THF Concentration Research Articles

Backbone-Substituted β-Ketoimines and Ketoiminate Clusters: Transoid Li2O2 Squares and D2-Symmetric Li4O4 Cubanes. Synthesis, Crystallography and DFT Calculations

The preparation and crystal structures of four β-ketoimines with bulky aryl nitrogen substituents (2,6-diisopropylphenyl and 2,4,6-trimethylphenyl) and varying degrees of backbone methyl substitution are reported. Backbone substitution “pinches” the chelate ring. Deprotonation with n-butyllithium leads to dimeric Li2O2 clusters, as primary laddered units, with an open transoid geometry as shown by crystal structures of three examples. The coordination sphere of each lithium is completed by one tetrahydrofuran ligand. NMR spectra undertaken in either C6D6 or 1:1 C6D6/d8-THF show free THF in solution and the chemical shifts of ligand methyl groups experience significant ring-shielding which can only occur from aryl rings on adjacent ligands. Both features point to conversion to higher-order aggregates when the THF concentration is reduced. Recrystallization of the materials from hydrocarbon solutions results in secondary laddering as tetrameric Li4O4 clusters with a cuboidal core, three examples of which have been crystallographically characterised. These clusters are relatively insoluble and melt up to 250 °C; a consideration of the solid-state structures indicates that the clusters with 2,6-diisopropylphenyl substituents form very uniform ball-like molecular structures that will only be weakly solvated.

Effect of Swelling on Multiple Energy Transfer in Conjugated Polymer Nanoparticles

Many key processes in conjugated polymers are strongly influenced by multiple energy transfer (i.e., exciton diffusion). We investigated the effect of solvent-induced swelling on the kinetics of multiple energy transfer in nanoparticles of the conjugated polymers PFBT and MEH-PPV. Multiple energy transfer between equivalent chromophores results in an increased rate of quenching by defects due to a cascading or funneling effect. The effects of swelling on energy transfer between polymer chromophores and the resulting exciton dynamics were modeled using a random walk on a lattice of chromophores. The simulation results show good agreement with experimental fluorescence quantum yield, and decay kinetics results at low to moderate THF concentrations. We found that the time scale for energy transfer between chromophores (∼5 ps for MEH-PPV nanoparticles and ∼100 ps for PFBT nanoparticles) is highly sensitive to swelling, slowing by an order of magnitude or more for swelled particles. The results support quenchi...

Hindrance of 1,4-dioxane biodegradation in microcosms biostimulated with inducing or non-inducing auxiliary substrates

A microcosm study was conducted to assess two biostimulation strategies (relative to natural attenuation) to bioremediate 1,4-dioxane contamination at a site in west Texas. Dioxane concentrations were relatively low (<300 μg/L), which represents a potential challenge to sustain and induce specific degraders. Thus, biostimulation was attempted with an auxiliary substrate known to induce dioxane-degrading monooxygenases (i.e., tetrahydrohyran [THF]) or with a non-inducing growth substrate (1-butanol [1-BuOH]). Amendment of 1-BuOH (100 mg/L) to microcosms that were not oxygen-limited temporarily enhanced dioxane biodegradation by the indigenous microorganisms. However, this stimulatory effect was not sustained by repeated amendments, which might be attributed to i) the inability of 1-BuOH to induce dioxane-degrading enzymes, ii) curing of catabolic plasmids, iii) metabolic flux dilution and catabolite repression, and iv) increased competition by commensal bacteria that do not degrade dioxane. Experiments with the archetype dioxane degrader Pseudonocardia dioxanivorans CB1190 repeatedly amended with 1-BuOH (500 mg/L added weekly for 4 weeks) corroborated the partial curing of catabolic plasmids (9.5 ± 7.4% was the plasmid retention ratio) and proliferation of derivative segregants that lost their ability to degrade dioxane. Addition of THF (300 μg/L) also had limited benefit due to competitive inhibition; significant dioxane degradation occurred only when the THF concentration decreased below approximately 160 μg/L. Overall, these results illustrate the importance of considering the possibility of unintentional hindrance of catabolism associated with the addition of auxiliary carbon sources to bioremediate aquifers impacted with trace concentrations of dioxane.

