Synthesis and thermal properties of hetero-bifunctional PLA oligomers and their stereocomplexes

Hetero-telechelic, low-molecular-weight polylactides (PLAs) were prepared by the zinc-catalyzed ring-opening polymerization of l-lactide or d-lactide using functional initiators and subsequent reaction with termination reagents, yielding –OH, –COOH, –NH₂ and –SH as functional chain ends. Structural characterization was performed by molecular weight analysis, NMR spectroscopy and MALDI-TOF mass spectrometry. The thermal behavior of the species was investigated by DSC, which revealed that the modification of the hydroxyl terminus lowered the number of lactic acid units within a PLA chain that can effectively participate in crystallization. Both the T_m and ΔH_m values for these polymers were lower compared to those of PLAs of comparable chain length with no modification of the hydroxyl end-group. In stereocomplexes prepared from equimolar amounts of the hetero-telechelic PLLAs and PDLAs, this suppressive effect on T_m and ΔH_m was also observed. Modification of the hydroxyl ends to produce –COOH, –NH₂ and –SH end groups reduced the stereocomplex T_m values to ～10–20 °C. The lower limit for the crystallization of the stereocomplexes was found at a DP of 5.     

Efficient Dispersants for TiO2 Nanopowder in Organic Suspensions

This article discusses the appropriate dispersant for titania (TiO₂) nanopowder in organic‐based suspensions. Four types of oleyl‐based dispersants, namely, oleyl alcohol, oleic acid, oleylamine, and oleyl phosphate, which have the functional groups hydroxyl (–OH), carboxyl (–COOH), amino (–NH₂), and phosphorous [–P(=O)(OH)₂], respectively, were compared for their ability to disperse TiO₂. Experimental results for zeta potential, adsorption, FT‐IR spectroscopy, and rheology, as well as theoretical calculations, indicate that dispersants with –P(=O)(OH)₂ and –NH₂ were more efficient than those with –COOH or –OH. The primary reason for this difference is related to the different interactions of TiO₂ with various dispersants and to different dispersion mechanisms. In addition to the major functional groups, –OH in the chemical structure of dispersants was important, as it might have other effects such as destabilization of the suspensions.     

Adsorption of binary CO2/CH4 mixtures using carbon nanotubes: Effects of confinement and surface functionalization

Effect of confinement and surface functionalization in carbon nanotubes (CNTs) on the competitive adsorption of a binary CO₂/CH₄ mixture has been investigated by grand canonical Monte Carlo simulations. Adsorption using CNTs with different functionalization arrangements, different diameters, different functionalization degrees, and different functional groups, such as –COOH, –CO, –OH, –CH₃, is investigated. Effects of (a) the pore textural properties, such as pore size and accessible surface area, and (b) the gas–adsorbent interaction, especially the electrostatic interaction, are discussed. From these results, we discuss the impact that variables such as confinement and surface functionalization have on the performance for CO₂ separation.     

Synthesis of organo-functionalized mesoporous silica hollow nanospheres via in situ generated template method

A facile one-pot method has been developed for the synthesis of organo-functionalized mesoporous silica hollow nanospheres using TEOS, (R′O)₃Si-R-Si(OR′)₃ or R-Si(OR′)₃ as silane precursors and CTAB as surfactant in ethanol–water/ammonia medium. The study shows that silica nanospheres formed by TEOS acts as in situ generated “soluble” template for the formation of hollow nanostructures. Different kinds of organic moieties such as –CH₂CH₂–, –C₆H₄–, –CH₂C₆H₄CH₂–, –CH₂CH₂CH₂NHCH₂CH₂CH₂–, –CH₂CH₂CH₂NH₂ could be successfully incorporated in the framework of hollow nanospheres.     

