Methacrylisobutyl Polyhedral Oligomeric Silsesquioxane Research Articles

Study of Water Sorption in Methacryl-Based Polyhedral Oligomeric Silsesquioxane (POSS) Dental Composites Using Molecular Dynamics Simulations.

Methacrylate-based polyhedral oligomeric silsesquioxane (POSS) is one of the new composites used as a dental resin. Both monofunctional methacryl isobutyl POSS (MIPOSS) and multifunctional methacryl POSS (MAPOSS) are reported to be possible resins that possess the desired properties for using them as dental resins. Our group's previous comparative study on these two resins showed that the MAPOSS composite has superior mechanical properties compared with the MIPOSS composite. In this article, molecular dynamic simulations (MD simulations) are performed to study the water sorption in these two composites. Water sorption in dental composites can have several effects on the material properties, performance, and longevity of dental restorations. Water sorption in MAPOSS and MIPOSS composites is analyzed by studying the hydrogen bonding, cluster analysis, density projection calculations, and diffusion coefficient calculation of water molecules within the resin matrix. MD simulations results are further used to understand the interaction of water molecules with the resin matrix comprehensively, which governs the composite's mechanical properties. The water sorption study showed that the MAPOSS composite has less water sorption capacity than the MIPOSS composite. The practical significance of this study is to find properties that affect dental restoration and longevity, which can help in the design of better materials for dental applications.

Molecular Simulations of Low-Shrinkage Dental Resins Containing Methacryl-Based Polyhedral Oligomeric Silsesquioxane (POSS)

Nanocomposites of methacrylate-based polyhedral oligomeric silsesquioxane (POSS) are used as resins in dentistry to fill dental cavities. In this article, molecular dynamics simulations (MDS) are used to study and understand the interactions of monofunctional and multifunctional methacrylate groups on hybrid resins containing POSS additives for dental applications. These interactions are further related to the structural properties of the nanocomposites, which in turn affect their macro-properties that are important, especially when used for specific uses such as dental resins. For monofunctional methacrylate, nanocomposite of methacryl isobutyl POSS (MIPOSS) and for multifunctional methacrylate, methacryl POSS (MAPOSS) are used in this study. Molecular dynamic simulations (MDS) are performed on both MIPOSS and MAPOSS systems by varying the amount of POSS. On a weight percent basis, 1%, 3%, 5%, and 10% POSS are added to the resin. Density calculations, stress-strain, and powder diffraction simulations are used to evaluate the macro-properties of these nanocomposites and compare them with the experimental findings reported in the literature. The observations from the simulation results when compared to the experimental results show that MDS can be efficiently used to design, analyze, and simulate new nanocomposites of POSS.

Temperature dependence of methanol and ethanol vapor sorption in polyhedral oligomeric silsesquioxane (POSS) containing methacrylate membranes

AbstractThis study aimed to determine the solubility and temperature dependence of methanol and ethanol vapor caused by the difference in the substituents of polyhedral oligomeric silsesquioxane (POSS)‐containing polymethacrylate membranes and the spacer length between the backbone and POSS backbone. Vapor sorption of methanol and ethanol was measured at 25°C, 35°C, and 45°C for three kinds of POSS‐containing polymer membranes, namely, poly(methacryl isobutyl POSS), poly(methacrylate isobutyl POSS), and poly(methacryl phenyl POSS). The primary structures of the three POSS‐containing polymer chains were columnar. The solubility of alcohol vapor on the POSS‐containing polymer membranes followed the mechanism of solid adsorption and not the general dissolution diffusion. The sorption amount at all three temperatures was related to the surface area of the cylindrical primary structure and the solid adsorption property of the alcohol molecule of the POSS substituent. The sorption amount increased because of the large surface area and adsorption property of alcohol molecules. Although a typical glassy polymer shows exothermic mixing and a rubbery polymer displays endothermic mixing, the sample with the POSS substituent of isobutyl group exhibited an unusual behavior of endothermic mixing despite being a glassy polymer.

