Molecular relaxation in cross-linked poly(ethylene glycol) and poly(propylene glycol) diacrylate networks by dielectric spectroscopy

The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-T_g relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.     

Effect of side chain architecture on dielectric relaxation in polyhedral oligomeric silsesquioxane/polypropylene oxide nanocomposites

Segmental and normal mode dynamics in polyhedral oligomeric silsesquioxane (POSS)/poly(propylene oxide) (PPO) non-reactive and reactive nanocomposites were investigated using a broadband dielectric relaxation spectroscopy (DRS) over wide ranges of frequency and temperature. Three POSS reagents with varying side chain architecture were selected for the study: OctaGlycidyldimethylsilyl (OG), TrisGlycidylEthyl (TG) and MonoGlycidylEthyl (MG). Spectra of OG and TG show a segmental (α) process at lower frequency and a local (β) relaxation at higher frequency, while MG displays only a local relaxation. Neat PPO has both segmental and normal mode (α_N) process. In POSS/PPO non-reactive nanocomposites, the presence of OG and TG causes a decrease in the time scale of α_N and α relaxation, while MG has no impact on the dynamics of PPO. Chemical reactions in POSS/PPO reactive nanocomposites lead to the formation of nanonetworks. Prior to the onset of reaction, POSS nanoparticles promote the motions of PPO chains, decrease the time scale of relaxation and give rise to thermodielectrically simple spectra. During the reaction, however, the network formation leads to spectral broadening and a gradual increase in the time scale of both segmental (α) and normal mode (α_N) relaxation. A detailed account of the effects of structure, concentration and dispersion of POSS in the matrix, molecular weight of PPO, extent of reaction and temperature on the molecular origin, temperature dependence and spectral characteristics of relaxation processes in POSS/PPO nanocomposites is provided.     

Binary blends of polyethers with fatty acids: A thermal characterization of the phase transitions

A series of binary blends of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and polytetrahydrofuran (PTHF), characterized by similar average molecular weights, with selected fatty acids (capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid) were prepared by melt mixing. Differential scanning calorimetry was applied to characterize the phase transitions of melting and crystallization, and a synergistic effect was found to occur for PEO/fatty acid blends, as evidenced by the values of the enthalpy of the phase transition. This effect was probably due to hydrogen bonding between PEO and the fatty (carboxylic) acids, which facilitated the formation of crystalline structures; an analysis of IR spectroscopy data showed a shift in the absorption bands of OH groups. The morphology development of the PEO/carboxylic acid blends, as observed with polarizing light microscopy, could be described as spherulitic growth with spontaneous selection of the lamellar thickness. The textures of the individual fibrils, consisting of stacks of several tens of lamellae corresponding to PPO and PTHF, were less regular than the texture of PEO and showed large macroscopic heterogeneity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 861–870, 2003     

Mechanical properties–morphology relationships in nano‐/microstructured epoxy matrices modified with PEO–PPO–PEO block copolymers

Epoxy‐based blends containing poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) (PEO–PPO–PEO) block copolymers with different PEO/PPO molar ratios have been investigated in order to analyze the effect of the generated morphologies and interactions between components on the mechanical properties of the blends. Mechanical, morphological and dynamic mechanical analyses indicate that the observed increase of flexural modulus can be related to the decrease of free volume. In modified systems that remain miscible, an increase of flexural modulus, strength and fracture toughness can be observed. Also, macrophase‐ and microphase‐separated systems show an increase of fracture toughness but not of flexural modulus and strength at low contents of block copolymers. Copyright © 2007 Society of Chemical Industry     

Reaction‐induced phase separation and resulting thermomechanical and surface properties of epoxy resin/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) blends cured with 4,4′‐diaminodiphenylsulfone

We investigated the phase separation, cure kinetics and thermomechanical properties of diglycidyl ether of bisphenol‐A/4,4′‐diaminodiphenylsulfone/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (TBCP) blends. Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy revealed that the blends exhibited heterogeneous phase morphology in which the TBCP formed dispersed domains in epoxy matrix, due to reaction induced phase separation. A fraction of phase‐separated PEO phase underwent partial crystallization whereas another fraction formed interphases between the dispersed domains and epoxy matrix. Moreover, the dispersed PEO chains improved the compatibility and interfacial adhesion between the matrix and domains and, consequently, significantly improved the mechanical properties of epoxy resin. Furthermore, the thermal degradation studies and contact angle measurements disclosed that the dispersed domains were well protected by the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44406.     

