Preparation of poly(-caprolactone) grafted titanate nanotubes

This work reported for the first time the surface functionalization of titanate nanotubes (TNTs) with biodegradable poly(-caprolactone) (PCL). A “grafting from” approach based on in situ ring-opening polymerization of -caprolactone from TNTs with a special surface modification was adopted to prepare the PCL-g-TNTs. The thickness of the grafted PCL shell can be controlled by increasing reaction time. After grafted with PCL, both the dissolubility and flexibility of the tubes were greatly improved. The obtained PCL-g-TNTs can easily disperse in several organic solvents, and the dispersal stability depends on solvent polarity and PCL shell thickness. Furthermore, the PCL immobilized on the surface of TNTs still possessed a good biodegradable capacity and could be completely decomposed in the presence of Pseudomonas (PS) lipase. The PCL-g-TNTs reported here are promising in biotechnology applications due to good dissolubility, flexibility, biocompatibility and the tubular nano-structure.     

Synthesis of tadpole-shaped copolyesters based on living macrocyclic poly(-caprolactone)

Synthesis of an asymmetric tadpole-shaped aliphatic copolyester consisting of a poly(-caprolactone) ring and two poly(l-lactide) tails was reported for the first time. First, a high molecular weight cyclic PCL macroinitiator (M_n = 31,000) was prepared by intramolecular photocross-linking of “living” chains. Polymerization of l-lactide was resumed by the tin dialkoxide containing macrocycles, thus making the targeted tadpole-shaped copolyester available. A preliminary investigation of the crystallization of these copolyesters was carried out by differential scanning calorimetry and polarized optical microscopy.     

Novel synthesis of -caprolactam from cyclohexanone-oxime via Beckmann rearrangement over mesoporous molecular sieves MCM-48

Vapor-phase synthesis of -caprolactam (-C) from cyclohexanone-oxime (CHO) has been studied at 1 atm and 300–400 °C using SiMCM-48 and AlMCM-48(X) with Si/Al molar ratios X in a fixed-bed, continuous flow reactor. The catalysts were characterized with ICP-AES, XRD, TEM, FT-IR, N₂-adsorption, ²⁷Al and ²⁹Si MAS NMR and TPD of ammonia. An increase of X value in AlMCM-48(X) enhances both the BET surface area and the unit cell parameter but diminishes the acid amount. In the reaction of CHO, benzene, toluene, ethanol and 1-hexanol were utilized as solvents. The CHO conversion increases with the reaction temperature, whereas the -C selectivity exhibits the opposite trend due to side reactions. The catalyst stability is greatly enhanced by using ethanol and 1-hexanol as the solvents due to their production of water vapor via dehydration. Excellent catalytic performance of AlMCM-48(10) is attained at 1 atm, 350 °C and W/Fc 74.6 g h/mol by using 1-hexanol in the feed; the CHO conversion and the -C selectivity exhibit higher than 99% and 90%, respectively, during at least 130 h process time.     

Enzymatic degradation of poly(propylene carbonate) and poly(propylene carbonate-co--caprolactone) synthesized via CO2 fixation

Poly(propylene carbonate) (PPC) and poly(propylene carbonate-co--caprolactone) (PPCCL) were synthesized via the zinc glutarate catalyzed copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) without and with -caprolactone (CL), respectively. In addition, poly(-caprolactone) (PCL) was prepared via the homopolymerization of CL with the aid of methyl triflate catalyst. The polymer products were characterized in terms of their chemical compositions, molecular weights, and thermal properties. Films of these polymers were tested with a series of enzymes (four different families and a total of 18 enzymes) in a phosphate buffer in order to characterize their enzymatic degradabilities. This is the first report demonstrating that PPC films exhibit positive enzymatic degradability with Rhizopus arrhizus lipase, esterase/lipase ColoneZyme A, and Proteinase K. Moreover, PPCCL films exhibited positive enzymatic degradability with most of the enzymes utilized in our study, and thus PPCCL has an enzymatic degradability comparable to that of PCL. In particular, the PPCCL films exhibit excellent enzymatic degradability with Pseudomonas lipase, Rhizopus arrhizus lipase, and esterase/lipase ColoneZyme A. Considering its excellent enzymatic degradability, the PPCCL terpolymer has potential biomedical applications. In conclusion, ZnGA-catalyzed copolymerizations of CO₂ and PO with or without CL are chemical fixation processes of CO₂ that can be used to produce enzyme-degradable aliphatic polymers.     

