Synthesis of four-armed poly(epsilon-caprolactone)-block-poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four-armed poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-b-PEO) copolymers were synthesized by ring-opening polymerization of ethylene oxide in the presence of four-armed poly(epsilon-caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt2) as a catalyst. The chemical structure of PCL-b-PEO copolymer was confirmed by H-1 NMR and C-13 NMR. The hydroxyl end groups of the four-armed PC L were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four-armed architecture of the copolymer. Physicochemical properties of the four-armed block copolymers differed from their starting four-armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four-armed block copolymer increased with PEO length and PEO content.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

Synthesis and characterization of novel polythiophenes containing poly(ethylene oxide) side chains

Thiophene copolymers and their derivatives with poly(ethylene oxide) side chains were synthesized. The starting monomers were 3-hexylthiophene and 2-(3-thienyl) ethanol with poly(ethylene oxide) grafted to the side chains. New functionalized polythiophenes were prepared by both chemical oxidation with FeCl3 and electropolymerization. The conjugating polymers were characterized. The structures of the polythiophene derivatives agreed with the design.

Morphological study on water-borne conducting polyaniline-poly(ethylene oxide) blends

Conducting polyaniline-poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide-angle X-ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three-phase model combining morphological factors instead of a two-phase model was proposed to explain the low-conductivity percolation threshold.

Isothermal crystallization kinetics of PEO in poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymers. I. Effect of the sofi-block length

The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) block in two poly(ethylene terephthalate) (PET)-PEO segmented copolymers was studied with differential scanning calorimetry. The Avrami equation failed to describe the overall crystallization process, but a modified Avrami equation, the Q equation, did. The crystallizability of the PET block and the different lengths of the PEO block exerted strong influences on the crystallization process, the crystallinity, and time final morphology of the PEO block. The mechanism of nucleation and the growth dimension of the PEG block were different because of the crystallizability of time PET block and the compositional heterogeneity. The crystallization of the PEO block was physically constrained by the microstructure of time PET crystalline phase, which resulted in a lower crystallization rate. However, this influence became weak with the increase in the soft-block length. (C) 2000 John Wiley & Sons, Inc.

Mechanical properties of poly(beta-hydroxybutyrate)/poly(ethylene oxide) blends

Tensile properties of poly (P-hydroxybutyrate)/poly (ethylene oxide) (PHB/PEO) blends were reported in this paper. It was found that the blends of PHB with different molecular-weight PEO exhibited different mechanical properties. The mechanical properties of the blends of PHB and PEO3 (M-w=0.3x10(6)) were very poor. However, the blends of PHB and PEO5 (M-w=5x10(6)) showed compatible in mechanical properties. Excellent synergism was observed not only in tensile stress and tensile elongation but also in modulus. Moreover, the ductility of the blends could be improved further under proper heat-treatment.

Nonisothermal crystallization kinetics: poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymer and poly(ethylene oxide) homopolymer

The nonisothermal crystallization behavior of polyethylene oxide (PEO) in poly(ethylene terephthalate)poly(ethylene oxide) (PETPEO) segmented copolymer and PEO homopolymer has been studied by means of differential scanning calorimetry, as well as transmission electron microscope. The kinetics of PEO in copolymer and PEO homopolymer under nonisothermal crystallization condition has been analyzed by Ozawa equation. The results show that Ozawa equation only describes the crystallization behavior of PEO-6000 homopolymer successfully, but fails to describe the whole crystallization process of PEO in copolymer because the secondary crystallization in the later stage could not be neglected. Due to the constraint of PET segments imposed on the PEO segments, a distinct two stage of crystallization of PEO in copolymer has been investigated by using Avrami equation modified by Jeziorny to deal with the nonisothermal crystallization data. In the case of PEO-6000 homopolymer, good linear relation for the whole crystallization process is obtained owing to the secondary crystallization does not occur under our experimental condition. (C) 2001 Elsevier Science Ltd. All rights reserved.

