Synthesis and characterization of poly(ester amide)s containing crystallizable amide segments

High molecular weight segmented poly(ester amide)s were prepared by melt polycondensation of 1,4-butanediol, dimethyl adipate and a preformed bisamide-diol based on 1,4-diaminobutane and ε-caprolactone. By varying the ratio of the bisamide-diol and 1,4-butanediol, a series of polymers was obtained with a hard segment content between 10 and 85 mol%. FT-IR and WAXD analysis revealed that the poly(ester amide)s crystallize in an α-type phase similar to the α-phase of even-even nylons. These polymers all have a micro-phase separated structure with an amide-rich hard phase and an ester-rich flexible soft phase. The polymers have a low and a high melt transition, corresponding with the melting of crystals comprising single ester amide sequences and two or more ester amide sequences, respectively. The low melt transition is between 58 and 70 °C and is independent of polymer composition. By increasing the hard segment content from 10 to 85 mol% the high melt transition increased from 83 to 140 °C while the glass transition temperature increased from −45 to −5 °C. Likewise, the elastic modulus increased from 70 to 524 MPa, the stress at break increased from 8 to 28 MPa while the strain at break decreased from 820 to 370%. Thermal and mechanical properties can thus be tuned for specific applications by varying the hard segment content in these segmented polymers.     

Ionic liquids based on guanidinium cations and TFSI anion as potential electrolytes

Sixteen new guanidinium salts based on small cations and TFSI⁻ anion were prepared and characterized. Physical and electrochemical properties of these products, including melting point, thermal stability, viscosity, conductivity and electrochemical window were investigated. Reducing symmetry of cations can reduce the melting points, and 12 products are liquids at room temperature. The viscosities of cg22TFSI, cg12TFSI and cg13TFSI were 45, 46 and 52 mPa s at 25 °C, respectively. Electrochemical and thermal stabilities of these ILs permitted them to become promising electrolytes used in electrochemical devices.     

Incorporation of different crystallizable amide blocks in segmented poly(ester amide)s

High molecular weight segmented poly(ester amide)s were prepared by melt polycondensation of dimethyl adipate, 1,4-butanediol and a symmetrical bisamide-diol based on ε-caprolactone and 1,2-diaminoethane or 1,4-diaminobutane. FT-IR and WAXD analysis revealed that segmented poly(ester amide)s based on the 1,4-diaminobutane (PEA(4)) give an α-type crystalline phase whereas polymers based on the 1,2-diaminoethane (PEA(2)) give a mixture of α- and γ-type crystalline phases with the latter being similar to γ-crystals present in odd-even nylons. PEA(2) and PEA(4) polymers with a hard segment content of 25 or 50 mol% have a micro-phase separated structure with an amide-rich hard phase and an ester-rich flexible soft phase. All polymers have a glass transition temperature below room temperature and melt transitions are present at 62-70 °C (T_m,1) and at 75-130 °C (T_m,2) with the latter being highest at higher hard segment content. The two melt transitions are ascribed to melting of crystals comprising single ester amide sequences and two or more ester amide sequences, respectively. These polymers have an elastic modulus in the range of 159-359 MPa, a stress at break in the range of 15-25 MPa combined with a high strain at break (590-810%). The thermal and mechanical properties are not influenced by the different crystalline structures of the polymers, only by the amount of crystallizable hard segment present.     

Physical and electrochemical properties of 1-(2-hydroxyethyl)-3-methyl imidazolium and N-(2-hydroxyethyl)-N-methyl morpholinium ionic liquids