Synthesis, characterization and investigation of the spectroscopic properties of novel peripherally 2,3,5-trimethylphenoxy substituted Cu and Co phthalocyanines, the computational and experimental studies of the 4-(2,3,5-trimethylphenoxy)phthalonitrile

4-(2,3,5-trimethylphenoxy)phthalonitrile ( 3 ) was firstly prepared via aromatic nucleophilic substitution reaction and characterized by FT-IR, mass spectrometry, 1 H and 13 C NMR techniques. The molecular structure of the compound ( 3 ) was optimized using Density Functional Theory (DFT/B3LYP) method with 6-311G(d,p) basis set in the ground state. The molecular geometric parameters which were obtained by X-ray single crystal diffraction method and the spectral results were compared with computed bond lengths and angles, vibrational frequencies and 1 H, 13 C NMR chemical shifts values of the compound ( 3 ). Also, Cu(II) and Co(II) phthalocyanines were synthesized by the treatment of dinitrile derivative with anhydrous CuCl 2 or CoCl 2 under N 2 atmosphere in dry n-pentanol at 140 o C. The new compounds have been determined by elemental analysis, FT-IR and electronic absorption. The UV-Vis spectra of the Cu(II) and Co(II) phthalocyanines were recorded with different concentration in THF and also with different solvents as DMF, DMSO, DCM, CHCl 3 , toluene.

Lithium naphthalenides in non-polar or in low-polarity media: some insights regarding their use as initiators in anionic polymerizations

The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.

Kinetics of methane hydrate formation in an aqueous solution of thermodynamic promoters (THF and TBAB) with and without kinetic promoter (SDS)

Kinetic studies concerning the combination of thermodynamic promoters (tetra-n-butyl ammonium bromide, TBAB and tetrahydrofuran, THF) and kinetic promoters (sodium dodecyl sulphate, SDS) have not yet been investigated in detail for methane hydrate system suitable for natural gas storage and transportation. In this work, experiments were conducted at an initial pressure conditions of 7.5 MPa and 276.15 K for pure water, SDS, TBAB, (TBAB + SDS), THF, (THF + SDS) and (THF + TBAB) aqueous systems for various concentrations. Similarly, at 5.5 MPa and 276.15 K, experiments were conducted for pure water, TBAB, (TBAB + SDS), THF and (THF + SDS) aqueous systems for various concentrations. In addition, at 3.0 MPa and 276.15 K, 0.05 and 0.1 mass fraction of TBAB, 0.005 and 0.01 mass fraction of THF and (0.01 + 0.1) mass fraction of (THF + TBAB) aqueous systems have been considered for the experiments. It has been observed that the methane hydrate formed from pure water with SDS shows higher moles of gas consumption per mole of water as compared to other aqueous systems at higher pressure. Also, the use of SDS with THF shows drastic increase in methane consumption as against semiclathrate hydrate/hydrate formed using TBAB aqueous system and pure water. At lower pressure, of about 3 MPa, gas consumption per mole of water in hydrate has found to enhance for a mixed promoter system containing (THF + TBAB) as compared with the other aqueous systems. Theoretical and actual gas storage capacity calculations has also been performed for various concentrations of THF and TBAB aqueous systems. This study essentially helps to understand the behaviour of TBAB and THF aqueous solution with and without SDS and mixed promoter system of (THF + TBAB) for methane hydrate formation desirable for applications like gas storage, transportation and gas recovery using hydrate-based gas separation method.

