Determination of the interaction within polyester-based solid polymer electrolyte using FTIR spectroscopy

Characterization and interaction behavior between Li⁺ ion and CO groups of a series polyester electrolyte have been thoroughly examined using Fourier transform infrared (FTIR). The “free/Li⁺ bonded” CO absorptivity coefficient of the LiClO₄/polyester can be determined quantitatively using FTIR spectrum ranging from 1800 to 1650 cm⁻¹ at 80 °C. Results from curve fitting show that the “free/Li⁺ bonded” CO absorptivity coefficient is 0.144 ± 0.005. The CO group of polymer electrolyte shows strong interaction with Li⁺ ion and a limit value of 95% “Li⁺ bonded” CO is approached in the polymer electrolyte system when the Li⁺ ion equivalent fraction is about 0.28. The molecular structure of polyester electrolyte does not affect significantly the efficiency of interaction between Li⁺ ion and CO.     

Photo-polymerisation effects on the carbonyl CO bands of composite resins measured by micro-Raman spectroscopy

The spectra of photo-polymerised composite resins, measured by the micro-Raman spectroscopy, are analysed in the frequency region of the CO carbonyl stretching bands. The band intensities at about 1700 and 1715 cm⁻¹ (the peak frequencies of the hydrogen bonded and free CO bands, respectively) decrease with the irradiation time and with the methacrylate monomer conversion. Consequently, a degree of apparent conversion (DAC) can be defined. It is shown that the intensity variations conserve the band-shape and allow the DAC measurements via the single frequency intensity ratio. Both the bands give rise to DAC values which exhibit a one-to-one dependence on the degree of CC conversion, in partial disagreement with previous results. The microscopic mechanisms, associated to the intensity decrease, are critically revised and discussed on the basis of the experimental findings.     

Synthesis and characterization of liquid crystalline copolymers with dual photochromic pendant groups

In order to study the photoreactivity and the optical properties of liquid crystalline copolymers with multiple photochromic groups, a series of novel liquid crystalline binary and ternary polyacrylates consisting of one (CC or NN) or dual (CC and NN) photochromic segments were synthesized and characterized considering their liquid crystalline, optical, and photochromic properties and their thermal stability. Achiral homopolymer P1 shows a smectic A phase (fan-shaped texture), and all chiral copolymers CP1-CP6 exhibit chiral nematic phases (cholesteric, oily streaks textures). The polymers show excellent solubility in common organic solvents such as chloroform, toluene, and THF. These polymers also exhibit good thermal stability, with decomposition temperatures (T_ds) greater than 373 °C at 5% weight loss, and beyond 440 °C at 50% weight loss under nitrogen atmosphere. UV irradiation caused E/Z photoisomerization at NN and CC segments of the synthesized photochromic copolymers leading to reversible and irreversible isomerizations, respectively. The synthesized liquid crystalline ternary copolymer CP6, containing two different photochromic NN and CC groups, is sensitive to different UV wavelengths and is notably interesting from the viewpoint of photochromic copolymers.     

A depth-resolved look at the network development in alkyd coatings by confocal Raman microspectroscopy

The formation of molecular networks related to the consumption of unsaturated carbon-carbon double bonds (CC) during oxidative drying of alkyd coating films incorporating unsaturated fatty acids was studied. The concentration of CC bonds was measured as a function of drying time and distance from the exposed film surface (depth) using confocal Raman microspectroscopy (CRM). The change in spatial distribution of the CC double bond concentration across the film cross section provides information on the kinetics of the oxidative cross-linking process in the alkyd films. It was found that the CC bond consumption is not homogeneous across the depth of the drying film. The results obtained allowed us to quantitatively monitor the progress of the drying process and the movement of the ‘drying front’ within the coating films. The drying profiles suggest that oxygen penetration into the coating film is a rate-limiting factor in the drying process. Depth profiles during the film forming process develop due to local variations in the oxygen solubility, diffusion coefficient of oxygen, and available amount of double bonds for cross-linking. The influence of several industrially relevant factors, like oil length of the alkyd resin, thickener, solvent, and drier on the film formation process is discussed. Depth resolution of the analytical approach and spatial accuracy of confocal Raman microspectroscopy are also treated.     