Various ionic liquids (ILs) were prepared via metathesis reaction from two kinds of 1-(2-hydroxyethyl)-3-methyl imidazolium ([HEMIm]⁺) and N-(2-hydroxyethyl)-N-methyl morphorinium ([HEMMor]⁺) cations and three kinds of tetrafluoroborate ([BF₄]⁻), bis(trifluoromethanesulfonyl)imide ([TFSI]⁻) and hexafluorophosphate ([PF₆]⁻) anions. All the [HEMIm]⁺ derivatives were in a liquid state at room temperature. In particular, [HEMIm][BF₄] and [HEMIm][TFSI] showed no possible melting point from −150 °C to 200 °C by DSC analysis, and their high thermal stability until 380-400 °C was verified by TGA analysis. Also, their stable electrochemical property (electrochemical window of more than 6.0 V) and high ionic conductivity (0.002-0.004 S cm⁻¹) further confirm that the suggested ILs are potential electrolytes for use in electrochemical devices. Simultaneously, the [HEMMor]⁺ derivatives have practical value in electrolyte applications because of their easy synthesis procedures, cheap morpholinium cation sources and possibilities of high Li⁺ mobility by oxygen group in the morpholinium cation. However, [HEMMor]⁺ derivatives showing high viscosity usually had lower ionic conductivities than [HEMIm]⁺ derivatives.     

Effect of cation structure on the electrochemical and thermal properties of ion conductive polymers obtained from polymerizable ionic liquids

Several onium cations having vinyl group formed ionic liquids after coupling with bis(trifluoromethanesulfonyl)imide. These monomers were polymerized, and the relation between onium cation structure and properties of thus polymerized ionic liquids was investigated. The polymerized ionic liquid having ethylimiadzolium cation unit showed the highest ionic conductivity of around 10⁻⁴ S cm⁻¹ at 30 °C among the obtained polymers reflecting the lowest glass transition temperature of −59 °C. These polymers were thermally stable and their decomposition temperatures were about 350 °C. The ionic conductivity of the polymerized ionic liquids decreased by both the addition of lithium bis(trifluoromethanesulfonyl)imide and the polymerization in the presence of cross-linker. However, the polymerized ionic liquid having 1-methylpiperidinium cation structure showed good lithium ion transference number of 0.43 at room temperature.     

Gel polymer electrolyte based on poly(acrylonitrile-co-styrene) and a novel organic iodide salt for quasi-solid state dye-sensitized solar cell

A gel polymer electrolyte based on poly(acrylonitrile-co-styrene) as polymer matrix and N-methyl pyridine iodide salt as I⁻ source was prepared. Controlling the concentration of polymer matrix of poly(acrylonitrile-co-styrene) at 17.5 wt.%, mixing the binary organic solvents mixture ethylene carbonate and propylene carbonate with 6:4 (w/w), and the concentration of N-methyl pyridine iodide and iodine with 0.5 and 0.05 M, respectively, the gel polymer electrolyte attains the maximum ionic conductivity (at 30 °C) of 4.63 mS cm⁻¹. Based on the gel polymer electrolyte, a quasi-solid state dye-sensitized solar cell was fabricated and its overall energy conversion efficiency of light-to-electricity of 3.10% was achieved under irradiation of 100 mW cm⁻².     

Recrystallization studies on isotropic cold-crystallized PET: Influence of heating rate

The nanostructural changes associated to the multiple melting behaviour of isotropic cold-crystallized poly(ethylene terephthalate) (PET) have been investigated by means of simultaneous wide- and small-angle X-ray scattering, using a synchrotron radiation source. Variations in the degree of crystallinity, coherent lateral crystal size and long period values, as a function of temperature, for two different heating rates are reported for cold-crystallized samples in the 100-190 °C range. The Interface Distribution Function analysis is also employed to provide the crystalline and amorphous layer thickness values at various temperatures of interest. Results suggest that samples crystallized at both low (T_a = 100-120 °C) and high (T_a = 160-190 °C) temperatures are subjected to a nearly continuous nanostructural reorganization process upon heating, starting immediately above T_g (≈80 °C) and giving rise to complete melting at ≈260 °C. For all the T_a investigated, a melting-recrystallization mechanism seems to take place once T_a is exceeded, concurrently to the low-temperature endotherm observed in the DSC scans. For low-T_a and slow heating rates (2 °C/min), a conspicuous recrystallization process is predominant within T_a + 30 °C ≤ T ≤ 200 °C. In contrast, for high-T_a, an increasingly strong melting process is observed. For both, high- and low-T_a, an extensive structural reorganization takes place above 200 °C, involving the appearance of new lamellar stacks simultaneously to the final melting process. The two mechanisms should contribute to the high-temperature endotherm in the DSC scan. Finally, the use of a high heating rate is found to hinder the material's overall recrystallization process during the heating run and suggests that the high-temperature endotherm is ascribed to the melting of lamellae generated or thickened during the heating run.     