Direct Preparation of Hollow Nanospheres with Kraft Lignin: A Facile Strategy for Effective Utilization of Biomass Waste

This work discusses the preparation and characterization of hollow nanospheres based on kraft lignin (KL). Kraft lignin is a by-product of the papermaking industry and an abundant renewable resource. It was determined that adding water to a KL/THF solution induced KL to form hollow nanospheres via self-assembly. Scanning electron microscopy and transmission electron microscopy confirmed the hollow nanosphere morphology. The shell thickness of the hollow nanospheres was tunable by adjusting the initial KL concentration in THF, making the nanospheres a potential material for the encapsulation and controlled release of guest molecules. Ultraviolet (UV) and Fourier transform infrared (FTIR) spectroscopy confirmed the π-π stacking of aromatic rings as an important and distinctive mechanism for the formation of hollow KL nanospheres. The nanospheres were obtained simply and inexpensively, and they exhibited the characteristics of biocompatibility, biodegradability, and low toxicity. These advantages make hollow KL nanospheres attractive for applications in nanoscience and nanotechnology. This study developed an economically feasible and facile strategy for the effective use of biomass waste in sustainable chemistry.

Biodiesel Production from Mustard Emulsion by a Combined Destabilization/Adsorption Process

AbstractTetrahydrofuran, added to the oil‐in‐water emulsions formed by the aqueous processing of yellow mustard flour, produced oil/water/THF miscellas containing 1–2 % water. The high water content prevented the direct conversion of the system to fatty acid methyl esters (FAME) through a single‐phase base‐catalyzed transmethylation process. Dehydration of these miscellas by adsorption on 4A molecular sieves at room temperature using either batch or continuous fixed‐bed systems successfully reduced the water content to the quality standards needed for biodiesel feedstock (0.3 %). Equilibrium adsorption studies for the uptake of water from oil/THF/water miscella phases at room temperature allowed quantitative comparison of the water adsorption capacity based on the oil and THF concentrations of the miscellas. Batch contact was used to investigate the dominant parameters affecting the uptake of water including miscella composition, adsorbent dose and contact time. The adsorption of the water was strongly dependent on adsorbent dose and miscella oil concentrations. The regeneration of molecular sieves by heating under nitrogen at reduced pressure for 6 h at 275 °C resulted in incomplete desorption of miscella components. The adsorption breakthrough curves in terms of flow rates, initial water and oil miscella concentrations were determined. The dehydrated miscella phases were reacted with methanol in a single‐phase base‐catalyzed transmethylation process with high yields (99.3 wt%) to FAME. The resulting FAME met the ASTM international standard in terms of total glycerol content and acid number.

Substrate-Dependent Oxidation with Alkyl Hydroperoxide Mediated By Iron Porphyrin Coordinated By Thiolate

Alkane and arene hydroxylation by cytochrome P450 is one of the most powerful chemical processes in biological systems. The highly reactive intermediate in cytochrome P450 catalysis has aroused broad interests and has been the subject for extensive investigations. SR complex successfully created by us is the first synthetic heme thiolate complex that retains its thiolate coordination structure during catalytic oxidation reaction. We have focused on the alkyl hydroperoxide-heme thiolate chemistry. We previously found that SR complex efficiently catalyzed one-electron oxidation of 2,4,6-tri-tert-butylphenol (TBPH) with cumene hydroperoxide (CHPO) or tert-butyl hydroperoxide to afford 2,4,6-tri-tert-butylphenoxyl radical (TBP•). Recently, 2-methyl-1-phenylpropan-2-yl hydroperoxide (MPPH) has been used as a mechanistic probe for O-O bond cleavage mode on catalysis of metal complex. MPPH is known to give benzyl radical-derived products and acetone via unstable alkoxyl radical in the case of homolytic O-O bond cleavage whereas it simply affords 2-methyl-1-phenyl-2-propanol (MPPOH) in the case of heterolysis. Here we report the substrate oxidation mechanism with CHPO and MPPH catalyzed by SR complex. We found that SR complex lost its thiolate coordination after the addition of MPPH (1 equiv. to SR complex) even in the presence of large excess amount of phenol with an electron-withdrawing substituent. On the other hand, the use of TBPH or 2,6-di-tert-butylphenol as a substrate lead to retention of the thiolate coordination. Next, equilibrium constant K’ values of THF coordination to SRs were determined by Benesi-Hildebrand plot (inverse of absorption spectral change versus inverse of THF concentration). We plot K’ versus reaction rate since correlation between the two factor was expected. The plot clearly showed that the reaction rate was almost proportionate to K’ value from high linearity of the plot in terms of SR complexes. This result suggests that hydroperoxide coordination step is rate-determining step. Putting together these results, alkyl hydroperoxide-heme-thiolate complex is suggested to be an actual active intermediate.

