Tailoring Amphiphilic Copolymers for Improved Aqueous Foam Stability.

Amphiphilic copolymers of various-molecular-weight (MW) poly(ethylene glycol) (PEG) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The first PEG series, poly(ethylene glycol)monomethacrylate (PEGMA, average Mn 200 and 400 MW), contained an -OH terminal group, and the second series, poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMMA, average Mn 200, 400, and 1000 MW), possessed an -OCH3 terminal group. A total of five PEG-functionalized copolymers contained the same hydrophobic monomer, butyl acrylate (BA), and were successfully reproduced via a one-pot synthesis. The resulting PEG-functionalized copolymers provide a systematic trend of properties including surface tension, critical micelle concentration (CMC), cloud point (CP), and foam lifetime based on the average MW of the PEG monomer and final polymer properties. In general, the PEGMA series produced more stable foams with PEGMA200 demonstrating the least change in foam height with time over a 10 min period. The important exception is that at elevated temperatures, the PEGMMA1000 copolymer had longer foam lifetimes. The self-assembling copolymers were characterized by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (NMR), attenuated total reflection Fourier transform infrared (FTIR-ATR), CMC, surface tension, dynamic light scattering (DLS), as a foam using a dynamic foam analyzer (DFA), and foam lifetime at ambient and elevated temperatures. The copolymers described highlight the importance of the PEG monomer MW and terminal end group for surface interaction and final polymer properties for foam stabilization.

Copolymer Reversible Addition-Fragmentation Chain Transfer Synthesis of Polyethylene Glycol (PEG) Functionalized with Hydrophobic Acrylates: A Study of Surface and Foam Properties.

A series of amphiphilic statistical copolymers involving poly(ethylene glycol) monomethacrylate (PEGMA, -OH terminated, average Mn 200 molecular weight) and various hydrophobic acrylates were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The gradient copolymers were characterized by gel-permeation chromatography (GPC), 1H nuclear magnetic resonance (NMR), and attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR). Solution properties of the copolymers were investigated utilizing surface tension measurement, dynamic light-scattering (DLS), as well as foam analysis using a dynamic foam analyzer (DFA). The PEG-functionalized copolymers showed a systematic trend depending on the hydrophobic moiety in properties including surface tension, critical micelle concentration (CMC), foam lifetime, and liquid drainage from the foam. Copolymers with alkyl-acrylates exhibited the best foam lifetime, demonstrating that the choice of hydrophobic moiety is crucial for foam stability. The PEG-functionalized materials described are considered promising additives for foam-stability purposes.

A Porous Chalcogen-Bonded Organic Framework.

The manner of bonding between constituent atoms or molecules invariably influences the properties of materials. Perhaps no material family is more emblematic of this than porous frameworks, wherein the namesake modes of connectivity give rise to discrete subclasses with unique collections of properties. However, established framework classes often display offsetting advantages and disadvantages for a given application. Thus, there exists no universally applicable material, and the discovery of alternative modes of framework connectivity is highly desirable. Here we show that chalcogen bonding, a subclass of σ-hole bonding, is a viable mode of connectivity in low-density porous frameworks. Crystallization studies with the triptycene tris(1,2,5-selenadiazole) molecular tecton reveal how chalcogen bonding can template high-energy lattice structures and how solvent conditions can be rationalized to obtain molecularly programmed porous chalcogen-bonded organic frameworks (ChOFs). These results provide the first evidence that σ-hole bonding can be used to advance the diversity of porous framework materials.

Crystal structure of 1,2-bis-(3,5-di-fluoro-phen-yl)ethane-1,2-dione.

The title compound, C14H6F4O2, crystallizes with half of a mol-ecule per asymmetric unit and exhibits bond lengths and angles typical of α-diketones. A network of C-H⋯F contacts and π-π stacking inter-actions is observed within the structure.

Correlation of Structure with Crystalline to Amorphous Phase Transitions of 1,3,6-Substituted Fulvene-Derived Molecular Glasses.

