AFM-tip-induced crystallization of poly(ethylene oxide) melt droplets

The AFM-tip-induced crystallization of poly(ethylene oxide) (PEO) melt droplets was studied. The melt droplets with a height of 50–100 nm and a lateral size of 2–3 μm were obtained by melting the PEO ultra-thin films on a mica surface. For the PEO samples with average molecular weights (M _n) ranging from 1.0 × 10³ g/mol to 1.0 × 10⁴ g/mol, the lateral perturbation from the AFM tip in the hard-tapping or nanoscratch modes could not induce the growth of the flat-on lamellae. In contrast, under AFM nanoindentation mode, the tip-induced crystallization occurred when a sufficiently high vertical tip force was applied to the melt droplets of PEO with M _n ⩾ 1.0 × 10⁴ g/mol. Moreover, the experimental results indicated that the AFM-tip-induced crystallization of PEO in the nanoindentation process had molecular weight dependence. Translated from Acta Polymerica Sinica, 2006, (4): 553–556 (in Chinese)     

Relaxations of confined chains in polymer nanocomposites: Glass transition properties of poly(ethylene oxide) intercalated in montmorillonite

The relaxation behavior of poly(ethylene oxide) (PEO), intercalated in montmorillonite, a naturally occurring mica-type silicate, was studied by differential scanning calorimetry (DSC) and thermally stimulated dielectric depolarization (or thermally stimulated current, TSC). The materials were synthesized by melt or solution-mediated intercalation. In both intercalates, the PEO chains were confined to ca. 0.8-nm galleries between the silicate layers. The solution intercalate contained a fraction of unintercalated PEO chains which exhibited a weak and depressed PEO melting endotherm in DSC. In contrast, the melt intercalate was “starved” such that almost all the PEO chains were effectively intercalated. For these melt intercalates, no thermal events were detected by DSC. TSC thermal sampling technique was used to examine the glass transition regions and to estimate the extent of cooperativity of chain motions. The motions of the intercalated PEO chains are inherently noncooperative relative to the cooperative T_g motions in the amorphous portion of the bulk polymer. This is presumably due to the strong confining effect of the silicate layers on the relaxations of the intercalated polymer. © 1997 John Wiley & Sons, Inc.     

Molecular motion in nanocomposites of poly(ethylene oxide) and montmorillonite

Motion of chains of poly(ethylene oxide) within the interlayer spacing of 2:1 phyllosilicate/montmorillonite was studied with ¹H and ¹³C NMR spectroscopy. Measurements of the ¹H NMR line widths and relaxation times across a large temperature range were used to determine the effect of bulk thermal transitions on polymer chain motion within the nanocomposites. The results were consistent with previous reports of low apparent activation energies of motion. Details of the frequency and geometry of motion were obtained from a comparison of the ¹³C cross‐polarity/magic‐angle spinning spectra and relaxation times of the nanocomposite with those of the pure polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1678–1685, 2001     

Thermal degradation investigation of poly(ethylene terephthalate)/fibrous silicate nanocomposites

Based on the fibrous silicates (palygorskite, PT) organically modified by water-soluble polyvinylpyrrolidone (PVP), poly(ethylene terephthalate) (PET) nanocomposite with good dispersion of the PT nano-particles was prepared via in situ polycondensation. The thermal degradation behavior of PET and PET/PT nanocomposite was investigated by thermogravimetric analysis (TGA) under non-isothermal conditions at various heating rates in air and nitrogen, respectively. The apparent activation energies of the samples were evaluated by Kissinger and Flynn-Wall-Ozawa method. It is suggested that, during thermal decomposition in nitrogen, the clay as a mass-transport protective barrier can slow down degradation of polymer, but the catalytic effect of metal derivatives in clays may accelerate the decomposition behavior of PET. The combination of these two effects determines the final thermal stability of nanocomposite. However, in air atmosphere, the oxidative thermal stability of PET/PT nanocomposite was obviously superior to that of pure PET.     