Miscibility and crystallization behavior of poly(beta-hydroxybutyrate)/poly(ethylene oxide) blends

The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) blends were studied by differential scanning calorimetry(DSC) and polarizing microscopy (POM). It is found that the miscibility is related to the composition of the blends. When the PEO content is over 20 percent, the miscible blends turn into partially miscible and the phase separation can be observed with POM. The addition of the PEO influences not only the morphology of PHB crystals and the radial growth rate of spherulites, but also the cold crystallization temperature.

Thermodynamics of blends of poly(ethylene oxide) with poly(methyl methacrylate) and poly(vinyl acetate): prediction of miscibility based on Flory solution theory modified by Hamada

Flory solution theory modified by Hamada et al. (Macromolecules, 1980, 13, 729) was used to predict the miscibility of blends of poly(ethylene oxide) with poly(methyl methacrylate) (PEO-aPMMA) and with poly(vinyl acetate) (PEO-PVAc). Interaction parameters of a PEO-aPMMA blend with the weight ratio of PEO/aPMMA = 50/50 at the temperature range of 393-433 K and PEO-PVAc blends with different compositions and temperatures were calculated from the determined equation-of-state parameters based on Flory solution theory modified by Hamada ed al. Results show that interaction parameters of the PEO-aPMMA blend are negative and can be comparable with values obtained from neutron-scattering measurements by Ito et al. (Macromolecules, 1987, 20, 2213). Also, interaction parameters and excess volumes of PEO-PVAc blends are negative and increase with enhancing the content of PEO and the temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.

Poly(epsilon-capralactone)/poly(ethylene oxide) diblock copolymer .2. Nonisothermal crystallization and melting behavior

The nonisothermal crystallization behavior and melting process of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide) (PEG) diblock copolymer in which the weight fraction of the PCL block is 0.80 has been studied by using differential scanning calorimetry (DSC). Only the PCL block is crystallizable, the PEO block with 0.20 weight fraction cannot crystallize. The kinetics of the PCL/PEO diblock copolymer under nonisothermal crystallization conditions has been analyzed by Ozawa's equation. The experimental data shows no agreement with Ozawa's theoretical predictions in the whole crystallization process, especially in the later stage. A parameter, kinetic crystallinity, is used to characterize the crystallizability of the PCL/PEO diblock copolymer. The amorphous and microphase separating PEO block has a great influence on the crystallization of the PCL block. It bonds chemically with the PCL block, reduces crystallization entropy, and provides nucleating sites for the PCL block crystallization. The existence of the PEO block leads to the occurrence of the two melting peaks of the PCL/PEO diblock copolymer during melting process after nonisothermal crystallization. The comparison of nonisothermal crystallization of the PCL/PEO diblock copolymer, PCL/PEO blend, and PCL and PEO homopolymers has been made. It showed a lower crystallinity of the PCL/PEO diblock copolymer than that of others and a faster crystallization rate of the PCL/PEO diblock copolymer than that of the PCL homopolymer, but a slower crystallization rate than that of the PCL/PEO blend. (C) 1997 John Wiley & Sons, Inc.

Poly(epsilon-caprolactone)/poly(ethylene oxide) diblock copolymer .1. Isothermal crystallization and melting behavior