High frequency impedance of poly(ethylene oxide) and related polymers doped with lithium perchlorate

High frequency complex impedance measurements at room temperature have been used to obtain dielectric constants, sample dimension ratios and conductivities for poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, doped with LiClO₄. The corrections required to compensate for artefacts due to instrumentation (leads, cables, etc.) at high frequencies are presented. It is concluded that an area/length ratio (A/l) of about 300 cm is preferable for high frequency work. Dielectric constants varied by less than an order of magnitude over a variety of samples, so that the conductivity of an irregularly shaped sample can be estimated from the dielectric relaxation frequency. It was also concluded that the depression of the impedance semicircle for semi-crystalline PEO was due mainly to the microstructure.     

Effects of amorphous silica nanoparticles and polymer blend compositions on the structural,thermal and dielectric properties of PEO–PMMA blend based polymer nanocomposites

The polymer nanocomposite (PNC) films consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrices dispersed with nanoparticles of amorphous silica (SiO₂) have been prepared by solution-cast method followed by melt-press technique. Effects of SiO₂ concentration (x?=?0, 1, 3 and 5 wt%) and PEO–PMMA blend compositional ratios (PEO:PMMA?=?75:25, 50:50, and 25:75 wt%) on the surface morphology, crystalline phase, polymer-polymer and polymer-nanoparticle interactions, melting phase transition temperature, dielectric permittivity, electrical conductivity, electric modulus and the impedance properties of the PNC films have been investigated. The crystalline phase of the PNC films decreases with the increase of PMMA contents which also vary anomalously with the increase of SiO₂ concentration in the films. The melting phase transition temperature and polymer-nanoparticle interactions significantly change with the variation in the compositional ratio of the blend polymers in the PNC films. It is observed that the effect of SiO₂ on the dielectric and electrical properties of these PNCs vary greatly with change in the compositional ratio of PEO and PMMA in the blends. The dielectric relaxation process of these films confirm that the polymers cooperative chain segmental dynamics becomes significantly slow when merely 1 wt% SiO₂ nanoparticles are dispersed in the polymer blend matrix.     

Physical aging in the mechanical properties of miscible polymer blends

Changes in mechanical properties during isothermal physical aging were investigated for three miscible blends: polystyrene (PS)/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO), PS/poly(vinylmethylether) (PVME), and poly(methylmethacrylate) (PMMA)/poly(ethyleneoxide) (PEO). The kinetics of stress relaxation was investigated for the blend, dilute in one component, and compared with that of the neat major component at equal temperature distances, Tg-T, from the midpoint glass transition temperature. It is demonstrated that for all three blends, the mean stress relaxation time (τ) does not scale with Tg-T. For PS/PPO and PS/PVME blends, the stress relaxation rates are faster compared to neat PS; for PMMA/PEO, they are slower than for neat PMMA. Two effects appear to be important in contributing to this discrepancy. First, addition of the second component produces a change in the packing density of the blend: less dense for PS/PPO and PS/PVME; more dense for PMMA/PEO. Comparison of average free volume hole sizes and fractional free volumes measured via orthopositronium annihilation lifetime measurements for all three blends versus the pure constituents are qualitatively consistent with this interpretation. Second, because of the presence of concentration fluctuations in the blend, it is expected that the initial stress decay is dominated by regions enriched in the more mobile component. From observations of the change in width of the stress relaxation time distribution, this effect appears to be particularly significant in the PS/PVME blend. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 483–496, 1997     

Lithium/polymer electrolyte interfacial instability

The stability of evaporated lithium with poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) and oxyethylene-oxymethylene copolymer, doped with lithium perchlorate, in ultra-thin-film cells, was studied by impedance spectroscopy at room temperature. The formation and growth of a passivating film at the lithium/PEO interface has been observed, under open circuit conditions. The thickness of the passivating layer was estimated by assuming the dielectric constant of the interfacial product. A more extensive interfacial reaction was observed in the case of PPO. A very fast interfacial reaction was observed between lithium and amorphous copolymer.     