Holographic polymer nanocomposites with ordered structures and improved electro-optical performance by doping POSS

Holographic polymer nanocomposites containing the liquid crystal (LC) have garnered a great deal of attention primarily because of their unique electric-switchable optical properties. Herein, three types of polyhedral oligomeric silsesquioxane (POSS) are doped into the holographic polymer nanocomposites to tune their ordered structure and electro-optical performance. These POSS dopants are methacryl POSS with eight reactive double bonds, methacrylisobutyl POSS with one reactive double bond, and aminopropylisobutyl POSS with nonreactive groups. Interestingly, methacryl POSS is primarily chemically bonded to the polymer network within the constructive regions, which deteriorates the diffraction efficiency and electro-optical performance due to the depressed ordered structures. In contrast, methacrylisobutyl POSS displays a negligible effect on the diffraction efficiency and electro-optical performance while significantly improving the thermostability of holographic polymer nanocomposites, although it is also chemically linked to the polymer network within the constructive regions. Distinctively, aminopropylisobutyl POSS mainly locates in the destructive regions and clearly improves the electro-optical performance and thermostability of holographic polymer nanocomposites.

Gel polymer electrolyte based on polymethyl methacrylate matrix composited with methacrylisobutyl-polyhedral oligomeric silsesquioxane by phase inversion method

A kind of organic-inorganic nanocomposite of methacrylisobutyl-polyhedral oligomeric silsesquioxane (MA-POSS) is synthesized and the nanocomposite as the modified filler is introduced into polymethyl methacrylate (PMMA) matrix to prepare gel polymer electrolyte (GPE) membrane used in lithium ion battery (LIB) through phase inversion method combined with liquid electrolyte adsorption. The results reflect that compared to the solvent evaporation technique, the electrochemical performances of the GPE corresponding to the membrane prepared by phase inversion method are more outstanding. Besides, the membrane also shows good mechanical strength. Compared to the GPE based on pure PMMA matrix, the comprehensive performances of the modified GPE are also enhanced a lot and the GPE with the mass of 10% MA-POSS exhibits the most favorable properties. The excellent performances are shown as follows: the ionic conductivity reaches to 2.77 × 10−3 S cm−1 at room temperature; the lithium ion transfer number is up to 0.40; the GPE is electrochemical stable below 5.5 V (vs. Li/Li+); the compatibility between GPE and lithium anode is satisfying and the ionic conductivity obeys the Arrhenius behavior.

General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX3 Peroskite Nanocrystals

The potential optoelectronic applications of perovskite nanocrystals (NCs) are primarily limited by major material instability arising from the ionic nature of the NC lattice. Herein, we introduce a facile and effective strategy to prepare extremely stable CsPbX3 NC–polymer composites. NC surfaces are passivated with reactive methacrylic acid (MA) ligands, resulting in the formation of homogeneous nanocubes (abbreviated as MA-NCs) with a size of 14–17 nm and a photoluminescence quantum yield above 80%. The free double bonds on the surface then serve as chemically addressable synthetic handles, enabling UV-induced radical polymerization. Critically, a bromide-rich environment is developed to prevent NC sintering. The composites obtained from copolymerizing MA-NCs with hydrophobic methyl methacrylate and methacrylisobutyl polyhedral oligomeric silsesquioxane monomers exhibit enhanced properties compared to previously reported encapsulated NCs, including higher quantum yields, remarkable chemical stability t...

POSS-pendanted in epoxy chain inorganic-organic hybrid for highly thermo-mechanical, permeable and hydrothermal-resistant coatings

Organic-inorganic hybrid is prepared by grafting nano-scaled methacrylisobutyl polyhedral oligomeric silsesquioxane (MA-POSS) onto glycidyl methacrylate (GMA) via the combining of free radical polymerization, epoxy opening reaction and atom transfer radical polymerization (ATRP) techniques. The obtained (MA-POSS)-pendanted epoxy hybrid, PGMA-g-P(MA-POSS), are discussed fot their highly thermo-mechnical property, hydrothermal resistance and permeability based on the self-assembled micelles. In THF solution, PGMA-g-P(MA-POSS) could self-assembly into 110–800 nm sphereric core-shell micelles, while, the pre-curing PGMA-g-P(MA-POSS) distributes 60–600 nm core-shell micelles because the developed three-dimensional network structure makes the PGMA chains twining and cross-linking tightly leading to the shrinkage of particles. These self-assembled micelles have provided the casted films with 0.19–14.4 nm surface roughness, significant water resistance (SCA = 113-123°), high thermal stability (Td = 300–600 °C) and strong adhesive strength (216–333 N). Compared with the poor adhesive strength for commercial epoxy resin (E-51) decreased from 393 N to 28 N after 15 hydrothermal cycles, the obtained PGMA-g-P(MA-POSS) displays super thermal endurance properties and humidity resistance by keeping a relative constant adhesive strength (from 340 N to 337 N). Furthermore, PGMA-g-P(MA-POSS) also gives much better permeability to the protective treated sandstone than E-51. Therefore, PGMA-g-P(MA-POSS) is prospected to serve as coatings with great potential 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 (Tg=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.