Electrochemical and spectral studies on the catalytic oxidation of nitric oxide and nitrite by high-valent manganese porphyrins at an ITO electrode

Catalytic oxidation of nitric oxide and nitrite by water-soluble manganese(III) meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (Mn(III)(4-TMPyP) was first studied at an indium-tin oxide (ITO) electrode in pH 7.4 phosphate buffer solutions. A stepwise oxidation of Mn(III)(4-TMPyP) through high-valent manganese porphyrin species has been observed by electrochemical and spectroelectrochemical (OTTLE) techniques. The formal potential of 0.63 V for the formation of OMn(IV)(4-TMPyP) has been estimated from OTTLE data. The product, oxoMn(IV) porphyrin, was relatively stable decaying slowly to Mn(III)(4-TMPyP) with a first-order rate constant of 3.7 × 10⁻³ s⁻¹. OMn(IV)(4-TMPyP) has been found to oxidize NO catalytically at potentials about 70 mV more negative than that previously reported for OFe(IV)(4-TMPyP) with good selectivity against nitrite. Nitrite was catalytically oxidized at potentials higher than 1.1 V presumably by OMn(V)(4-TMPyP). OMn(IV)(4-TMPyP) was observed as an intermediate species. Nitrate has been confirmed to be a final product of the electrolysis at 1.2 V, while at 0.8 V nitrite left unchanged, demonstrating that OMn(IV)(4-TMPyP) could not oxidize nitrite. A possible schemes of the catalytic oxidation of NO by OMn^IV(4-TMPyP) and NO₂⁻ by OMn(V)(4-TMPyP) have been proposed.     

Oxidation of single-walled carbon nanotubes in dilute aqueous solutions by ozone as affected by ultrasound

A clean and simple wet chemical process using dilute aqueous ozone (O₃) solution with or without ultrasound (US) was used to functionalize single-walled carbon nanotubes (SWCNTs). Both O₃ and O₃/US treatments greatly increased the stability of SWCNTs in water. Results of X-ray photoelectron spectroscopy (XPS) showed that the surface oxygen to carbon atomic ratio increased by more than 600% after 72 h of O₃ treatment. Moreover, the effective particle size of SWCNTs was reduced from the initial 4400 to ∼300 and ∼150 nm, after 24 h of O₃ and O₃/US treatment, respectively. The zeta potential of treated SWCNTs decreased from 3.0 to −35.0 mV (at pH 4) after 2 h of treatment with both O₃ and O₃/US. Based on the XPS results, the oxidation pathway was proposed: at the onset of the oxidation reaction, the CC double bond was first converted to COH which was then oxidized to CO and OCOH concurrently. Oxidation reactions could be described well with first order expressions. Treatment time controlled the extent of surface oxidation and subsequently the stability and dispersion of SWCNTs in water.     

Raman microspectroscopy study of structure, dispersibility, and crystallinity of poly(hydroxybutyrate)/poly(l-lactic acid) blends

The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) blends are investigated by using Raman microspectroscopy. Four kinds of PHB/PLLA blends with a PLLA content of 20, 40, 60, and 80 wt% were prepared from chloroform solutions. Differences in the Raman microspectroscopic spectra between the spherulitic and nonspherulitic parts in the blends mainly lie in the CO stretching band and C-O-C and C-C skeletal stretching bands of PHB and PLLA. In addition to such bands, the Raman spectra of spherulitic structure in the blends show a band due to the CH₃ asymmetric stretching mode at an unusually high frequency (3009 cm⁻¹), suggesting the existence of a C-H?OC hydrogen bond of PHB in the spherulite. The existence of C-H?OC hydrogen bond is one of the unambiguous evidence for the crystallization of PHB component in the blends. Therefore, it is possible to distinguish Raman bands due to each component in the spectra of blends. Raman spectra of the spherulitic structure in the blends are similar to a Raman spectrum of pure crystalline PHB, while those of the nonspherulitic parts in the blends have each component peak of PHB and PLLA. The present study reveals that the PHB component is crystallized in the blends irrespective of the blend ratio, and that both components are mixed in the nonspherulite parts. The crystalline structure of PHB and the nonspherulitic parts of PLLA in the blends are characterized, respectively, by the unique band of C-H?OC hydrogen bond at 3009 cm⁻¹ and CCO deformation bands near 400 cm⁻¹.     

