Blends of metal acetates and polyurethanes containing pyridine groups II. SAXS and EXAFS studies

Polyurethanes containing pendant pyridine units were blended with various metal acetates and studied by small-angle x-ray scattering (SAXS) and extended x-ray absorption fine structure spectroscopy (EXAFS) to better understand the microscopic effect of blending on these materials. An earlier investigation found a dramatic enhancement in mechanical properties after blending, which suggests at least two pyridine units were coordinating to a single cation. This coordination would enable the cation to act as a cross-linking site, which could then cause the observed changes in mechanical properties. To determine the effect of complexation on the microphase-separated domain structure, small-angle x-ray scattering patterns were collected. Neutralization with a metal acetate increased the scattered intensity, which can be explained by an increase in electron density contrast but may also have been due to an improvement in phase separation. The distance between lamellar domains was basically unaffected by the addition of metal acetate, with the exception of nickel acetate. In this instance the distance decreased, which was caused by an improvement of packing inside the hard segments. EXAFS at the nickel and zinc edges indicated that the same qualitative changes occurred in the local environments around both cations after blending versus the unblended acetates. The magnitude of the first shell peak in the radial structure function (RSF) increased significantly upon blending, a result that is difficult to rationalize. The higher shell peaks exhibited significant changes in position and magnitude upon blending, which indicates substantial local rearrangement around the metal cation These fundamental changes in the EXAFS spectra may have been due to complexation between the cation and the pyridine group, but the results were not conclusive. © 1994 John Wiley & Sons, Inc.     

Miscible blends of zinc-neutralized sulfonated polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide)

Zinc-neutralized sulfonated polystyrene ionomers (ZnSPS) and poly(2,6-dimethyl 1,4-phenylene oxide) homopolymer (PXE) form miscible blends up to at least 7.8 mol % sulfonation, as measured by thermal and mechanical criteria. The addition of an equal weight of PXE raises the glass transition temperature of ZnSPS by 40–50°C. However, this miscibility is not achieved by eradicating the microdomain structure present in ZnSPS, even though the PXE coils are considerably larger than the spacings between ionic aggregates. Small-angle x-ray scattering indicates that while the average interaggregate spacing is roughly the same in ZnSPS and its 50/50 blend with PXE at a given sulfonation level, the extent of phase separation is reduced upon PXE addition, indicating that more ionic groups are dispersed in the matrix. Factors influencing miscibility in the ZnSPS/PXE materials and related blends are discussed.     

Relationship between Localization of PBSU in Interlamellar/Interfibrillar Regimes and Double Peaks in DSC/SAXS in its Blend with PVDF

In this work, phase segregation and localization of PBSU have been investigated with the combination of SAXS and DSC in its blend with PVDF. After stepwise crystallization of PVDF and PBSU, there are double melting peaks of PBSU in DSC and double scattering peaks in SAXS. It has been demonstrated that double peaks can be attributed to the localization of PBSU in interlamellar/interfibrillar region in pre-formed PVDF crystal framework. In the case of low content of PBSU in blend, PBSU is trapped into the interlamellar region of PVDF crystals, resulting in the alternating lamellae crystal of them and the first peak (with low-q) in SAXS. The enhanced confinement effect produces thinner PBSU lamellae, corresponding to the lower melting temperature in DSC. Upon increasing its content in blend, some PBSU segregates in interfibrillar regions in addition to the enrichment in interlamellar regions of PVDF crystal framework. The larger space and higher concentration of PBSU in interfibrillar-regions contribute to periodic lamellae structure of PBSU with higher thickness, which is the reason for the second peak (with high-q) in SAXS and DSC. Our results not only clarify the relationship between localization of PBSU in interlamellar/interfibrillar regions and double peaks in DSC/SAXS, but also provide a novel strategy to detect the interlamellar and interfibrillar segregation of low-T_m component in miscible crystalline/crystalline blend.