Composite optical fiber polarizer with ternary copolymer overlay for large range modulation of phase difference

In this work, a ternary copolymer composed of (E)-2-(4-((4-isocyanophenyl) diazenyl) phenoxy) ethyl methacrylate (2-CN), methacrylisobutyl polyhedral oligomeric silsesquioxane (MAPOSS) and 2,2,2-trifluoroethyl methacrylate (TFEMA) is synthesized and used as the overlay for composite optical fiber, in which cage-like POSS component and fluorine-containing component are used to reduce refractive index, and azobenzene component is used to finely manipulate the refractive indices in two orthogonal directions through photo-induced orientation under irradiation of polarized light. Before irradiation, the refractive index of terpolymer (1.4503) is slightly higher than that of the core material (1.4489) of commercial silica single-mode fiber, which is obtained by optimizing the amount of each monomer. After the irradiation of 435 nm polarized light, refractive indices of the overlay in two orthogonal directions decrease, and two values have been finely manipulated so that one is higher and another is lower than the refractive index of the fiber core by optimizing irradiation time. In this way, a radial loss type fiber polarization modulator is obtained. By changing the polarization direction of the irradiation at 435 nm, the polarization of propagating light at 1550 nm in the fiber can also be modulated continuously. The maximum change of phase difference is about 300°, making the device useful as a quarter-wave plate or a half-wave plate.

POSS-based glycidyl methacrylate copolymer for transparent and permeable coatings

ABSTRACTPolyhedral oligomeric silsesquioxane (POSS)-based glycidyl methacrylate (GMA) hybrid copolymers of P(GMA-MAPOSS) are prepared by methacrylisobutyl polyhedral oligomeric silsesquioxane (MAPOSS) and GMA via free radical polymerization used as coatings. Their morphologies and particle size distributions in CHCl3 solution are characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The effect of MAPOSS content on surface wettability, transparency and permeability of casted films, the adhesive strength, and thermostability of hybrid copolymers are further characterized by scanning electron microscopy (SEM), static contact angle (SCA), UV-Vis, mercury porosimeter, mechanical testing, differential scanning calorimetry (DSC), and thermogravimetry (TGA). Compared with the homogeneous surface of PGMA film, the surface of P(GMA-MAPOSS) film exhibits heterogeneous morphology due to the bulky volume of MAPOSS tending to agglomerate onto the film surface. This micro-rough structure helps to enhance the surface hydrophobicity (100–112° water SCA). While the surface of cured P(GMA-MAPOSS) film obtains a very homogeneous micro-rough morphology without any agglomeration due to the restricted movements of MAPOSS by 250 nm core-shell particles in CHCl3 solution. Therefore, the cured P(GMA-MAPOSS) film provides with superior luminousness (>98%), strong adhesive strength (748.2 Pa), and high thermostability (Tg = 115°C). Particularly, the chemically involved MAPOSS into PGMA can effectually improve the permeability of traditional epoxy resin. It is believed that the POSS-based GMA hybrid copolymers P(GMA-MAPOSS) will have great potential applications as transparent and permeable coatings.

UV-curable POSS-fluorinated methacrylate diblock copolymers for icephobic coatings

Abstract Low surface energy materials have been extensively investigated for building icephobic surfaces in recent years. Polydimethylsiloxane (PDMS) and fluoropolymers have been introduced to this field, while control of their structures is of importance to produce deicing surfaces. In this work, fluorinated methacrylate block copolymers containing polyhedral oligomeric silsesquioxane (POSS) moieties were synthesized by reversible addition-fragmentation chain transfer polymerization and transformed into thiolated-copolymers by aminolysis to adjust the self-assembly and modify surface morphology. The icephobic coatings were developed via UV-curable thiol-ene reaction with tunable amounts of thiol-modified POSS-fluorinated methacrylate diblock copolymers with vinyl-functionalized PDMS and thiol-functionalized PDMS. Characterizations of atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle showed the evidence of the POSS-fluorinated diblock copolymers on the outmost surface of the coatings. Owing to the crystallization of perfluoroalkyl side groups, the coatings containing thiol-modified poly(methacrylisobutyl POSS)- b -poly(2-perfluorooctylethyl methacrylate) ( S17F ) exhibited excellent icephobicity, and water droplets could rebound completely on all S17F -containing surfaces at both normal and tilt modes before freeze even at −15 °C. The ice shear strengths of the prepared UV-cured coatings were about one-eighth of that on bare aluminum surface, while the coating containing 5% S17F achieved the lowest ice shear strength of 105 ± 12 kPa. It was found that the icephobicity of these coatings were attributed primarily to the synergistic effect of the POSS-fluorinated methacrylate diblock copolymer and the PDMS component.