Fabrication, biomolecular binding, in vitro drug release behavior of sugar-installed nanoparticles from star poly(-caprolactone)/glycopolymer biohybrid with a dendrimer core

Star poly(amido amine)-b-poly(-caprolactone)-b-poly(d-gluconamidoethyl methacrylate) (PAMAM–PCL–PGAMA) block copolymers with a dendrimer core were synthesized from the ring-opening polymerization of -caprolactone using a hydroxyl-terminated dendrimer poly(amido amine) initiator followed by the direct atom transfer radical polymerization of unprotected glycomonomer. The self-assembly and the biomolecular binding of PAMAM–PCL–PGAMA with Concanavalin A (Con A) were investigated by NMR, UV–vis, dynamic light scattering, and transmission electron microscopy, respectively. Multivalent sugar-installed vesicles and large compound aggregates were self-assembled from these dendritic copolymers in aqueous solution, demonstrating thermodynamically more stable than those self-assembled from linear counterpart. Moreover, these copolymers presented specific biomolecular binding with Con A lectin compared with bovine serum albumin, while both the lower mobility and the higher spatial hindrance within dendritic copolymers, to some extent, limited the clustering between sugar and Con A. Furthermore, these star copolymer nanoparticles showed a higher drug-loading efficiency and less burst release compared with linear counterpart. This work provides a method not only for the synthesis of star PCL/glycopolymer biohybrid with a dendrimer core but also for the fabrication of sugar-installed nanoparticles with tunable clustering ability, good drug-loading efficiency, and controlled drug-release profile useful for targeted drug delivery system.     

Novel synthetic strategy toward shape memory polyurethanes with a well-defined switching temperature

Shape memory polyurethanes (SMPUs) have been synthesised via a novel synthetic methodology, resulting in an improvement of the phase separation in the multi-block structure of the polyurethane and in its shape memory properties. ABA block copolymers based on semi-crystalline poly(-caprolactone) and amorphous poly(propylene oxide) (PPO) were used as precursor for the SMPUs. For their synthesis, poly(-caprolactone) diols have been converted into isocyanate end-capped prepolymers by using a mixture of 3(4) isocyanato-1-methyl-cyclohexylisocyanate isomers, after which a coupling with low-T_g poly(propylene oxide) oligomers is done. The shape memory polymers are obtained by reaction of the ABA block copolymers with hexamethylenediisocyanate and 1,4-butanediol as chain extender. Using this new strategy, a flexible segment (PPO) was introduced between the hard and the switching segments of the SMPU. For comparison, SMPUs without flexible segment have also been prepared with the conventional synthetic route. DSC, isostrain experiments and cyclic shape memory tests revealed narrower switching temperatures for the SMPUs including a flexible segment.     

Development of mesoporous Al,B-MCM-41 materials: Effect of reaction temperature on the catalytic performance of Al,B-MCM-41 materials for the cyclohexanone oxime rearrangement

A series of aluminum–boron–silicate MCM-41 mesoporous materials and their counterparts treated with NH₄F aqueous solution were synthesized and characterized by using XRD, MAS NMR, nitrogen physisorption, DRIFT, TG-DTA, TP/MS and pyridine adsorption. All of the samples showed typical MCM-41 structural and textural properties. ²⁷Al MAS NMR showed that the aluminum environment was mainly four-coordinated and six-coordinated aluminum for non-fluorinated samples and fluorinated ones, respectively. Boron was in the trigonal framework environment at ca. catalytic reaction temperatures and the NH₄F treatment did not affect the boron environment in our Al,B-MCM-41 materials. All of the Al,B-MCM-41 materials studied contained both Brønsted and Lewis acid sites. However, the strong acid Brønsted/Lewis ratios decreased in the fluorinated catalysts. Moreover, the influence of temperature was studied on the cyclohexanone oxime conversion and the product selectivity in the 623–798 K range. Results indicated that temperatures lower than 748 K favored Beckmann rearrangement to -caprolactam, whereas, at higher temperatures the main reaction was cyclohexanone oxime hydrolysis to cyclohexanone. The aluminum–boron–silicate MCM-41 mesoporous materials treated with NH₄F improved both the selectivity to -caprolactam (related mainly to boron content) and their life span (related to their lower ratios of strong Brønsted/Lewis acid sites).     

