Autoxidation of thiols with cobalt(II)phthalocyanine-tetra-sodium sulfonate attached to poly(vinylamine), 6. Immobilized catalysts by crosslinking of poly(vinylamine)

Poly(vinylamine), being both carrier and promotor of the thiol oxidation catalyst cobalt(II)phthalocyanine-tetra-sodium sulfonate (CoPc(NaSO₃)₄), was crosslinked with α,α′-dichloro-p-xylene, thus yielding porous hydrophilic networks. The effects of experimental parameters such as stirring speed, particle size, degree of crosslinking, distribution of catalytic sites (CoPc(NaSO₃)₄) in the catalyst particles, pH, temperature, and thiol concentration were investigated. Reaction rates observed for the immobilized catalyst system appeared to be 4–30 times lower as compared with the water soluble polymeric catalyst system but still higher than those of the polymer free CoPc(NaSO₃)₄ catalyst. At a stirring speed around 3 · 10³ rpm not the mass transfer from the bulk to the catalyst particles but intra-particle diffusion limits the reaction rate. Accordingly, an uncrosslinked polymeric catalyst anchored to silica, with catalytic sites situated close to the particle surface, exhibited comparatively high activity, i.e. only four times lower than the soluble polymeric catalyst. In addition, the heterogeneous catalyst systems showed resemblance in kinetic behaviour with the soluble polymeric thiol oxidation catalyst.     

Synthesis of amphiphilic polystyrene–ionene diblock copolymers with controlled block lengths

Amphiphilic polystyrene-ionene diblock copolymers with blocks of controlled molecular weights were synthesized by a new method. The preparation starts with the anionic polymerization of styrene with 3-(dimethylamino)propyl-lithium as initiator, yielding tertiary amino end-functionalized polystyrenes of molecular weights that can be varied over a wide range from 1 to 100kg/mol, and a relatively low polydispersity (M?_w/M?_n = 1.1–1.4). The crucial step in this method is the stepwise coupling of the reactive end-group of the polystyrene with bromo- and tertiary-amino-terminated monodisperse oligomeric 2,4-ionenes. The amphiphilic polymers with well-defined block lengths were characterized by thin-layer chromatography, end-group titration and elemental analysis. Amphiphilic block copolymers with a monodisperse ionene block consisting of up to 10 quaternary ammonium groups could be derived.     

Effect of [Mn(acac)3] and its combination with 2,2′-bipyridine on the autoxidation and oligomerisation of ethyl linoleate

In this study we investigated the autoxidation and oligomerisation of ethyl linoleate (EL) catalysed by [Mn(III)(acac)₃] (acac=2,4-pentanedionate) and its combination with 2,2-bipyridine (bpy), in comparison with the EL catalysed by Co(II) 2-ethylhexanoate (Co-EH). EL is a model compound for the alkyd resin in alkyd paints, Co-EH is a common drying catalyst for alkyd paints, and [Mn(acac)₃] and the [Mn(acac)₃]/bpy combination are potential new drying catalysts. The autoxidation of EL was studied through time-resolved Raman spectroscopy, oxygen uptake measurements, and peroxide amount determination. To follow the oligomerisation of EL in time, size exclusion chromatography was used. Head-space GC-MS measurements were performed to determine the amounts of hexanal and pentanal that were formed as volatile byproducts during the autoxidation of EL. The autoxidation rates of EL in the presence of Co-EH and [Mn(acac)₃]/bpy were found to be similar, while the rate in the presence of [Mn(acac)₃] was slower. The extent of EL oligomerisation was much higher for [Mn(acac)₃] compared to the other catalysts. Different mechanisms are proposed for the mode of action for each of the catalysts: Co-EH is primarily a hydroperoxide decomposition catalyst, as is [Mn(acac)₃], only less active. The [Mn(acac)₃]/bpy combination probably forms the very reactive complexes [Mn(III)(acac)₂(bpy)]⁺ and [Mn(II)(acac)₂(bpy)], which are responsible for a very high autoxidation rate, but also for significant degradation of the formed EL oligomers via β-scission reactions due to the promotion of alkoxy radical formation.     