BDI∗MgX(L) where X = nBu and OtBu and L = THF, py and DMAP. The rates of kinetic exchange of L where BDI∗ = CH{C(tBu)N-2,6-iPr2C6H3}2

BDI∗MgnBu(THF) and rac-LA to produce heterotactic PLA have been shown to increase from Pr=0.5–0.65 from DCM to neat THF. The increase in concentration of THF from MTHF=0 in toluene to neat THF is shown to occur by THF dissociation as deduced by 1H NMR studies. In related systems where X=nBu and OtBu and with ligands L=THF, py and DMAP similar processes occur by which external exchange of L occurs with added free ligand. For X=nBu and L=THF, the activation parameters for the dissociation process are ΔH╪=7.0±0.5kcalmol−1 and ΔS╪=−11.6±0.4calmol−1 and for X=OtBu and L=THF are ΔH╪=11.1±1.0kcalmol−1 and ΔS╪=−3.3±3.9calmol−1. The BDI∗(R=tBu) is notably larger than BDI(R=Me) and this limits the use of THF to coordinate during catalysis. The three coordinate complex BDI∗MgnBu has been structurally characterized by single crystal X-ray crystallography: where Mg–N=2.010(4) and 2.026(4)Å and Mg–C=2.117(5)Å, with N–Mg–N=94.2(2)° and N–Mg–C=130.0(2)° and 135.8(2)°. The related complexes BDI∗MgnBu(L), where L=py and DMAP have similar structural features.

A simple LC–MS/MS method for the determination of cortisol, cortisone and tetrahydro-metabolites in human urine: Assay development, validation and application in depression patients

Chronic stress as well as major depressive disorders is associated with cortisol metabolism. Two enzymes modulate cortisol (F) and cortisone (E) interconversion: 11β-hydroxysteroid dehydrogenase type 1 and type 2 (11β-HSD1 and 11β-HSD2). Furthermore, F and E were inactivated by 5α and 5β reductases to their tetrahydro-metabolites: tetrahydrocortisol (THF), allo-tetrahydrocortisol (5α-THF) and tetrahydrocortisone (THE). To better understand depression a LC-MS/MS method for simultaneous determination of F, E THF, 5α-THF and THE in human urine has been developed and validated. The quantification range was 0.1–160ngmL−1 for F and E, and 0.2–160ngmL−1 for the tetrahydro-metabolites, with >86.1% recovery for all analytes. The nocturnal urine concentrations of F, E and tetrahydro-metabolites in 12 apparently healthy male adult volunteers and 12 drug-free male patients (age range, 20–50 years) with a diagnosis of depression were analyzed. A series of significant changes in glucocorticoid metabolism can be detected: F/E ratios and (THF+5α-THF)/THE ratios as well as F and THF concentrations were significantly higher in depression patients than in healthy subjects (p<0.05); 5α-THF/F ratios, 5α-THF/THF ratios as well as 5α-THF concentrations were significantly lower in depression patients (p<0.05). The results pointed to the decreased 11β-HSD2 activity and a dysfunction in the 5α-reductase pathway in depressed patients. This method allows the assessment of 11β-HSD1/2 and 5α/β-reductase activities in a single analytical run providing an innovative tool to explain the potential etiology of depression.