Efficient ring-opening polymerization of -caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

A number of new anilido-imine–Al complexes ortho-C₆H₄(CHNAr¹)(NAr²)AlMe₂ [Ar¹ = C₆H₅, Ar² = C₆H₅ (2a); Ar¹ = 2,6-Me₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2b); Ar¹ = 2,6-Et₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2c); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2d); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2e)] were synthesized, characterized and used as initiators for the ring-opening polymerization of -caprolactone in the presence of benzyl alcohol. The effect of initiator structure and reaction conditions, such as benzyl alcohol/Al molar ratio and reaction temperature on the reactivity, and polymer molecular weight were investigated. The polymerization of -caprolactone initiated by these complexes was found to take place in an immortal fashion.     

Cs exchanged phosphotungstic acid as an efficient catalyst for liquid-phase Beckmann rearrangement of oximes

Cs exchanged phosphotungstic acid is a highly efficient and environmentally benign solid acid catalyst for the liquid-phase Beckmann rearrangement of ketoximes to the corresponding amides. The catalysts Cs_xH_3−xPW₁₂O₄₀ (x = 1.5, 2, 2.5 and 3) were prepared by a titration method. The characterization results indicated that the primary Keggin structure remained intact after exchanging the protons with Cs ions. Moreover, the Cs exchanged catalysts were insoluble and exhibited larger BET surface area than the parent acid. The catalysts exhibited high reactivity and selectivity for the formation of -caprolactam, the precursor of Nylon 6, from cyclohexanone oxime. The catalyst can be recovered after reaction without any structural transformation.     

Acid- and base-catalyzed hydrolyses of aliphatic polycarbonates and polyesters

Poly(propylene carbonate) (PPC) was synthesized by the zinc glutarate catalyzed copolymerization of carbon dioxide and propylene oxide (PO). Hydrolytic degradability of the PPC polymer was examined in tetrahydrofuran solutions containing 10 wt.% acidic or basic aqueous solutions of varying pH using viscometry and GPC analysis. Further, the hydrolysis behaviors of all PPC solutions were compared with those of poly(-caprolactone) (PCL) and poly(d,l-lactic acid) (PLA). All polymers studied show higher degradability in strong basic conditions than in strong acidic conditions, but very low degradability in moderate acidic, basic and neutral conditions. Moreover, PPC is degraded less in strong acidic conditions than the polyesters, while in strong basic conditions, the polycarbonate is more easily degraded. The difference in degradabilities of these polymers in acidic conditions is associated with the different nucleophilicities of their carbonyl oxygen atoms, while in basic conditions the differences are associated with the different electrophilicities of the corresponding carbonyl carbon atoms. With regard to the hydrolysis results and the structural and chemical nature of the polymer backbones, degradation mechanisms are proposed for the acid- and base-catalyzed hydrolyses of PPC, PCL and PLA.     

Modelling and simulation of a gas–solids dispersion flow in a high-flux circulating fluidized bed (HFCFB) riser

Radial solids velocity profiles were computed on seven axial levels in the riser of a high-flux circulating fluidized bed (HFCFB) using a two-phase 3-D computational fluid dynamics model. The computed solids velocities were compared with experimental data on a riser with an internal diameter of 76 mm and a height of 10 m, at a high solids flux of 300 kg m⁻² s⁻¹ and a superficial velocity of 8 m s⁻¹. Several hundreds of experimental and numerical studies on CFBs have been carried out at low fluxes of less than 200 kg m⁻² s⁻¹, whereas only a few limited useful studies have dealt with high solids flux. The k– two-phase turbulence model was used to describe the gas–solids flow in an HFCFB. The model predicts a core–annulus flow in the dilute and developed flow regions similar to that found experimentally, but in the region of highest solids concentration it is somewhat overpredicted at the level close to the inlet.     

Aerobic oxidation of alcohols over novel crystalline MoVO oxide

Novel crystalline MoVO oxide was employed as the catalyst in the aerobic oxidation of alcohols to the corresponding carbonyl compounds. Reactions were mainly conducted at 353 K in pure oxygen or air (1 atm). The selectivities for benzaldehydes were more than 95% in all cases. The conversions of benzyl alcohols varied from 10% to 99% depending on the substituent. A Hammett plot gave a moderate ρ-value of −0.249 (r² = 0.98), suggesting that the reaction processes may involve hydride abstraction. The oxidation of primary alkanols afforded aldehydes, and secondary alcohols were mainly dehydrated to olefins. It was found that the conversion of linear alkanols decreased with the length of alkanols. Kinetic analysis showed that catalytic reaction rate was first-order dependent on the concentrations of substrate and of catalyst. The apparent activation energy was estimated to be 45.7 kJ mol⁻¹. Catalytic reactions took place on the 6- or 7-member rings on the a–b basal plane, where highly dense unsaturated metal cation centers and oxygen anion might serve as catalytic active sites.     