Preparation and characterization of poly(ethylene carbonate)/poly(lactic acid) blends

Poly(ethylene carbonate)/poly(lactic acid) blends were successfully prepared by means of a solution film-casting method, and their physicochemical properties were investigated. PEC/PLA blends exhibit partial miscibility and are characterized by the interaction of the ester and carbonic ester groups. One such interaction is between partial charges in –C–O– in –O–C=O of PLA and the carbonyl –C=O of PEC. Another is between –C–O– in –O–C=O of PLA and –C–O– in –CH₂–O– of PEC. The value of T_g varies by more than 10 °C across the blends. PEC does not significantly influence the melting temperature of neat PLA, but non-spherical spherulites are formed in PEC-rich blends, whereas the spherulites are spherical with an average size of 30 μm in PLA-rich blends. Crystallization of PLA is influenced by the addition of flexible PEC and by the proportion of PLA in the blends. Interestingly, addition of at least 10 wt% PLA increased T_g, with a crystallinity, X_c of 47% and better thermal degradation properties, with the temperature at 5 wt% weight loss (T_d5) more than 30 °C higher than for neat PEC.     

An In Situ DRIFTS Study on SCR of NO with NH3 Over V2O5/AC Surface

Selective catalytic reduction (SCR) of NO with NH₃ on an activated coke supported V₂O₅ (V₂O₅/AC) catalyst was studied at 200 °C by in-situ diffuse reflectance infrared Fourier transform spectroscopy. Results indicate that NH₃ is adsorbed in the forms of coordinated NH₃, NH₄ ⁺ and –NH₂. V₂O₅ promotes formation of –NH₂. NO is oxidized to NO₂ in the presence of O₂. –NH₂ and NO₂ are the intermediates of the SCR reaction.     

Control of particle size and carboxyl group distribution in soap‐free emulsion copolymerization of methyl methacrylate–ethyl acrylate–acrylic acid

Polymer microspheres with narrow size distribution and with carboxyl groups on their surfaces were synthesized by soap‐free emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA), and acrylic acid (AA), and the distribution of –COOH in the latex was determined by conductometric titration. Effects of ingredients on polymerization, latex particle size (D_p), and its distribution, and the distribution of –COOH were investigated. Results showed that monomer conversion and the amount of embedded –COOH (E_a) decreased, and D_p increased with increasing amounts of NH₄HCO₃. The amounts of surface –COOH (S_a) and water –COOH (F_a) and the number of –COOH on each square centimeter of the particles' surface (S_d) increased with increasing amounts of NH₄HCO₃ and AA. With the increase of initiator (APS) and AA, D_p deceased. E_a increased with the increase of AA. F_a increased and then remained constant, and S_d decreased with the increase of initiator. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 433–438, 2004     

Acid properties of solid acid from petroleum coke by chemical activation and sulfonation

A novel solid acid was prepared from petroleum coke by KOH chemical activation and concentrated H₂SO₄ sulfonation. The solid acid was characterized by XRD, FT-IR and solid-state NMR. The characterization results show that the chemical activation and sulfonation lead to three functional Brønsted acid sites: –OH, –COOH and –SO₃H on the solid acid. The probe molecules experimental reveal that the acid strength of the solid acid is stronger than that of SO₄²⁻ /ZrO₂, but slightly weaker than that of 100% H₂SO₄. The catalytic performance was evaluated by the esterification of oleic acid with methanol. The results indicate that this solid acid catalyst is very active, corresponding to high conversion (72%) of esterification reaction. In addition, the spent solid acid can be recovered by simple regeneration process.     

Adsorption and temperature programmed desorption of NO,NO + O2, NO2 and NO + NO2 over CoH-ZSM-5

The NO₂, NO (O₂) adsorption and temperature programmed desorption (TPD) were studied systematically to probe into the selective catalytic reduction of NO by methane (CH₄–SCR) over CoH-ZSM-5 (SiO₂/Al₂O₃ = 25, Co/Al = 0.132–0.312). Adsorption conditions significantly affect the adsorption of NO, NO₂ and NO + O₂. Adsorbed NO species are unstable and desorbed below the reactive temperature 523 K. Increasing adsorption temperature results in the decrease of the adsorbed NO species amount. The amount of –NO_y species formed from NO₂ adsorption increases with the increase of NO₂ concentration in the adsorption process, while decreases significantly with the increase of adsorption temperature. Though NO species are adsorbed weakly on CoH-ZSM-5, competitive adsorption between NO and –NO_y species decreases the amount of adsorbed –NO_y species. Similar desorption profiles of NO₂ were obtained over CoH-ZSM-5 while they were contacted with NO₂ or NO + O₂ followed by TPD. If NO₂ was essential to form adsorbed –NO_y species, the amount of adsorbed –NO_y species for NO + O₂ adsorption should be the least among the adsorptions of NO₂, NO + O₂ and NO + NO₂ because of the lowest NO₂ concentration and highest NO concentration. In fact, the amount of adsorbed –NO_y species is between the other two adsorption processes. These indicate that the formation of adsorbed –NO_y species may not originate from NO₂.     