Challenges in predicting ΔrxnG in solution: the mechanism of ether-catalyzed hydroboration of alkenes.

Ab initio (coupled-cluster and density-functional) calculations of Gibbs reaction energies in solution, with new entropy-of-solvation damping terms, were performed for the ether-catalyzed hydroboration of alkenes. The goal was to test the accuracy of continuum-solvation models for reactions of neutral species in nonaqueous solvents, and the hope was to achieve an accuracy sufficient to address the mechanism in the "Pasto case": B2H6 + alkene in THF solvent. Brown's SN2/SN1 "dissociative" mechanism, of SN2 formation of borane-ether adducts followed by SN1 alkene attack, was at odds with Pasto's original SN2/SN2 hypothesis, and while Brown could prove his mechanism for a variety of cases, he could not perform the experimental test with THF adducts in THF solvent, where the higher THF concentrations might favor an SN2 second step. Two diboranes were tested: B2H6, used by Pasto, and (9BBN)2 (9BBN = 9-borabicyclo[3.3.1]nonane, C8H15B), used by Brown. The new entropy terms resulted in improved accuracy vs traditional techniques (∼2 kcal mol(-1)), but this accuracy was not sufficient to resolve the mechanism in the Pasto case.

Hydrate phase equilibria of CO2 + N2 + aqueous solution of THF, TBAB or TBAF system

We report hydrate dissociation conditions of CO2 (15 and 30mol%)+N2 (85 and 70mol%) in the presence of aqueous solutions of THF, TBAB or TBAF. The concentrations of TBAB and TBAF in the aqueous solutions are 5wt% and 9wt% while THF concentration in aqueous solution is 3mol%. Two different experimental techniques including isochoric pressure search method and a DSC method are used to measure the hydrate dissociation conditions. A comparison is finally made with the literature data. It is expected that this study provides better understanding of hydrate phase equilibria associated with CO2 capture.

Hydrate phase equilibrium measurements for (THF + SDS + CO2 + N2) aqueous solution systems in porous media

Hydrate-based gas separation is a promising technology for CO2 capture and storage. Hydrate phase equilibrium data are the most basic information for hydrate formation and dissociation. The effects and mechanism of the additive mixture (mole fraction 1%, 2%, 3%, 4% and 5% tetrahydrofuran, THF, with 1000mg/L sodium dodecyl sulphate, SDS) on the hydrate phase equilibrium (THF+SDS+CO2+N2+H2O system) were investigated using an isochoric method. The experimental results showed that the presence of THF resulted in a substantial decrease of the hydrate phase equilibrium pressure. The rate of decrease of the hydrate phase equilibrium pressure with THF concentrations slowed down as the THF concentration exceeded a mole fraction of 3%. An improved model with the PR equation of state associated with a modified Huron–Vidal second-order model mixing rule and non-random two liquid model was proposed further to predict hydrate phase equilibrium. The predictions showed an acceptable agreement with the experimental data. When the hydrate phase equilibrium pressure was higher than 2.00MPa, the absolute average deviations of the predicted results were obviously smaller.

Intramolecular Cascade Lactone Cyclization of Dicoumarol Derivatives Promoted by Tributyltin Chloride

Dicoumarols, derived from aldehydes with ortho hydroxy substitution (5 and 7), were successfully cyclized by Sn(n-Bu)3Cl in THF as a reaction medium. Catalytic cycle reveals the formation of HO-Sn-O=C cyclic intermediate which is rearranged and isomerized to the cyclic lactone. N-butane was released by Sn(n-Bu)3Cl leaving behind Sn(n- Bu)2(OH)Cl keeping the catalytic route continued unless the two butane attached to tin were also consumed. The products produced were characterized using 1H, 13C{1H}-NMR, high resolution EI-MS, IR and elemental analyses. Single crystals of 6 were grown in P1 space group from concentration in THF and structurally studied using X-ray diffraction analysis. All the spectroscopic and analytical studies supported the formation of the cyclized products. Keywords: Sn(n-Bu)3Cl, dicoumarol, intramolecular cyclization, single crystal study, lactone.

