Polymorphism of the poly(ethylene oxide)/Li triflate complexes

We hereafter present the study of the high concentration zone of the PEO/Li triflate phase diagram. This system was found to form three different molecular complexes. Their thermal behaviour was elucidated by use of three complementary techniques: Calorimetry, X-ray diffraction and optical microscopy.     

Synthesis and characterization of poly(ethylene oxide)/polylactide/poly(ethylene oxide) triblock copolymer

Poly(ethylene oxide/polylactide/poly(ethylene oxide) (PEO/PL/PEO) triblock copolymers, in which each block is connected by an ester bond, were synthesized by a coupling reaction between PL and PEO. Hydroxyl‐terminated PLs with various molecular weights were synthesized and used as hard segments. Hydroxyl‐terminated PEOs were converted to the corresponding acid halides via their acid group and used as a soft segment. Triblock copolymers were identified by Fourier transform infrared spectroscopy, ¹H NMR, and gel permeation chromatography. Differential scanning calorimetry (DSC) and X‐ray diffractometry of PEO/PL/PEO triblock copolymers suggested that PL and PEO blocks were phase‐separated and that the crystallization behavior of the PL block was markedly affected by the presence of the PEO block. PEO/PL/PEO triblock copolymers with PEO 0.75k had two exothermic peaks (by DSC), and both peaks were related to the crystallization of PL. According to thermogravimetric analysis, PEO/PL/PEO triblock copolymer showed a higher thermal stability than PL or PEO. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2545–2555, 2002     

Morphology of poly(ethylene oxide)/poly(vinyl acetate) blends

The morphology of poly(ethylene oxide)/poly(vinyl acetate) (PEO/PVAc) blends was examined using small angle X-ray scattering (SAXS) and optical microscopy. The morphological and structural parameters of the blends are dependent on both composition and crystallization conditions. Optical microscopy revealed that blend samples prepared by solution casting crystallized with volume-filling crystals up to a composition of 30/70 wt% PEO/PVAc; at higher PVAc content there was no evidence of crystallization in the temperature range studied. Pure PEO always crystallized with a spherulite-hedrite morphology. The formation of spherulites was relatively favoured at lower crystallization temperatures and by addition of PVAc to PEO. Small angle X-ray intensity profiles were analyzed using a recently developed methodology and it was found that, for a given crystallization temperature, the amorphous and interphase thicknesses increased with increasing PVAc content but that the average crystalline thickness was independent of composition. The morphological and structural properties of the PEO/PVAc blends were attributed to the presence of non-crystallizable material in both the interlamellar and interfibrillar regions.     

Thermal ageing of poly(ethylene oxide)/poly(3,4-ethylenedioxythiophene) semi-IPNs

The thermal stability study of a conducting semi-IPN has been reported. The thermo-oxidation of poly(ethylene oxide) (PEO)/poly(3,4-ethylenedioxythiophene) (PEDOT) semi-Interpenetrating Polymer Network (semi-IPN) was studied at 80 °C in open air. The degradation was followed by spectrophotometry in the visible and near infrared range, cyclic voltamperometry and thermogravimetric analysis. Fluorescence spectrophotometry allowed for the identification of OH by-product originated in the PEO network degradation by the use of a chemiluminescent probe, typically terephthalic acid. The formation of hydroxyl radicals damaged the PEDOT chains as checked by infrared spectroscopy. The mechanism of degradation is further confirmed (i) by introducing a radical scavenger or (ii) by performing a thermal ageing under inert atmosphere; in both cases the semi-IPN life-time is tremendously increased.     

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SC CO₂) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO₂ treatment. The enhancement of PEO crystallization with SC CO₂ treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO₂ treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO₂ treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004     

Dielectric relaxation spectroscopy in poly(ethylene oxide)/water systems

The dielectric properties of poly(ethylene oxide) (PEO) are studied by dielectric relaxation spectroscopy measurements in wide ranges of frequency (5–2×10⁹ Hz) and temperature (193 − 300 K). PEO/water systems are also studied in a wide range of water content h (0 − 0.85 grams of water per grams of dry PEO). The measurements allow to distinguish between the dipolar secondary mechanism γ and effects related to free charge motion. The data are analyzed within the formalisms of permittivity, ϵ*, and electric modulus, M*. The water has been found to plasticize the dipolar process and to affect strongly the conduction process. A critical water content h_c, h_c = 0.13, has been found for the mechanism of charge transport.     

