Mixed Solvent Of Tetrahydrofuran Research Articles

Acid-Cleavable Aromatic Polymers for the Fabrication of Closed-Loop Recyclable Plastics with High Mechanical Strength and Excellent Chemical Resistance.

Although closed-loop recycling of dynamic covalent bond-based plastics does not require catalysts, their mechanical strength and chemical stability remain a major concern. In this study, closed-loop recyclable poly(aryl imine) (PAI) plastics with high mechanical strength and excellent chemical resistance are fabricated by copolymerizing aromatic amines and aromatic aldehydes through dynamic imine bonds. The resulting PAI plastic with a tensile strength of 58.2 MPa exhibits excellent chemical resistance and mechanical stability in acidic and basic aqueous solutions and various organic solvents. The PAI plastics can be depolymerized in a mixed solvent of tetrahydrofuran (THF)/HCl aqueous solution through the dissociation of imine bonds, and the monomers can be facilely recovered with high purity and isolated yields due to the solubility difference between the aromatic amines and aromatic aldehydes in selective solvents. The efficient closed-loop recycling of the PAI plastic can also be realized through monomer conversion because the hydrolysis of the aromatic aldehydes generates aromatic amines. The recovered monomers can be used to re-fabricate original PAI plastics. This PAI plastic can be selectively recovered from complicated mixed polymer waste streams due to the mild depolymerization conditions of the PAI plastic and its high stability in most organic solvents.

Acid‐Cleavable Aromatic Polymers for the Fabrication of Closed‐Loop Recyclable Plastics with High Mechanical Strength and Excellent Chemical Resistance

AbstractAlthough closed‐loop recycling of dynamic covalent bond‐based plastics does not require catalysts, their mechanical strength and chemical stability remain a major concern. In this study, closed‐loop recyclable poly(aryl imine) (PAI) plastics with high mechanical strength and excellent chemical resistance are fabricated by copolymerizing aromatic amines and aromatic aldehydes through dynamic imine bonds. The resulting PAI plastic with a tensile strength of 58.2 MPa exhibits excellent chemical resistance and mechanical stability in acidic and basic aqueous solutions and various organic solvents. The PAI plastics can be depolymerized in a mixed solvent of tetrahydrofuran (THF)/HCl aqueous solution through the dissociation of imine bonds, and the monomers can be facilely recovered with high purity and isolated yields due to the solubility difference between the aromatic amines and aromatic aldehydes in selective solvents. The efficient closed‐loop recycling of the PAI plastic can also be realized through monomer conversion because the hydrolysis of the aromatic aldehydes generates aromatic amines. The recovered monomers can be used to re‐fabricate original PAI plastics. This PAI plastic can be selectively recovered from complicated mixed polymer waste streams due to the mild depolymerization conditions of the PAI plastic and its high stability in most organic solvents.

Intramolecular and Intermolecular Interaction Switching in the Aggregates of Perylene Diimide Trimer: Effect of Hydrophobicity

The research on perylene diimide (PDI) aggregates effectively promotes their applications in organic photovoltaic solar cells and fluorescent sensors. In this paper, a PDI fabricated with three peripheral PDI units (N, N'-bis(6-undecyl) perylene-3,4,9,10-bis(dicarboximide)) is investigated. The trimer shows different absorption and fluorescence properties due to hydrophobicity when dissolved in the mixed solvent of tetrahydrofuran (THF) and water. Through comprehensive analysis of the fluorescence lifetime and transient absorption spectroscopic results, we concluded that the trimer underwent different excited state kinetic pathways with different concentrations of water in THF. When dissolved in pure THF solvent, both the intramolecular charge-transfer and excimer states are formed. When the water concentration increases from 0 to 50% (v/v), the formation time of the excimer state and its structural relaxation time are prolonged, illustrating the arising of the intermolecular excimer state. It is interesting to determine that the probability of the intramolecular charge-transfer pathway will first decrease and then increase as the speed of intermolecular excimer formation slows down. The two inflection points appear when the water concentration is above 10% and 40%. The results not only highlight the importance of hydrophobicity on the aggregate properties of PDI multimers but also guide the further design of PDI-based organic photovoltaic solar cells.