Synthesis and optical properties of three novel functional polyurethanes bearing nonlinear optical chromophoric pendants with different π electron conjugation bridge structure

High molecular weight functional polyurethanes bearing large π electron conjugated chromophoric pendants with different conjugation bridge structure, poly(1a), poly(1b), and poly(1c), were synthesized and characterized by FTIR, ¹H NMR and UV-vis absorption spectra. Their optical properties were evaluated by optical limiting and nonlinear optical analyses. The results show that these polymers possess good optical limiting and large nonlinear optical properties, which are attributed to the long D-π-A conjugated π electron structure of the NLO-chromophoric segment. Poly(1a) with CC double bond as π electron conjugation bridge shows better optical limiting property than poly(1b) and poly(1c) with CN or NN double bond as conjugation bridge structure under the same linear transmittance, while poly(1c) with NN double bond as π electron conjugation bridge of the NLO-chromophoric segment is superior on nonlinear optical properties to poly(1a) and poly(1b) with CC and CN double bonds as π electron conjugation bridge structure, respectively.     

Ethylene polymerization with homogeneous nickel-diimine catalysts: effects of catalyst structure and polymerization conditions on catalyst activity and polymer properties

Ethylene polymerization was carried out using three nickel α-diimine catalysts ((ArNC(An)-C(An)NAr)NiBr₂ (1), (ArNC(CH₃)-C(CH₃)NAr)NiBr₂ (2) and (ArNC(H)-C(H)NAr)NiBr₂ (3); where An=acenaphthene and Ar=2,6-(i-Pr)₂C₆H₃) activated with modified methylaluminoxane (MMAO) in a slurry semi-batch reactor. We investigated the effects of ethylene pressure, reaction temperature, and α-diimine backbone structure variation on the catalyst activity and polymer properties. Changes in the α-diimine backbone structure had remarkable effect on the polymer microstructure as well as the catalyst activity. Catalyst 2 produced polymer with the highest molecular weight, while Catalyst 3 produced polymer with the lowest molecular weight. In addition, Catalyst 2 produced polymer with the lowest melting point, while Catalyst 3 produced the highest melting level exhibiting a melting behavior typical of high-density polyethylene (HDPE). With all the three catalysts, polymer molecular weight tended to decrease with increasing polymerization temperature due to the increase in chain transfer rates. In general, there was no clear and consistent trend observed for the effects of ethylene pressure on the polymer molecular weight. However, in polyethylene produced with Catalyst 2, the molecular weight was independent of ethylene pressure suggesting that chain transfer to ethylene may be a dominant mechanism for this catalyst.     

Thermodynamic modeling of liquid-fluid phase equilibrium in supercritical ethylene + copolymer + co-solvent systems using the PC-SAFT equation of state

Copolymers are important in the manufacture of new polymeric materials with specific characteristics. For linear polymers, thermodynamic models based on the thermodynamic perturbation theory are interesting, since this theory regards the association between monomers. In this work, cloud points of mixtures of copolymers (PEH, PEP, PEAA and PEVA) (PEP: poly(ethylene-co-propylene); PEAA: poly(ethylene-co-acrylic acid); PEH: poly(ethylene-co-1-hexene); PEVA: poly(ethylene-co-vinyl acetate)), a supercritical fluid (C₂) and co-solvents (C₁, C₂, C₃, nC₄, 1C₄, 1C₆, AA, VA, He, N₂, CO₂) (C₁: methane; C₂: ethane; C₂: ethylene; C₃: propane; nC₄: n-butane; 1C₄: 1-butene; 1C₆: 1-hexene; AA: acrylic acid; VA: vinyl acetate; He: helium; N₂: nitrogen; CO₂: carbon dioxide) were modeled using the PC-SAFT equation of state (Perturbed Chain-Statistical Associating Fluid Theory) with a one-type van der Waals mixing rule by fitting one single interaction parameter. Pure component parameters for the supercritical fluid and co-solvents were obtained by regression of vapor pressure and density data of saturated liquid, while pure component parameters for polymers that compose the copolymers were obtained by regression of pure liquid PVT data. Binary interaction and pure component parameter estimation was performed by using the modified maximum likelihood method. Relative deviations between the calculated and experimental cloud points show that the PC-SAFT model had an excellent performance.     