Restricted self-diffusion in an aqueous solution of poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) triblock copolymer

 The self-diffusion behavior of a triblock copolymer (PEO–b– PPO–b–PEO) in an aqueous solution of 20% (m/m) was investigated during a temperature-induced phase transition from liquid to gel state using pulsed field gradient NMR and static light scattering. The measured self-diffusivity shows a strong dependence on the observation time in the gel phase indicating the existence of diffusion barriers in the size range of about 0.6 μm. Additional static light-scattering measurements show a structure in the same size range of several hundred nanometers, which is far above molecular or micellar sizes and thus, has to be caused by larger clusters. The similarity in the space scales suggests that the restriction of molecular propagation is correlated with the grain boundaries between the domains of the poly-crystalline structure formed by the arranged micelles. Received: 28 October 1996 Accepted: 21 March 1997     

Polymer-layered silicate nanocomposites based on poly(ε-caprolactone)

Poly(ε-caprolactone) nanocomposites based on montmorillonite modified with hexadecyltrimethylammonium bromide (M-HTAB) were prepared by the in situ polymerization technique. As a result, nano-structured PCL/M-HTAB systems were obtained. It was found that the molecular weight of PCL decreased with an increase in silicate content in the system. Within the investigated range of molecular weight, crystallization behavior of poly(ε-caprolactone) was affected only by the presence of M-HTAB. A silicate loading of higher than 10 wt.% reduced both crystallinity degree and the crystallization rate of PCL. The structure of obtained intercalated nanocomposites depended on the amount of montmorillonite in the systems. The periodicity of clay layers, estimated by X-ray diffraction, was found to be high at increased silicate loading in the nanocomposite. Since PCL and SAN are miscible, an attempt was made to use PCL/M-HTAB systems as a modifier for SAN matrix. Apparently, a quantity as small as 0.66 wt.% of M-HTAB in such blends induced a clear increase in material stiffness. An increase of Young's modulus of more than 40% in comparison to neat SAN was observed at 5.65 wt.% silicate loading.     

Electrical characterization of poly(ethylene oxide)–clay nanocomposites prepared by microwave irradiation

Poly(ethylene oxide) (PEO)–clay (montmorillonite, hectorite, and laponite) nanocomposites were prepared by a melting intercalation procedure induced by microwave irradiation. The influence of parameters such as the time of irradiation, power, amount and relative ratio of the reagents, and relative humidity was investigated. X-ray diffraction, differential scanning calorimetry, elemental microanalysis, Fourier transform infrared, and scanning electron microscopy techniques were applied to characterize the resulting nanocomposites. Techniques involving impedance spectroscopy, thermoelectric power, and electrical polarization in the solid state were used to characterize the electrical properties of the nanocomposites. The electrical behavior of these PEO–silicate nanocomposites, including those containing an excess of alkaline metal salts in comparison with that of similar systems prepared by alternative procedures such as direct intercalation from polymer solutions or melting intercalation, was also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3249–3263, 2003     

Internal pressure of solid poly(ethylene oxide) 6000 swollen with liquid poly(ethylene oxide) 200

Internal pressures (P_i) have been measured at low external pressure for solid poly(ethylene oxide) 6000 and solid poly(ethylene oxide) 6000 swollen with 5% by weight liquid poly(ethylene oxide) 200. Values of P_i are low (P_i < 10⁸ Pa at 10°). The effect of swelling with liquid, which is located exclusively within the disordered layers of the solid, is that expected on the basis of additivity.     

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     

Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains

The mean-square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.     

FTIR assessment of poly(ethylene oxide) irradiated in solid state,melt and aqeuous solution

FTIR spectroscopy was used to study poly(ethylene oxide), PEO, irradiated in solid and molten aggregate states and as aqueous solutions of various concentrations. The changes in shape and width of –C–O–C– complex absorption intensities at around 1112 cm^?1 were the most prominent. On irradiation of solid samples in contact with air shrinking of –C–O–C– complex and increase in its absorption intensities indicated predominant degradation. Crosslinking prevailed on irradiation of molten PEO and of its aqueous solutions in nitrogen atmosphere and manifested itself as widening of –C–O–C– absorption and decrease of corresponding intensities. Partial or complete merging of CH₂ wagging vibrations at 1342 cm^?1 and 1360 cm^?1 that are characteristic of crystalline PEO into a single absorption at around 1350 cm^?1 indicated amorphization what was observed for samples that had reduced degree of crystallinity determined by differential scanning calorimetry. DSC could not discriminate between degradation and crosslinking while the changes in width and shape of –C–O–C– complex were independent of the changes in crystallinity. Comparison of FTIR spectra of the same PEO samples obtained as thin film and as KBr pellets revealed that pellet preparation results in a number of spectral artefacts.     