Cluster Analysis of Soluble Organic Fractions in Two Low-Rank Coals

A brief overview of the composition and structure of soluble organic compounds as well as organic macromolecules in coal is sufficient to support the development of the coal chemical industry and realize the clean, effective, and high value-added exploitation of coal. In this study, 14 groups of extracts were analyzed by a gas chromatograph-mass spectrometer; seven stages of solvent-graded extraction were carried out on two typical low-rank coals, and the extracted substance spectrum data were processed by principal component analysis and cluster analysis to investigate the molecular makeup and structure of the soluble organic compounds in the two coals. CS2 had a better extraction effect on aromatic hydrocarbons, and methanol was better for the enrichment and separation of oxygenated compounds. Hexane and petroleum ethers have a good extraction effect for aliphatic hydrocarbons; benzene has a good effect for the extraction of nitrogenous compounds; acetone has a greater extraction rate for alcohols; tetrahydrofuran has a more obvious extraction effect for ketones; the mixed solvent of tetrahydrofuran and methanol has a greater extraction rate for esters.

Precise synthesis of α,ω-chain-end functionalized poly(dimethylsiloxane) with azide groups based on metal-free ring-opening polymerization and a quantitative azidation reaction

We have so far developed a method for the controlled ring-opening polymerization of cyclotrisiloxane catalyzed by strong organobasic compounds to produce various chain-end functionalized polysiloxanes with controlled number-average molar mass (Mn) and narrow molar-mass dispersity (ÐM) values. In this study, well-defined α,ω-chain-end functionalized poly(dimethylsiloxane) with azide groups (N3-PDMS-N3) possessing a narrow ÐM range (ÐM = 1.04) and a relatively high Mn of up to 28.2 kg mol−1 was precisely synthesized in a mixed solvent of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) in the presence of quaternary ammonium salts as catalysts; N3-PDMS-N3 was obtained by converting α,ω-chain-end functionalized PDMS with bromomethyl groups (Br-PDMS-Br), which was prepared by polymerizing hexamethylcyclotrisiloxane (D3), water, and 1,3-trimethylene-2-n-propylguanidine (TMnPG) as the monomer, the initiator, and the catalyst, respectively. It was necessary to choose proper solvents depending on the Mn of Br-PDMS-Br to achieve the complete conversion of the bromomethyl groups by the azidation reaction. Moreover, we demonstrate the model reaction of copper-catalyzed 1,3-dipolar cycloaddition between N3-PDMS-N3 and phenylacetylene. As a result, the cycloadducted compound was exclusively obtained while maintaining a low ÐM value of 1.06 by employing copper(I) bromide and triethylamine as the catalyst and the ligand, respectively. This system was also effective for a polymer-polymer coupling reaction. Indeed, we successfully synthesized an ABA-type triblock copolymer where A and B are polystyrene (PS) and PDMS segments by reacting N3-PDMS-N3 with ω-chain-end functionalized PS with an alkynyl group.

Self-Assembly of Single-Diamond-Surface Networks.

Biological scaffolds with hyperbolic surfaces, especially single gyroid and single-diamond structures, have sparked immense interest for creating novel materials due to their extraordinary physical properties. However, the ability of nature to create these unbalanced surfaces has not been achieved in either lyotropic liquid crystals or block copolymer phases due to their thermodynamical instability in these systems. Here, we report the synthesis of a porous silica scaffold with a single-diamond-surface structure fabricated by self-assembly of the poly(ethylene oxide)-b-polystyrene-b-poly(L-lactide) and silica precursors in a mixed solvent of tetrahydrofuran and water. The single-diamond structure with tetrahedral interconnected frameworks was revealed by the electron crystallographic reconstruction. We assume that the formation of single networks is induced by the structural transition and related to the energetic change due to the fluctuations of the Gaussian curvature. This work may provide new insights into these biologically relevant surfaces and related self-assembly systems.

Self‐Assembly of Single‐Diamond‐Surface Networks

AbstractBiological scaffolds with hyperbolic surfaces, especially single gyroid and single‐diamond structures, have sparked immense interest for creating novel materials due to their extraordinary physical properties. However, the ability of nature to create these unbalanced surfaces has not been achieved in either lyotropic liquid crystals or block copolymer phases due to their thermodynamical instability in these systems. Here, we report the synthesis of a porous silica scaffold with a single‐diamond‐surface structure fabricated by self‐assembly of the poly(ethylene oxide)‐b‐polystyrene‐b‐poly(L‐lactide) and silica precursors in a mixed solvent of tetrahydrofuran and water. The single‐diamond structure with tetrahedral interconnected frameworks was revealed by the electron crystallographic reconstruction. We assume that the formation of single networks is induced by the structural transition and related to the energetic change due to the fluctuations of the Gaussian curvature. This work may provide new insights into these biologically relevant surfaces and related self‐assembly systems.