Organic/inorganic hybrids by linear PDMS and caged MA-POSS for coating

Novel organic/inorganic hybrids of PDMS-b-PMMAm-b-P(MA-POSS)n are synthesized by linear poly(dimethylsiloxane) (PDMS) macroinitiator initiating methyl methacrylate (MMA) and caged methacrylisobutyl-polyhedral oligomeric silsesquioxane (MA-POSS) via a two-step ATRP technique. The chemical structures of obtained hybrids are proved to be PDMS-b-PMMA408-b-P(MA-POSS)4.5, 8.2, 13.6 with molecular weight of 50,090–58,650 g mol−1 (PDI = 1.215–1.391). With the increase of P(MA-POSS)n content from 0%wt to 23.93%wt, the glass transition temperature of PDMS-b-PMMA408-b-P(MA-POSS)n is enhanced from 95 °C to 137 °C, and the corresponding storage modulus of mechanical property is increased from 579 ± 3 MPa to 902 ± 5 MPa. The surface of PDMS-b-PMMA408-b-P(MA-POSS)8.2 film casting from CHCl3 solution obtains higher water contact angle (120°) and higher water adsorption (Δf = −2300 Hz), but lower viscoelasticity (ΔD = 26 × 10−6) than the film casting from tetrahydrofuran (THF) solution (114°, Δf = −1540 Hz, ΔD = 52 × 10−6). This is because that 200–500 nm core/shell micelles of PMMA core and PDMS/P(MA-POSS) shell formed in CHCl3 solution are favor of the migration of PDMS and P(MA-POSS) onto film surface to improve the surface roughness (2.480 nm) and to get silicon-rich surface (14.62%) than 220 nm P(MA-POSS) core/PMMA shell/PDMS-corona micelles formed in THF solution (0.906 nm, 7.86%). Therefore, the accumulated P(MA-POSS) cages on the film surface are able to store absorbed water but do not increase the viscoelasticity of film. The results indicate that PDMS-b-PMMA408-b-P(MA-POSS)n are promising to be the solvent-dependent coating materials.

Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m2 generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer.

Enhanced bone cell functions on poly(ε-caprolactone) triacrylate networks grafted with polyhedral oligomeric silsesquioxane nanocages

Poly(ε-caprolactone) triacrylate (PCLTA) developed in our laboratory is a photo-crosslinkable, injectable, and biodegradable polymeric biomaterial for diverse tissue engineering applications. To engineer its physical properties for bone regeneration, we incorporated PCLTA networks with a photo-reactive methacryl isobutyl polyhedral oligomeric silsesquioxane (POSS), which is a silicon-based monomer with a nano-sized cage. Homogeneous nanohybrid networks were prepared by photo-crosslinking POSS with two PCLTAs having molecular weights of ∼7000 and ∼20,000 g/mol at the POSS weight compositions (ϕPOSS) of 0–20%. The lower-molecular-weight PCLTA resulted in amorphous networks while the higher one resulted in semi-crystalline networks. POSS nanocages tethered in the PCLTA networks greatly enhanced the mechanical and rheological properties, but did not significantly alter the surface wettability and the capability of adsorbing serum proteins from cell culture media. Better mouse pre-osteoblastic MC3T3-E1 cell attachment, spreading, and proliferation were found on the stiffer PCLTA20k networks than on the PCLTA7k ones, and on the networks with ϕPOSS of 10–20% than the networks containing no POSS. Mineralization of MC3T3-E1 cell cultured for two weeks showed a significantly higher alkaline phosphatase activity and more mineralized nodules on the PCLTA20k networks with ϕPOSS of 10–20%, in correlation with their enhanced mechanical properties. The present results indicated that this series of nanohybrid PCLTA/POSS networks with improved mechanical properties and osteoconductivity has great potential as scaffolding materials for bone repair and regeneration.