Electrospun poly(3‐hexylthiophene)/poly(ethylene oxide)/graphene oxide composite nanofibers: effects of graphene oxide reduction

In this article, we report on the production by electrospinning of P3HT/PEO, P3HT/PEO/GO, and P3HT/PEO/rGO nanofibers in which the filler is homogeneously dispersed and parallel oriented along the fibers axis. The effect of nanofillers' presence inside nanofibers and GO reduction was studied, in order to reveal the influence of the new hierarchical structure on the electrical conductivity and mechanical properties. An in‐depth characterization of the purity and regioregularity of the starting P3HT as well as the morphology and chemical structure of GO and rGO was carried out. The morphology of the electrospun nanofibers was examined by both scanning and transmission electron microscopy. The fibrous nanocomposites are also characterized by differential scanning calorimetry to investigate their chemical structure and polymer chains arrangements. Finally, the electrical conductivity of the electrospun fibers and the elastic modulus of the single fibers are evaluated using a four‐point probe method and atomic force microscopy nanoindentation, respectively. The electrospun materials crystallinity as well as the elastic modulus increase with the addition of the nanofillers while the electrical conductivity is positively influenced by the GO reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

Factors influencing the size of PEO complexes with a tyrosine-rich polypeptide

Aqueous complexes of PEY1, a 36 100 Da random synthetic peptide of tyrosine (50 mol %) and glutamic acid (50 mol %), with poly(ethylene oxide) (PEO) were studied as functions of PEO molecular weight, mixing ratio of PEO and PEY1, and the presence of calcium ions. Without calcium ions, the complexes were water soluble, with each complex consisting of a single PEO chain with many bound PEY1 chains. In the presence of 1 mM calcium ions, PEY1 formed colloidal aggregates with intermediate molecular weight PEO (10(5) to 10(6) Da). By contrast, very high molecular weight PEO (8 x 10(6) Da) with calcium ions formed large hydrogels when mixed with PEY1. It is proposed that PEY1 molecules completely bind to low molecular PEO and thus are deactivated from causing the coupling of multiple PEO chains, whereas deactivation of PEY1 on very high molecular weight PEO clusters is a slower process, giving an opportunity for cluster-cluster aggregation.     

Thermosensitive sol–gel transition behaviors of poly(ethylene oxide)/aliphatic polyester/poly(ethylene oxide) aqueous solutions

The thermoreversible gelation of Pluronic [poly(ethylene oxide) (PEO)–polypropylene oxide (PPO)–PEO] aqueous solutions originates from micelle formation and micelle volume changes due to PEO–water and PPO–water lower critical solution temperature behavior. The micelle volume fraction is known to dominate the sol–gel transition behavior of Pluronic aqueous solutions. Triblock copolymers of PEO and aliphatic polyesters, instead of PPO, were prepared by hexamethylene diisocyanate coupling and dicyclohexyl carbodiimide coupling. Through changes in the molecular weight and hydrophobicity of the polyester middle block, the hydrophobic–hydrophilic balance of each block was systematically controlled. The following aliphatic polyesters were used: poly(hexamethylene adipate) (PHA), poly(ethylene adipate) (PEA), and poly(ethylene succinate) (PESc). With the hydrophobicity and molecular weight of the middle block increasing, the critical micelle concentration at the same critical micelle temperature decreased, and the absolute value of the micellization free energy increased. The micelle size was rather insensitive to temperature but slightly decreased with increasing temperature. PEO–PHA–PEO and PEO–PEA–PEO triblock copolymers needed high polymer concentrations to form gels. This was ascribed to the tight aggregation of PHA and PEA chains in the micelle core due to strong hydrophobic interactions, which induced the contraction of the micelle core. However, because of the relatively hydrophilic core, a PEO–PESc–PEO aqueous solution showed gelation at a low polymer concentration. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 772–784, 2004     

Lamellar structure of poly(ethylene oxide) molecular complexes

The phase diagrams of some binary systems such as poly(ethy lene oxide)-p-dihalogenobenzene, poly(ethylene oxide)-resorcinol and poly(ethylene oxide)-p-nitrophenol show the existence of molecular complexes with a well definite stoichiometry. The crystal structure of these molecular complexes has been determined by wide-angle X-ray diffraction. The morphology of these molecular complexes crystallized from the melt is investigated by differential scanning calorimetry and small angle X-ray scattering. PEO-p-dichlorobenzene and PEO-resorcinol complexes crystallize from the melt as extended chains (EC) or integral folded chain (IFC) lamellar crystals. As observed for PEO oligomers, the fraction of EC crystals of PEO-resorcinol increases with the crystallization temperature. However EC crystals are present in a larger range of crystallization temperatures than for pure PEO. On the other hand, the PEO-p-nitrophenol complex crystallizes over all the studied crystallization temperature range as stable non integral folded chain (NIFC) crystals. Explanations related to the crystal structure of these complexes and to their mode of growth are invoked to explain these two deeply different lamellar morphologies.     

Morphology and interpenetrated growth of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends

Morphology development and growth process of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends are studied by means of polarizing optical microscopy and atom force microscopy in this paper. Thin films with different film thicknesses were used to follow the growth processes of spherulites and dendrites. It is shown that, when one component spherulite grows, the other component in the melt is always excluded from the spherulite. The excluded component may reenter into the spherulite through diffusion depending on amorphous volume fraction of spherulite and segmental mobility of molecules, which leads to the occurrence of interpenetrated growth. This mechanism was analyzed in detail in this paper.     

