Uncharged Sulfoxide-Containing Homopolymers with Programmable Thermoresponsive Behaviors

Although significant advances have been made in synthesizing noble sulfoxide-containing polymers that respond to temperature changes by showing lower critical solution temperature (LCST), achieving the opposite effect, upper critical solution temperature (UCST), has proven very challenging due to their high hydrophilicity. In this work, we synthesized two homopolymers containing sulfoxide and ester groups that demonstrate (1) two distinctive and precisely controllable LCST and UCST values depending on the pendant ester hydrophobicity and (2) dipole–dipole interactions as the sole mechanism for UCST phase transition which were unknown before. Accordingly, two new uncharged methacrylate monomers, 3-((2-methoxy-2-oxoethyl)sulfinyl)propyl methacrylate (MSPM) and 3-((2-ethoxy-2-oxoethyl)sulfinyl)propyl methacrylate (ESPM), are synthesized and comparatively studied and subsequently polymerized via reversible addition–fragmentation chain transfer. By adding a “methylene (−CH2−)” group, the homopolymer of ESPM shows UCST at around 37 °C when mixed with methanol and water. On the other hand, the homopolymer of MSPM showed the opposite behavior, LCST, in pure water. The reason for the distinct thermoresponsive behaviors lies in two independent mechanisms. One mechanism is hydrogen bonding between sulfoxide and water, which causes LCST. The other mechanism is dipole–dipole complexes between sulfoxides, which results in UCST. Sulfoxides are hydrogen bonding (H-bonding) acceptors which can form H-bonding with H-bond donor molecules like water. However, they are not able to form insoluble polymeric aggregates (globules) at low temperatures. To test the role of the dipole–dipole interaction, acetonitrile, which disrupts sulfoxide–sulfoxide dipole–dipole interaction, was introduced into the system. We observed a gradual decrease in the cloud point (TcU) of PESPM in the methanol–water mixture, dropping from 24.6 to 10.7 °C with increasing acetonitrile amount. This confirms the presence of dipole–dipole interactions among sulfoxides. Overall, our findings indicate that incorporating a highly polar component, such as sulfoxide (which has a dipole moment of approximately 4 D), along with appropriate hydrophobic groups, is a promising strategy for designing and synthesizing polymers with well-defined and predictable thermoresponsive properties

Reactive Molecular Dynamics Simulations of Self-Assembly of Polytwistane and Its Application for Nanofibers

We investigated the self-assembly and mechanical properties of polytwistane (PT), particularly a seven-strand PT rope, using reactive force field-based molecular dynamics simulations at different temperatures. We show that upon self-assembly due to strong van der Waals interaction among PT units, PTs form a twisted structure (ropelike) with a twisting angle of ∼0.16 rad/nm at 300 K, which makes them mechanically stronger. The PT rope has high Young’s modulus (∼0.45 TPa) at 300 K. Interestingly, Young’s modulus increases with temperature for the seven-strand PT rope, whereas it decreases with temperature for a single-strand PT. This is because in the case of the seven-strand PT, the twisting angle also contributes to the elastic property of the PT rope and twisting depends on the temperature. We estimate a maximum load transfer of ∼1.1 and ∼3.3 nN to the central unit at 100 and 300 K, respectively. Hence, the amount of load transfer critically depends on the twisting in the rope. The fracture behavior of the single-strand PT and seven-strand PT rope is also investigated. We find two major mechanisms of PT fracture: in the first case, an acetylene-like structure is attached with one of the twistane units at the breaking region. In the second case, all the three sp3 C–C bonds of the participating twistane units break, creating three sp2 C sites along the breaking region. In the case of the PT rope, the fracture in the individual strands occurs in a sequential manner. We predict that the self-assembled twisted PT rope is a promising candidate for carbon fiber applications where mechanical properties are of interest

Extraction of Thiophenic Sulfur Compounds from Model Fuel Using a Water-Based Solvent