Optical microscopy and conductivity of poly(ethylene oxide) complexed with KI salt

The optical microscopy, crystallinity and ion conductivity of PEO complexed with potassium iodide (KI) salt are present. The spherulite structure derived from polarized optical microscopy (POM) suggested the ion induces different spherulite structures from that without salt. The size of the spherulites decreases with increasing salt concentration and is completely destroyed with KI salt content of 20 wt% (O-K ratio 15:1). This result concurs with the X-ray diffraction and DSC studies, that PEO crystallinity is reduced upon addition of KI salt. Upon elevating the temperature, the POM micrographs elucidate degradation of the spherulite structure when smaller crystallites begin to melt before the melting temperature of SPE, and become completely opaque above PEO melting temperature (T_m). The pseudo-activation energy derived from variable temperature conductivity measurements of about 0.24 eV is similar to that of PEO-lithium salt systems and suggested the identical PEO segmental motion governs the fundamental ion movement. Stable PEO-K complex (T_m from 135 to 155 °C) is formed after annealing at 120 °C for 12 h. However, the conductivity is about one order smaller compared to lithium salt due to the shorter hopping distance of the heavier potassium ion.     

Phase diagram of a cellulose solvent: N-methylmorpholine-N-oxide-water mixtures

The phase diagram of the N-methylmorpholine-N-oxide-H₂O mixtures from 0 to 100% has been determined. Three crystalline hydrates have been identified, the already known monohydrate, a dihydrate and a hydrate composed of 8 water molecules per NMMO. The melting temperature of the 8H₂O-NMMO hydrate is −47 °C with a melting enthalpy of about 80 J/g. The region between 25 and 55% of water does not show any crystallisation, but a glass transition around −60 to −100 °C.     

Thermally reactive phenylethynyl-terminated bis(benzylester) and bis(amide) monomers based on semi-enzymatically produced 6-phenylethynyl picolinic acid

The synthesis and isolation of 6-phenylethynyl picolinic acid (PEPCA; IUPAC name: 6-(2-phenylethynyl)pyridine-2-carboxylic acid) was first demonstrated when Acinetobacter sp. strain F4 was used to biotransform diphenylacetylene to the ring-fission product that underwent facile ring closure to form PEPCA in the presence of ammonium ions. Here, the structure and properties of PEPCA were confirmed by comparison with those of PEPCA that was chemically synthesized. In the chemical route, commercially available 6-bromopicolinic acid was first converted to methyl 6-bromopicolinate using methyl iodide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The resulting methylester was coupled with phenylacetylene by the palladium-catalyzed reaction to yield methyl 6-phenylethynyl picolinate, which was then hydrolyzed by sodium carbonate to afford PEPCA. Both enzymatically and chemically synthesized PEPCA were used to prepare its thermally reactive bis(benzylester) and bis(amide) derivatives. Thus, three phenylethynyl-terminated bis(amide) derivatives were synthesized by treating PEPCA with 1,3-phenylenediamine, 4,4′-oxydianiline or 4,4′-(hexafluoroisopropylidene)dianiline via dicyclohexylcarbodiimide (DCC)-mediated amidation. The bis(benzylester) derivative was prepared from PEPCA and α,α′-dibromo-p-xylene. All the intermediates and final products were characterized by FT-IR, NMR, MS and elemental analysis. The thermal properties of PEPCA and the reactive derivatives were characterized by DSC and TGA. The exothermic peaks of three bis(amide) derivatives were at least 20-40 °C lower than typically reported for the phenylethynyl compounds. Lowered reaction temperatures observed for the thermally-induced free radical polymerization of phenylethynyl groups were attributed to the strong electron-withdrawing capability of the pyridine moiety. Bis(amide) derivatives exhibited excellent thermal stability after previously cured at 300 °C for 30 min and 350 °C for 30 min.     