     

Nano-scale structure change of amphiphilic di-block copolymer by blend

The phase transition and nano-scale ordered structure of four types of blends prepared from four di-block copolymers, consisting of hydrophilic poly(ethylenoxide) and hydrophobic poly(methacrylate) derivative, PEO_m-b-PMA(Az)_n having different PEO molecular length and same degree of polymerization of PMA(Az) were investigated. All blend systems formed hexagonal packed PEO cylinder structure, which was same with the nano-scale structure of these parent block copolymers. The SAXS and AFM observation suggested that the size of hexagonal structure of blend was larger than the average size of parent block copolymers. The melting enthalpy of PEO in blends was larger than the average value of parent block copolymers. DSC, SAXS and AFM observations indicated the miscible blend systems.     

Phase morphology of blends of polycarbonate with poly(methyl methacrylate-co-cyclohexyl methacrylate), and of polycarbonate with poly(methyl methacrylate) by solid state nuclear magnetic resonance,differential scanning calorimetry,and transmission electron microscopy

The miscibility of polycarbonate (PC) with poly(methyl methacrylate-co-cyclohexyl methacrylate) (PMCHM) and with poly(methyl methacrylate) (PMMA) was studied by nuclear magnetic resonance (NMR) ¹H spin-lattice relaxation time in the rotating frame (¹H T_1p), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). A blend of PC/PMCHM (50/50 wt/wt) with the acrylic component PMCHM, a copolymer of PMMA and poly(cyclohexyl methacrylate) (80/20 wt/wt), shows only one T_1p value, which indicates high miscibility in this blend. A blend of PC/PMMA (50/50 wt/wt) shows two ¹H T_1p values, which are similar to those of the homopolymers PC and PMMA. These results indicate high immiscibility. The “domain size” calculated from NMR results of the miscible blend PC/PMCHM is approximately 40 Å. The results of DSC and TEM are similar to the NMR results. However, TEM results show the presence of 3% PC domains in the PC/PMCHM blend, which are not seen by NMR or DSC. Those PC domains are approximately 500 Å. A strong intramolecular repulsion in the copolymer PMCHM and specific intermolecular interactions between PC and PMMA may explain the miscibility in the PC/PMCHM system. © 1994 John Wiley & Sons, Inc.     

Characterization and properties of polyethylene blends I. Linear low-density polyethylene with high-density polyethylene

A blend system of linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with high-density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), Raman longitudinal-acoustic-mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman-LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single-step drop in the scattered intensity (I_Hv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of the typical miscible blends.     

Effect of transesterification products on the miscibility and phase behavior of poly(trimethylene terephthalate)/bisphenol A polycarbonate blends

Blends of poly(trimethylene terephthalate)/bisphenol A polycarbonate (PTT/PC) with different compositions were prepared by melt blending. The effect of transesterification on the miscibility and phase behavior of the blends was studied using DSC, DMA, and ¹H NMR. The DMA results revealed a two-phase system with partial miscibility. DSC thermograms of the first heating scan showed a crystallizable system in which addition of PC-phase reduces the degree of crystallinity. However, the cooling and also the second heating scans revealed the complete miscibility of all the blends. It was concluded that annealing at 300 °C (to remove thermal history of the blends) caused the constituents to undergo the transesterification reaction, which changes the blend to a miscible system. The miscibility is due to formation of block copolymers with different block lengths which also suppress the crystallization of the system. The degree of randomness and sequence lengths of the copolymers were determined to analyze the extent of transesterification reaction and structure of the system. It was observed that as the reaction progresses, the degree of randomness increases and the sequence length of the copolymers decreases. Moreover, both increase of reaction time and temperature increased the extent of reaction. The results of DSC and ¹H NMR showed that a small amount of reaction is needed to change this system to a miscible blend.     