Melt crystallization kinetics of polyhedral oligomeric silsesquioxane under non-isothermal conditions

Melt crystallization of polyhedral oligomeric silsesquioxane (POSS) was studied by differential scanning calorimeter (DSC), X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). The SEM analysis showed that POSS samples are aggregated in micrometric size. Additionally, FTIR spectra confirmed intermolecular interactions among carbonyl groups. All samples showed that the Ozawa exponent ranged from 1 to 2.6 and the Ozawa crystallization rate constant was found to decrease with increasing temperature and reduction of average X(T). This suggests that these POSS crystallized slower as the temperature increased. The ∆EX(T) values for isobutyl POSS increased monotonically until X(T)=0.4, and for the methacryl isobutyl POSS the ∆EX(T) values decreased. After this point ∆EX(T) showed similar values for both POSS samples. The presence of the methacryl radical in POSS cages interfered in the crystallization process due to the hysteric hindrance among POSS–POSS cages.

POSS end-capped diblock copolymers: Synthesis, micelle self-assembly and properties

Polyhedral oligomeric silsesquioxane (POSS) end-capped diblock copolymers are synthesized using aminopropylisobutyl POSS (ap-POSS-Br) to initiate atom transfer radical polymerization (ATRP) of methylmethacrylate (MMA) and methacrylisobutyl POSS (MA-POSS). Their chemical structures are confirmed as ap-POSS–PMMA152.0-b-P(MA-POSS)4.3, 4.8, 10.0 with 19,840–24,770gmol−1 by 1H NMR and SEC. In tetrahydrofuran (THF) solution, the obtained diblock copolymers could self-assemble into 150–300nm core–shell micelles as ap-POSS/MA-POSS core and PMMA shell, or 164nm core–shell–crown micelles as P(MA-POSS) core, PMMA shell and ap-POSS crown when P(MA-POSS) content is increased. These micelles can produce typical films with lower surface roughness (0.816–1.690nm), lower water absorption and lower viscoelasticity, but higher hydrophobicity (112–126° water contact angle) and higher thermostability in glass transition temperature Tg>110°C and decompose temperature Td>380°C than pure POSS–PMMA film. In this study, the results strongly support the potential application of the POSS end-capped diblock copolymers as the coatings.

Photo-polymerization of photocurable resins containing polyhedral oligomeric silsesquioxane methacrylate

Photocurable resins, bisphenol A propoxylate glycerolate diacrylate (BPA-PGDA, containing two hydroxyl) and bisphenol A propoxylate diacrylate (BPA-PDA), with fixed photoinitiator (Irgacure 907) concentration and various contents of methacrylisobutyl polyhedral oligomeric silsesquioxane (MI-POSS) were prepared and characterized by FTIR spectroscopy, scanning electron microscope and differential photocalorimetry. The MI-POSS molecules form crystals or aggregated particles in the cured resin matrix. The BPA-PGDA series photocurable resins show higher viscosity and lower photo-polymerization reactivity than the BPA-PDA series resins. The photo-polymerization rate and conversion of BPA-PGDA series are improved with increasing MI-POSS content. On the contrary, the photo-polymerization behavior of BPA-PDA series photocurable resins remains nearly unchanged by the addition of MI-POSS. Hydrogen-bonding interaction between the hydroxyl of BPA-PGDA and the siloxane of MI-POSS tends to attract and concentrate these acrylate double bonds around MI-POSS particles and thus enhances the photo-polymerization rate and conversion.

Tailoring Micelle Formation and Gelation in (PEG−P(MA-POSS)) Amphiphilic Hybrid Block Copolymers

We demonstrate that hydrophobic POSS (polyhedral oligomeric-silsesquioxane) nanoparticles, added to block copolymer solutions of poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomericsilsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks respectively, could be employed to tailor their micelle formation, gelation, and rheological performance. For example, the hydrodynamic size of the micelles, formed by PEG5k-b-P(MA-POSS)3.6, increased from 13.6 ± 1.0 to 56.9 ± 3.7, an increase of more than four times, with 0.1 wt % (with respect to block copolymer) POSS nanoparticles in solution. However, the micelles retain their spherical morphology with core−shell structure as evidenced by calculating the values of dimensionless ratios, Rg/Rh for micelles as a function of added POSS nanoparticles content. For P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymers, which is associative in nature, addition of POSS nanoparticles resulted in formation of more robust and stronger hydrogels with a significantly higher storage modulus, G′, yield strengths, σy, and lower critical gelation concentration, cg, as compared with those for the pristine triblock copolymer. The presence of eight vinyl groups, attached to the POSS nanoparticles under investigations, is also exploited for further enhancement of rheological properties of the hydrogels with UV treatment. Finally, gel formation is induced in aqueous solutions of PEG5k-b-P(MA-POSS)3.6 diblock copolymer by introducing P(MA-POSS)-b-PEG10k-b-P(MA-POSS) triblock copolymer chains, and the rheological performance of the produced hydrogels, with certain compositions, is even superior to that of pure triblock copolymer gel.