Crystallization,thermal behavior,and compatibility of poly(ethylene oxide)/poly(propylene oxide) blends

Isothermal and nonisothermal crystallization kinetics of different poly(ethylene oxide)/poly(propylene oxide) blends were investigated by means of differential scanning calorimetry (DSC). Glass transition temperature of quenched samples have also been reported. Phase morphologies and poly(ethylene oxide) spherulite growth rates were analyzed by polarizing light transmission microscopy. Results show morphological changes along with regime transitions of poly(ethylene oxide) crystal growth. Kinetic analyses of the data suggest that, although the blend behaves as a noncompatible, phase-separated system, there exists a certain degree of interaction between polymer chains. © 1996 John Wiley & Sons, Inc.     

Studies of photooxidative degradation of poly(vinyl chloride)/poly(ethylene oxide) blends

The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004     

Effect of aging on fractional crystallization of poly(ethylene oxide) component in poly(ethylene oxide)/poly(3‐hydroxybutyrate) blends

The effect of aging on the fractional crystallization of the poly(ethylene oxide) (PEO) component in the PEO/poly(3‐hydroxybutyrate) (PHB) blend has been investigated. The partial miscibility of the PEO/PHB blends with high PEO molecular weight (M_v = 2.0 × 10⁵ g/mol) was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis. The fractional crystallization behavior of the PEO component in the PEO/PHB blends with low PEO content (not more than 30 wt% of PEO), before and after aging under vacuum at 25 °C for 6 months, were compared by DSC, fourier transform infrared microscopic spectroscopy, small angle X‐ray diffraction, and scanning electron microscopy. It was confirmed that nearly all the PEO components remain trapped within interlamellar regions of PHB for the PEO/PHB blends before aging. Under this condition, the crystallization of PEO is basically induced by much less active heterogeneities or homogeneous nucleation at high supercoolings. While, after the same PEO/PHB samples were stored at 25 °C in vacuum for 6 months, a part of the PEO component was expelled from the interlamellar region of PHB. Under this condition, the expelled PEO forms many separate domains with bigger size and crystallizes at low supercoolings by active heterogeneous nucleation, whereas the crystallization of PEO in the interlamellar region is still mainly induced by less active heterogeneities or homogeneous nucleation at extreme supercoolings. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2665–2676, 2005     

Thermal degradation of poly(vinyl chloride)/poly(ethylene oxide) blends: Thermogravimetric analysis

Thermal stability of poly(vinyl chloride)/poly(ethylene oxide) (PVC/PEO) blends has been investigated by thermogravimetric analysis (TGA) in dynamic and isothermal heating regime. PVC/PEO blends were prepared by hot-melt extrusion (HME). According to TG analysis, PEO decomposes in one stage, while PVC and PVC/PEO blends in two degradation stages. In order to evaluate the effect of PEO content on the thermal stability of PVC/PEO blends, different criteria were used. It was found that thermal stability of PVC/PEO blends depends on the blend composition. The interactions of blends components with their degradation products were confirmed. By using multiple heating rate kinetics the activation energies of the PVC/PEO blends thermal degradation were calculated by isoconversional integral Flynn–Wall–Ozawa and differential Friedman method. According to dependence of activation energy on degree of conversion the complexity of degradation processes was determined.     

The thermal analysis of polymer blends of poly(ethylene oxide)/poly(methyl methacrylate)

Thermal analysis of the PEO/PMMA system show for the blends with higher molecular weight PMMA two glass transition temperatures in the 75–80 w/w% PMMA range. Thermal treatment is accompanied by a shift of this composition range of two Tg to lower PMMA contents. On the other hand observed melting point depression in the 0–60 w/w% PMMA range indicate compatibility of the blend components. Small negative interaction parameters approaching zero with increasing PMMA content of the blend, support the possible incompatibility in the observed composition range of two Tg.

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Zusammenfassung Die Thermoanalyse des Systemes PEO/PMMA ergab für Gemische mit PMMA höheren Molekülgewichtes zwei Glasumwandlungspunkte /Tg/ im Bereich 75–80 m/m% PMMA. Eine Wärmebehandlung ist vom Verschieben dieses Bereiches mit den zwei Tg in Richtung niedrigerem PMMA-Gehalt begleitet. Weiterhin zeigt die Schmelzpunktserniedrigung im Bereich 0–60 m/m% PMMA die Kompatibilität der Gemischkomponenten. Kleine negative, mit steigendem PMMA-Gehalt des Gemisches gegen Null haltende Wechselwirkungsparameter unterstreichen die Möglichkeit einer Inkompatibilität im beobachteten Bereich der zwei Tg.

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120–230°. 2 3590 . . . 150°, . .

     

Compatibility of poly(ethylene oxide)/poly(vinyl chloride) blends by differential scanning calorimetry

This article refers to a study of the thermal behaviour of poly(ethylene oxide) and poly(vinyl chloride) blends in the solid state. The compatibility has been examined by differential scanning calorimetry. The influence of molecular masses of the polymers on their compatibility has been shown. The equilibrium melting temperatures decrease in the mixture, such behaviour being progressively greater with the PEO reduction. The melting temperature of blends increases linearly with the crystallization temperature for a wide range of undercooling. Values of the parameters χ₁₂ and B have been obtained.