Morphological investigations of block sulfonated poly(arylene ether ketone) copolymers as potential proton exchange membranes

A series of block sulfonated poly(arylene ether ketone) (SPAEK) copolymers with different block lengths and ionic contents were synthesized by a two‐stage process. The morphology of these block SPAEK copolymers was investigated by various methods, such as differential scanning calorimetry (DSC), transmission electron microscope (TEM), and small angle X‐ray scattering (SAXS). Dark colored ionic domains of hundreds of nanometers spreading as a cloud‐like belt were observed in TEM images. The sizes of the ionic domains as a function of block copolymer composition were determined from SAXS curves. The results for the evolution of ionic domains revealed that the block copolymers exhibited more clearly phase‐separated microstructure with increasing ionic contents and hydrophobic sequence lengths. Proton conductivity is closely related to the microstructure, especially the presence of large interconnected ionic domains or ionic channels. Block SPAEK membranes have interconnected ionic clusters to provide continuous hydrophilic channels, resulting in higher proton conductivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of sol‐gel polymerization of tetraethylorthosilicate on internal aggregate structure in zinc‐neutralized ethylene‐methacrylic acid ionomers

Sol‐gel reactions of tetraethylorthosilicate have been performed in three different zinc‐neutralized ethylene‐methacrylic acid copolymer ionomers for the purpose of creating nanostructured organic‐inorganic materials with enhanced properties. Extended X‐ray absorption fine structure (EXAFS) spectroscopy was used to understand the effect of this in situ reaction on ionic aggregate morphology. EXAFS spectra showed that no large changes occurred in the aggregate structure, indicating that the internal environment of the aggregates did not nucleate the reaction, at least to the extent that the ionic domains were significantly undisrupted. However, small changes in EXAFS patterns were evident. These changes could be a result of nucleation of the reaction at the edges of the aggregates, or aggregate size rearrangement caused by the insertion of inorganic moieties into the polymer. However, the results indicate that the latter cannot include significant amounts of unaggregated zinc ions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 197–200, 2001     

Crystallization behavior of P(EN‐co‐ET) copolyesters: Crystallization kinetics and morphology revealed by DSC,time‐resolved SAXS analysis,and TEM

The crystallization kinetics and morphology of PEN/PET copolyesters were investigated using differential scanning calorimetry (DSC), time‐resolved small‐angle X‐ray scattering (TR‐SAXS), and transmission electron microscopy (TEM). The Avrami exponents obtained using DSC were approximately 3 for homo PEN and 4 for all the copolyesters. The 3‐parameter Avrami model was successfully fitted to the invariants with respect to the time obtained from TR‐SAXS, and the exponent values were similar to those obtained from DSC. Moreover, the Avrami rate constants obtained from TR‐SAXS showed marked temperature‐sensitive decreases in all samples, like those obtained from DSC. This indicates that not only could changes in morphological parameters be obtained from the analysis of TR‐SAXS data but also crystallization kinetics. The changes in the morphological parameters determined from the SAXS data indicate that the minor components, dimethyl terephthalate (DMT) segments, are rejected into the amorphous phase during crystallization. In the TEM study, copolyesters crystallized at temperature above 240 °C grew into both the α‐ and β‐form, although 240 °C is the optimum condition for the β‐form crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 805–816, 2005     

The Structural Features of Low Molecular Weight Ionic Diblock Polymers Based on Group Transfer Polymerized Methacrylates

Abstract

The solid-state ordered structures formed by low M _a ionic diblock copolymers of less than 10,000 g/mol, made by group-transfer polymerization of methacrylates, were studied. The unquaternized diblocks exhibit no structure via small-angle x-ray scattering (SAXS) and are apparently below their critical value of XN in a disordered melt state at room temperature. However, the amine salt ionomers exhibit morphologies ranging from dispersed spheres to lamellae which were investigated by SAXS and transmission electron microscopy (TEM). The morphology depends strongly on the size and proportion of the blocks, the extent of quaternization, and the concentration of the blocks in the casting solution.     