Micelle Formation and Gelation of (PEG−P(MA-POSS)) Amphiphilic Block Copolymers via Associative Hydrophobic Effects

A series of well-defined amphiphilic di- and triblock copolymers have been synthesized, using atom transfer radical polymerization, with poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomeric silsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks, respectively. The detailed self-assembly behavior of the amphiphilic macromolecules in aqueous media was studied using both static and dynamic light scattering (SLS and DLS) techniques. The evolution of block copolymer micelle formation in THF/water mixture (20/80 v/v) was monitored as the THF evaporated from the solvent mixture. Initially the block copolymer chains existed as unimers in solution, followed by the formation of smaller aggregates (R(h) < 2 nm) after 30 min, eventually growing in size to reach an equilibrium size when all the THF evaporated within 24 h. The micelles formed by the block copolymers were found to be kinetically unstable (not frozen); i.e., they tended to revert to individual copolymer chains on dilution. The hydrodynamic radii, R(h), of the micelles varied with the degree of polymerization (DP) of the hydrophobic P(MA-POSS); for example, for PEG(5K)-b-P(MA-POSS), an increase from R(h) approximately 13.3 +/- 1.1 nm to R(h) approximately 17.5 +/- 1.4 nm was observed with a nominal change in the DP of P(MA-POSS) from 4 to 6. The micelles formed by the triblock copolymers (P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)) were comparable in size to the diblock copolymer micelles; e.g., R(h) approximately 14.0 +/- 1.3 nm was found for P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4). The micellar structures created by the triblocks in aqueous media were "flowerlike", where the PEG middle block adopted a loop conformation in the micelle corona. In addition to micelles, larger aggregates formed by P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS) were also detected in solution. The larger aggregates may suggest a contribution from some PEG blocks adopting an extended conformation with one end dangling in solution, causing gelation at higher copolymer concentrations via intermicellar interactions. The P(MA-POSS)(4)-b-PEG(10K)-b- P(MA-POSS)(4) formed a gel in water at approximately 8.8 wt % copolymer concentration. No gel formation by diblock copolymers was observed; however, the addition of a small amount of triblock copolymer to an aqueous solution of diblock copolymer results in gel formation. Finally, rheological behavior of the obtained gels was also investigated.

Peroxide-activated paint removers in aerospace applications

Low surface energy materials have been extensively investigated for building icephobic surfaces in recent years. Polydimethylsiloxane (PDMS) and fluoropolymers have been introduced to this field, while control of their structures is of importance to produce deicing surfaces. In this work, fluorinated methacrylate block copolymers containing polyhedral oligomeric silsesquioxane (POSS) moieties were synthesized by reversible addition-fragmentation chain transfer polymerization and transformed into thiolated-copolymers by aminolysis to adjust the self-assembly and modify surface morphology. The icephobic coatings were developed via UV-curable thiol-ene reaction with tunable amounts of thiol-modified POSS-fluorinated methacrylate diblock copolymers with vinyl-functionalized PDMS and thiol-functionalized PDMS. Characterizations of atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle showed the evidence of the POSS-fluorinated diblock copolymers on the outmost surface of the coatings. Owing to the crystallization of perfluoroalkyl side groups, the coatings containing thiol-modified poly(methacrylisobutyl POSS)-b-poly(2-perfluorooctylethyl methacrylate) (S17F) exhibited excellent icephobicity, and water droplets could rebound completely on all S17F-containing surfaces at both normal and tilt modes before freeze even at −15 °C. The ice shear strengths of the prepared UV-cured coatings were about one-eighth of that on bare aluminum surface, while the coating containing 5% S17F achieved the lowest ice shear strength of 105 ± 12 kPa. It was found that the icephobicity of these coatings were attributed primarily to the synergistic effect of the POSS-fluorinated methacrylate diblock copolymer and the PDMS component.