Thiophene, benzothiophene, and dibenzothiophene were extracted from isooctane using water and aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, sodium hydroxide, ammonium hydroxide, and sodium chloride at different concentrations, as solvents or extractants. The sulfur compound in isooctane at a definite concentration comprises model fuel. It was observed that the extraction ability of water is enhanced by adding those solutes or reagents. The aim of this work is to establish water-based solutions as an economic extractant for desulfurization of model fuel containing thiophenic sulfur compounds, by choosing the appropriate concentration of those aqueous extractants and using them at the most suitable extractive condition. The best result was obtained from aqueous hydrochloric acid solution, whose maximum sulfur removal efficiency toward thiophene, benzothiophene, and dibenzothiophene was 50, 28.2, and 26.8%, respectively. The effect of operational parameters on extraction, such as solvent/model fuel volume ratio, temperature, stirring speed, extraction time, and extraction cycle, was explored. The extraction temperature of 50 °C and 2:1 solvent/model fuel volume ratio under stirring at 1000 rpm for 60 min were found to be the optimum operating conditions. Finally, liquid–liquid equilibria of the ternary mixture (thiophene + isooctane + aqueous HCl) were obtained at 40, 50, 60, and 70 °C at atmospheric pressure, and the equilibrium data were correlated with Othmer–Tobias and Hand correlations

Nickel(0)-Catalyzed Asymmetric Hydrocyanation of 1,3-Dienes

1,2-Bis-diarylphosphinites are excellent ligands for the Ni(0)-catalyzed hydrocyanation of certain types of 1,3-dienes. 1-Phenyl-1,3-butadiene, 1-vinyl-3,4-dihydronaphthalene, and 1-vinylindene undergo highly regioselective hydrocyanation under ambient conditions to give exclusively the 1,2-adducts in good to excellent yields. Using bis-1,2-diarylphosphinites derived from d-glucose, the highest enantioselectivities to-date for asymmetric hydrocyanation of 1,3-dienes (70−83% ee's) have been obtained

Syntheses and Applications of 2-Phosphino-2‘-alkoxy-1,1‘-binaphthyl Ligands. Development of a Working Model for Asymmetric Induction in Hydrovinylation Reactions

Among the handful of monophosphine ligands that effect asymmetric hydrovinylation of vinylarenes, 2-diphenylphosphino-2‘-methoxy-1,1‘-binaphthyl (MOP) is among the most accessible. Addition of a methyl group at the 3‘-position of this ligand significantly improves the enantioselectivity of hydrovinylation of prototypical alkenes. Introduction of a chiral phospholane at the C2 position of this scaffolding has no effect on the enantioselectivity. These results are consistent with a model proposed for the asymmetric induction for this exacting reaction

Comparative studies of extraction ability of organic solvents to extract thiophene from model fuel

The thiophene extraction from model fuel by using N-methyl-2-pyrrolidone [NMP], dimethylformamide [DMF] and ethylene glycol [EG] as solvents had been carried out at atmospheric pressure. It is found that NMP showed the best performance with 98% removal of thiophene for 1 h. A detail parametric study was performed to investigate the effect of different process parameters on the extraction of thiophene by using NMP as the solvent. Finally Box-Behnken design (BBD) explores the relationship between output, sulfur removal efficiency and inputs parameters like time, temperature and solvent to model fuel volume ratio.</p

Hot Giant Fullerenes Eject <i>and</i> Capture C₂ Molecules: QM/MD Simulations with Constant Density

Quantum chemical molecular dynamics (QM/MD) simulations using periodic boundary conditions show that hot giant fullerene (GF) cages can both eject and capture C2 molecules dependent on the concentration of noncage carbons in the simulated system, and that the cage size can therefore both increase and decrease under high temperature conditions. The reaction mechanisms for C2 elimination and incorporation involve sp3 carbon defects and polygonal rings larger than hexagons, and are thus closely related to previously described mechanisms (Murry, R. L.; Strout, D. L.; Odom, G. K.; Scuseria, G. E. Nature 1993, 366, 665). The atoms constituting the cage are gradually replaced by the two processes, suggesting that a fullerene cage during high-temperature synthesis is a dissipative structure in the sense of Ilya Prigogine’s theory of self-organization in nonequilibrium systems. Explicit inclusion of Lennard-Jones-type helium or argon noble gas atoms is found to increase the GF shrinking rate. Large GFs shrink at a greater rate than small GFs. The simulations suggest that in an idealized, closed system the fullerene cage size may grow to a dynamic equilibrium value that depends on initial cage size, temperature, pressure, and overall carbon concentration, whereas in an open system cage shrinking prevails when noncage carbon density decreases as a function of time

