Calorimetry and thermogravimetry as tools for the assessment of the thermal stability of polyoxide-based nonionic surfactants

Differential scanning calorimetry (DSC) and thermogravimetry (TGA) have been used to evaluate the thermal stability of nonionic surfactants. We have studied monofunctional diblock copolymers of poly(ethylene oxide-propylene oxide) (R-PEO–PPO–OH, where R length is linear C₄ or C_12–14) as nonionic surfactants. It was observed that the thermal stability was dependent on the copolymer structure. Moreover, the higher the EO/PO ratio in the copolymers the higher the oxidative thermal stability. The autoxidation exhibits exothermic behaviour and the enthalpy related to the process depends on the EO/PO ratio. The initial temperatures of degradation obtained from DSC and TGA were in agreement.     

Polyimide-polydimethylsiloxane copolymers containing nitrile groups

A novel series of nitrile-containing polyimide-polydimethylsiloxane copolymers was prepared by polycondensation reaction of 4,4′-oxydiphthalic anhydride with a mixture of an aromatic diamine, namely 2,6-bis(3-aminophenoxy)benzonitrile, and bis(aminopropyl)oligodimethylsiloxane of controlled molecular weight, in different ratios. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidone, N,N-dimethylformamide as well as in less polar solvents such as chloroform, and can be cast from solution into thin flexible films. The inherent viscosity was in the range of 0.43-0.55 dL/g. The polymers showed good thermal stability, the decomposition temperature being above 430 °C. They exhibited a glass transition temperature in the range of 149-219 °C, with reasonable interval between glass transition temperature and decomposition temperature. The surface morphology was investigated by scanning electron microscopy. The water dynamic contact angles were measured by tensiometric method. The free surface energy was evaluated based on Owens and Wendt equation. A composite film based on a polyimide-polydimethylsiloxane copolymer and pyrite ash powder has been prepared and its nanoactuation has been investigated.     

A new strategy for basic drug extraction in aqueous medium using electrochemically enhanced solid-phase microextraction

This work describes an electrochemically enhanced solid-phase microextraction (EE-SPME) method using a mild negative potential (-0.6 V) for the enhanced extraction of the selected basic drugs in a pure aqueous matrix and urine samples. The EE-SPME method gave a more effective extraction of drugs (primarily via electrophoresis and complementary charge interaction) compared to that obtained with SPME (without applying a potential, and which is based on passive partitioning). The EE-SPME method eliminated the need for alkalizing, derivatizing the drugs, or modifying the fiber coating before extraction. The analysis of methamphetamine (MA) and amphetamine (AM) was selected as a typical example to demonstrate in detail the advantages of EE-SPME over SPME. Based on the results obtained, 3-min extraction efficiency for both the amphetamines using EE-SPME was better than that of 30-min using SPME. The developed EE-SPME-GC method exhibited wide linear ranges (2-1000 ng mL(-1)) for both the amphetamines with R(2) larger than 0.99, and the method detection limits (MDLs) for AM and MA were 0.26 and 0.12 ng mL(-1), respectively. In addition, the EE-SPME method developed was also successfully applied to enhance the extraction of several other basic drugs (ephedrine, 3,4-methylenedioxyamphetamine (MDA), atropine, methadone, cocaine, codeine, acetylcodeine and papaverine) with preconcentration factors from 157 to 2199, indicating the potential applicability of this method in the field of forensic, clinical and pharmaceutical analysis.     

PREPARATION AND CHARACTERIZATION OF INCLUSION COMPLEXES OF TWO-ARM LINEAR AND FOUR-ARM STAR-SHAPED POLY（ε-CAPROLACTONE）S WITH α-CYCLODEXTRIN

<正>Both four-arm star-shaped poly（ε-caprolactone） （4sPCL） and two-arm linear PCL （2LPCL） were synthesized and their inclusion complexation withα-cyclodextrin （α-CD） were studied. The inclusion complexes （ICs） formed between the PCL polymers andα-CD were characterized by 1H-NMR, DSC, TGA, WAXD, and FT-IR, respectively. Both branch arm number and molecular weight of the PCL polymers have apparent effect on the stoichiometry （CL:CD, mol:mol） of these ICs. All these analytical results indicate that the branch arms of the PCL polymers are incorporated into the hydrophobicα-CD cavities and their original crystalline properties are completely suppressed. Moreover, the inclusion complexation between two-arm linear or four-arm star-shaped PCL polymers andα-CD not only enhances the thermal stability of the guest PCL polymers but also improves that ofα-CD.     