Polyurethanes with monodisperse rigid segments based on a diamine–diamide chain extender

Polyether(bisurethane‐bisurea‐bisamide)s (PEUUA) based on poly(tetramethylene oxide) (PTMO) were synthesized by chain extension of PTMO endcapped with a diisocyanate (DI), and a diamine–diamide extender. The prepolymers were PTMOs with molecular weights between 1270 and 2200 g mol^?1, either endcapped with 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (2,4‐TDI), or 1,6‐hexane diisocyante (HDI) and with a low content of free diisocyanate (<0.1 wt %). The diamine–diamide (6A6) extender was based on hexamethylene diamine (6) and adipic acid (A). In this way, segmented polyurethanes with monodisperse rigid segments (DI‐6A6‐DI) were obtained. The PEUUAs were characterized by DSC as well as temperature‐dependent FTIR and DMTA. The mechanical properties of the polymers were evaluated by compression set and tensile test measurements. The polyurethanes with monodisperse rigid segments displayed low glass transition temperatures, almost temperature‐independent rubbery plateaus and sharp melting temperatures. The crystallinities of the hard segments were 70–80% upon heating and 40–60% upon cooling. The rate of crystallization was moderately fast as the supercooling (T_m ? T_c) was in the order 36–54°C. The polyurethanes based on HDI had a much higher rubber modulus as compared to the MDI and 2,4‐TDI‐based polymers, because of a higher degree of crystallinity and/or a higher aspect ratio of the crystallites. The HDI residues are flexible and not sterically hindered and could therefore be more easily packed than MDI or 2,4‐TDI residues. Polyurethanes with monodisperse DI‐6A6‐DI hard segments have interesting properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis, structure and magnetic properties of the first copper(II) complex with an (E)-4-aryl-4-oxo-2-butenoato ligand

A new binuclear Cu(II) complex with an (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato ligand (L) was successfully synthesized and characterized by elemental analysis and IR-spectroscopy. The structures of (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoic acid (HL), and the corresponding (tetrakis)-μ-[(E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato]-bis(ethanol)-copper(II) complex, [Cu₂L₄(C₂H₅OH)₂], were determined by single crystal X-ray analyses and are preliminarily discussed. This is the first complex of a transition metal with ligand L, as well as the first determined crystal structure of a metal complex with this type of ligand. Analysis of the magnetic susceptibility measurements of the isolated [Cu₂L₄(C₂H₅OH)₂] · H₂O complex shows the existence of a strong anti-ferromagnetic intradimer coupling, with an exchange integral value 2J of −260 cm⁻¹.     

Transition metal complexes with Girard reagent-based ligands, Part I: Synthesis and crystal structure of the first cobalt(III) complexes with Schiff base derivative of Girard reagent

A new ligand, pyridoxilidene Girard-T hydrazone, [H₃L]Cl₂ · 2H₂O, and its octahedral cobalt(III) complexes [Co(HL)(NO₂)₃] · H₂O (1) and [Co(HL)₂](PF₆)₃ (2) were synthesized. The X-ray analysis of (1) showed that the complex has a mer-octahedral configuration formed by coordination of the tridentate ONO neutral Schiff-base molecule and three monodentate N-bonded NO₂ groups. Hydrogen bonds and intermolecular interactions for this complex are discussed. Complex (2) also has a mer-octahedral configuration. The ligand and complexes were characterized by elemental analysis, conductometric and magnetochemical measurements, IR and UV–Visible, ¹H and ¹³C NMR spectra.     

Synthesis and properties of monodisperse hydroxy-terminated oligomers of 1,4-butanediol and 2,4-toluene diisocyanate

The synthesis of monodisperse hard segments containg 2,4-TDI and 1,4-butanediol by a simple technique is described. High purity material is obtained in good yield. The structures of these hard segments are confirmed by proton n.m.r., ¹³Cn.m.r., and i.r. Glass transition temperatures and melting temperatures are reported. The T_g′s of the hard segments are inversely proportional to the reciprocal of their molecular weights. The T_m′s show an odd-even effect relative to the number of 2,4-TDI units in the hard segment.     

Synthesis and electrochemical and in situ spectroelectrochemical characterization of manganese, vanadyl, and cobalt phthalocyanines with 2-naphthoxy substituents

