One-phase Blend Research Articles

Relationship between Ion Transport and Phase Behavior in Acetal-Based Polymer Blend Electrolytes Studied by Electrochemical Characterization and Neutron Scattering

We have studied ion transport in electrolytes created by blending two different polymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymers covered in this study are poly(ethylene oxide) (PEO), poly(1,3,6-trioxocane) (P(2EO-MO)), and poly(1,3-dioxolane) (P(EO-MO)). Ion transport is quantified by the product κρ+ which is defined as the efficacy of the electrolytes, where κ is conductivity and ρ+ is the current fraction determined by the Bruce–Vincent method. Polymer blends can be either one-phase or macrophase-separated. We used small-angle neutron scattering (SANS) to distinguish between these two possibilities. The random phase approximation (RPA) was used to interpret SANS data from one-phase blends. The effect of added salt on polymer blend thermodynamics is quantified by an effective Flory–Huggins interaction parameter. All polymer blends were one-phase in the absence of salt. Adding salt in small concentrations results in macrophase separation in all cases. One-phase systems were observed in the PEO/P(EO-MO)/LiTFSI blends at high salt concentrations. In most of the polymer blend electrolytes, the measured κρ+ was either lower than or comparable to that of the homopolymer electrolytes. An exception to this was one-phase PEO/P(EO-MO)/LiTFSI blends electrolytes at high salt concentrations.

Percolation threshold study of a plastic–elastomeric matrix based composite material for bipolar plates in proton exchange membrane fuel cells

Bipolar plate materials play an important role in designing a cost-effective fuel cell. This research aims to develop a polymer matrix based composite bipolar plate material for proton exchange membrane fuel cells. The polymers investigated are a vinyl ester resin (VER) and two elastomers including polyurethane (PU) and ethylene–propylene–diene monomer (EPDM). The VER alone and the blend of VER with either PU or EPDM makes the one-phase, one-phase blend, or two-phase blend matrices. These matrices will be incorporated within the conductive fillers including Cytec DKD carbon fiber (DKD), Asbury synthetic graphite grade 4012 flake (4012), and grade TC 307 high-surface flake (307). A percolation threshold study was conducted and two-phase blend matrix can achieve lower percolation thresholds. The composite material with 65 vol.% of two-phase bend matrix (60 vol.% VER and 40 vol.% EPDM), and 35 vol.% of conductive fillers (21 vol.% DKD, 5 vol.% 4012 and 9 vol.% 307) is found to have low electrical properties with improved mechanical properties.

Miscibility of α-methyl styrene copolymers—extension of the mean-field treatment for the case of two copolymers

An extension of the mean-field approach for the case of two statistical copolymers is described which allows the analysis of copolymer–copolymer blends of the type A x B 1− x +C y B 1− y where the copolymer (A x B 1− x ) with the mole fraction of monomer A ( x A)=constant is miscible with the (C y B 1− y ) copolymer between y=1 and a single composition limit y= y 1, where y 1>0. Mixtures of poly(α-methyl styrene- co-acrylonitrile) copolymer of azeotrope composition (28.8 wt% acrylonitrile) mixed with statistical methyl methacrylate/acrylonitrile copolymers have been studied and one-phase blends have been found with methyl methacrylate/acrylonitrile copolymers of composition up to 21 wt% acrylonitrile. Estimated segmental interaction parameters acting in the system were positive.

Blends of rigid and flexible macromolecules: poly(benzimidazole) mixed with poly(vinyl acetate- stat-vinyl alcohol) copolymers

Miscibility in a series of blends, derived from poly(benzimidazole) (PBI) and a range of poly(vinyl acetate- stat-vinyl alcohol) [PV(Ac/OH)] copolymers with vinyl alcohol contents between 20 and 73 mol%, has been studied by differential scanning calorimetry, dynamic mechanical thermal analysis, Fourier transform infra-red spectroscopy (FTi.r.), scanning electron microscopy and optical haze measurements. The results show that as the vinyl alcohol content of the copolymer component increases, the level of dispersion of the two components of the blend improves. While no one-phase blends, miscible at the molecular level, were obtained, the levels of dispersion in blends with PV(Ac/OH) compositions of 56.0 and 73.0 mol% vinyl alcohol were good enough to allow the formation of optically clear films. An enhanced storage modulus ( E′) for blend 5, which was larger than that for PBI alone, was also obtained. Evidence for significant hydrogen bonding between the blend components was found from FTi.r. measurements, but none of the blends exhibited a single glass transition temperature. Consequently it is estimated that the phase-domain sizes for the well-dispersed blends lie in the range: 20 nm<domain size<500 nm, which are larger than one would expect from single-phase miscible blends.