THF Exchange and Molecular Dynamics in the Series (BDI)MgX(THF), Where X = Bun, NEt2, and OBut and BDI = 2-[(2,6-Diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]pent-2-ene

The complexes (BDI)MgX(THF), where X = Bu(n), NEt2, and OBu(t), are shown to undergo THF exchange at low added concentrations of THF by a dissociative mechanism: X = Bu(n), ΔH(#) (kcal mol(-1)) = 13.4 ± 0.4 and ΔS(#) (cal mol(-1) K(-1)) = 6.3 ± 1.6; X = NEt2, ΔH(#) (kcal mol(-1)) = 15.2 ± 0.5 and ΔS(#) (cal mol(-1) K(-1)) = 11.4 ± 2.3; X = OBu(t), ΔH(#) (kcal mol(-1)) = 16.4 ± 0.3 and ΔS(#) (cal mol(-1) K(-1)) = 9.5 ± 1.3. The apparent aryl group rotations involving the BDI ligands have, within experimental error, the same activation parameters as the THF dissociation, which suggests that the two are correlated involving a three coordinate reactive intermediate akin to what is well-known for related (BDI)ZnR compounds involving three-coordinate trigonal planar Zn(2+). At higher concentrations of THF for X = Bu(n) and OBu(t), but not for X = NEt2, the coalescence temperatures for apparent aryl group rotation are depressed from those of the pure compounds in toluene-d8, and evidence is presented that this correlates with an associative interchange process which becomes dominant in neat THF. We estimate the Ia mechanism to have activation parameters: ΔH(#) (kcal mol(-1)) = 5.4 ± 0.1 and ΔS(#) (cal mol(-1) K(-1)) = -20.9 ± 0.3 for X = Bu(n) and ΔH(#) (kcal mol(-1)) = 8.3 ± 0.8 and ΔS(#) (cal mol(-1) K(-1)) = -19.8 ± 3.0 for X = OBu(t). For the complex (BDI)MgBu(n)(2-MeTHF), the dissociative exchange with added 2-MeTHF occurs more readily than for its THF analogue, as expected for the more sterically demanding Lewis base O-donor: ΔH(#) (kcal mol(-1)) = 12.8 ± 0.5 and ΔS(#) (cal mol(-1) K(-1)) = 8.6 ± 1.8. At very low temperatures in toluene-d8, restricted rotation about the Mg-O(THF) bond is observed for the complexes where X = NEt2 and OBu(t) but not for the complex where X = Bu(n). These observations, which have been determined from dynamic NMR studies, are correlated with the reactivities of these complexes in solution.

Preparation and Properties of Electrospun PVC Nanofiber

Nanofibrous membranes based on poly (vinyl chloride) (PVC) were prepared by electrospinning. The morphology of nanofibrous was observed under field emission scanning electron microscope (FE-SEM) and effects of instrument parameters including electric voltage, tip to collector distance, and solution parameters such as PVC concentration and mixed solvent of THF and DMF (50:50) were evaluated. The beads on the fiber were formed with low concentration of PVC. The dielectric constant, thermal properties and crystallinity of the electrospun membranes were characterized by precision LCR meter, and differential thermal analysis (DTA), respectively. It was found that smooth surface of electrospun PVC nanofiber had a high ionic conductivity and their thermal properties were improved comparing with PVC sheet.

Thermodynamic surface properties of [BMIm][NTf2] or [EMIm][NTf2] binary mixtures with tetrahydrofuran, acetonitrile or dimethylsulfoxide

The surface tension, σ, of binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf2] with tetrahydrofuran (oxolane, thf), acetonitrile, dimethylsulfoxide ((methylsufinyl)methane, dmso) and of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [EMIm][NTf2] with dimethylsufoxide was measured between (293.15 and 313.15)K using the pendant drop method. On the basis of experimental σ values and activity coefficients of solutes in their solutions with ionic liquid obtained from vapor pressure measurement, Gibbs excess surface concentrations of thf, acetonitrile or dmso in mixtures with [BMIm][NTf2] or [EMIm][NTf2] were determined. The results are discussed in terms of possible interactions between ILs and aprotic polar substances.