Nanostructured latex films from poly(butyl methacrylate) latex cross-linked with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock macro-cross-linker

Biphasic polymer latexes were synthesized by a seeded swelling and polymerization method. The latexes were composed of a poly(butyl methacrylate) core and a poly(ethylene oxide) rich shell cross-linked with poly(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock diol diacrylate macro-cross-linker. Nanostructured films were obtained by annealing the biphasic polymer latexes at a temperature between the glass-transition temperatures of the core latex and the cross-linked poly(ethylene oxide) based shell. Atomic force microscope images of the latex film revealed that the poly(butyl methacrylate) core phase is confined in the poly(ethylene oxide)-rich continuous phase with the form of separate nanosized spheres.     

Synthesis of cyclic oligo(ethylene adipate)s and their melt polymerization to poly(ethylene adipate)

We present here the first synthesis of cyclic oligo(ethylene adipate)s(COEAs) via pseudo-high dilution condensation reaction of adipoyl chloride with ethylene glycol, and the synthesis of corresponding poly(ethylene adipate)(PEA) via the melt polymerization of COEAs. The structure of COEAs was characterized and proved by 1H-NMR and MALDI-TOF mass measurements. The effects of organic base, reaction temperature and the ratio of adipoyl chloride to ethylene glycol on the yield of COEAs were studied, and the optimum reaction condition was revealed. PEA, a diacid and diol based semi-crystalline green aliphatic polyester, was synthesized by the melt polymerization of COEAs using Ti(n-C4H9O)4 as catalyst and 1,10-decanediol as initiator at 200 °C, which follows the polycondensation-coupling ringopening polymerization method. Our strategy should be applicable to the synthesis of versatile aliphatic polyesters based on diacid and diol monomers, which have potential applications as biocompatible and biodegradable materials.     

Characterization and demulsification of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers

Four poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers with different molecular weights and PPO/PEO composition ratios were synthesized. The characterization of the PEO-PPO-PEO triblock copolymers was studied by surface tension measurement, UV-vis spectra, and surface pressure method. These results clearly showed that the CMC of PEO-PPO-PEO was not a certain value but a concentration range, in contrast to classical surfactant, and two breaks around CMC were reflected in both surface tension isotherm curves and UV-vis absorption spectra. The range of CMC became wider with increasing PPO/PEO composition ratio. Surface pressure Pi-A curves revealed that the amphiphilic triblock copolymer PEO-PPO-PEO molecule was flexible at the air/water interface. We found that the minimum area per molecule at the air/water interface increased with the proportion of PEO chains. The copolymers with the same mass fractions of PEO had similar slopes in the isotherm of the Pi-A curve. From the demulsification experiments a conclusion had been drawn that the dehydration speed increased with decreased content of PEO, but the final dehydration rate of four demulsifiers was approximate. We determined that the coalescence of water drops resulted in the breaking of crude oil emulsions from the micrograph.     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

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     

Unperturbed dimensions of poly(ethylene oxide)

The intrinsic viscosities of fractions of poly(ethylene oxide) in the molecular weight range 1.5 × 10³ to 10⁶ have been measured at 25°C in benzene, carbon tetrachloride, and acetone; at 35°C in 0.45M aqueous potassium sulfate; and at 50°C in methyl isobutyl ketone and diethylene glycol diethyl ether. The latter three are practically theta solvents. The value of (r₀² /M)^1/2 for poly(ethylene oxide) is calculated to be 0.84 Å from the molecular weights of the high molecular weight fractions, and their intrinsic viscosities in the theta solvents and acetone. Erroneous values result if the usual methods of determination are applied to the data obtained for the low molecular weight (<10⁴) fractions or to the intrinsic viscosities in the very good solvents, benzene and carbon tetrachloride.     