Thermal and mechanical characterization of poly(vinyl chloride)-b-poly(butyl acrylate)-b-poly(vinyl chloride) obtained by single electron transfer - degenerative chain transfer living radical polymerization in water

This work reports the synthesis of several copolymers of poly(vinyl chloride)-b-poly(n-butyl acrylate)-b-Poly(vinyl chloride) prepared by single electron transfer/degenerative chain transfer mediated living radical polymerization (SET-DTLRP) in a two step process: first, a bifunctional macroinitiator of α,ω-di(iodo)poly(butyl acrylate) [α,ω-di(iodo)PBA] was synthesized by SET-DTLRP in water at 30 °C. The obtained macroinitiator was further reinitiated also by SET-DTLRP leading to the formation of the desired product. Several copolymers were synthesized in a 5L pilot reactor with different molecular weights and relative amounts of PBA and PVC. The possibility of synthesizing flexible materials made of PVC without using normal free plasticizes is extremely important for the industry. After processing the materials in a two-roll mill laboratorial equipment, the block copolymers were characterized concerning thermal and mechanical. The materials characterized in this study were prepared in a 5L pilot reactor under similar conditions to be used in industrial scale.     

Phase behavior of biodegradable amphiphilic poly(l,l-lactide)-b-poly(ethylene glycol)-b-poly(l,l-lactide)

This study describes the miscibility phase behavior in two series of biodegradable triblock copolymers, poly(l-lactide)-block-poly(ethylene glycol)-block-poly(l-lactide) (PLLA-PEG-PLLA), prepared from two di-hydroxy-terminated PEG prepolymers (M_n = 4000 or 600 g mol⁻¹) with different lengths of poly(l-lactide) segments (polymerization degree, DP = 1.2-145.6). The prepared block copolymers presented wide range of molecular weights (800-25,000 g mol⁻¹) and compositions (16-80 wt.% of PEG). The copolymer multiphases coexistance and interaction were evaluated by DSC and TGA. The copolymers presented a dual stage thermal degradation and decreased thermal stability compared to PEG homopolymers. In addition, DSC analyses allowed the observation of multiphase separation; the melting temperature, T_m, of PLLA and PEG phases depended on the relative segment lengths and the only observed glass transition temperature (T_g) in copolymers indicated miscibility in the amorphous phase.     

Spectroscopic investigation of Rose Bengal/cyclodextrin interactions in aqueous solution: the case of the hydroxypropyl-cyclodextrins

The interaction of Rose Bengal (RB) with hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD) has been studied in water and in acetate buffer at pH 4.5 by UV–Vis absorption, fluorescence spectroscopy and Induced Circular Dichroism at 298 K. Evidence of the complex formation between the RB and all HP-CDs have been obtained both in water and in buffer. Binding constants and stoichiometry of RB/HP-CD complexes in water have been determined by applying the modified Benesi-Hildebrand equation to the fluorescence measurements.     

PREPARATION AND CHARACTERIZATION OF INCLUSION COMPLEXES OF TWO-ARM LINEAR AND FOUR-ARM STAR-SHAPED POLY(ε-CAPROLACTONE)S WITH α-CYCLODEXTRIN

Both four-arm star-shaped poly(ε-caprolactone) (4sPCL) and two-arm linear PCL (2LPCL) were synthesized and their inclusion complexation with α-cyclodextrin (α-CD) were studied. The inclusion complexes (ICs) formed between the PCL polymers and α-CD were characterized by 1H-NMR, DSC, TGA, WAXD, and FT-IR, respectively. Both branch arm number and molecular weight of the PCL polymers have apparent effect on the stoichiometry (CL:CD, mol:mol) of these ICs. All these analytical results indicate that the branch arms of the PCL polymers are incorporated into the hydrophobicα-CD cavities and their original crystalline properties are completely suppressed. Moreover, the inclusion complexation between two-arm linear or four-arm star-shaped PCL polymers and α-CD not only enhances the thermal stability of the guest PCL polymers but also improves that of α-CD.     