Molecular and crystal structure of poly(tetramethylene adipate) α form based on synchrotron X-ray fiber diffraction

The molecular and crystal structure of the α form of poly(tetramethylene adipate) (PTMA) was analyzed using synchrotron X-ray fiber diffraction data. The crystals belong to the monoclinic system of space group P2₁/n. The unit cell constants are a=0.6776(6), b=0.7904(6), c (fiber axis)=1.442(1) nm and β=135.6(1)°. The final crystal structure was obtained by the linked-atom least-squares refinement, which gave an R-factor of 0.130 for 103 observed spots and 64 unobserved reflections. The molecular structure deviates slightly from the fully extended conformation in the ester part. The torsional angle CH₂-CH₂-O-C(O) was found to be 155°. The CO groups of the corner and center chains in a unit cell are closely located along the c-axis and are related by the crystallographic 2₁-axes along the b-axis at z=1/4 and z=3/4. The total dipole moment arising from the CO groups is oriented in one direction at z=1/4, and in the opposite direction at z=3/4. Owing to the close arrangement of the CO groups between neighboring chains along the fiber axis, the c-projected cell dimensions and the setting angle of the polymer chain are different from those of the orthorhombic form of polyethylene and the β form of PTMA.     

Influence of cross-linker concentration on the cross-linking of PDMS and the network structures formed

The cross-linking of linear di-vinyl-terminated poly(dimethylsiloxanes) (PDMS) with tetrakis(dimethylsiloxane) was studied in the presence of different concentrations of the cross-linker (H/V = ratio of Si-H groups of the cross-linker and CC bonds). The consumption of the Si-H and CC bonds was monitored simultaneously by in situ Confocal Raman Microscopy (CRM) and ATR-FTIR spectroscopy. When formulations with H/V ≥ 1.0 are cross-linked at low temperature (25 °C) in air and atmospheric humidity conditions, hydrosilylation and secondary reactions occur simultaneously at early stages of the reaction. For H/V = 1.0 the CC bonds are also consumed by side reactions.Films cross-linked from formulations with different H/V ratios were studied by NMR imaging, swelling/extraction experiments and SEM. Films cross-linked with H/V = 1.0 showed a slower magnetization decay due to the presence of a large percentage of extractable material not connected to the cross-linked network. After extraction, all the films show faster relaxation behavior, explained by the presence of two types of chemical cross-links as well as one type of physical cross-links. These cross-links result from the occurrence of hydrosilylation and secondary reactions and counterbalance each other at different H/V ratios.     

Maleic anhydride-grafted polypropylene: FTIR study of a model polymer grafted by ene-reaction

Ene-grafting of maleic anhydride on polypropylene previously enriched in double bonds by β-scission was promoted in order to obtain model grafted polypropylene. Ene-grafting was carried out in the presence of a radical-scavenger in order to limit at a minimum side-grafting and in presence of catalyst (SnCl₂) in order to maximise the ene-grafting. Nevertheless, it does not lead to high grafting content.Ene-grafted PP confirms the single end-grafted succinic anhydride FTIR assignment at 1792 cm⁻¹ (CO symmetric stretching) while a disubstitution is also observed leading to a shift to a 1784 cm⁻¹ absorption band. This latter band was more generally assigned to interacting anhydride (CO) instead of an assignment to the particular polyanhydride species (as previously assigned by our team [De Roover B, Sclavons M, Carlier V, Devaux J, Legras R, Momtaz A. J Polym Sci, Part A: Polym Chem 1995;33:829. [14]]).     