A novel AIEE polymer sensor for detection of Hg2+ and Ag+ in aqueous solution

A novel AIEE (aggregation-induced emission enhancement)-active conjugated polymer incorporating thiazole and tetraphenylethene (TPE) was designed and synthesized via Pd-catalyzed Sonogashira coupling reaction. The polymer shows typical AIEE phenomena, and emits green fluorescence in the mixed solvent of tetrahydrofuran (THF) and water, reaching a maximum fluorescence intensity when the fraction of water is 90%. In the aqueous phase (fw = 90%), the polymer sensor exhibits “turn-off” fluorescence quenching responses towards Hg2+ and Ag+ over other cations, such as Li+, K+, Ca2+, Mg2+, Ba2+, Zn2+, Cd2+, Co2+, Ni2+, Pb2+, Cu2+, Al3+ and Fe3+. The obvious fluorescence change (bright yellow to weak emission) can be clearly observed by the naked eyes.

Superhydrophobic porous surface fabricated via phase separation between polyhedral oligomeric silsesquioxane-based block copolymer and polyethylene glycol

A superhydrophobic porous film was fabricated by a simple phase separation process between a polyhedral oligomeric silsesquioxane (POSS) based diblock polymer (P) and polyethylene glycol (PEG) in selective solvents. The POSS-based hybrid diblock polymer was synthesized using a two-step atom transfer radical polymerization method. The polymer, along with PEG, was dissolved in mixed solvents of tetrahydrofuran (THF) and ethanol (AC), and then dip-coated onto the glass slides to form a coating film. After PEG was washed away using water, the polymer film with nano-micrometer dual-scale roughness on the slides was formed due to the phase separation. Then, a superhydrophobic porous film was obtained after surface modification with low surface energy material. The effects of POSS content, P/PEG ratio, and AC/THF ratio were investigated. The results showed that the water contact angle increased with the PEG content within a certain range and the surface roughness was enhanced after adding AC. When the POSS content was 25.3% (P2), the ratio of P2/PEG was 5:5 and AC/THF was 3:7, the film after modification had a static water contact angle of 155.1° and a sliding angle of 6.5°, demonstrating superhydrophobicity.

Tailoring the grooved texture of electrospun polystyrene nanofibers by controlling the solvent system and relative humidity.

In this study, we have successfully fabricated electrospun polystyrene (PS) nanofibers having a diameter of 326 ± 50 nm with a parallel grooved texture using a mixed solvent of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF). We discovered that solvent system, solution concentration, and relative humidity were the three key factors to the formation of grooved texture and the diameter of nanofibers. We demonstrated that grooved nanofibers with desired properties (e.g., different numbers of grooves, widths between two adjacent grooves, and depths of grooves) could be electrospun under certain conditions. When THF/DMF ratio was higher than 2:1, the formation mechanism of single grooved texture should be attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. When THF/DMF ratio was 1:1, the formation mechanism of grooved texture should be ascribed to the formation of wrinkled surface on the jet surface at the early stage of electrospinning and subsequent elongation into a grooved texture. Such findings can serve as guidelines for the preparation of grooved nanofibers with desired secondary morphology.

New Morphologies and Phase Transitions of Rod–Coil Dendritic–Linear Block Copolymers Depending on Dendron Generation and Preparation Procedure

Amphiphilic rod–coil dendritic–linear block copolymers PEG(Gm)-b-PMPCS (where m is the number of dendron generation, and m = 1, 2, 3) composed of a semirigid Percec-type dendron with hydrophilic poly(ethylene glycol) (PEG) tails and a rod-like mesogen-jacketed liquid crystalline polymer, poly{2,5-bis[(4′-methoxy-phenyl)oxycarbonyl]styrene} (PMPCS), were successfully prepared. The self-assembled structures undergo a transition from vesicles through large compound vesicles (LCVs) to short cylindrical micelles with increasing dendron generation. PEG(G2)-b-PMPCS forms stable LCVs with porous surfaces of a narrow size distribution in a mixed solvent of tetrahydrofuran and water. The formation mechanism of the supramolecular structure with nano- and microsized scales is studied through changing the rate of water addition. It is composed of two steps: morphological transformation and vesicles fusion or differentiation. Vesicles are precursors for LCVs regardless of what the initial morphology is. However, the fi...