Poly(1,3,4-oxadiazole-ether-imide)s and their polydimethylsiloxane-containing copolymers

Poly(1,3,4-oxadiazole-ether-imide)s were prepared by thermal imidization of poly(amic-acid) intermediates resulting from the solution polycondensation reaction of a bis(ether-anhydride), namely 2,2′-bis-[(3,4-dicarboxyphenoxy)phenyl]-1,4-phenylenediisopropylidene dianhydride, with different aromatic diamines containing 1,3,4-oxadiazole ring, such as 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 2,5-bis[p-(4-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2-(4-dimethylaminophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole. Poly(1,3,4-oxadiazole-ether-imide)-polydimethylsiloxane copolymers were prepared by polycondensation reaction of the same bis(ether-anhydride) with equimolar quantities of an aromatic diamine having 1,3,4-oxadiazole ring and a bis(aminopropyl)polydimethylsiloxane oligomer of controlled molecular weight. A solution imidization procedure was used to convert quantitatively the poly(amic-acid) intermediates to the corresponding polyimides. All the polymers were easily soluble in polar organic solvents such as N-methylpyrrolidone and N,N-dimethylacetamide. The polymers showed good thermal stability with decomposition temperature being above 400 °C. Solutions of some polymers in N-methylpyrrolidone exhibited blue fluorescence, having maximum emission wavelength in the range of 370-412 nm.     

Neodymium alk(aryl)oxides-dialkylmagnesium systems for butadiene polymerization and copolymerization with styrene and glycidyl methacrylate

The application of well-defined neodymium alkoxides/aryloxides in combination with dialkylmagnesium reagents for 1,3-butadiene (BD) polymerization and copolymerization with styrene (St) and glycidyl methacrylate (GMA) has been investigated. The trinuclear complex Nd₃(Ot-Bu)₉(THF)₂ (1) provided a low-activity system for BD polymerization, even at high temperature, but with a high trans-1,4 stereospecificity (trans-1,4≈95%). Aryloxide complexes Nd(O-2,6-t-Bu₂-4-Me-Ph)₃(THF) (2) and Nd(O-2,6-t-Bu₂-4-Me-Ph)₃ (3) were found to give more active systems. The polymerization displayed a controlled character, i.e. a precise control of the molecular weight and a low polydispersity (M_w/M_n<1.30) for high catalyst concentration, keeping the same level of stereocontrol over the polymerization course. The statistical copolymerization of BD and styrene with those systems was successful. High-molecular weight copolymers (M_n up to 50?000 g mol⁻¹) with noticeable styrene content (3-15 mol%) were synthesized. Determination of the microstructure by ¹³C-NMR showed exclusively trans-1,4-BD-St sequences. The livingness of BD polymerization encouraged attempts of diblock copolymerization with GMA. In this case, low-molecular weight polymers with variable polydispersities were obtained (M_n<20?000 g mol⁻¹; M_w/M_n=1.4-5.0). The composition of the copolymers was analyzed by ¹H- and ¹³C-NMR and IR spectroscopies. SEC analyses confirmed the true nature of the diblock copolymer. The influence of the alkylating agent on those (co)-polymerizations was briefly studied. Finally, the mechanism of polymerization is also discussed.     

Influence of complexation on the composition of equilibrium phases in the system of Ce2(SO4)3-La2(SO4)3

The cocrystallization of Ce₂(SO₄)₃ and La₂(SO₄)₃ is studied in aqueous and H₂SO₄ (150 g/dm³) solutions at 25 °C and 64 °C. The effect of the formation of inner sphere sulfate complexes of the type LnSO ₄ ⁺ in determining the composition of the equilibrium phases is revealed.      

