Effect of ionic liquids on the structural,thermal, and in vitro degradation properties of poly(ε‐caprolactone) synthesized in the presence of Candida antarctica lipase B

The study provides detailed information on the differences in the structural, thermal and degradation properties of poly(ε‐caprolactone) synthesized in two different ionic liquids, 1‐butyl‐3‐methylimidazolium hexafluorophosphate [bmim][PF₆] and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][NTf₂], regarding its further usage in the pharmaceutical field. The polymer structure confirms the presence of both linear polymer chains with end‐functional hydroxyl groups allowing covalent coupling of the therapeutic agents, and cyclic macromolecules, both affecting the degree of crystallinity of polymer. The highest macrocyclic content (64%) after 7 days of polymerization at 80 °C was observed for [bmim][NTf₂]. For [bmim][PF₆], the macrocyclic content value was not dependent on the reaction time and remained at a similar level (10–14% at 80 °C). The results of degradation test revealed that hydrolytic degradation of ester bonds is more pronounced for PCLs synthesized in [bmim][NTf₂], due to their lower degree of crystallinity compared with PCLs obtained in [bmim][PF₆]. A high purity, low polydispersity index of the obtained polymers and high yield of the process (ca., 90%) indicate that ionic liquids seem to be promising solvents for the synthesis of biomedical polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43728.     

Kinetic analysis of Li|Li+ interphase in an ionic liquid electrolyte

Kinetic analysis of the Li|Li⁺ interphase in an electrolyte based on N-metyl-N-propylpyrrolidinium bis(trifluoromethanesulfon)imide ionic liquid (MPPyrrTFSI) and lithium bis(trifluoromethanesulfon)imide salt (LiTFSI) was performed. Li|electrolyte|Li and LiC₆|electrolyte|Li cells were galvanostatically charged/discharged in order to form solid electrolyte interphase (SEI) protecting layer. SEM images showed that the surface of both Li and LiC₆ anodes was covered with small particles. The fitting procedure of electrochemical impedance data taken at different temperatures gave three resistances (R _el, R _SEI, R _ct) and hence, three lnR = f(T ^?1) straight lines of different slopes. Specific conductivity and activation energy of the conduction process of the liquid electrolyte, were ca. σ = 2.5 mS cm^?1 (at T = 25.0 °C) and $ E_{\text{el}}^{\# } $  = 15 kJ mol^?1. Activation energy for the conduction process in the SEI layer was ca. 56 kJ mol^?1 in the case of the metallic lithium and 62 kJ mol^?1 for the graphite anode. Activation energy of the charge transfer process, $ E_{\text{ct}}^{\# } $ , for Li and LiC₆ anodes was 71 and 65 kJ mol^?1, respectively. Analysis of literature data for different electrolytes suggests that the $ E_{\text{ct}}^{\# } $ value for Li⁺ reduction may be approximated by 57 ± 5 kJ mol^?1. Activation energy for the diffusion processes in the graphite electrode, detected from the Warburg coefficient, was ca 74 kJ mol^?1.     

Preparation and characterization of extruded nanocomposite based on polycarbonate/butadiene‐acrylonitrile‐styrene blend filled with multiwalled carbon nanotubes

Nanocomposites of polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) with multiwall carbon nanotubes (MWCNT) prepared by masterbatch dilution are investigated in this work. Melt compounding with twin screw extruder is followed by complete characterization of morphology, rheological‐, mechanical‐, and thermal‐properties of the nanocomposites. Light‐transmission‐ and scanning electron microscopy shows the preferential location of MWCNT in the PC. Nevertheless, relatively good dispersion in the whole matrix is achieved, what is corroborated with the specific mechanical energy. The study of viscoelastic properties of PC/ABS‐MWCNT shows the fluid–solid transition below 0.5 wt % MWCNT. Beyond this point the continuous nanofiller network is formed in the matrix promoting the reinforcement. Addition of 0.5 wt % MWCNT reduces ductility of PC/ABS and enhances Young's modulus by about 30% and yield stress by about 20%. Moreover, theoretical values of stiffness calculated within this work agree with the experimental data. Electrical conductivity, showing percolation at 2.0 wt % MWCNT, are influenced by processing temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40271.     

Effect of sugars on the mechanical and thermal properties of agarose gels

The present study examines the thermal and mechanical properties of agarose/sugar mixtures using micro-DSC (Differential Scanning Calorimetry) and Dynamic Mechanical Thermal Analyser. In DSC experiments, addition of sugar was reflected in a broad exothermic event compared to sharp transitions generated by the aqueous agarose preparation. At high levels of co-solute, agarose networks show a reduced enthalpic content per gram of the polymer thus arguing for a transformation to a more entropic finely stranded networks of reduced number of junctions zones, the networks exhibited long large deformation properties. At high levels of sugar, agarose samples show a mechanical spectrum that can be modelled according to the WLF/free-volume theory, which requires an entropic lightly cross-linked network.     

The nucleation and growth of a lead phosphate film on homogeneous lead amalgam

The electrochemical oxidation of Pb(Hg) in acidic phosphate medium results in formation of a monomolecular PbHPO₄ passivating film. Analysis of potentiostatic current-time transients demonstrated that the crystallization occurred through a 2-dimensional progressive nucleation and growth mechanism. The potential dependence of the combined nucleation and crystallization rate constants was [7.8 ± 0.7 mV/decade]^?1. The formation of a soluble lead phosphate species prior to film growth was observed under certain conditions. Examination of it curves in this region by the low overpotential form of the Cottrell equation indicated that the soluble species was PbHPO₄.     