Study on the enzymatic degradation of PBS and its alcohol acid modified copolymer

Enzymatic hydrolytic degradation of polybutylene succinate (PBS), poly(polybutylenesuccinate-co-1,4-cyclohexane dimethanol) (PBS/CHDM) and poly(polybutylene succinate-co-diglycolic acid) (PBS/DGA) in mixed solvent of tetrahydrofuran (THF) and toluene was examined. Lipase was used as catalyst to degrade polymers with molecular weight of more than 100,000, and the molecular weight of products ranged from hundreds to thousands. Thermal decomposition temperatures of all products were below 250°C. The degradation products of both PBS/CHDM and PBS/DGA showed two melting points at about 85 and 99°C. Mass spectrometry (MS) was employed to obtain the molecular weight of oligomers extracted from the products, which proved to be low-polyesters with the molecular weight of less 1,000. The butanediol (BDO) monomer was found in PBS/CHDM degradation product for the first time.

Reversible thermoresponsive behavior of poly(2-chloroethyl vinyl ether-alt-maleic anhydride) in mixed solvent of tetrahydrofuran/hexane

Poly(2-chloroethyl vinyl ether-alt-maleic anhydride) can exhibit lower critical solution temperature-type phase behavior reversibly by tuning the solvent composition in mixed solvent of tetrahydrofuran (THF) and hexane. The effect of solvent composition and polymer concentration on cloud point of polymer solution was investigated. The cloud point temperature for high molecular weight polymer was lower than that for lower molecular weight polymer. High resolution 1H NMR spectra in mixed solvent of THF-d 8 and hexane were also measured for comprehending thermoresponsive behavior of polymer solution in molecular level; however, any discontinuous change in the NMR signals around the cloud point could not be recognized.

Studies on the electrospun submicron fibers of SIS and its mechanical properties

AbstractThe submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Porous Structures of Polymer Films Prepared by Spin Coating with Mixed Solvents under Humid Condition

We investigate the effects of interfacial energy between water and solvent as well as polymer concentration on the formation of porous structures of polymer films prepared by spin coating of cellulose acetate butyrate (CAB) in mixed solvent of tetrahydrofuran (THF) and chloroform under humid condition. The interfacial energy between water and the solvent was gradually changed by the addition of chloroform to the solvent. At a high polymer concentration (0.15 g/cm3 in THF), porous structures were limited only at the top surfaces of CAB films, regardless of interfacial energies, due to the high viscosity of the solution. At a medium concentration (approximately 0.08 g/cm3 in THF), CAB film had relatively uniform pores at the top surface and very small pores inside the film because of the mixing of the water droplets with THF solution. When chloroform was added to THF, pores at the inner CAB film had a comparable size with those at the top surface because of the reduced degree of the mixing between the water droplets and the mixed solvent. A further decrease in polymer concentration (0.05 g/cm3 in THF) caused the final films to have a two-layer porous structure, and the size of pores at each layer was almost the same.

Structural features and mechanical properties of in situ–bonded meshes of segmented polyurethane electrospun from mixed solvents

The relationships between the structural features and mechanical properties of electrospun segmented polyurethane (SPU) meshes and electrospinning parameters such as formulation (e.g., polymer concentration and solvent mixing ratio) and operation parameters (e.g., applied voltage, air gap, and flow rate) were studied with the use of a mixed-solvent system of tetrahydrofuran (THF) and N,N-dimethylacrylamide (DMF). After the relationships between the structure of electrospun SPU and the operation parameters under a fixed SPU concentration of single THF solution were established, SPU was electrospun from the mixed solvent of THF and DMF with different mixing ratios [DMF content: 5, 10, and 30% (v/v)]. Scanning electron microscopy showed that an increase in DMF ratio significantly enhances the degree of bonding between SPU fibers at contact sites and decreases the diameter of fibers formed. The porosimetric characterization showed the following: (1) The porosity of the electrospun SPU meshes decreased with an increase of DMF ratio. (2) The pore size distribution exhibited three representative peaks of different void sizes (i.e., approximately 5, 20, and 70 microm). (3) The proportion of the 20-microm void markedly decreased with an increase in DMF ratio. A tensile test on the meshes showed that an increase in DMF ratio induces an increase in elasticity of the mesh. Such a regulation of the structural features and mechanical properties of electrospun SPU meshes using a mixed-solvent system with low- and high-boiling-point solvents may be useful in the engineering of SPU-fiber based matrices or scaffolds.