Hemicucurbit[6]uril a Macrocyclic Ligand with Unusual Complexing Properties

The complex formation of the macrocyclic ligand hemicucurbit[6]uril with various salts has been studied in aqueous solution. Due to the low solubility of this ligand the formation of complexes results in an increase of the amount of ligand present in solution. From these measurements the stability constants of the complexes formed are calculated. Hemicucurbit[6]uril only forms cation complexes with cobalt(II), nickel(II) and the uranylion. All other cations examined e.g. silver(I), lead(II) and copper(II) do not form detectable complexes in aqueous solution. For a better understanding of the complexation behaviour some quantum mechanical chemical calculations are performed with Gaussian.Dedicated to Prof. H. Möhwald on the occasion of his 60th birthday.     

Effect of β-cyclodextrin on spectroscopic properties of ochratoxin A in aqueous solution

Ochratoxin A (OTA) is a nephrotoxic mycotoxin produced by several fungal species, mainly Aspergillus ochraceus, A. carbonarius and Penicillium verrucosum. It contaminates many foodstuffs, particularly cereals and their derivatives, coffee, beer, wine and cocoa, and represents a serious health threat both to humans and animals. Spectroscopic properties of OTA solutions depend on the pH, solvent polarity and can be influenced by the presence of cyclodextrins (CDs). In this work, the effect of β-CD on spectroscopic properties of OTA in aqueous solutions has been investigated by means of absorption and steady-state fluorescence at different pHs (range 3.5–9.5). Binding constants of OTA/β-CD inclusion complexes have been determined by applying modified Benesi-Hildebrand equation. A 1:1 stoichiometry of OTA/β-CD complexes has been observed at all tested pHs.     

Thermodynamic properties of chloro-complexes of silver chloride in aqueous solution

Available data on the solubility of silver chloride in aqueous solutions of HCl, NaCl, KCl, LiCl, and NH₄Cl, along with potentiometric measurements of the activity of Ag⁺ in aqueous NaCl–NaClO₄ mixtures, have been analyzed to obtain the thermodynamic properties of the (AgCl)⁰, AgCl ₂ ^– , AgCl ₃ ^2– , and AgCl ₄ ^3– complexes. Results obtained include the stability constants of the complexes and 25°C, the virial parameters needed to calculate the activity coefficients of the complexes and the heats of the reactions by which they are formed. These results are sued to calculate tables of recommended values for the solubility of silver chloride in the host solutions as a function of concentration from 0 to 150°C and to make a critical evaluation of the reliability of previously published data.     

Novel drug delivery systems based on the complexes of block ionomers and surfactants of opposite charge

In this paper we have evaluated a novel family of polymer-surfactant complexes formed between block ionomers and oppositely charged surfactants. Complexes between cationic copolymer poly(ethylene oxide)-g-polyethyleneimine (PEO-g-PEI) and sodium salt of oleic acid, natural nontoxic surfactant, are prepared and characterized. These systems self-assemble in aqueous solutions into particles with average size of 50–60 nm, which can solubilize hydrophobic dyes (Yellow OB) and drug molecules (paclitaxel). The use of the biologically active surfactants as components of block ionomer complexes is demonstrated for the complexes from PEO-g-PEI and all-trans-retinoic acid. Binding of relatively soluble drugs with block ionomers is illustrated using PEO-b-poly(sodium methacrylate) and doxorubicin. Overall these studies suggest that block ionomer complexes can be used to prepare a variety of soluble and stable formulations of biologically active compounds, and have potential application as drug delivery systems     

Studies of an inclusion complex of a redox-active barbiturate with β-cyclodextrin

The effects of β-cyclodextrin (β-CD) on the spectral properties and electrochemical behaviour of barbitone sodium were studied using electrochemical and optical techniques. The apparent changes in the UV-visible absorption spectrum and fluorescence quenching of the barbiturate upon addition of β-CD afford clear evidence of the inclusion complex formation of β-CD in aqueous solutions. The redox acitivity of barbitone sodium in both the absence and presence of β-CD was assessed by an electrochemical method in 0.05 M potassium nitrate-nitric acid (pH 1.8) solution. While the complexation reaction remains is equilibrium, the apparent formation constant of the inclusion complex could be obtained by either spectral or electrochemical methods. Quantitative evaluation of the data gave 326 l mol⁻¹ under equilibrium conditions at 20°C. Possible conclusions are discussed on the basis of environmental changes around the barbiturate molecules on inclusion.