Transparency enhancement in semicrystalline PEEK through variation of polymer morphology

We report a processing window in which transparent semicrystalline poly(ether ether ketone) (PEEK) can be produced. The transparent PEEK film reported is 100 μm in thickness and has light transmittance of 54%; while ordinary semicrystalline PEEK film of the same thickness and degree of crystallinity, but produced outside the processing window, is virtually opaque (with the light transmittance close to 0%). First processing conditions for producing the transparent PEEK film are discussed, and second characterization of the transparent PEEK film is detailed. Results suggest that the main processing condition for developing the transparent PEEK film is forming temperature, defined as the highest temperature that the film is exposed to during thermal treatment. Using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and small-angle x-ray scattering (SAXS), we characterized morphology of the PEEK films. TEM shows that the morphology in the transparent PEEK film has a locally oriented lamellar structure, instead of the commonly observed spherulites or sheaves. DSC results suggest that the new morphology is formed in the melt with a high density of residual crystals that act as nucleating agents during the crystallization process, which is known as a self-seeding effect. SAXS spectra show that specimens with higher forming temperature produce broader diffraction peak at larger Q value that is defined as 4π sin θ/λ. We conclude from the study that the light transmittance enhancement is morphology related, and can be achieved through control of processing conditions. © 1996 John Wiley & Sons, Inc.     

Block polyelectrolytes in aqueous environments

Analogous to the self-assembly of low-molecular-weight amphiphiles in aqueous solutions, the formation of spherical micelle-like aggregates has been observed in systems of amphiphilic block copolymers in water. The aggregates, often called micelles due to structural similarities with surfactant associates, are found to exist above the critical micelle concentration (cmc). The micellization of amphiphilic block copolymers has been investigated using a wide range of techniques, such as size-exclusion chromatography (SEC), static and dynamic light scattering (SLS and DLS), small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS), transmission electron microscopy (TEM), viscometry, and steady-state fluorescence spectroscopy. The present lecture is a review of recent work in our laboratory concerning the micellization of ionic block copolymers. These high-molecular-weight amphiphiles may contain one or more of a variety of ionic blocks, such as poly(4-vinylpyridinium alkyl halides), poly(metal acrylates), poly(metal methacrylates) and sulfonated polystyrene. In water, such polymers are referred to as block polyelectrolytes, as they combine the colloidal behavior of block copolymers with the long-range electrostatic interactions of polyelectrolytes. Early work in this field has been reviewed by Selb and Gallot.¹     

EXAFS studies of nickel nafion ionomers

Nafion membranes neutralized with Ni²⁺ have been examined by extended x-ray absorption fine-structure (EXAFS) and x-ray absorption near-edge-structure (XANES) spectroscopy. The results indicate that in both the dry and water-soaked membranes, the nickel is in an octahedral site with six oxygen atoms as nearest neighbors. The degree of disorder in the Ni? O distance is comparable to that in ionic crystals in both the dry and hydrated materials. A contribution from a second shell of neighbors is very weak in the dry samples but, surprisingly, this contribution is strongly accentuated in the hydrated membranes. The data indicate that this contribution is due to neighboring Ni²⁺ cations. Thus the water absorption seems to enhance the local ordering of the cation environment. The local structure does not depend strongly on the concentration of ionic groups in the materials.     

Synthesis and characterization of catalytic iridium nanoparticles in imidazolium ionic liquids

The reduction of [Ir(cod)Cl](2) (cod=1,5-cyclooctadiene) dissolved in 1-n-butyl-3-methyl tetrafluoroborate, hexafluorophosphate and trifluoromethane sulphonate ionic liquids in the presence of 1-decene by molecular hydrogen produces Ir(0) nanoparticles. The formation of these nanoparticles follows the two-step [A-->B, A+B-->2B (k(1),k(2))] autocatalytic mechanism. The same mean diameter values of around 2-3 nm were estimated from in situ TEM and SAXS analyses of the Ir(0) nanoparticles dispersed in the ionic liquids and by XRD of the isolated material. XPS and EXAFS analyses clearly show the interactions of the ionic liquid with the metal surface demonstrating the formation of an ionic liquid protective layer surrounding the iridium nanoparticles. SAXS analysis indicated the formation of an ionic liquid layer surrounding the metal particles with an extended molecular length of around 2.8-4.0 nm depending on the type of the anion.     