An investigation into the crystalline to amorphous phase transitions of prepared 1,3,6-substituted pentafulvenes showed the expected reversible heated melt and cooling recrystallization in only a few examples. Systematic incorporation of bulky substituents at the 6-position of the fulvene ring led to the nonreversible thermal behavior, rendering phases that were locked into glassy, vitrified states. These molecular glasses produced physically translucent and amorphous features with glass transition temperatures in the range of 61-77 °C, comparable with high-strength plastics such as polyethylene terephthalate. Additionally, the melting point transitions and the resulting heat of fusion values were found to be directly influenced by the nature of the 6-position substituent. Single crystal X-ray crystallography showed that in some cases, fulvenes possessing fused aromatics exhibited a high degree of intermolecular π-π stacking. These results point to a class of molecular glass formers as host materials possessing tunable bulk properties for potentially new optical applications.

Crystal structures of 6-cyclo-propyl-1,3-diphenylfulvene and 6-(2,3-di-meth-oxy-naphth-yl)-1,3-di-phenylfulvene.

The title compounds, 6-cyclo-propyl-1,3-diphenylfulvene, C21H18, [systematic name: 5-(cyclo-propyl-methyl-idene)-1,3-di-phen-yl-cyclo-penta-1,3-diene], 1, and 6-(2,3-di-meth-oxy-naphth-yl)-1,3-diphenylfulvene, C30H24O2, {systematic name: 5-[(3,4-di-meth-oxy-naphthalen-2-yl)methyl-idene]-1,3-di-phenyl-cyclo-penta-1,3-di-ene}, 2, were prepared from 1,3-di-phenyl-cyclo-penta-diene, pyrrolidine, and the corresponding aldehydes in an ethano-lic solution. Each structure crystallizes with one mol-ecule per asymmetric unit and exhibits the alternating short and long bond lengths typical of fulvenes. A network of C-H⋯C ring inter-actions as well as C-H⋯O inter-actions is observed, resulting in the compact packing found in each structure.

Exploiting the Site Selectivity of Perfluoropyridine for Facile Access to Densified Polyarylene Networks for Carbon-Rich Materials.

Fluorinated molecules containing reactive functionalities are of great interest to the materials community as these compounds can be used to prepare fluorinated polymers with desirable physical and electronic properties. Despite their potential, many of these compounds are limited by their synthesis which generally requires transition-metal-catalyzed coupling reactions or harsh fluorinating conditions. Perfluoroheteroaromatic compounds provide a unique solution to this problem as compounds such as perfluoropyridine can undergo SNAr reactions with a wide range of simple nucleophiles in a controlled and regioselective manner. Herein we report the transition-metal-free synthesis of a pool of highly soluble high aromatic content (HAC) perfluoropyridine-based thermosetting precursors and compounds of interest which can be easily obtained from readily available chemical precursors using simple nucleophilic chemistries. These thermally active monomers cure readily, in 350-400 °C temperature ranges, into highly densified polyaryelene networks and demonstrate decomposition temperatures well above 400 °C and high char yields at 900 °C, making these promising materials for high-temperature applications as well as templates for carbon-based nanomaterials.

mer-Tri-chlorido-tris-(tetra-hydro-thio-phene-κS)iridium(III): preparation and comparison with other mer-tri-chlorido-tris-(tetra-hydro-thio-phene-κS)metal complexes.

The title complex, [IrCl3(C4H8S)3], was prepared according to a literature method. A suitable crystal was obtained by diffusion of pentane into a di-chloro-methane solution and analyzed by single-crystal X-ray diffraction at 100 K. The title complex is isotypic with mer-tri-chlorido-tris-(tetra-hydro-thio-phene-κS)rhodium(III). However, the orientation of the tetra-hydro-thio-phene rings is different from an earlier report of mer-tri-chlorido-tris-(tetra-hydro-thio-phene-κS)iridium(III) deposited in the Cambridge Structural Database. The IrS3Cl3 core shows a nearly octa-hedral structure with various bond angles within 1-2° of the perfect 90 or 180° expected for an octa-hedron. The structure of the title compound is compared with the previous iridium complex as well as the rhodium and other octa-hedral metal tris-tetra-hydro-thio-phene compounds previously structurally characterized. DFT calculations were performed, which indicate the mer isomer is significantly lower in energy than the fac isomer by 50.1 kJ mol-1, thereby accounting for all compounds in the CSD being of the mer geometry. Powder X-ray diffraction of the bulk material showed that the preparation method yielded only the isomorph reported in this communication.