Kevin A. Cavicchi

Fluorinated polyhedral oligomeric silsesquioxane-based shape amphiphiles: molecular design, topological variation, and facile synthesis

This paper reports the design and synthesis of fluoroalkyl-functionalized polyhedral oligomeric silsesquioxane (FPOSS)-based shape amphiphiles with two distinct topologies: (i) mono-tethered FPOSS-poly(e-caprolactone) (PCL) and (ii) FPOSS tethered with two polymer chains possessing different compositions, namely, polystyrene (PS) and PCL, denoted as PS–(FPOSS)–PCL. The synthetic strategy features an efficient “growing-from” and “click-functionalization” approach. From a monohydroxyl-functionalized heptavinyl POSS, a PCL chain was grown via ring opening polymerization (ROP) of e-caprolactone; subsequent thiol–ene “click” chemistry with 1H,1H,2H,2H-perfluoro-1-decanethiol allowed the facile introduction of seven perfluorinated alkyl chains onto the POSS head. Similarly, PS–(FPOSS)–PCL was synthesized from a PS precursor bearing both hydroxyl group and heptavinyl POSS at the ω-end, which was prepared by living anionic polymerization and hydrosilylation. The compounds were fully characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography. The introduction of perfluorinated molecular cluster into polymers is expected to make them surface-active while the interplay between crystallization and fluorophobic/fluorophilic bulk phase separation in these shape amphiphiles shall lead to intriguing self-assembly behavior and novel hierarchical structures. This study has demonstrated FPOSS as a versatile building block in the construction of shape amphiphiles and established a general and efficient method to introduce such fluorous molecular clusters into polymers.

Large-Scale Roll-to-Roll Fabrication of Ordered Mesoporous Materials using Resol-Assisted Cooperative Assembly

Roll-to-roll (R2R) processing enables the rapid fabrication of large-area sheets of cooperatively assembled materials for production of mesoporous materials. Evaporation induced self-assembly of a nonionic surfactant (Pluronic F127) with sol-gel precursors and phenolic resin oligomers (resol) produce highly ordered mesostructures for a variety of chemistries including silica, titania, and tin oxide. The cast thick (>200 μm) film can be easily delaminated from the carrier substrate (polyethylene terephthalate, PET) after cross-linking the resol to produce meter-long self-assembled sheets. The surface areas of these mesoporous materials range from 240 m(2)/g to >1650 m(2)/g with these areas for each material comparing favorably with prior reports in the literature. These R2R methods provide a facile route to the scalable production of kilograms of a wide variety of ordered mesoporous materials that have shown potential for a wide variety of applications with small-batch syntheses.

The poor solubility of ureidopyrimidone can be used to form gels of low molecular weight N-alkyl urea oligomers in organic solvents

A synthesis strategy for low molecular weight organogelators using the ureidopyrimidinone (UPy) group is reported. The prepared gelators showed robust thermal reversible gelation abilities in various solvents, including dimethyl sulfoxide. The morphology of the dried gels was determined using scanning electron microscopy, revealing a macroscopic porous structure of the gels. Rheology was performed to determine storage (G′) and loss modulus (G″) confirming network gel structures.

Morphology Control in Mesoporous Carbon Films Using Solvent Vapor Annealing

Ordered mesoporous (2-50 nm) carbon films were fabricated using cooperative self-assembly of a phenolic resin oligomer with a novel block copolymer template (poly(styrene-block-N,N-dimethyl-n-octadecylamine p-styrenesulfonate), (PS-b-PSS-DMODA)) synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the high Tg of the PS segment and the strong interactions between the phenolic resin and the PSS-DMODA, the segmental rearrangement is kinetically hindered relative to the cross-linking rate of the phenolic resin, which inhibits long-range ordering and yields a poorly ordered mesoporous carbon with a broad pore size distribution. However, relatively short exposure (2 h) to controlled vapor pressures of methyl ethyl ketone (MEK) yields significant improvements in the long-range ordering and narrows the pore size distribution. The average pore size increases as the solvent vapor pressure during annealing increases, but an upper limit of p/p0 = 0.85 exists above which the films dewet rapidly during solvent vapor annealing. This approach can be extended using mesityl oxide, which has similar solvent qualities to MEK, but is not easily removed by ambient air drying after solvent annealing. This residual solvent can impact the morphology that develops during cross-linking of the films. These results illustrate the ability to fine-tune the mesostructure of ordered mesoporous carbon films through simple changes in the processing without any compositional changes in the initial cast film.