Perfluorosulfonated ionomers membranes: Melt‐processing and characterization for ion exchange applications

Perflurosulfonated ionomers membranes with different ionic‐exchange capacity were successfully fabricated via melt‐extruding and casting of their –SO₂F precursors. A systematical investigation of the thermal stability, crystallinity, and rheological properties of the precursors was performed to secure their optimized processing conditions. The tensile properties of acid‐form membranes are found to increase with base‐hydrolysis time, where a tensile strength of 38.2 MPa is readily obtained after 24 h's base‐hydrolysis. The content of –SO₂F or –SO₃H containing side‐chains plays an important role in the thermal stability, rheological, and mechanical properties of the precursor or the acid‐form membranes. The strong ionic interactions, attributed to the –SO₃H groups, lead to decreased crystallinity and tensile strength for different IEC membranes. The acid‐form membranes exhibit good proton conductivity and low methanol crossover in comparison with reference Nafion membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39944.     

100% selective yield of m-nitroaniline by rutile TiO2 and m-phenylenediamine by P25-TiO2 during m-dinitrobenzene photoreduction

Photoreduction of m-dinitrobenzene (25 μmol) in the deaerated aqueous iso-propanol exhibits 100% selective yield of m-nitroaniline (25 μmol) by rutile TiO₂ (50 mg) or m-phenylenediamine (25 μmol) by P25-TiO₂ separately under 8 and 4 h of UV light irradiation (125 W Hg arc, 10.4 mW/cm²), respectively. It revealed that insertion of a second –NO₂ in nitrobenzene ring has an important role in expediting –NO₂ reduction to –NH₂ as compared to a negligible reduction of nitrobenzene under similar conditions, indicating that electron withdrawing groups lower the electron density on –NO₂ present on meta position and favor quick reduction of the –NO₂ group.     

Countercurrent fractionation of methylol-terminated perfluoropolyoxyalkylene oligomers by supercritical carbon dioxide

A methylol-terminated perfluoropolyether having a broad molecular weight distribution has been countercurrent fractionated with supercritical carbon dioxide using an isothermal increasing pressure profile. Depending on the selected physical conditions, a fractionation as a function of the molecular weight has been observed while the influence of different end-groups, present as admixtures, on the solubility was negligible. As a consequence, the different –CF₂H, –CF₂Cl, –CF₂CH₂OH and –COOX (X = CH₂CH₃ or H) end-groups content in the fractions reflected their non-statistical distribution in the starting mixture. This last finding opens the way to a deeper investigation of the reason for this structural diversification. Based on a full evaluation of the multi-step process for the synthesis of the methylol-terminated perfluoropolyether it appears that these end-groups originate from different stability/reactivity of PFPE-reagents and PFPE-intermediates involved in the whole process. These differences are not only function of the specific reaction and experimental conditions considered, but also depend on the PFPE chain length (i.e. molecular weight of the species).     

Synthesis and Characterization of Ethylene‐Bridged Copolycarbosilazane as Precursors for Silicon Carbonitride Ceramics

An ethylene‐bridged copolycarbosilazane precursor of copolysilylethylenediamine (co‐PSDA) is synthesized by polycondensation of ethylenediamine with the mixture of vinylmethyldichlorosilane and methyldichlorosilane in the presence of triethylamine as acid absorbing agent. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR, ¹H NMR and ¹³C NMR) spectral analysis of the as‐synthesized co‐PSDA suggests a structure of ethylene‐bridged polycarbosilazane having –Si–N–C–C–N– as backbone chain with –CH=CH₂, –H and –CH₃ attached to Si as side groups. Co‐PSDA can be cross‐linked at 80°C using 2, 2‐azobisisobutyronitrile as initiator through the polyaddition of the vinyl group and dehydrogenation/deamination of Si–H and N–H. Then the cross‐linked co‐PSDA precursor is pyrolyzed at 1000°C in argon, giving out amorphous silicon carbon nitride (SiCN) ceramics with a high ceramic yield of 76 wt%. The obtained SiCN ceramics consist of nitrogen‐rich silicon sites of SiN₄ as predominant component and some SiCN₃ sites, which should arise from the breaking of N–C bonds below 600°C and the formation of active N–Si bonds.     