Metallo (Mn, Co, VO) phthalocyanines bearing peripheral 2-naphthoxy groups were synthesized by cyclotetramerisation of the corresponding phthalonitrile derivative. The phthalocyanine compounds were characterized by elemental analyses, mass, FT-IR and UV–vis spectral data. Three intense bands in the electronic spectra clearly indicate the absorptions resulting from naphthyl groups along with the Q and B bands of the phthalocyanines. Electrochemical and spectroelectrochemical measurements exhibit that incorporation of redox active metal ions, Co^II and Mn^III, into the phthalocyanine core extends the redox capabilities of the Pc ring including the metal-based reduction and oxidation couples of the metal. Presence of molecular oxygen in the electrolyte system affects the voltammetric and spectroelectrochemical responses of the cobalt and manganese phthalocyanines due to the interaction between the complexes and molecular oxygen. Interaction reaction of oxygen with CoPc occurs via an “inner sphere” chemical catalysis process. While CoPc gives the intermediates [O₂⁻–Co^IIPc⁻²]⁻ and [O₂²–Co^IIPc⁻²]²⁻, MnPc forms μ-oxo MnPc species. An in situ electrocolorimetric method has been applied to investigate the color of the electro-generated anionic and cationic forms of the complexes for possible electrochromatic applications.     

Structural investigations of (9‐ethyl‐carbazol‐6‐yl) methyl methacrylate/methyl acrylate copolymers using two‐dimensional NMR spectroscopy

(9‐Ethyl‐carbazol‐6‐yl) methyl methacrylate/methyl acrylate (E/A) copolymers of different compositions were prepared by solution polymerization by varying the molar infeed ratio, using AIBN as initiator at 60°C. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be r_E = 1.16 ± 0.02 and r_A = 0.69 ± 0.01 whereas those calculated from RREVM method were found to be r_E = 1.18 and r_A = 0.68. The molecular weights (M_w) and polydispersity index (PDI, M_w/M_n) were determined using gel permeation chromatography (GPC). Glass transition temperatures (T_g) for different compositions of E/A copolymers were determined using differential scanning calorimetry (DSC). Copolymer molar outfeed ratio (F_E) was calculated from ¹H NMR spectra. The α‐methyl, methine, backbone methylene, and quaternary carbon resonance signals of the copolymers were distinguished using ¹³C{¹H}, DEPT‐45, ‐90, and ‐135 NMR techniques. The α‐methyl and β‐methylene showed compositional and configurational sensitivity up to pentad and tetrad level, respectively, whereas methine showed only compositional sensitivity up to pentad level. Unambiguous assignments for ¹H and ¹³C{¹H} NMR spectra were done by correlating 1D (¹H, ¹³C{¹H}, DEPT) and 2D (HSQC, TOCSY) NMR data. The spectral assignments for carbonyl region were done by studying higher bond order couplings by heteronuclear multibond correlation (HMBC) spectra. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5595–5606, 2006     

Synthesis of poly(1‐hexene)s end‐functionalized with phenols

Electrophilic alkylations of phenol/2,6‐dimethylphenol were performed with vinylidene‐terminated poly(1‐hexene)s using BF₃·OEt₂ catalyst. Vinylidene‐terminated poly(1‐hexene)s with M_n varying from 400 to 10000 were prepared by bulk polymerization of 1‐hexene at 50 to ?20 °C using Cp₂ZrCl₂/MAO catalysts. The phenol/2,6‐dimethylphenol‐terminated poly(1‐hexene)s was characterized by NMR (¹H, ¹³C), UV, IR and vapor phase osmometer (VPO). The isomer distribution (ortho, para and ortho/para) was determined by ¹³P NMR using a phosphitylating reagent, namely 2‐chloro‐1,3,2‐dioxaphospholane. The number‐average degree of functionality (F_n) >0.9 with >95% para selectivity could be achieved using low‐molecular‐weight oligomers of poly(1‐hexene)s. Copyright © 2005 Society of Chemical Industry     

Karrooite green pigments doped with Co and Zn: Synthesis,color properties and stability in ceramic glazes

The solid-state synthesis and stabilization of Co doped (Mg_1−xCo_xTi₂O₅), Zn doped (Mg_1−xZn_xTi₂O₅) and Co- and Zn-codoped karrooite solid solutions (Mg_0.8−xZn_0.2Co_xTi₂O₅ and (Mg_0.5Zn_0.5)_1−xCo_xTi₂O₅) were investigated. In addition, the optical spectra, color properties and technological performance of (Co,Zn)-karrooite compositions as new green ceramic pigments were also analyzed. XRD characterization revealed for the first time the high solid solubility of Zn²⁺ in MgTi₂O₅ karrooite at 1200 ºC (between 60 and 80 mol% per Mg or karrooite formula unit). In contrast, the reactivity and stabilization of karrooite phase decreased in the case of Co²⁺ doping. Interestingly, codoping with Zn²⁺ ions at high molar ratios (Zn:Mg ratio equal to 1:1) enhanced the reactivity and enabled the stabilization of (Co,Zn)-MgTi₂O₅ karrooite solid solutions, even with high Co²⁺ loadings (20 mol% per karrooite formula unit). The (Co,Zn)-MgTi₂O₅ pigments exhibited yellowish-green colors associated to Co²⁺ ions allocated in octahedral M1 and M2 sites of karrooite lattice, and becoming more intense and less yellow the higher the Co content. However, Zn²⁺ codoping produced less saturated green colors with similar green but lower yellowish hues. The obtained pigments were not stable enough within the tested ceramic glazes, giving rise to turquoise colorations due to cobalt leaching and incorporation into tetrahedral sites of the glassy phase. The stability of Co-karrooite green pigments was higher in a Ca- and Zn-enriched ceramic glaze (B) fired at a higher temperature (1050 °C).     

