PSQs that contained benzyl xanthate structures (XAPSQs) were employed as macroinitiators for grafting acrylamide monomers. The use of XAPSQs for the radical polymerization with acryloylmorpholine (ACMO), N,N-dimethylacrylamide (DMAA) or N-isopropylacrylamide enabled the preparation of the respective grafted PSQ, in which no cross-linked product was formed. The results of the graft polymerizations from XAPSQs supported the interpretation that the reversible addition-fragmentation chain transfer polymerization progressed effectively using the technique known as macromolecular design via the interchange of xanthate. The introduction of polymerized ACMO and DMAA units provided an amphiphilic property to the grafted PSQ. In addition, the PSQs containing poly(ACMO) components showed reversible hydrophobic aggregation behavior at approximately 80°C in aqueous solution. The polysilsesquioxane (PSQ) containing ethylxanthate groups was used for the graft polymerization of several acrylamide monomers by MADIX process. The controlled graft polymerization gave the PSQs containing the polymeric components as the graft chains. The introduction of the polymers provided an amphiphilic property to the polysilsesquioxaneane. In addition, the grafted PSQ containing poly(acryloyl morpholine) showed a thermoresponsive property in an aqueous solution. The reversible hydrophobic aggregation of the polysilsesquioanes was observed at ca. 80°C.

Preparation of functional spherical polysilsesquioxane/gold nanoparticle composites and their applications in DNA assay

Functional spherical solid and hollow particles of polysilsesquioxanes (PSQs) containing amine, thiol, and vinyl groups were prepared by polymerizing organotrialkoxysilanes (OTASs) containing corresponding chemical groups. Fluorescent PSQ particles were prepared by physically entrapping Rhodamine 6G, Coumarin 7, and Fluoresceine sodium salts. The intensity of fluorescent light increased initially with increasing amount of entrapped fluorophores and then leveled off or decreased slightly after reaching a maximum value. PSQ particles containing gold nanoparticles (GNPs), both inside and on the surface, were prepared by the in situ reduction of gold ions by the PSQ particles. When the reduction reaction was carried out for extended periods of time, the GNP that had formed inside the poly(3-mercaptopropyl)silsesquioxane (PMPSQ) and polyvinylsilsesequioxane (PVSQ) particles underwent interesting morphological changes. PSQ particles containing amine and thiol groups fixed the GNPs on the surface, which could be utilized further in binding amine-modified oligo-DNA strands. The aggregation of PSQ/GNP particles combined with complementary oligo-DNA strands was examined to demonstrate that these particles could be applied to DNA assays and isolation. The particles were characterized by scanning electron microscopy, transmission electron microscopy, solid state nuclear magnetic resonance spectroscopy, ultraviolet/visible spectroscopy, and fluorescence microscopy.

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.

A New Amphiphilic and Thermoresponsive Polysilsesquioxane Having Alkoxyethylamide Group

Abstract The polysilsesquioxanes (PSQ) having alkoxyethylamide groups were prepared from the silane coupling reagents, prepared by addition reaction of alkoxyethylamines to (3-isocyanatopropyl)triethoxysilane, by condensation under acidic conditions. In the obtained PSQs, those having bis(methoxyethyl)amide or bis(ethoxyethyl)amide group showed reversible thermoresponsive phase separation in an aqueous solution. The PSQs formed by the co-condensation of such silane coupling reagents, the feed mole ratio of which were changed, also showed the thermoresponsive aggregation at the temperatures reflected with the ratios of alkoxyethyl groups.

One step preparation of spherical silicon resins from immiscible reaction mixtures

Spheres of silicon resins with different compositions were prepared in one-step reaction from mixtures of water and water-insoluble precursors of polysiloxanes (PSO) and polysilsesquioxanes (PSQ) using different amines as catalysts. The presence of PSO and PSQ in the spheres was confirmed by their mechanical properties and FTIR spectroscopy. Spheres of pure PSO were obtained from only dimethoxymethylvinylsiloxane (DMMVS) and 3-mercaptopropylmethyldimethoxysilan (MPMDMS) when the reaction was induced with appropriate catalysts. DMMVS and MPMDMS always gave the most promising results regarding the formation of discrete solid spheres with the minimum tendency to form monolithic solids or fluid-like, premature products. The spheres were characterized by optical microscopy, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The mixtures containing larger amounts of PSO precursors commonly gave lower yields and softer spheres.

Preparation of Stimuli-responsive Polysilsesquioxane Grafted Block Copolymer of Acrylamide Monomers

The polysilsesquioxanes (PSQs) having the graft block copolymer of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAA), which showed the different sequence and number of the monomer units, were obtained by RAFT process. In addition, the PSQ derivatives containing other organic functional groups besides the grafted polymers were prepared by the use of chloromethylphenyl groups on the starting PSQ. Through the formation of ester bond and quarternary ammonium salt, phenol, triethylamine, and N,N-dimethylaniline groups were introduced into the grafted PSQ, respectively. In the behaviors of reversible thermoresponsive aggregation caused by poly(NIPAM) component, the almost same Lowest Critical Solution Temperature such as 34 °C was observed for the grafted PSQs, although the poly(DMAA), phenol groups, and/or the quarternary ammonium salts were existed on the same PSQ backbone. As an additional function, the presence of phenol groups led to pH responsive solubility in water. The solubility of the PSQs in water was also affected by hydrophilic property of the amines to form the quarternary ammonium salts. In addition, a kind of chromism, which related with pH value, was observed in the case containing N,N-dimethylaniline moieties.

Substituent effects on microstructure and polymerization of polyalkylsilsesquioxanes.

Hie-Joon Kim, Jin-Kyu Lee,* Jin-Bum Kim, Eun Su Park,Sung-Jun Park, Dae Young Yoo, and Do Y. Yoon*School of Chemistry, Seoul National UniVersitySeoul 151-747, KoreaReceiVed August 10, 2001Recently, there has been a great deal of interest in polysilses-quioxanes (PSSQs) for advanced technology as low-dielectricinsulators in microelectronic devices