Thiophene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s: Synthesis, characterisation and optical properties

This work describes the synthesis and characterisation of two types of thiophene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s (PAE-PAV) copolymers, whose repeating units (-Ph-CC-Th-CHCH-Ph-CHCH-)_n, 5, and (-Th-CC-Ph-CC-Th-CHCH-Ph-CHCH-)_n, 8a-c, consist, respectively, of a 1:2 and a 2:2 ratio of triple bond/double bond moieties. Comparison of their photophysical, electrochemical and photovoltaic properties has been carried out. Although similar electrochemical data (HOMO: −5.43 eV, LUMO: ∼−3.15 eV, ) as well as identical thin film absorption behaviour (λ_a=500 nm, ) were obtained for both types of materials, significant differences in their thin film photoluminescence behaviour and photovoltaic properties were observed. While polymer 5 shows a fluorescence maximum at λ_e=568 nm (with a fluorescence quantum yield of Φ_f=7%), a total fluorescence quenching was observed in 8. Far better photovoltaic performance was obtained from solar cells (set up: ITO/PEDOT:PSS/active layer/LiF/Al; active layer consisting of 5 or 8b as donor and PCBM as acceptor in a 1:3 ratio by weight) designed from 5 than from 8b. Open circuit voltage, V_OC, as high as 900 mV and power conversion efficiency, η_AM1.5, around 1.2% were obtained. This can be attributed to the 1:2 triple bond/double bond ratio as well as the grafting of shorter octyloxy and 2-ethylhexyloxy side chains in 5 and to its comparatively higher molecular-weight.     

Non-isothermal crystallization and thermal transitions of a biodegradable, partially hydrolyzed poly(vinyl alcohol)

A study has been made of the non-isothermal crystallization behavior and thermal transitions of a biodegradable, partially hydrolyzed poly(vinyl alcohol) with 80% degree of saponification (PVA80). Possible sample degradation was first investigated, but no significant degradation or dehydration was detected using FTIR and DSC under the experimental condition. The non-isothermal crystallization of PVA80 was analyzed with Ozawa equation, and the Mo method of combining Ozawa and Avrami equations. Ozawa equation was only applicable in a narrow temperature range from 80 to 100 °C. The deviation from the Ozawa equation is not due to the secondary crystallization or the quasi-isothermal nature of the treatment. It is only a result of the large relative difference of the relative crystallinity values under different cooling rates. The Mo method demonstrated a success in the full temperature range investigated. The isoconversional method developed by Friedman failed to estimate the activation energy for this non-isothermal crystallization. Thermal transitions of PVA80 are associated with its complex hydrogen-bonding interactions. The melt-crystallized PVA80 sample, as that from film casting, followed by annealing at 60 and 80 °C, has a broad melting temperature range measured by DSC and FTIR. It was found that the melting behavior of a semicrystalline polymer can be probed via a non-crystalline hydrogen-bonded CO band using FTIR. The glass transition temperature T_g of PVA80 was raised about 20 °C, after the sample was melt-crystallized. The intensity of the hydrogen-bonded CO band increases when temperature was increased from 110 to 180 °C, due to the promoted hydrogen-bonding interactions between the CO groups in the amorphous phase and the hydroxyl groups from the crystalline phase, which is also the main reason for the increased T_g transition.     

Preparation of poly(3,3′-dialkynyl-2,2′-bithiophene-5,5′-diyl) with high coplanarity and effective π-conjugation system

New head-to-head type polythiophenes with acetylenic -CCR side groups, HH-P3(CCR)Th (R=n-C₁₀H₂₁, n-C₆H₁₃, n-C₄H₉), were prepared by palladium-catalyzed polycondensation of the corresponding dibromo-monomers by using Me₃SnSnMe₃ as the polycondensing agent. The single crystal structure of the monomer revealed high coplanarity of the bithiophene unit, and the derived polymer showed a UV-vis absorption peak at approximately 520 nm. The λ_max position was red-shifted from those of regioregular poly(3-alkylthiophene)s (385 and 430 nm for HH- and HT-type polymers, respectively). These data indicate that the newly synthesized polythiophene with the -CCR group has a highly coplanar structure with a large effective π-conjugation system.