Investigation of ash deposit formation during co-firing of coal with sewage sludge, saw-dust and refuse derived fuel

Blends of a South African bituminous “Middleburg” coal and alternative fuels (sewage sludge, saw-dust and refuse derived fuel) have been fired in the slagging reactor to examine the effect of the added fuel on slagging propensity of the mixtures. Two ceramic deposition probes have been used to investigate the initial stages of slagging at 1300 °C and 1200 °C, at 0.5 s and 2 s residence times, respectively. The deposition rates and the deposit structures have been different for the two probes used.Substantial impact of sewage sludge has been observed. The initially formed deposits have become rapidly molten and they flow around the deposition probes, particularly when the sewage sludge fraction exceeds 15% by thermal input and the gas flow temperature exceeds the ash melting point. A 5% addition of the refuse derived fuel (RDF) has increased the deposition rate by almost a factor of two. Large RDF ash particles have been observed in the deposits.The slagging propensity has been correlated with the slagging index based on the ratio of fluxing oxides to sintering oxides. Intensive slagging has been observed when the index is in the 0.75-2 range. Moving away from this range in either direction has decreased the slagging intensity.     

Studies on poly(vinylidene fluoride)-clay nanocomposites: Effect of different clay modifiers

Montmorillonite clay based poly(vinylidene fluoride) nanocomposites were prepared by melt-mixing. The clays used included unmodified clay, a commercially available ammonium based clay, and two organically modified clays prepared by cation exchange with hexadecylpyridinium chloride and with octadecyltriphenylphosphonium bromide. PVDF-clay nanocomposites were processed in a mini twin-screw extruder. The structure of nanocomposites, analyzed using WAXD and TEM, indicated different extents of the clay dispersion depending on the modifier. PVDF formed β-phase crystals in the presence of organically modified clay when crystallized from its melt; in contrast, α-crystals were formed in the absence of clay and with unmodified clay. SAXS analysis indicated that the long period and crystalline lamella thickness decreased with the addition of clay. The melting and crystallization temperatures increased around 10 and 13 °C, respectively, with 5 wt% of phosphonium modified clay, which was the highest among the clays used. Further, the clay served as a nucleating agent for PVDF matrix, as observed by hot-stage polarized optical microscopy. The average spherulitic radius, determined from small angle light scattering, decreased with clay content. The elongation at break increased around 200% with the addition of only 5 wt% of ammonium clay. The storage and loss moduli of the nanocomposites were significantly higher than those of PVDF throughout the temperature range. Dielectric measurements showed a maximum increase of about 8 units of dielectric constant at 1 Hz frequency with 5 wt% organoclay.     

Supercritical CO2 as an efficient medium for layered silicate organomodification: Preparation of thermally stable organoclays and dispersion in polyamide 6

In this study, the preparation of organoclays via a new process using supercritical carbon dioxide is described. This method turns out to be very efficient with various surfactants, in particular nonwater-soluble alkylphosphonium salts. The influence of the surfactant as well as of the clay nature on the thermal stability of the organoclay is evaluated by thermogravimetric analysis. Phosphonium-based montmorillonites are up to 90 °C more stable than ammonium-based montmorillonites. Moreover, the use of hectorite adds another 40 °C of thermal stability to the phosphonium-modified clays. These organomodified clays have been melt-blended with polyamide 6 and morphology as well as fire properties of the nanocomposites are discussed, in terms of influence of the stability of organoclays. For the first time, comparison of nanocomposites based on clay organomodified by ammonium and phosphonium salts of the very same structure is reported.     