Ultrafine Amorphous Co–Fe–B Catalysts for the Hydrolysis of NaBH4 Solution to Generate Hydrogen for PEMFC

For hydrogen generation from alkaline sodium borohydride (NaBH₄) solution, Co–Fe–B catalysts with different Co/(Co + Fe) molar ratios (χ_Co) were prepared by the chemical reduction of CoCl₂ and FeCl₃ ethanol solution with KBH₄ solution. The X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the as‐prepared Co–Fe–B catalysts were in amorphous form and ultrafine. The hydrogen generation measurements showed that as‐prepared Co–B and Co–Fe–B catalysts exhibited excellent catalytic activity. Co–Fe–B with the Co/(Co + Fe) molar ratio (χ_Co) of 0.85 was the best. Its maximum hydrogen generation rate at 298 K was 4,310 mL min^–1 g^–1, while the Co–B was 2,773 mL min^–1 g^–1. The enhanced activity could be attributed to large active surface area, electron transfer from B and Fe to active Co sites, and improvement in the dispersion of Co–B with Fe₂O₃. The activation energy of Co–Fe–B catalyst with the molar ratio χ_Co = 0.85 was decreased to 29.09 kJ mol^–1 as compared to 30.85 kJ mol^–1 obtained with Co–B.     

Synthesis of branched polyethylene by ethylene homopolymerization with a novel (α‐diimine)nickel complex in the presence of methylaluminoxane

Branched polyethylene (PE) was prepared with a novel (α‐diimine)nickel(II) complex of 2,3‐bis(2,6‐dimethylphenyl)‐butanediimine nickel dichloride {[2,6‐(CH₃)₂C₆H₃? N?C(CH₃)C(CH₃)?N? 2,6‐(CH₃)₂C₆H₃]NiCl₂} activated by methylaluminoxane in the presence of a single ethylene monomer. The influences of various polymerization conditions, including the temperature, Al/Ni molar ratio, Ni catalyst concentration, and time, on the catalytic activity, molecular weight, degree of branching, and branch length of PE were investigated. According to gel permeation chromatography, the weight‐average molecular weights of the polymers obtained ranged from 1.7 × 10⁵ to 6.0 × 10⁵, with narrow molecular weight distributions of 2.0–3.5. The degree of branching in the polymers rapidly increased with the polymerization temperature increasing; this led to highly crystalline to totally amorphous polymers, but it was independent of the Al/Ni molar ratio and catalyst concentration. At polymerization temperatures greater than 20°C, the resultant PE was confirmed by ¹³C‐NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons). The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1123–1132, 2002; DOI 10.1002/app.10398     

Role of the bases and phosphoryl bases of phospholipids in the autoxidation of methyl linoleate emulsions