Correlation between interactions, miscibility, and spherulite growth in crystalline/crystalline blends of poly(ethylene oxide) and polyesters

Crystalline/crystalline blend systems of poly(ethylene oxide) (PEO) and a homologous series of polyesters, from poly(ethylene adipate) to poly(hexamethylene sebacate), of different CH₂/CO ratios (from 3.0 to 7.0) were examined. Correlation between interactions, miscibility, and spherulite growth rate was discussed. Owing to proximity of blend constituents' T_g's, the miscibility in the crystalline/crystalline blends was mainly justified by thermodynamic and kinetic evidence extracted from characterization of the PEO crystals grown from mixtures of PEO and polyesters at melt state. By overcoming experimental difficulty in assessing the phase behavior of two crystalline polymers with closely spaced T_g's, this work has further extended the range of polyesters that can be miscible with PEO. The interaction parameters (χ₁₂) for miscible blends of PEO with polyesters [poly(ethylene adipate), poly(propylene adipate), poly(butylene adipate), and poly(ethylene azelate) with CH₂/CO = 3.0-4.5] are all negative but the values vary with the polyester structures, with a maximum for the blend of PEO/poly(propylene adipate) (CH₂/CO = 3.5). The values of interactions are apparently dependent on the structures of the polyester constituent in the blends; interaction strength for the miscible PEO/polyester systems correlate in the same trend with the PEO crystal growth rates in the blends.     

Microstructural Development of Uniaxial Stretched Anneal-Oriented Syndiotactic Polystyrene and its Blend with Poly (2,6-dimethyl-1,4-phenylene oxide): DSC,WAXD, SAXS and FTIR Studies

Studies have been done on strain-induced microstructure development in syndiotactic polystyrene (s-PS) and its blends with poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) in 70/30 and 50/50 compositions of stretched annealed samples. Wide-angle X-ray showed that crystal orientation is less in annealed blend samples compared to annealed pure s-PS for a higher draw ratio. It increases with annealing, and relaxation occurs after a certain annealing temperature at above 180° for both s-PS and s-PS/PPO 70/30 blends. No crystal orientation was observed in the blend of s-PS/PPO 50/50 stretched samples. Small angle X-ray scattering (SAXS) shows the inclusion of amorphous PPO chains in between s-PS crystals lamella. Fourier transform infrared (FTIR) spectroscopy shows that the s-PS molecular chain packing band at 905 cm^?1 is enhanced due to annealing in oriented samples and saturates to around 0.63. The crystal chain relaxation is lower than amorphous chains of s-PS. The molecular chains of amorphous PPO are less oriented into the blend matrix, whereas its relaxation is enhanced during heat treatment and reaches an optimum value after full relaxation. The different behaviors of orientation and relaxation of s-PS and PPO chains into the blend matrix produce superstructures.     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Polyethers for biomedical applications: Bulk and surface characterisation of crosslinked blends of poly(ethylene oxide) and poly(propylene oxide)

Bulk and surface properties of crosslinked and non-crosslinked blends of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPOX) were studied for the elucidation of the behaviour of these materials in contact with blood. In the crosslinked blends the hydrophilic character increased with increasing PEO content, as concluded from swelling experiments and contact angle determinations. D.s.c. and dynamic mechanical measurements indicated the occurrence of phase separation in the blends and d.s.c. showed that on equilibration with water the PEO phase loses its crystallinity. F.t.-i.r.-a.t.r. analysis of the surface of crosslinked PPOX-PEO films showed an enrichment of the surface with PEO. These observations indicate that the good blood-compatibility of PPOX-PEO blends might be explained by the presence of an amorphous, PEO-enriched, hydrophilic surface.     