Numerical studies of a tube-in-tube helically coiled heat exchanger

In the present study a tube-in-tube helically coiled (TTHC) heat exchanger has been numerically modeled for fluid flow and heat transfer characteristics for different fluid flow rates in the inner as well as outer tube. The three-dimensional governing equations for mass, momentum and heat transfer have been solved using a control volume finite difference method (CVFDM). The renormalization group (RNG) k– model is used to model the turbulent flow and heat transfer in the TTHC heat exchanger. The fluid considered in the inner tube is compressed air at higher pressure and cooling water in the outer tube at ambient conditions. The inner tube pressure is varied from 10 to 30 bars. The Reynolds numbers for the inner tube ranged from 20,000 to 70,000. The mass flow rate in the outer tube is varied from 200 to 600 kg/h. The outer tube is fitted with semicircular plates to support the inner tube and also to provide high turbulence in the annulus region. The overall heat transfer coefficients are calculated for both parallel and counter flow configurations. The Nusselt number and friction factor values in the inner and outer tubes are compared with the experimental data reported in the literature. New empirical correlations are developed for hydrodynamic and heat-transfer predictions in the outer tube of the TTHC.     

Structure and magnetic properties of Fe1−xCox nanowires in self-assembled arrays

Fe_1−xCo_x nanowires in self-assembled arrays with varying compositions were produced by the template-assisted pulsed electrochemical deposition method. The structural and magnetic properties of the arrays were investigated using several experimental techniques. TEM analyses indicated that the nanowires were regular, uniform, 8 μm in length and 50 nm in diameter. The results of X-ray diffraction indicated that the body-centered-cubic (bcc) (α), face-centered-cubic (fcc) (γ), and hexagonal-close-packed (hcp) () Fe–Co phases appeared in different compositions. Magnetic measurements showed that the coercivity and squareness of the hysteresis loops of the Fe_1−xCo_x changed with their compositions, which may be attributable to shape anisotropy. The room temperature ⁵⁷Fe Mössbauer spectra of the arrays of the Fe_1−xCo_x nanowires revealed strong shape anisotropy.     

Fischer-Tropsch Synthesis: Catalyst activation of low alpha iron catalyst

Activation with three different gases (H₂, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H₂ generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe₅C₂ and Magnetite with only 12% -Fe_2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe₅C₂ than -Fe_2.2C. The initial high (64%) content of -Fe_2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe₅C₂ increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe₅C₂ and 16% -Fe_2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H₂ to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO₂ selectivity.     

HDS of benzothiophene and dihydrobenzothiophene over sulfided Mo/γ-Al2O3

The hydrodesulfurization (HDS) of benzothiophene (BT) and dihydrobenzothiophene (DHBT) was studied over a sulfided Mo/γ-Al₂O₃ catalyst at 5 MPa and 280 and 300 °C. In the absence of H₂S, benzothiophene reacted by hydrogenation to dihydrobenzothiophene and by hydrogenolysis to ethylbenzene (EB), and dihydrobenzothiophene reacted by hydrogenolysis to ethylbenzene. H₂S inhibited both hydrogenation and hydrogenolysis, but the latter much more strongly. The reverse inhibition was observed for 2-methylpiperidine (MPi). In the presence of H₂S and/or 2-methylpiperidine, dihydrobenzothiophene reacted to ethylbenzene as well as by total hydrogenation to octahydrobenzothiophene, and on to ethylcyclohexenes and ethylcyclohexane. Dihydrobenzothiophene did not react back to benzothiophene at and below 300 °C, while the equivalent tetrahydrodibenzothiophene reacted fast to an equilibrium with tetrahydrodibenzothiophene, due to stabilization of the vinylic bond by the alkyl groups. The observed products and kinetic results were explained by a model in which the CS bonds were mainly broken by hydrogenolysis.     