Thermally induced crystallization of mechanosynthesized chlorapatite–titania composite nanopowders

The thermally induced crystallization of mechanosynthesized chlorapatite–titania composite nanopowder was investigated. Firstly, the composite nanopowder was produced after 5 h of milling. The mechanosynthesized powder was annealed in the range 900–1300 °C for 1 h. The 5 h milled sample showed the crystallite size and lattice strain of about 23±1 nm and 0.0107±0.00054, respectively. During the subsequent annealing, crystallization of the milled sample at 900 °C and severe decomposition of nanocomposite at 1300 °C were detected. Accordingly, the fraction of crystalline phase reached a maximum around 96±4% at 900 °C and then declined to 80±4% at 1300 °C. The lattice strain decreased drastically to about 0.0002±0.00001 at 1300 °C, while the crystallite size increased significantly to around 277±14 nm. Based on the obtained data, the unit cell volume of CAp went down during the thermal treatment due to the ion exchange reaction between chlorapatite and titania. According to the electron microscopic observations, the morphological features of composite nanopowders were influenced strongly by the annealing temperature. The 5 h milled sample was composed of spheroidal particles with an average size of about 35 and 190 nm before and after annealing at 900 °C, respectively. At 1100 °C, the coalescence of nanospheres was dominant. Finally, a porous composite structure comprised of coarse grains with an average size of about 1 μm along with finer grains with a mean size of around 100 nm was formed at 1300 °C.     

Thermal decomposition of pyrotechnic mixtures containing either aluminum or magnesium powder as fuel

Thermal behavior of energetic materials is critical to safe production, storage, handling or even demilitarization. In this work, the thermal behavior of Al, Mg, CuO, KMnO₄ and also three mixtures containing Al + CuO, Mg + CuO and Mg + KMnO₄ were studied experimentally using differential scanning calorimetry and thermogravimetry. These mixtures are sometimes used as pyrotechnic mixtures in military industries. Also, the influence of different heating rates (5, 10, 15 and 20 °C/min) on the DSC behavior of the mixtures was verified. The results showed that as the heating rate was increased, melting points and ignition temperatures of the mixtures were increased. On the other hand, TG-DSC analysis for Mg + KMnO₄ mixture indicates that this mixture melts at 283.0 °C and decomposed at 292.1 °C. By replacing KMnO₄ with CuO as the oxidizer of the magnesium, these temperatures enhanced to 368.7 °C and 408.3 °C, respectively. However, replacing Mg with Al in the Mg/CuO mixture decreases the melting and ignition temperatures of the mixture to 231.4 °C and 271.9 °C, respectively. The activation energy for each pyrotechnic mixture was computed. Also, the values of ΔS^#, ΔH^# and ΔG^# of their reaction were calculated.     

Poly(trimethylene terephthalate) copolyester containing ethylene glycol moieties. Part 1: Crystallization kinetics and melting behavior

A copolyester was characterized to have 91 mol% trimethylene terephthalate unit and 9 mol% ethylene terephthalate unit in a random sequence by using ¹³C NMR. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization kinetics in the temperature range (T_c) from 180 to 207 °C. The melting behavior after isothermal crystallization was studied by using DSC and temperature modulated DSC (TMDSC). The exothermic behavior in the DSC and TMDSC curves gives a direct evidence of recrystallization. No exothermic flow and fused double melting peaks at T_c = 204 °C support the mechanism of different morphologies. The Hoffman-Weeks linear plot gave an equilibrium melting temperature of 236.3 °C. The kinetic analysis of the growth rates of spherulites and the morphology change from regular to banded spherulites indicated that there existed a regime II → III transition at 196 °C.     