P(HB-co-HV)/PVPh的相容性与聚集态结构

采用差热扫描分析、红外光谱、固体核磁、小角X光散射等方法研究了聚(β-羟基丁酸酯-co-β-羟基戊酸酯(P(HB-co-HV))/聚(对-羟基苯乙烯)(简称PVPh)共混物的相容性和形态。结果表明两组分间形成较强的分子间氢键,形成完全相容的共混体系。固体核磁结果表明P(HB-co-HV)/PVPh(50/50)在3.4nm尺寸上是完全均相的。小角X光散射结果表明,在等温结晶的共混物中无定形的PVPh分子分散在P(HB-co-HV)片晶之间与非晶的P(HB-co-HV)分子形成非晶区,从而使非晶区加宽,长周期增加。     

Transmission electron microscopy study of phase morphology in polypropylene/ethylene-octene copolymer blends

Blends of polypropylene (PP) and ethylene-octene copolymers (EOC) were investigated by transmission electron microscopy (TEM) and by differential scanning calorimetry (DSC). The EOC contained 28, 37, 40 or 52 wt% of octene. Only the 50/50 PP/EOC ratio was used for all blends. None of the blends was fully miscible, there was always two-phase morphology. TEM observation followed by image analysis by ImageJ software revealed that the largest particles were in blend containing EOC-28 and the smallest were in blend with EOC-52. The coarsening rate at 200 °C was evaluated by TEM. The glass transition temperature (T_g) shift indicated partial miscibility. Partial miscibility was then confirmed by direct observation of bright PP lamellae in EOC dark phase.     

Structure of reactively extruded rigid PVC/PMMA blends

A novel route for producing polymer blends by reactive extrusion is described, starting from poly (vinyl chloride)/methyl methacrylate (PVC/MMA) dry blend and successive polymerization of MMA in an extruder. Small angle X‐ray scattering (SAXS) measurements were applied to study the monomer's mode of penetration into the PVC particles and to characterize the supermolecular structure of the reactive poly(vinyl chloride)/poly(methyl methacrylate) (PVC/PMMA) blends obtained, as compared to the corresponding physical blends of similar composition. These measurements indicate that the monomer molecules can easily penetrate into the PVC sub‐primary particles, separating the PVC chains. Moreover, the increased mobility of the PVC chains enables formation of an ordered lamellar structure, with an average d‐spacing of 4.1 nm. The same characteristic lamellar structure is further detected upon compression molding or extrusion of PVC and PVC/PMMA blends. In this case the mobility of the PVC chains is enabled through thermal energy. Dynamic mechanical thermal analysis (DMTA) and SAXS measurements of reactive and physical PVC/PMMA blends indicate that miscibility occurs between the PVC and PMMA chains. The studied reactive PVC/PMMA blends are found to be miscible, while the physical PVC/PMMA blends are only partially miscible. It can be suggested that the miscible PMMA chains weaken dipole–dipole interactions between the PVC chains, leading to high mobility and resulting in an increased PVC crystallinity degree and decreased PVC glass transition temperature (T_g). These phenomena are shown in the physical PVC/PMMA blends and further emphasized in the reactive PVC/PMMA blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Miscibility and specific interactions in polyacrylonitrile/ poly(p‐vinylphenol) blends

A rare miscible polyacrylonitrile (PAN) blend system is reported. PAN is miscible with poly(p‐vinylphenol) (PVPh) as shown by thermal and spectroscopic studies. A single glass transition temperature was found in each blend. Infrared spectroscopic studies showed that the hydroxyl band of PVPh and the cyano band of PAN shifted to lower frequencies upon blending, showing the existence of specific interactions between the two polymers. The involvement of cyano groups in specific interactions was further evidenced by the development of a high‐binding‐energy N1s peak in each blend from X‐ray photoelectron spectroscopic studies.     

EXAFS analysis of plasticized zinc-neutralized sulfonated polystyrene ionomers

The interaction of several plasticizers with the zinc cation in zinc-neutralized sulfonated polystyrene was examined with extended x-ray absorption fine structure (EXAFS) spectroscopy. Glycerol and water were found to interact strongly with the zinc cation, plasticizing the ionic aggregates. At full solvation by glycerol, the zinc atom was found to be coordinated by three glycerol molecules. Dioctylphthalate, acetonitrile, and toluene, which are unable to coordinate to the zinc cation, were found to have a minimal effect on the cation's local structure.