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.     

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.     

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.     

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.     

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.     

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.     

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.     

FTIR investigation of the influence of diisocyanate symmetry on the morphology development in model segmented polyurethanes

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol (M_n=1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans-1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (CO) peaks. Depending on the structure of the diisocyanate used, while the intensity of free CO peaks around 1720-1730 cm⁻¹ decreased, the intensity of H-bonded CO peaks around 1670-1690 cm⁻¹, which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of CO region and analysis of the relative absorbances in CO region.     

Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS)

Analysis of hydrothermally-treated and weathered coals by X-ray photoelectron spectroscopy (XPS) was carried out, and the XPS C(1s) and N(1s) spectra obtained were curve-resolved into four peaks (C-C/CC/C-H, C-O, CO, and O-CO) and three peaks (pyridinic-N, pyrrolic-N, and quaternary-N), respectively. Upon hydrothermal treatment, the amount of carbon-oxygen forms decreased; while the ratio of pyridinic-N increased and quaternary-N decreased. On the other hand, some bituminous coals were subjected to natural weathering and laboratory oxidation, which gave opposite results compared to the hydrothermal treatment. The changes in the carbon-oxygen and organic nitrogen forms were discussed in terms of the effect of hydrothermal treatment and weathering (oxidation). Also, the XPS analysis of various kinds of coals (43 SS coals) was carried out, and the amounts of carbon-oxygen and organic nitrogen forms were discussed in terms of coal rank (carbon content).     

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.     

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.     

Curing dynamics and network formation of cyanate ester resin/polyhedral oligomeric silsesquioxane nanocomposites

Curing dynamics and network formation of cyanate ester resin (PT-30)/TriSilanolPhenyl polyhedral oligomeric silsesquioxane (POSS) nanocomposites were studied by means of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry MTDSC), Fourier transform infrared (FTIR) and Raman spectroscopies. The incorporation of the POSS showed a strong catalytic effect (decrease in curing temperature and activation energy) on the curing reaction of PT-30. The activation energy of the PT-30 decreased with increasing POSS content. The most effective catalytic effect was observed at 5 wt% of the POSS. Both FTIR and Raman spectra monitored the formation of triazine (i.e. cyanurate) ring in the PT-30 and its nanocomposites with the POSS. Raman spectra revealed that the PT-30 resin preferentially reacted with -OH group in the POSS firstly to form a -O-(CNH)-O- bond, rather than react with itself to form the triazine rings, during the network formation of the PT-30/POSS nanocomposites. The strong catalytic effect of the POSS on the curing process of the PT-30 appears to be due to the formation of this -O-(CNH)-O- bond.     

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.     

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.     

Analysis of the interaction using FTIR within the components of OREC composite GPE based on the synthesized copolymer matrix of P(MMA-MAh)

Poly(methyl methacrylate-maleic anhydride) (P(MMA-MAh)) has been synthesized from methyl methacrylate (MMA) and maleic anhydride (MAh) monomers. The molar ratio of monomers was found to be 1MAh:8MMA. The molecular weight of copolymer was determined in the order 10⁴ (g/mol).Rectorite modified with dodecyl benzyl dimethyl ammonium chloride (OREC) was used as a filler additive to modify gel polymer electrolytes (GPEs) which consisted of P(MMA-MAh) used as polymer matrix, propylene carbonate (PC) as a plasticizer and LiClO₄ as lithium ion producer. Characterization of interaction of CO in PC and copolymer with Li⁺ and OH group on OREC surface has been thoroughly examined using FTIR. The quantitative analysis of FTIR shows that the absorptivity coefficient a of copolymer/LiClO₄, PC/LiClO₄, PC/OREC and copolymer/OREC is 0.756, 0.113, 0.430 and 0.602, respectively, which means that the Li⁺ or OH bonded CO is more sensitive than free CO in FTIR spectra. The limit value of bonded CO equivalent fraction of copolymer/LiClO₄, PC/LiClO₄, PC/OREC and copolymer/OREC is 55, 94, 57 and 26%, respectively, which implies that all the interaction within the components is reversible and the intensity of interaction is ordered as PC/LiClO₄, PC/OREC, copolymer/OREC and copolymer/LiClO₄.