Synthesis and characterization of poly(1-vinyl-3-alkylimidazolium) iodide polymers for quasi-solid electrolytes in dye sensitized solar cells

A series of new poly(1-vinyl-3-alkylimidazolium) iodide polymers with different alkyl derivatives such as methyl, propyl and perflurodecyl have been synthesized. The alkyl substituent influenced some properties such as solubility, thermal stability, glass transition and crystallinity of the polymers. For instance, polymer having the propyl substituent was soluble in solvents of intermediate polarity such as acetonitrile, chloroform and THF, the one with the methyl substituent was only soluble in very polar solvents such as water and methanol and the fluorinated polymer was only soluble in DMF. The alkyl substituent also influenced the thermal stability in the order methyl > propyl > perflurodecyl and all the polymers thermally decomposed between 250 and 400 °C in nitrogen. The poly(1-vinyl-3-alkyl-imidazolium) iodide polymers having propyl and methyl substituents were amorphous polymers showing a glass transition temperature of 43 and 21 °C, respectively; and perflurodecyl polymers were semi-crystalline with a Tm at 153 °C and a Tg at 20 °C, as indicated by differential scanning calorimetry.Polymer electrolytes were formulated as mixtures of the ionic liquid 1-methyl-3-propylimidazolium iodide and the poly(1-vinyl-3-alkylimidazolium) iodide polymers. These polymer electrolytes showed ionic conductivities in the range of 10⁻³ to 10⁻⁷ S/cm at room temperature which strongly depended on the ionic liquid content. Finally, poly(1-vinyl-3-propyl-imidazolium) iodide was used to obtain gel electrolytes by adding it to a typical acetonitrile electrolyte used in dye sensitized solar cells (DSSCs). Solar cells with 1 cm² area prepared using the polymer gel electrolyte yielded a maximum light-to-electricity conversion efficiency of 3.73%.     

Thermal behavior and characteristics of fired geopolymers produced from local Cameroonian metakaolin

The thermal behavior along with certain characteristics of geopolymers produced from local Cameroonian metakaolin and heated up to 1000 °C were examined. Geopolymers fired up to 900 °C had the same physical aspect as initial ones and those fired at 1000 °C warped, were glazed and blistered. The TG showed elimination of water according to two stages. The dilatometric curves of preheated samples showed shrinkage between 90 and 250 °C followed by expansion and sintering. The samples heated up to 700 °C were amorphous and new crystalline phases appeared around 900 °C. The microstructure of geopolymers heated between 300 and 900 °C showed progressive disruption and the linear shrinkage increased. The water absorption of the samples fired up to 700 °C increased slightly and tremendously around 900 °C. A drastic decrease of compressive strength was observed with the samples fired between 300 and 900 °C. Hence, the characteristics of geopolymers lessened with elimination of the water which forms hydration spheres around the compensating cations (Na⁺) opposed to tetrahedral groups AlO₄⁻ along with transformation of amorphous phase.     

Thermal stability of gelatin gels: Effect of preparation conditions on the activation energy barrier to melting

10, 20, and 40 wt.% aqueous gelatin gels were prepared under isothermal (annealing at 15, 20, and 25 °C for 15 to 120 min) and nonisothermal (cooling at 1 °C min⁻¹) conditions. Isoconversional kinetic analysis of DSC data on gel melting (gel-sol transition) of all types of gels revealed significant variations in the activation energy throughout the process. Activation energy barrier to melting of isothermally prepared gels was in the range 160-190 kJ mol⁻¹ and found to increase with increasing the annealing temperature that was the major effect discovered. Activation energy barrier to melting of nonisothermally prepared gels was determined to be around 120-140 kJ mol⁻¹ and increase with increasing the concentration. Local reversibility of the gel melting was demonstrated by using temperature modulated DSC.     

Thermal and crystalline behaviour of silk fiborin/nylon 66 blend films

A series of blend films of silk fibroin (SF) with nylon 66 were prepared by the common solution cast method. DSC analysis of every blend sample showed a large and broad endothermic peak around 150 °C. For SF/nylon 66 samples containing 10 and 30 wt% SF, large spherulites were observed and their melting processes were recorded using a polarizing microscope with hot-stage. Furthermore, a detailed study on 30 wt% SF sample indicated a distribution of two distinct spherulites: large spherulites in part A and much smaller ones in part B. In WAXD pattern, the large spherulites presented new peaks different from nylon 66 or silk's characteristic peaks that were ever reported, while the small ones assumed triclinic form of normal nylon 66. SEM showed that the SF and nylon 66 were nearly miscible in all ratios except that of 50 wt% SF.