Phase structural formation and oscillation in polystyrene-block-polydimethylsiloxane thin films

The solvent-induced spherical structure in a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymer was obtained and stabilized by preparing both the bulk and thin films from propylene glycol methyl ether acetate (PGMEA) solutions. The diblock copolymer possessed a total molecular weight of 42 kDa with a PS volume fraction of 72.2%, and it formed a cylindrical phase structure in the equilibrium bulk state. During thermal annealing, only changes in the sphere size and packing rearrangement were found. In contrast, a unique structure evolution route was observed during solvent treatments. Under a controlled vapour of a PS selective solvent, an oscillation of the structural transition between spheres and cylinders was observed in the thin films. The kinetics of this oscillation of structural transition was found to be closely related to the solvent vapour concentration and film thickness. This experiment revealed a unique ordering pathway towards the equilibrium structure in the thin film for this strongly segregated PS-b-PDMS diblock copolymer.

Synthesis and Polymerization of Substituted Ammonium Sulfonate Monomers for Advanced Materials Applications

Sulfonated polymers have found use as ion-exchange membranes for use in fuel cells, water purification, electroactive devices, and inorganic materials templating and synthesis. Improving the materials for these applications and opening up new applications requires the ability to synthesis targeted or more complex sulfonated polymers, which includes tailoring the chemistry (copolymerization across a wider range of solubility) and/or polymer architecture (block, graft, nanoparticle). This article will summarize the recent work using sulfonated monomers with substituted ammonium counterions as a versatile route for enabling this goal. Two main benefits of these monomers are as follows. First, they are useful for preparing amphiphilic copolymers, which is a challenge using traditional acidic or alkali salt forms of sulfonated monomers. Second, sulfonated polymers with substituted ammonium counterions are useful polymers for obtaining unique material properties, such as organo-gelation of low polarity solvents or obtaining ionic liquid polymers for the fabrication of solid polymer electrolytes.

Investigation of the relationships between the thermodynamic phase behavior and gelation behavior of a series of tripodal trisamide compounds

The solution behavior of a series of tris(2-aminoethyl)amine (TREN) based trisamide derivatives in organic solutions was investigated with a focus on organogelation. First, the general solution behavior of eight compounds was investigated and qualitatively interpreted using the regular solution model and solubility parameter theory. Second, the phase behavior of one trisamide in aromatic solvents, where gels were formed, was investigated in more detail. A correlation was found between the sol–gel transition temperature and the thermodynamic liquidus lines. The prediction of the liquidus lines using the regular solution model and solubility parameter theory reproduced the shape and scaling of the gel transition temperature vs. composition in different aromatic solvent solutions. Good fits of the gel transition temperature vs. composition were obtained using the thermodynamic parameters of the components with one additional fitting parameter to account for entropic contributions to the solution non-ideality. Based on these results the regular solution model was used to calculate the melting temperatures of two different trisamides at the minimum gelation concentration (MGC) in different aromatic solvents. The dependence of the MGC on the minimum undercooling required for gelation is discussed. The assumptions and limitations of the model are also discussed to aid in its more general application to organogelator thermodynamics.