Investigation of Morphologies of One- and Two-Phase Blends of Isotactic Poly(propene) with Random Poly(ethene-co-1-butene)

50/50 wt % blends of isotactic polypropene (i-PP) with metallocene-based random poly(ethene-co-1-butene) (PEB) were prepared with 1-butene content varied from 52 to 100 wt %. The melt miscibility of the i-PP/PEB blends as a function of 1-butene content was studied by investigating the morphologies of the blends in the solid state by phase-imaging tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was found that i-PP is melt miscible with PEB for 1-butene contents of ≈88 wt % (miscibility window). Differential scanning calorimetry (DSC) analysis showed a slower and hindered i-PP crystallization in the miscible or partially miscible blends. Intensive investigations on the apparently one-phase blend were performed by optical microscopy, small-angle X-ray scattering and dynamic mechanical analysis.

Thermal diffusivity and conductivity of PMMA/PC blends

A miscible PMMA/PC blend was prepared by a rapid casting method, and its miscibility was confirmed by d.s.c. The specific heat capacity of the two-phase blend ( 5 5 ) was larger than that of the one-phase blend. The thermal diffusivity and the conductivity of the blend ( 5 5 ) slightly decreased with the increase of temperature up to 450–460 K (LCST), and then decreased abruptly with increasing of temperature. The thermal diffusivity at solid state was always smaller than the one estimated by the linear relation with PC content, while in liquid state it always changed linearly with PC content. On the other hand, the experimental thermal conductivity in the liquid state was always smaller than the value estimated by the linear relationship with PC content, while in the solid state it changed linearly. Finally, we discussed adaptability of prediction equations appearing in literature to the conductivity. The Filippov, NEL and power law equations were found to describe adequately the thermal conductivities of PC/PMMA blends in liquid and solid states.

Blends of poly(ethylene oxide) with chitosane acetate salt and with dibuturylchitin: Structure and morphology

This paper presents the results of a study of the chemical structure and morphology of polyblends of chemically modified chitin and chitosane with poly(ethylene oxide). Poly(ethylene oxide)(PEO) forms a compatible one-phase blend with chitosane acetate salt (PEO/CHIACA) and a non-compatible two phase blend with dibutyrylchitin (PEO/DBCHI). The compatible one-phase blend of PEO/CHIACA is formed due to the formation of strong hydrogen bonds between ether groups in PEO and hydroxy groups in CHIACA. Chemical and crystalline morphological structure is discussed here.

Effect of steric restrictions on the enhancement of miscibility through hydrogen bonding in blends of modified poly(α‐methyl styrene) with polymers containing acceptor sites

AbstractTwo series of copolymers have been prepared from α‐methylstyrene and α‐methylstyrene units modified by the incorporation of the hydrogen‐bond donor units, methyl carbinol and trifluoromethyl carbinol, designated PαMS (I) and PαMS (II), respectively. It has been observed that if the concentration of the donor unit exceeds 4 mol %, one‐phase blends can be prepared with a series of polymers containing hydrogen‐bond acceptor sites such as poly(vinyl acetate), poly(vinyl pyrrolidone), poly(4‐vinyl pyridine), and some poly(alkyl acrylate)s, none of which are miscible with the unmodified PαMS. All the one‐phase blends formed are stable at temperatures above the glass transition temperature, Tg, of the blend, but eventually phase separate when the temperature is increased sufficiently. These lower critical cloud‐point curves have been measured for a wide range of the blends and act as an indicator of the effectiveness of the hydrogen bonds in enhancing one‐phase blend formation. The Tg's of the blends are in many cases higher than those calculated from the simple rule of mixtures and reflect the reduction in chain mobility in the blends caused by extensive hydrogen bonding. The results demonstrate the effect that specific interactions have in enhancing miscibility in binary polymer blends. © 1993 John Wiley &amp; Sons, Inc.