Morphologies of an Amphiphilic Diblock Copolymer of Poly (Ethylene Oxide)-b-Polystyrene and Its Blends with Poly (2,6-Dimethyl-1,4-Oxide)

Systems containing block copolymers are of great interest due to the ability of copolymers to self-assemble into a variety of structured, ordered, or partially ordered morphologies. A fascinating morphology of two-dimensional arrays of hexagonal-like holes was observed for the first time in the diblock copolymer of poly (ethylene oxide)-b-polystyrene (PEO-b-PS) by transmission electron microscopy (TEM). The blends of PEO-b-PS with poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) were obtained by solution blending, and the morphologies of PEO nano-dispersed particles in PPO/PS matrix were observed by atomic force microscopy (AFM) and TEM. Using the film forming technique on water/air interface, the core-shell morphology with PEO as shells was obtained in PEO-b-PS/PPO blends. Thus, three different morphologies were obtained by controlling preparation conditions. Especially, PEO-b-PS self-organized into the hexagonal-like holes patterns was first found to our knowledge.     

通过状态方程预测无定形和可结晶共混聚合物的压力-体积-温度和超摩尔体积（英文）

In this work the statistical mechanical equation of state was developed for volumetric properties of crystal ine and amorphous polymer blends. The Ihm–Song–Mason equations of state (ISMEOS) based on temperature and density at melting point (Tm andρm) as scaling constants were developed for crystalline polymers such as poly(propylene glycol)+poly(ethylene glycol)-200 (PPG+PEG-200), poly(ethylene glycol) methyl ether-300 (PEGME-350)+PEG-200 and PEGME-350+PEG-600. Furthermore, for amorphous polymer blends con-taining poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)+polystyrene (PS) and PS+poly(vinylmethylether) (PVME), the density and surface tension at glass transition (ρg andγg) were used for estimation of second Virial coefficient. The calculation of second Virial coefficients (B2), effective van der Waals co-volume (b) and correction factor (α) was required for judgment about applicability of this model. The obtained results by ISMEOS for crys-talline and amorphous polymer blends were in good agreement with the experimental data with absolute aver-age deviations of 0.84%and 1.04%, respectively.     

Dynamic rheological analysis of a miscible blend showing strong interactions

The rheological behavior of miscible blends was studied through oscillatory shear measurements. Two miscible blends were selected to compare with athermal blending cases, i.e. the hydrogen bonding poly(4-vinyl phenol)/poly(ethylene oxide) (PVPh/PEO) blend and the weakly interacting polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) (PS/PPO) blend. The homopolymers and the blends were characterized over a wide experimental window using the time-temperature superposition principle.The horizontal shift factor, a_T, does not vary appreciably with composition for PS/PPO, whereas a strong compositional dependence is observed for the PVPh/PEO blends. Additions of up to 30 wt% of PEO to PVPh produce only minor changes in the value of rubber plateau modulus (G_N⁰), while G_N⁰ increases steadily after this concentration. The G_N⁰ values follow athermal blending models [J. Polym. Sci., Part B: Polym. Phys. 25 (1987) 2511; J. Polym. Sci., Part B: Polym. Phys. 26 (1988) 2329] in the case of PS/PPO but not of PVPh/PEO. Values of η_0b for PVPh/PEO blends were estimated from weighed relaxation spectra. The three measured parameters, a_T, G_N⁰ and η₀ show a turning point around 20-30 wt% of PEO, which corresponds to a 41-54 mol% of PEO, in correlation with the previously reported observation of a maximum in the deformation-induced uniaxial orientation behavior of PEO component near this composition [Macromolecules 32 (1999) 8509].     

Simultaneously enhanced cryogenic mechanical behaviors of cyanate ester/epoxy resins by poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) (PEO‐PPO‐PEO) block copolymer and clay

Cryogenic mechanical properties are important parameters for thermosetting resins used in cryogenic engineering areas. The hybrid nanocomposites were prepared by modification of a cyanate ester/epoxy/poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐PPO‐PEO) system with clay. It is demonstrated that the cryogenic tensile strength, Young's modulus, ductility (failure strain), and fracture resistance (impact strength) are simultaneously enhanced by the addition of PEO‐PPO‐PEO and clay. The results show that the tensile strength and Young's modulus at 77 K of the hybrid nanocomposite containing 5 wt% PEO‐PPO‐PEO and 3 wt% clay were enhanced by 31.0% and 14.6%, respectively. The ductility and impact resistance at both room temperature and 77K are all improved for the hybrid composites. The fracture surfaces of the neat BCE/EP and its nanocomposites were examined using scanning electron microscopy (SEM). Finally, the dependence of the coefficients of thermal expansion (CTE) on the clay and PEO‐PPO‐PEO contents was examined by thermal dilatometer. POLYM. COMPOS., 38:2237–2247, 2017. © 2015 Society of Plastics Engineers     