Determination of lithium transference number in PEO-DME-LiClO4 modified with alumina powders of various surface acidity

The effect of alumina additives bearing various surface groups on conductivity and lithium cation transference numbers in poly(ethylene oxide) dimethyl ether (PEO-DME)-LiClO₄ electrolytes is examined. It is demonstrated that an increase in the conductivity and lithium transference number in composite electrolytes compared to pure PEO-DME-LiClO₄ electrolyte is observed in the limited salt concentration range. Both quantities seem to depend mostly on ionic species mobility. Also, their salt concentration dependence resembles that of viscosity of electrolytes studied. The conduction mechanism is discussed on the basis of conductivity, transference numbers and ionic association studies.     

Liquid-crystalline phases formed by symmetrical azines with different terminal chains: Thermal,optical and electrical study

One series of symmetrical azine-type liquid crystals were synthesized and their chemical structure identified by FTIR, NMR, high resolution mass spectrometry-electro spray ionization (MS-ESI) and elemental analysis. The absorption (UV–vis), photoluminescence (PL) and thermoluminescence (TL) features of the compounds are documented. X-ray diffraction was employed to evaluate their phase transitional behaviour. Their mesomorphic properties were investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). Terminal groups of the liquid crystals had an effect on their mesomorphic properties. Azine with alkoxysemiperfluorinated end-groups (A1) exhibited smectic C (SmC) phase, whereas azine with octadecyloxy end chains (A3) showed SmC and SmA phases. Azine with 5″-octyl-2,2′:5′,2″-terthiophene groups (A2) exhibited only nematic phase. Different types of N and SmC textures were found and investigated by POM technique. Azine with thiophene groups (A2) has an absorption band about 138 nm batochromically shifted compared to the analogous band of other compounds. The lowest optical band gap value (2.34 eV) was detected for A2. Azines emitted violet or green light. The thermoluminescence emission of azines occurred at about 390–440 nm wavelengths. Current–voltage measurements were performed on ITO/compound/Alq₃/Al and ITO/TiO₂/compound/Alq₃/Al devices before and after light irradiation. To prepare TiO₂ layer, sol–gel technique was applied.     

A study of thermal,optical and electrical properties of new branched triphenylamine-based polyazomethines

A series of branched aromatic polyazomethines have been obtained by high temperature solution polycondensation of 4,4′,4″-triformyltriphenylamine with 3,3′-dimethoxybenzidine with different feed molar ratio. For three polymers additional condensation of chain end groups with monofunctional monomers such as 4-formyltriphenylamine or 2-naphthylamine was carried out. Moreover, two model compounds were prepared and investigated for comparison with branched polymers. The structures of polymers and models were characterized by means FTIR, ¹H, ¹³C NMR spectroscopy, elemental analysis and gel permeation chromatography (GPC). UV–vis properties of the thin films of the polymers and compounds were investigated on the glass substrate. Eg of the branched polymers was found about 2.47 eV. UV–vis and FTIR spectroscopy for iodine doped compounds were investigated. Doping decreased the value of Eg of the branched polyazomethines to about 1.71 eV. Refractive index (n) for branched polyazomethines was found about 1.97, while for the doped compounds was a little higher (～2.48). Absorption (UV–vis) properties of the doped with iodine branched imines were investigated additionally after heating in different temperatures from 50 to 200 °C. Intensity of photoluminescence of branched imines in relation to 9,10-diphenylanthracene was found in the range 0.2–1.0% and 2.7–43.7% in dependence on the excitation wavelengths. Current–voltage (I–V) measurements were performed on ITO/TiO₂/polymer/Al, ITO/polymer/Alq₃/Al and ITO/TiO₂/polymer/Alq₃/Al devices in the dark and during irradiation with light (under illumination 1000 W/m²). The sol–gel technique was applied to prepared TiO₂ layer. TiO₂ layers and devices were investigated by Atomic Force Microscopy (AFM). Moreover, properties of these branched polymers were compared with the linear polyazomethine based on 3,3′-dimethoxybenzidine and 4,4′-diformyltriphenylamine.     

α‐Amino acids as initiators of ε‐caprolactone and L,L‐lactide polymerization

Biodegradable polymers/oligomers were successfully synthesized through a ring‐opening polymerization of ε‐caprolactone and L ,L ‐lactide, initiated by L ‐arginine and L ‐citrulline. The α‐amino acid initiators are natural, operationally simple, inexpensive, environmentally friendly and safe for human health. The polymerizations were performed with no solvents and without introducing any metal impurities. The chemical structures of the polymers obtained were elucidated using ¹H NMR, ¹³C NMR and Fourier transform infrared spectroscopies. In addition, incorporation of α‐amino acid molecules into the polymer chain was confirmed using matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry. Due to the significant biological activity of L ‐arginine and L ‐citrulline, these α‐amino acid initiators may open a new route for the synthesis of functional polymers especially for pharmaceutical applications. Copyright © 2011 Society of Chemical Industry