Influence of hydrogen bonding on the formation of one-phase blends in binary mixtures of modified poly(α-methyl styrene) with alkyl acrylate, alkyl methacrylate and di-alkyl itaconate polymers

Two series of poly(α-methyl styrene), PαMS, based copolymers have been synthesized. In the PαMS (I) series the phenyl ring in the α-methyl styrene unit has been modified to varying degrees by the introduction of a methyl carbinol unit, whereas the trifluoro methyl carbinol unit has been used in the PαMS (II) series. These groups are potential hydrogen bond donor sites of differing acidic strength. It has been found that the introduction of these specific interaction sites allows the formation of one-phase blends with polymers containing an acceptor site, with which unmodified poly(α-methyl styrene) is immiscible. When these acceptor polymers are poly(alkyl acrylate)s and poly(alkyl methacrylate)s then one-phase blends are obtained with the methyl, ethyl and t-butyl derivatives. The range of one-phase blends can be extended to include the n-propyl derivatives if the modified PαMS are mixed with poly(di-alkyl itaconate)s. Glass transition temperatures, T g and lower cloud point (LCP) temperatures have been recorded for all the one-phase blends. The T g values are usually higher than predicted by the simple rule of mixtures and all blends then phase separate on raising the temperature well above T g. These observations, and the differences in phase equilibrium behaviour exhibited amongst the various blends, are discussed in relation to steric restrictions to hydrogen bond formation, and the effect of both the number and strength of the hydrogen bonds formed on the phase stability of the blends.

Enhancement of miscibility in blends of poly (vinyl methyl ether) and poly (α-methylstyrene)s modified by incorporation of hydrogen-bonding sites

Poly (α-methylstyrene) and poly (vinyl methyl ether) do not form one-phase blends when mixed together. This situation can be changed if the poly (α-methylstyrene) is modified by introducing hydrogen-bond donor groups into the phenyl ring. Two groups of differing donor strength, methylcarbinol and trifluoromethylcarbinol, were selected, and modified poly (α-methylstyrene) samples, with varying degrees of substitution of these groups, were prepared. If the amount of the modifying group incorporated exceeded 4 mol% then one-phase blends of these copolymers with poly (vinyl methyl ether) could be prepared. The effect of the number and strength of these hydrogen-bonding sites on the phase stability of the blends was measured by locating the lower critical phase separation temperature in each blend. The glass transitions of the blends were found to be normally higher than those predicted from a simple rule of mixtures and reflect the extent of hydrogen-bond formation in the blends. This behaviour could, in part, be described by the K wei equation.

Interpenetrating polymer network of poly(vinyl chloride) and polymethacrylates

AbstractA curable polymeric composite was prepared using equal weights of poly(vinyl chloride) (PVC), reactive polyfunctional methacrylate monomers, and inorganic fillers. Peroxide initiated in situ polymerization of the polyfunctional methacrylate monomers in the PVC matrix produced an interpenetrating polymer network (IPN) structure. The polymerization kinetics and the degree of polymerization were investigated using differential scanning calorimetry (DSC), carbon‐13 nuclear magnetic resonance (13C NMR), and solvent extraction. All measurements indicated that during polymerization, the PVC is either crosslinked by or grafted onto the methacrylate three‐dimensional network structure. The rheological properties of the composite were measured before curing using a Rheometrics mechanical spectrometer and found to exhibit mainly viscous behavior and diminished elasticity. The PVC and the methacrylate monomers form a two‐phase system when mixed at room temperature. However, when heated to 100°C the PVC dissolves in the monomers and forms a one‐phase optically clear blend with a single glass transition temperature. In the presence of peroxide, the one‐phase blend is stable and does not separate out upon cooling and storing at room temperature.

Isothermal enthalpy studies of poly(methyl methacrylate) stereoisomers and their blends

The residual enthalpies of slow cooled atactic and isotactic poly(methyl methacrylate) were measured as a function of temperature. The samples were found to contain exothermic amorphous heats which decreased linearly with temperature below their respective Tg ’s. Blends of atactic and isotactic poly(methyl methylcrylate) were found to be one or two phase by differential scanning calorimetry depending on the method of preparation. The redisual enthalpies of the blends were lower than the pure components for the one-phase blend and a weight average of the pure components for the one-phase blend and a weight average of the pure components for the two-phase blend. Polymer-polymer heats of mixing were calculated by comparing the residual enthalpies of the blends to that of the pure components. The magnitude of the polymer-polymer heat of mixing is shown to be a measure of the extent of interaction of the blend relative to the pure components.