Polyether-segmented nylon hemodialysis membranes. II. Morphologies and permeability characteristics of polyether-segmented nylon 610 membrane prepared by the phase inversion method

The relationships between the morphologies and the permeability characteristics as dialysis membrane of polyether-segmented nylon 610 (PE-Ny610) have been investigated. PE-Ny610 used are poly(propylene oxide) (PPO)-segmented nylon 610 containing 25 wt % PPO (PPO-Ny610) and poly(ethylene oxide) (PEO)-segmented nylon 610 containing 15 wt % PEO (PEO-Ny610). The morphologies in the cross section of the membranes exhibit the cellular porous structures due to liquid-liquid phase separation. On the other hand, the structures of the surfaces are mainly composed of the crystalline spherulite due to liquid-solid phase separation. These morphologies are little affected by the composition ratio of the coagulant, calcium chloride/methanol/water mixture. PEO-Ny610 membranes have shown superior membrane performances to the PPO-Ny610 membrane. The effect of PEO content in PEO-Ny610 on the adhesion of platelet onto the PEO-Ny610 film surface was investigated and it is concluded that PEO-Ny610 having > 10 wt % PEO shows a good nonthrombogenicity equal to PPO-Ny610. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1713–1721, 1997     

Demulsification efficiency of some novel styrene/maleic anhydride ester copolymers

Four demulsifiers were prepared in three steps. In the first step, styrene and maleic anhydride were copolymerized. In the second step, a long‐chain alcohol (dodecanol) was reacted with the prepared copolymer to form the monoesterified copolymer. In the final step, the resulting product was further esterified with poly(propylene oxide) (PPO)–poly(ethylene oxide) (PEO) block copolymers of different molecular weights (1.1, 2.5, 3.0, 5.0, and 8.0 × 10³) and different PPO/PEO ratios. The demulsification efficiency of these demulsifiers was investigated with the bottle test (Sany glass). The effects of the molecular weight and ratio of the PPO–PEO block copolymers on the demulsification efficiency were studied. The demulsification efficiency could be enhanced from 66% by an individual demulsifier to 100% by demulsifier blends. The surface‐active and thermodynamic properties of the prepared demulsifiers were measured at 25, 35, and 45°C. The kinematics of the demulsification process were photographed with a binocular microscope. The demulsification mechanism was found to occur in three stages, that is, adsorption and flocculation, coalescence, and channel formation followed by separation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Miscibility of blends of poly(methyl methacrylate) and oligodiols based on a bisphenol A nucleus and ethylene oxide or propylene oxide branches

Cloud-point curves of blends of poly(methyl methacrylate) (PMMA) with a series of oligodiols based on a bisphenol A nucleus and short branches of poly(ethylene oxide) or poly(propylene oxide) (BPA-EO or BPA-PO), and with PEO and PPO oligomers, were obtained using a light transmission device. Experimental results were fitted with the Flory-Huggins model using an interaction parameter depending on both temperature and composition. For PMMA/PEO and PMMA/PPO blends, the miscibility increased when increasing the size of the diol, due to the significant decrease in the entropic and enthalpic terms contributing to the interaction parameter. This reflected the decrease in the self-association of solvent molecules and in the contribution of terminal OH groups to the mismatching of solubility parameters. For PMMA/BPA-EO blends, a decrease of the entropic contribution to the interaction parameter when increasing the size of the oligodiol was also found. However, the effect was counterbalanced by the opposite contribution of combinatorial terms leading to cloud-point curves located in approximately the same temperature range. For PMMA/BPA-PO blends, the interaction parameter exhibited a very low value. In this case, the effect of solvent size was much more important on combinatorial terms than on the interaction parameter, leading to an increase in miscibility when decreasing the oligodiol size. For short BPA-PO oligodiols no phase separation was observed. The entropic contribution of the interaction parameter exhibited an inverse relationship with the size of the oligodiols, independent of the nature of the chains bearing the hydroxyls and the type of OH groups (primary or secondary). This indicates that the degree of self-association of solvent molecules through their OH terminal groups, was mainly determined by their relative sizes.