Behavior of Hydrophobic Polyelectrolyte Solution in Mixed Aqueous/Organic Solvents Revealed by Neutron Scattering and Viscosimetry

We investigate in this paper the influence of the improvement of the solvent quality on the structure and the viscous properties of solutions of an hydrophobic polyelectrolyte, poly(styrene-co-sodium styrenesulfonate): PSS. The solvent used is a mixture of water and an organic solvent, THF, which is also slightly polar. We use small angle neutron scattering in the semidilute regime and viscosimetry as a function of concentration in dilute and semidilute unentangled regime. The structure, namely the scattering from all chains, is characterized by a maximum ("polyelectrolyte peak"). Its position and amplitude depends, at a given sulfonation rate of PSS, on the solvent quality through the added amount of organic solvent (THF). These evolutions with the THF amount are more pronounced when the sulfonation rate f is low (more hydrophobic polyelectrolyte) and the amount of added THF is high. Adding THF to hydrophobic PSS (f = 0.50 or f = 0.38), diminishes also the "shoulder" visible in the log I - log q plot and associated with the pearl size. It is therefore proposed that when THF is added to aqueous polyelectrolyte solutions, the pearls are dissolved and the chain conformation evolves from the pearl-necklace shape already reported in pure water toward the string-like conformation in pure water for fully sulfonated PSS. An addition of THF also reduces the important low q upturn found with hydrophobic polyelectrolyte solutions: the large aggregates are dissolved by THF. The upturn can become for PSSNa f = 0.38, after adding enough THF (50%), even smaller than that for the charged hydrophilic case PSSNa f = 0.82, in water. This can mean that in the quasi-fully charged PSS at f = 0.82 there are still hydrophobic effects in water, which is disagreeing with our recent reports, or that the electrostatics contribution to the upturn is reduced due to a lower dielectric permittivity. Concerning the hydrophilic polyelectrolyte, poly(sodium-2-acrylamido-2-methylpropanesulfonate)-co-(acrylamide): AMAMPS, no evolution in structure occurs until 25% THF. The viscosimetry variation with THF fraction is in good agreement with the scattering one up to 25%: though little dependent on THF for AMAMPS, and for hydrophilic PSSNa, it increases for hydrophobic PSSNa in agreement with the chain expansion signaled by scattering. At 50% THF concentration, the hydrophilic polyelectrolyte shows new surprising behaviors: the scattering of PSSNa is no longer characteristic of polyelectrolytes, and AMAMPS solutions display an unexpected viscosity decrease.

Photoresponsive submicron-sized hollow spheres obtained from amphiphilic azobenzene-containing random copolymer

This article reports the formation, morphology control, and photoresponsive properties of submicron-sized hollow spheres of an amphiphilic azobenzene-containing random copolymer (PEAPE). The hollow spheres were obtained by diluting the polymer disperse at 50 vol% water content with THF–water (v:v = 1:1) and slowly removing THF by evaporation. The size and shell thickness of the hollow spheres were determined by the polymer initial concentration in THF, water addition rate, and diluent volume. The ratio of the average shell thickness to the hollow sphere size was mainly affected by the diluent volume. By adjusting these factors, the size and shell thickness of the hollow spheres could be well controlled. The photoisomerization study indicated that hollow spheres possessed a compactly packed shell with density similar to that of their counterparts with solid interiors. Upon UV light irradiation, the hollow spheres in dispersions showed different photoresponsive properties depending on their size and shell thickness. For the “vesicle-like” spheres with a thin shell, photoinduced disaggregation was observed when irradiated with the 365 nm UV light.