Methyl linoleate, emulsified in borate buffer with sodium lauryl sulfate, was used to study the pro- or antioxidant effect of 0-phosphocholine, 0-phosphoethanolamine, 0-phosphoserine, as well as the corresponding nonphosphoryl compounds. Oxygen uptake was calculated from rate data obtained at 37 C with an oxygen electrode. The results were similar for the corresponding phosphoryl and nonphosphoryl bases. 0-Phosphocholine and choline had little effect at either pH 7.9 or 10.2. 0-Phosphoethanolamine and ethanolamine significantly increased oxygen uptake at pH 7.9, but significantly decreased uptake at pH 10.2. 0-Phosphoserine and serine decreased oxygen uptake at both pH values. The catalytic activities of the bases investigated may be attributed to their functional groups. The phosphoryl and β-hydroxy groups exhibited no catalytic activity in the autoxidation of methyl linoleate emulsions at either pH 7.9 or 10.2. The α-carboxyl amino group of 0-phosphoserine and serine decelerated autoxidation at both pH values. The amino group H₃N⁺ of the primary amine accelerated autoxidation, but the H₂N: group and the reverse effect. Since the quaternary amino group (CH₃)₃N⁺ did not affect autoxidation at either pH 7.9 or 10.2, we concluded that the presence of the N−H bond may be necessary for the prooxidant activity of an amine, and that the presence of a pair of free electrons on the nitrogen of an amine is necessary for its antioxidant activity. Kinetically, the autoxidation of methyl linoleate emulsion without added base was in agreement with Farmer’s proposed mechanism involving a bimolecular dissociation of hydroperoxides. However, methyl linoleate emulsion at pH 7.9 and 37 C in the presence of ethanolamine or 0-phosphoethanolamine was autoxidized by a mechanism involving a combined mono- and bimolecular dissociation of hydroperoxides. Submitted as partial requirement for a Ph.D. degree in Agricultural Chemistry. Presented in part at the AOCS Meeting, San Francisco, April 1969.     

The use of bimodal blends of vinyl ester monomers to improve resin processing and toughen polymer properties

Vinyl ester (VE) monomers with bimodal molecular weight distributions were prepared by reacting methacrylic acid with blends of monodisperse epoxy resins ranging in molecular weight from 350-7000 g/mol. Monodisperse vinyl ester monomers were prepared from epoxy resins of a single molecular weight. The extent of vinyl ester formation was found to be near complete and side reactions, such as etherification, did not occur to a significant extent. The viscosities of these vinyl ester resins were measured as a function of styrene content. It was found that resin viscosity, η, increased exponentially and predictably as both the styrene content (S) decreased and as the number average molecular weight (M_n) of the vinyl ester monomers increased: η∼exp(M_n)/exp(S). Cure kinetics studies showed that the vinyl ester reactivity ratio decreased to 0.1 from 0.6 for bimodal blends relative to monodisperse resins while the styrene reactivity ratio increased from 0.4 to 0.6. Thus, the microgels in bimodal blends were smaller than in monodisperse resins. Emissions studies proved that decreasing the styrene content reduced the VOC emission rate and total emissions. Higher VE molecular weights decreased the overall emissions due to a reduction in monomer mobility. T_g decreased from 143 to 125 °C as M_n of the VE monomers increased from 540 to 920 g/mol; yet, T_g of these bimodal blends were still equal to or greater than that of commercial VE resins (∼125 °C). The fracture toughness of bimodal blends increased from ∼100 to ∼330 J/m² as VE M_n increased from 540 to 920 g/mol because of matrix toughening. The fracture properties did not improve as the styrene content increased from 35 to 45 wt% because of corresponding changes in the morphology. Yet, there were numerous low VOC bimodal formulations with fracture properties in excess of the low VOC Dow Derakane 441-400 (110 J/m²) and even the industry standard Derakane 411-350 (240 J/m²).     

Ethylammonium nitrate enhances the extraction of transition metal nitrates by tri-n-butyl phosphate (TBP)

Several molecular polar solvents have been used as solvents of the more polar phase in the solvent extraction (SX) of metals. However, the use of hydrophilic ionic liquids (ILs) as solvents has seldomly been explored for this application. Here, the hydrophilic IL ethylammonium nitrate (EAN), has been utilized as a polar solvent in SX of transition metal nitrates by tri-n-butyl phosphate (TBP). It was found that the extraction from EAN is considerably stronger than that from a range of molecular polar solvents. The main species of Co(II) and Fe(III) in EAN are likely [Co(NO₃)₄]²⁻ and [Fe(NO₃)₄]⁻, respectively. The extracted species are likely Fe(TBP)₃(NO₃)₃ and a mixture of Co(TBP)₂(NO₃)₂ and Co(TBP)₃(NO₃)₂. The addition of H₂O or LiCl to EAN reduces the extraction because the metal cations coordinate to water molecules and chloride ions stronger than to nitrate ions. This study highlights the potential of using hydrophilic ILs to enhance SX of metals.     