Bis(4′-phenyl-2,2′:6′,2″-terpyridine)ruthenium(II): Holding the {Ru(tpy)2} embraces at bay

The solid state structure of [Ru(Phtpy)₂][PF₆]₂ · 4MeCN has been determined (Phtpy = 4′-phenyl-2,2′:6′,2″-terpyridine); [Ru(Phtpy)₂]²⁺ cations pack into sheets by virtue of {M(tpy)₂}₂ embraces, and the MeCN solvent molecules are involved in NH–C interactions which prevent the efficient packing of adjacent sheets. Comparisons with related structures lead to some generalizations about packing motifs in salts containing [M(Phtpy)₂]²⁺ or [M(pytpy)₂]²⁺ cations (pytpy = 4′-pyridyl-2,2′:6′,2″-terpyridine).     

Performance of Pd catalysts supported on nanocrystalline α-Al2O3 and Ni-modified α-Al2O3 in selective hydrogenation of acetylene

Nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ have been prepared by sol–gel and solvothermal methods and employed as supports for Pd catalysts. Regardless of the preparation method used, NiAl₂O₄ spinel was formed on the Ni-modified α-Al₂O₃ after calcination at 1150 °C. However, an addition of NiO peaks was also observed by X-ray diffraction for the solvothermal-made Ni-modified α-Al₂O₃ powder. Catalytic performances of the Pd catalysts supported on these nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ in selective hydrogenation of acetylene were found to be superior to those of the commercial α-Al₂O₃ supported one. Ethylene selectivities were improved in the order: Pd/Ni-modified α-Al₂O₃–sol–gel > Pd/Ni-modified α-Al₂O₃-solvothermal ≈ Pd/α-Al₂O₃–sol–gel > Pd/α-Al₂O₃-solvothermal  Pd/α-Al₂O₃-commerical. As revealed by NH₃ temperature program desorption studies, incorporation of Ni atoms in α-Al₂O₃ resulted in a significant decrease of acid sites on the alumina supports. Moreover, XPS revealed a shift of Pd 3d binding energy for Pd catalyst supported on Ni-modified α-Al₂O₃–sol–gel where only NiAl₂O₄ was formed, suggesting that the electronic properties of Pd may be modified.     

Fabrication and Physical Properties of Poly(ε‐Caprolactone)/Modified Graphene Nanocomposite

A chemical strategy is attempted to modify graphene for its facilitated dispersion in poly(ε‐caprolactone) (PCL) matrix. Herein, graphite oxide is subjected to sequential treatment with phenyl isocyanate and vitamin C (VC) to yield graphene nanosheets (iG‐VC). It is noteworthy that following the reduction treatment, iG‐VC graphene sheets exfoliate within the PCL matrix and show appreciable interfacial compatibility with PCL matrix in organic solvent by virtue of improved polarity from isocyanate treatment. The tensile yield strength and Young's modulus of the PCL/iG‐VC composite exhibit pronounced enhancement as compared to neat PCL, despite of mere composition of graphene sheets. The tensile yield stress of composite is increased notably to reach 18.6 MPa at 3 wt% graphene sheets as compared to neat PCL. Likewise, Young's modulus of composite is observed to increase from 370 to 470 MPa at 5 wt% graphene sheets. Moreover, the crystallization temperature (T _c) and crystallinity of PCL increase significantly upon incorporation of small amount of iG‐VC. Ultimately, functional role of iG‐VC graphene sheets is demonstrated in enhancing electrical conductivity of PCL‐based nanocomposites. The plausible mechanisms are also proposed to explain the increased T _c, improved mechanical property, and improved electrical conductivity of PCL/iG‐VC composite.

     

Adsorption mechanism and property of novel composite material PMAA/SiO2 towards phenol

In this paper, functional macromolecule poly(methacrylic acid) (PMAA) was grafted on the surface of silica gel particles using 3-methacryloxypropyl trimethoxysilane (MPS) as intermedia, and the grafted particle PMAA/SiO₂ with strong adsorption ability for phenol was prepared. The adsorption mechanism and properties of PMAA/SiO₂ for phenol were researched by static and dynamic methods. The experimental results showed that PMAA/SiO₂ possesses strong adsorption ability for phenol with interaction of three kinds of hydrogen bonds including peculiar O–Hπ hydrogen bond (aromatic hydrogen bond) and O–HOC π hydrogen bond. The saturated adsorption amount could reach up to 162.88 mg g⁻¹. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and temperature were found to have great influence on the adsorption amount. Finally, PMAA/SiO₂ was observed to possess excellent reusability properties as well.