The interfacial tension of poly(ethylene oxide) and poly(propylene oxide) oligomers

Summary The interfacial tensions of a series of poly(ethylene oxides) (PEO) and poly(propylene oxides) (PPO) have been measured using a pendant drop technique. A drop of PEO was formed under the PPO, in a thermostatted cell usually at 73 °C, and it was photographed using parallel monochromatic light from a laser.The interfacial tensions were measured for a series of polymers of different molecular weights and were found to increase with increasing PPO molecular weight but to decrease slightly with increasing PEO molecular weight. The dependence on PPO molecular weight is explained as due to the adsorption of hydroxy end groups of the PPO at the PEO interface. When these end groups were "replaced by methoxy groups, the adsorption no longer took place and the interfacial tension increased.

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Zusammenfassung Die Grenzflächenspannungen einer Reihe von Polyäthylenoxyden (PEO) und Polypropylenoxyden (PPO) wurden mittels der Methode des hängenden Tropfens gemessen. Ein Tropfen aus PEO wurde erzeugt unter PPO in einer temperierten Zelle bei gewöhnlich 73 ° C und wurde in parallelem monochromatischem Licht eines Lasers photographiert.Die Grenzflächenspannungen wurden für eine Reihe von Polymeren mit unterschiedlichem Molekulargewicht gemessen und nahmen zu mit steigendem PPO-Molekulargewicht, nahmen aber leicht ab mit zunehmendem PEO Molekulargewicht. Die Abhängigkeit vom PPO Molekulargewicht wird erklärt als Effekt der Adsorption von Hydroxyl-Endgruppen des PPO an der PEO Grenzfläche. Ersetzt man diese Endgruppen durch Methoxyl-Gruppen, beobachtet man keine Adsorption und die Grenzflächenspannung nimmt zu.

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With 2 figures and 4 tables     

Janus-type dendrimer-like poly(ethylene oxide)s

A straightforward and original methodology allowing the synthesis of Janus-type dendrimer-like poly(ethylene oxide)s (PEOs) carrying orthogonal functional groups on their surface is described. The use of 3-allyloxy-1,2-propanediol (1) as a latent AB2-type heterofunctional initiator of anionic ring-opening polymerization (AROP) of ethylene oxide (EO) and of selective branching agents of PEO chain ends served to construct the two dendrons of these dendrimer-like PEOs, following a divergent pathway. Thus, the first PEO generation of the first dendron was grown by AROP from 1 followed by the reaction of the corresponding alpha-allyl,omega,omega'-bishydroxy- heterofunctional PEO derivative with 2-(3'-chloromethybenzyloxymethyl)-2-methyl-5,5-dimethyl-1,3-dioxane (2) used as a branching agent. This afforded the dendron A with four latent peripheral hydroxyls protected in the form of two ketal rings. The remaining alpha-allylic double bond of the PEO thus prepared was transformed into two hydroxyl groups using OsO4 in order to create the first PEO generation of the dendron B by AROP of EO. Allyl chloride (3) was then used as another (latent) branching agent to react with the terminal hydroxyl of the corresponding PEO chains. Deprotection under acidic conditions of the ketal groups of dendron A, followed by AROP of EO, afforded the second PEO generation on this face. This alternate and divergent procedure, combining AROP of EO and selective branching of PEO branches, could be readily iterated, one dendron after the other up to the generation six, leading to a Janus-type dendrimer-like PEO exhibiting a total mass of around 300 kg/mol and possessing 64 peripheral groups on each face. The possibility of orthogonal functionalization of the surfaces of such Janus-type dendritic PEOs was exploited. Indeed, a dendron of generation 4 was functionalized with hydroxyl functions at its periphery, whereas the other was end-capped with either tertiary amino or disulfide groups. In a variant of this strategy, azido groups and acetylene could also be orthogonally introduced at the periphery of the fourth generation Janus-type dendrimer-like PEO and subjected to polycondensation by a 1,3-dipolar cycloaddition reaction. This afforded a necklace-like covalent assembly of dendrimer-like PEOs through the formation of stable [1,2,3]-triazole linkages.