Surface modification of ABS by photocatalytic treatment for electroless copper plating

Surface roughness of acrylonitrile–butadiene–styrene (ABS) resin prior to metallization is treated generally with sulphuric/chromic acid system. However, the presence of chrominum (VI) ion imposes serious environmental problems. In this work, TiO₂ photocatalytic treatment was used to enhance the adhesion strength between the ABS surface and the electroless copper film. Effects of the TiO₂ content, irradiation time and UV power upon the surface topography, surface characterization and the adhesion strength were investigated. The results indicated that the surface hydrophilicity of ABS resin and the adhesion strength between the electroless copper film and ABS surface increased with an increase in the UV power and a prolongation in irradiation time, and did not increase linearly with an increase of TiO₂ content. Though the surface topography of ABS changed little, the adhesion strength reached 1.25?kN/m, which was higher than that in the optimal H₂SO₄–MnO₂ colloid. The surface chemistry results indicated that –COOH and –OH groups formed with the photocatalytic treatment and the absorption strengths increased with the UV power. XPS analysis results further demonstrated that the contents of C=O and –COOH reached 6.4 and 4.9% with the photocatalytic treatment, which was much higher than that of the H₂SO₄–MnO₂ colloid (3.9 and 3.1%). The high contents of C=O and –COOH groups enhanced the surface hydrophilicity of the ABS resin and improved the adhesion strength between the electroless copper film and ABS resin. The results indicated that the photocatalytic treatment was an environment-friendly and effective method to replace the commercial wet chemical process for ABS surface modification.     

Facile preparation of BN coatings on graphite substrates and their binding strength

To decrease the curing temperature and achieve excellent binding strength of BN coatings on graphite substrates, a proper Al(H₂PO₄)₃ binder has been carefully designed where MgAl₂O₄ and poly vinyl alcohol (PVA) were used as the curing agent and the dispersant, respectively. XRD, SEM, TEM and DSC showed that the desired binding phase AlPO₄ had been successfully obtained, where MgAl₂O₄ and PVA worked synergistically to lower the curing temperature down to 70–100 °C and promote the formation of AlPO₄. Such optimized binder might have formed hydrogen bond with –NH₂ and –OH groups on the BN flakes. It might also form hydrogen bond with-OH and –COOH groups on graphite substrates to ensure an optimal binding strength of 5.5 N (～22 MPa) as suggested by the scratch tests. This work affords a better understanding on the curing chemistry of Al(H₂PO₄)₃ and the binding mechanism between BN flakes, AlPO₄ binding phases and graphite substrates.     

New dicarbonyl-o-semiquinonato rhodium complexes

Two novel dicarbonyl rhodium complexes with 3,6-di-tert-butyl-o-semiquinones containing back bonded –OCH₃ and –F substituents were synthesized and characterized. The number of analogous dicarbonyl-o-semiquinonato rhodium complexes is discussed from the viewpoint of the phenomenon of “bending crystals”.     

Preparation of Rh-containing polycarbonate films and the study of their chemical properties in the polymer

RhCl[P(C₆H₅)₃]₃ complexes have been incorporated in polycarbonate (PC) as a dispersion medium using cosolvent (THF). The interactions between Rh(I) complexes and polycarbonate polymer molecules are studied by infrared spectroscopy and thermal analysis. The reaction chemistry of Rh in PC films has been investigated by reacting Rh sites in PC with small gaseous molecules like CO, H₂, D₂, O₂, NO, C₂H₂, and C₂H₄ in the temperature range 25∼150°C. Various Rh–carbonyls, –hydride, –nitrosyl, and –superoxo dioxygen species formed in PC films are characterized by infrared spectroscopy. The Rh complexes in PC are easily reduced by reacting them with H₂ gas and such reduction results in the formation of small Rh metal particles of 20∼30 Å in diameter in PC. The Rh complexes in PC show interesting catalytic reactivities such as hydrogenation of olefin and acetylene, oxidation of CO, reduction of NO, methanol synthesis from CO or CO_2, and oxidation of alcohol under relatively mild conditions.     