The isothermal crystallization and melting behavior of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide)(PEO) diblock copolymer has been studied by WAXD, SAXS, and DSC methods. Only the PCL block is crystallizable; the PEO block of weight fraction 20% cannot crystallize, although its corresponding homopolymer has strong crystallizability. The long period, amorphous layer, and crystalline lamella of the PCL/PEO block copolymer all increase with the rise in the crystallization temperature, and the thickness of the amorphous layer is much larger than that of crystalline lamella due to the existence of the PEO block in the amorphous region. The isothermal crystallization of the PCL/PEO block copolymer is investigated by using the theory of Turnbull and Fischer. It is found that the amorphous PEO block has a great influence on the nucleation of PCL block crystallization, and the extent of this influence depends on crystallization conditions, especially temperature. The outstanding characteristics are the phenomenon of the double melting peaks in the melting process of the PCL/PEO block copolymer after isothermal crystallization at different temperatures and the transformation of melting peaks from double peaks to a single peak with variations in the crystallization condition. They are related mainly to the existence of the PEO block bonding chemically with the PCL block. In summing up results of investigations into the crystallization and melting behavior of the PCL/PEO block copolymer, it is interesting to notice that when the PCL/PEO block copolymer crystallizes at three different crystallization temperatures, i.e., below 0 degrees C, between 0 and 35 degrees C, and above 35 degrees C, the variation of peak melting temperature is similar to that of overall crystallization rates in the process of isothermal crystallization. The results can be elucidated by the effect of the PEO block on the crystallization of the PCL block, especially its nucleation. (C) 1996 John Wiley & Sons, Inc.

THE COMPATIBILITY AND MORPHOLOGY OF CHITOSAN-POLY(ETHYLENE-OXIDE) BLENDS

Thermal behavior and morphology of blends prepared by solution casting of mixtures of chitosan and poly( ethylene oxide) were studied by means of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The preliminary results indicate that both melting point and crystallinity depend on the composition of the blends, and that they exhibit minimum values when the blend contains 50% chitosan. From the prediction of melting point depression analysis, the compatibility of the blends shows a transition at this specific composition. This conclusion was further confirmed by observation of the morphology.

MISCIBILITY STUDIES OF POLY(ETHYLENE OXIDE)-POLY(VINYL ACETATE) BLENDS BY VISCOMETRY METHODS

The intrinsic viscosities of poly(ethylene oxide)-poly(vinyl acetate) blends (PEO-PVA) have been measured in chloroform as a function of molecular weights of blend components and compositions. The interaction parameters Delta b obtained from the modified Krigbaum and Wall theory and the differences between the intrinsic viscosities of polymer mixtures and the weight-average intrinsic viscosities of the two blend components were both used to characterize the extent of miscibility of the blend mixtures. (C) 1995 John Wiley and Sons, Inc.

COMPATIBILIZATION OF POLYPROPYLENE POLY(ETHYLENE OXIDE) BLENDS AND CRYSTALLIZATION BEHAVIOR OF THE BLENDS

The compatibilization of incompatible polypropylene (PP)/poly(ethylene oxide) (PEO) blends was studied. The experimental results showed that the graft copolymer [(PP-MA)-g-PEO] of maleated PP (PP-MA) and mono-hydroxyl PEO (PEO-OH) was a good compatibilize

IMPEDANCE STUDY OF THE INTERFACES BETWEEN LITHIUM, POLYANILINE, LITHIUM-DOPED MNO2 AND MODIFIED POLY(ETHYLENE OXIDE) ELECTROLYTE

Impedance study was carried out for the interfaces between lithium, polyaniline (PAn), lithium-doped MnO2 and modified poly(ethylene oxide) (PEO) electrolyte under various' conditions. The interfacial charge-transfer resistances R(ct) on PEO/PAn, R(ct) on PEO/LiMn2O4 increase with depth-of-discharge and decrease after the charge of the cell containing modified PEO as electrolyte. The charge-transfer resistance R(ct) on PEO/PAn is higher than R(ct) on PEO/LiMn2O4 under the same condition, since inserted species and mechanism are different for both cases. In the case of PAn, an additional charge-transfer resistance might be related to the electronic conductivity change in discharge/charge potential range, as it was evident from a voltammetry curve. With increasing cycle numbers, the charge-transfer resistance increases gradually. The impedance results also have shown that at low frequency the diffusion control is dominant in the process of the charge and discharge of Li/PEO/PAn or Li/PEO/LiMn2O4 cell. The diffusion coefficients have been calculated from impedance data.