Control of Ordering and Structure in Soft Templated Mesoporous Carbon Films by Use of Selective Solvent Additives

The structure of ordered mesoporous carbons fabricated using poly(styrene-block-N,N,-dimethyl-n-octadecylamine p-styrenesulfonate) (PS-b-PSS-DMODA) as the template and phenolic resin (resol) as the carbon source can be easily manipulated by inclusion of low concentrations of low volatility selective solvents in the casting solution. Casting from neat methyl ethyl ketone yields a disordered structure even upon thermal annealing. However, addition of both dioctyl phthalate (DOP, PS selective) and dimethyl sulfoxide (DMSO, resol and PSS-DMODA selective) at modest concentrations to this casting solution provides sufficient mobility to produce highly ordered films with cylindrical mesopores. The DOP acts to swell the hydrophobic domain and can more than double the mesopore size, while the DMSO acts to swell the resol phase. Moreover, the surface area of the mesoporous carbons increases significantly as the meosopore size increases. This is a result of the decrease in wall thickness, which can be ascertained by the constant d-spacing of the mesostructure as the pore size increases. This behavior is counter to the typical effect of pore swelling agents that increase the pore size and decrease the surface area. Moreover, with only 4 wt % DOP/DMSO in the solution (20 wt % relative to solids), the scattering profiles exhibit many orders of diffraction, even upon carbonization, which is not typically observed for soft templated films. Variation in the concentration of DOP and DMSO during casting enables facile tuning of the structure of mesoporous carbon films.

Role of Amphiphilic Block Copolymer Composition on Pore Characteristics of Micelle-Templated Mesoporous Cobalt Oxide Films

Block copolymer templating is a versatile approach for the generation of well-defined porosity in a wide variety of framework chemistries. Here, we systematically investigate how the composition of a poly(methoxy poly[ethylene glycol] methacrylate)-block-poly(butyl acrylate) (PMPEG-PBA) template impacts the pore characteristics of mesoporous cobalt oxide films. Three templates with a constant PMPEG segment length and different hydrophilic block volume fractions of 17%, 51%, and 68% for the PMPEG-PBA are cooperatively assembled with cobalt nitrate hexahydrate and citric acid. Irrespective of template composition, a spherical nanostructure is templated and elliptical mesostructures are obtained on calcination due to uniaxial contraction of the film. The average pore size increases from 11.4 ± 2.8 to 48.5 ± 4.3 nm as the length of the PBA segment increases as determined from AFM. For all three templates examined, a maximum in porosity (∼35% in all cases) and surface area is obtained when the precursor solids contain 35-45 wt % PMPEG-PBA. This invariance suggests that the total polymer content drives the structure through interfacial assembly. The composition for maximizing porosity and surface area with the micelle-templating approach results from a general decrease in porosity with increasing cobalt nitrate hexahydrate content and the increasing mechanical integrity of the framework to resist collapse during template removal/crystallization as the cobalt nitrate hexahydrate content increases. Unlike typical evaporation induced self-assembly with sol-gel chemistry, the hydrophilic/hydrophobic composition of the block copolymer template is not a critical component to the mesostructure developed with micelle-templating using metal nitrate-citric acid as the precursor.

Syntheses of quaternary ammonium-containing, trithiocarbonate RAFT agents and hemi-telechelic cationomers

We reported herein a facile and high-yield approach to synthesize a series of trithiocarbonate RAFT agents containing quaternary ammonium functionality in the “R-group”. This new synthetic route first involves the optimized synthesis of 4-(bromomethyl)-N,N,N-trialkyl benzyl ammonium bromide compounds (Br-Ph-NR3, R = Me, Et and Bu), which were subsequently reacted with the alkyl trithiocarbonate anion to directly produce the trithiocarbonate RAFT agent. It was found that the quaternary ammonium group partially degraded when the RAFT agents were used in polymerizations at 120 °C. This issue was overcome by using lower polymerization temperature, which when combined with column chromatography, afforded high purity α-N,N,N-trialkyl benzyl ammonium hemi-telechelic cationomers.