Concave reagents 29 [1] Dendrimer fixed concave pyridine

A concave pyridine 1c has been attached to dendrimers of the Fréchet type by an ethylenoxide linker on the convex outside of the catalyst. Two generations of dendrons [G-1]-OH , [G-2]-OH , [G-1]-Br and [G-2]-Br and of dendrimers with 4,4′-dihydroxybiphenyl ( 3 ) and 1,1,1-tris(4-hydroxyphenyl)ethane ( 4 ) as di- and trivalent cores [G-1] ₂ –[C2] , [G-1] ₃ –[C3] and [G-2] ₃ –[C3] have been synthesized. The resulting molecules possess up to twelve concave catalytic pyridine centers on the outside of the molecules, and can be used as selective catalysts in the base catalyzed addition of alcohols to diphenylketene.     

Structure and in vivo anticalcification properties of a polymeric calcium–sodium–phosphocitrate organic–inorganic hybrid

This paper describes the synthesis, characterization and crystal structure of an organic–inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl₂·2H₂O and Na₄(HPC)·3H₂O in water, at pH 2. Its structure is polymeric with Ca(PC)₂(H₂O) “monomers” connected through Na⁺ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H₂O oxygens. CaO(C) distances are in the 2.446(2)–2.586(2) Å range. There is a short distance of 2.477(1) Å between Ca and the ester O from C–O–PO₃H₂. All –COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from –PO₃H₂. Na ions are six-coordinate surrounded by –COOH’s. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na–phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H₅PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H₅PC) giving nearly quantitative (95%) plaque inhibition.     

Selective removal of antibiotics over MgAl2O4/C3N4/YMnO3 photocatalysts: Performance prediction and mechanism insight

A simple polyacrylamide gel method combined with low temperature sintering technology has been used to synthesize the C–O functional groups grafted MgAl₂O₄/C₃N₄/YMnO₃ (MAO–CN–YMO) heterojunction photocatalysts with enhanced visible-light-induced photodegradation toward oxytetracycline hydrochloride (OTC-HCl). A variety of characterization methods are used to gain insight into the phase purity, crystal structure, microstructure, functional group information, elemental composition, surface defect, light response capability, and photocatalytic activity of the as-synthesized samples. The influences of the mass ratios of m_CN/m_YMO, m_CN/m_MAO, and m_MAO/(m_CN + m_YMO) in CN–YMO, CN–MAO, and MAO–CN–YMO heterojunction photocatalysts on the photocatalytic activity for the degradation of OTC-HCl was also discussed, and the optimal mass ratio of m_MAO/(m_CN + m_YMO) is identified as 15 wt%. The photocatalytic experiments confirmed that the MAO–CN–YMO heterojunction photocatalysts had high selectivity for the degradation of antibiotics. The prediction of the photocatalytic activity of the MAO–CN–YMO heterojunction photocatalysts for the degradation of OTC-HCl was made by a variety of intelligent algorithm models. The results of the whale optimization algorithm are highly consistent with the experimental results. Combined with the energy band theory and the characterization results of high-performance liquid chromatography–tandem mass spectrometry, the free radicals in the reaction solution preferentially attacked the –CH₃, –NCH₂, and –OH of OTC-HCl during the degradation of OTC-HCl by MAO–CN–YMO heterostructure photocatalysts, and then attack –C=O and –C=O–NH₂, and finally perform ring-opening reaction to degrade OTC-HCl into nontoxic and harmless products of small molecules such as CO₂, H₂O, and NH₄⁺. This work provides a new idea for the development of novel double p–n junction MAO–CN–YMO heterojunction photocatalysts for antibiotic degradation and the prediction of photocatalytic activity of multiple heterojunction photocatalysts by intelligent algorithms.