Influence of a mixing solvent with tetrahydrofuran and N,N‐dimethylformamide on electrospun poly(vinyl chloride) nonwoven mats

AbstractWe evaluated the effects of the solvent composition with respect to the solution concentration, applied electric field, and tip‐to‐collector distance on the morphology of electrospun poly(vinyl chloride) (PVC) fibers. The solvent volume ratio was strongly correlated with the diameter of the electrospun fibers with respect to the other processing parameters. Electrospun PVC fibers dissolved in tetrahydrofuran (THF) had diameters ranging from 500 nm to 6 μm; those dissolved in N,N‐dimethylformamide (DMF) had an average diameter of 200 nm. The diameters of the electrospun fibers were obtained from narrow to broad distributions with the solvent composition. Also, the diameters of fibers electrospun from a mixed solvent of THF and DMF were less than 1 μm. The mechanical properties of electrospun PVC nonwoven mats depended on the fiber orientation and linear velocity of the drum surface. With increasing linear velocity of the drum surface, electrospun PVC fibers were arranged toward the machine direction, and the dimensions of the spiral path were shorter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2259–2268, 2002

Crystal structure of tris(methylcyclopentadienyl) tetrahydrofuranatosamarium

The first crystal structure of tris(methylcyclopentadienyl) tetrahydrofuranato (THF) lanthanide complexes, (CH3 Cp)3Sm · THF, is determined. The complex crystallizes from mixed solvents of tetrahydrofuran and hexane as a monomer in the orthorhombic space group Pc21 n with the unit cell parameters a = 9.135(2) A, b = 13.263(2) A, c = 16.176(3) A, and Z = 4.

Relationship between Pyrolysis Reactivity and Aromatic Structure of Coal

Illinois No. 6 coal was depolymerized by treatment with trifluoromethanesulfonic acid in methylcyclopentane at 120 °C. The yield of tetrahydrofuran (THF) extract was increased to 89 wt %. This increase was explained by the cleavage of bridges between aromatic units. The extract (TSd fraction) was further hydrogenated using a Ru/carbon catalyst in a mixed solvent of THF and acetic acid at 120 °C for 12−72 h under a hydrogen pressure of 10 MPa. Phenolic resin and polystyrene samples were used as references and were also hydrogenated over Ru/Al2O3 catalyst under the same conditions. After hydrogenation for 72 h, the aromaticity of the hydrogenated TSd fraction (H-TSd fraction), fa, decreased to 0.33 from the original value, 0.6. The pyrolysis reactivity of the treated coals was evaluated using a Curie-point pyrolyzer (CPP) at 500−764 °C in a stream of helium. The reactivity of the TSd fraction was greatly enhanced as a result of the hydrogenation, and 96 wt % of the H-TSd fraction was converted to volatiles during the pyrolysis at 764 °C. A good correlation between the aromaticity and the yield of volatiles was found for both the treated coals and phenolic resins, but not for the polystyrenes. This suggests that pyrolysis reactivity was related to the aromatic structures of the main chains, and that those structures were changed by the hydrogenation.

Conductometric study of lithium halides and thiocyanate in the mixed solvents of tetrahydrofuran and 2-ethyl-1-hexanol

Ion association constants of lithium chloride, bromide and thiocyanate were evaluated by means of conductometry in the mixed solvents of THF (εr=7.58) and 2-ethyl-1-hexanol (εr=7.58) at 25°C. The mixed solvents were assumed to have a nearly constant permittivity but different solvation abilities. Lithium bromide gave a minimum on the molar conductivity Λ (S cm2 mol−1)−c1/2 curve at a rather low salt concentration (cmin=4.9×10−3 mol dm−3) in THF; however, the cmin increased suddenly to 1.2×10−2 mol dm−3 by the addition of 1.0 vol.% alkanol, and increased gradually by the further addition of the alkanol. The cmin for LiSCN increased gradually with increasing content, up to 30 vol.% of the alkanol. The conductivities of LiBr and LiSCN were analyzed by our method to obtain the formation constants of the ion pair (K1), the triple ions (2Li++X−⇌Li2X+, Li++2X−⇌LiX2−; K2=K3) and the quadrupole (K41) in THF, whereas quadrupole formation constants were not needed for explaining the conductivities in the mixed solvents. In the higher concentration range of LiBr and LiSCN in THF, the ion pair and the quadrupole were found to be the predominant species over the single ions or the triple ions. The increase in cmin with increasing content of 2-ethyl-1-hexanol was in good accordance with the decrease in the formation constants of the higher aggregations. A linear relation (the slope of −1.0) was given between log(K2/K1) and log cmin for LiBr and LiSCN in the binary solvent systems. Lithium chloride gave no minimum, not only in THF but also in the mixed solvents, at least ≤10 vol.% of 2-ethyl-1-hexanol, because of a strong trend to form the quadrupole.