Synthesis and Characterization of Novel Polymeric-Schiff Bases and Their Complexes

An investigation of the solid state conductivity of polymeric-Schiff bases derived from the condensation reaction of polyacrylamide and an aldehyde (4-methoxybenzaldehyde and 4-chlorbenzaldehyde) has been carried out and Co(II) and Ni(II) complexes have been prepared. Polymeric-Schiff bases and their metal complexes were characterized by molar conductance, magnetic susceptibility, and electronic and IR spectral studies. Conductivity measurements were carried out at 20 °C in dimethylformamide to determine the electrolytic behavior. The ¹H-NMR and ¹³C-NMR spectra, elemental analysis, and viscosity average molecular mass (M _v) of the polymeric-Schiff bases and their complexes were determined. All of the polymer–metal complexes showed high thermally stability. The DC conductivities of the solid samples were measured using a four-probe technique.     

Equilibrium and spectroscopic studies on the complexation of tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)lanthanoids(III) with tris(2,4-pentanedionato)cobalt(III) as complex ligand

Complexation equilibrium between tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)lanthanoids(III) (Ln(tta)₃, Ln=La, Eu, and Lu) and tris(2,4-pentanedionato)cobalt(III) (Co(acac)₃) has been studied by the liquid–liquid distribution technique. A 1:1 adduct of [Ln(tta)₃Co(acac)₃], i.e., a binuclear complex, was formed in benzene, and the stability constants were determined to be 10^4.64, 10^2.95, and 10^2.07 for La, Eu, and Lu respectively. The molar absorptivity of Co(acac)₃ for the ¹T_1g←¹A_1g transition increased with the adduct formation with Ln(tta)₃ in the order of Lu≪Eu<La. A ⁵⁹Co NMR study showed that a resonance of Co(acac)₃ shifted to the higher field with the adduct formation. The chemical exchange between free and complexed Co(acac)₃ was very slow in La but fast in Lu, while both the slow- and fast-exchange species existed in Eu.     

In situ immobilization of cobalt phthalocyanine on the mesoporous carbon ceramic SiO2/C prepared by the sol–gel process. Evaluation as an electrochemical sensor for oxalic acid

The mesoporous carbon ceramics SiO₂/20 wt% C (S_BET = 160 m² g⁻¹) and SiO₂/50 wt% C (S_BET = 170 m² g⁻¹), where C is graphite, were prepared by the sol–gel method. Scanning electron microscopy images and the respective element mapping showed that, within the magnification used, no phase segregation was detectable. The materials containing 20 and 50 wt% of C presented electric conductivities of 9.2 × 10⁻⁵ and 0.49 S cm⁻¹, respectively. These materials were used as matrices to support cobalt phthalocyanine (CoPc), prepared in situ on their surfaces, to assure homogeneous dispersion of the electroactive complex in the pores of both matrices. The surface densities of cobalt phthalocyanine on both matrix surfaces were 0.014 mol cm⁻² and 0.015 mol cm⁻² for materials containing 20 and 50 wt% of C, respectively. Pressed disk electrodes made with SiO₂/50 wt% C/CoPc and SiO₂/20 wt% C/CoPc were tested as sensors for oxalic acid. The electrode was chemically very stable and presented very high sensitivity for this analyte, with a limit of detection, LOD = 5.8 × 10⁻⁷ mol L⁻¹.     

Structure-property relations of poly(propylene oxide) block copolymers with monodisperse and polydisperse crystallisable segments

Segmented block copolymers with poly(propylene oxide) and crystallisable segments were synthesized and their structure-property relations studied. As crystallisable segments, amide units based on poly(p-xylylene terephthalamide), were used. The length of the amide segment was varied and these segments either had a monodisperse or random length distribution (polydisperse). The poly(propylene oxide) used was end capped with 20 wt% ethylene oxide (EO-tipped) and had a molecular weight of 2300 g/mol (M_n, incl. EO-tips). These segmented block copolymers are model block copolymers to gain insight in the structure-properties behaviour of related semi-crystalline segmented block copolymers, like polyether(urethane-urea)s. The morphology of the polyether(ester-amide)s (PEEA) was studied with TEM, the thermal properties with DSC and DMTA and the crystalline structures with WAXD. The elastic behaviour of the block copolymers was investigated in tensile and compression.Phase separation in PEEA's with crystallisable, short and monodisperse amide segments occurred by crystallisation, while with crystallisable random amide segments phase separation occurred through liquid-liquid demixing in combination with crystallisation. With short monodisperse amide segments, morphology of dispersed ribbons with a high aspect ratio was observed. PEEA's containing these monodisperse amide segments had higher moduli and better elastic properties as compared to PEEA's with random length amide segments. Increasing the length of the monodisperse amide segment increased the modulus and decreased the compression set of the corresponding blockcopolymers.