Investigation of the Electronic Spectra and Excited-State Geometries of Poly(<i>para</i>-phenylene vinylene) (PPV) and Poly(<i>para</i>-phenylene) (PP) by the Symmetry-Adapted Cluster Configuration Interaction (SAC-CI) Method

The symmetry-adapted cluster-configuration interaction (SAC-CI) method has been used to investigate the optical and geometric properties of the oligomers of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PP). Vertical singlet and triplet absorption spectra and emission spectra have been calculated accurately; the mean average deviation from available experimental results lies within 0.2 eV. The chain length dependence of the transition energies has been improved in comparison to earlier TDDFT and MRSDCI calculations. The present analysis suggests that conventional TDDFT with the B3LYP functional should be used carefully, as it can provide inaccurate estimates of the chain length dependence of the excitation energies of these molecules with long π conjugation. The T1 state was predicted to be at a lower energy, by 1.0−1.5 eV for PPV and by 0.9−1.7 eV for PP, than the S1 state, which indicates a localized T1 state with large exchange energy. By calculating the SAC-CI electron density difference between the ground and excited states, the geometry relaxations due to excitations can be analyzed in detail using electrostatic force theory. For trans-stilbene, the doubly excited 2Ag state was studied, and the calculated transition energy of 4.99 eV agrees very well with the experimental value of 4.84 eV. In contrast to previous ab initio calculations, we predict this doubly excited 21Ag state to lie above the 11Bu state

Hot Giant Fullerenes Eject <i>and</i> Capture C₂ Molecules: QM/MD Simulations with Constant Density

Quantum chemical molecular dynamics (QM/MD) simulations using periodic boundary conditions show that hot giant fullerene (GF) cages can both eject and capture C2 molecules dependent on the concentration of noncage carbons in the simulated system, and that the cage size can therefore both increase and decrease under high temperature conditions. The reaction mechanisms for C2 elimination and incorporation involve sp3 carbon defects and polygonal rings larger than hexagons, and are thus closely related to previously described mechanisms (Murry, R. L.; Strout, D. L.; Odom, G. K.; Scuseria, G. E. Nature 1993, 366, 665). The atoms constituting the cage are gradually replaced by the two processes, suggesting that a fullerene cage during high-temperature synthesis is a dissipative structure in the sense of Ilya Prigogine’s theory of self-organization in nonequilibrium systems. Explicit inclusion of Lennard-Jones-type helium or argon noble gas atoms is found to increase the GF shrinking rate. Large GFs shrink at a greater rate than small GFs. The simulations suggest that in an idealized, closed system the fullerene cage size may grow to a dynamic equilibrium value that depends on initial cage size, temperature, pressure, and overall carbon concentration, whereas in an open system cage shrinking prevails when noncage carbon density decreases as a function of time

Hot Giant Fullerenes Eject <i>and</i> Capture C₂ Molecules: QM/MD Simulations with Constant Density

Quantum chemical molecular dynamics (QM/MD) simulations using periodic boundary conditions show that hot giant fullerene (GF) cages can both eject and capture C2 molecules dependent on the concentration of noncage carbons in the simulated system, and that the cage size can therefore both increase and decrease under high temperature conditions. The reaction mechanisms for C2 elimination and incorporation involve sp3 carbon defects and polygonal rings larger than hexagons, and are thus closely related to previously described mechanisms (Murry, R. L.; Strout, D. L.; Odom, G. K.; Scuseria, G. E. Nature 1993, 366, 665). The atoms constituting the cage are gradually replaced by the two processes, suggesting that a fullerene cage during high-temperature synthesis is a dissipative structure in the sense of Ilya Prigogine’s theory of self-organization in nonequilibrium systems. Explicit inclusion of Lennard-Jones-type helium or argon noble gas atoms is found to increase the GF shrinking rate. Large GFs shrink at a greater rate than small GFs. The simulations suggest that in an idealized, closed system the fullerene cage size may grow to a dynamic equilibrium value that depends on initial cage size, temperature, pressure, and overall carbon concentration, whereas in an open system cage shrinking prevails when noncage carbon density decreases as a function of time