Phase behavior in copolymer blends of poly (p-chlorostyrene-co-o-chlorostyrene) and phenylsulfonylated poly (2,6-dimethyl-1,4-phenylene oxide)

The miscibility of random copolymers of o-chlorostyrene and p-chlorostyrene [P (oClSt-co-pClSt)] with partially phenylsulfonylated poly (2,6-dimethyl-1,4-phenylene oxide) (SPPO) copolymers has been studied, using differential scanning calorimetry (DSC) to establish T_g behavior. It already has been established that the isomeric effect of the chlorine substitution on miscibility is large. Thus the para-chloro-substituted styrenic homopolymer is miscible with all SPPOs containing more than ～ 5 mol % phenylsulfonylation, whereas the ortho-chloro-substituted homopolymer is immiscible with the entire range of SPPO copolymer compositions (and also with the respective homopolymers). As a result of this asymmetric behavior of the homopolymers, the width of the window of miscibility in blends now investigated containing copolymers with high pClSt content and SPPO is much greater than in the corresponding blends containing copolymers with large mole fraction of oClSt. These differences are reflected in the corresponding χ parameters calculated from analysis of the data. It was also found that the miscibility is temperature dependent and that the regime in the copolymer-copolymer composition plane shrank as the equilibrium temperature increased, results indicative of LCST behavior. © 1994 John Wiley & Sons, Inc.     

Chain orientation in polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) blends

The differential orientation of polymer chains has been measured in polystyrene (PS)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) compatible blends. Density measurements are reported as a function of binary blend composition at 23°C. Drawing was performed by solid-state coextrusion. PS/PPO blend compositions of 90/10 and 75/25 were drawn within sandwiches of polyethylene at 145°C and isotactic polypropylene at 155°C, i.e. at ca. 25°C above the glass transition temperatures of the two blends. The change in Fourier-transform infrared dichroisms on drawing these blends was measured at 906 and 1190 cm^?1, corresponding to predominantly PS and PPO, respectively. The orientation of PS and PPO was observed as a function of draw ratio λ in the range 1–5; orientations increased with λ for both PS and PPO in both blends but to different degrees. Both polymers decreased in orientation with increasing PPO content. Annealing with fixed ends showed that the PPO chains disorient more slowly than those of PS. All binary systems were found to be amorphous and compatible.     

Photochemical degradation of blends of polystyrene and poly(2,6 -dimethyl-1,4-phenylene oxide)

Blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) that cover the entire compositional range have been subjected to the action of singlet oxygen from microwave discharge, dye-sensitized reaction, and photochemical oxidation. With the applied analytical technique, which consisted of infrared (IR) analysis, including ATR technique and a spectroscopic method combined with chemical analysis for hydroperoxide groups, it was not possible to detect any effect of the singlet oxygen treatment. For that reason singlet oxygen does not appear to be important to the initiation of the photooxidation of these blends. In connection with photochemical oxidation the interaction observed between the two components probably involves energy transfer from PS to PPO. This interaction results in the enhancement of reactions in PPO that lead to greater carbonyl group formation and crosslinking. Simultaneously, the probability of chain scission in the PS is lowered with increased PPO content, found by determining the changes in the molecular weights.     

Single crystals of poly(2,6-dimethyl-1,4-phenylene)oxide

Summary Poly(2,6-dimethyl-1,4-phenylene)oxide crystals obtained from 0.1%-pinene solutions by isothermal growth at temperatures from 80–90 as well as 100 °C, were investigated by optical and X-ray diffraction techniques. A study has been made by differential scanning calorimetry in order to measure the melting point, glass transition and melting point depression temperatures of mixtures of the polymer with-chloro-naphthalene.The densities of the dry mats of single crystals were measured by a flotation method.

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Zusammenfassung Poly(2,6-dimethyl-1,4-phenylen)oxid Kristalle, die aus 0,1% igen-Pinen-Lösungen durch isothermes Wachstum bei Temperaturen von 80–90 sowie 100 °C erhalten wurden, wurden optisch und röntgenographisch untersucht. Mit der Differential-scanning-Kalorimetrie ergaben sich die Werte des Schmelzpunkts, der Glastemperatur und der Schmelzpunktdepressionen von Mischungen des Polymeren mit-Chlornaphthalin. Die Dichten der trockenen Matten aus Einkristallen wurde mit der Flotationsmethode gemessen.

     

Crack propagation in poly(2,6-dimethyl-1,4-phenylene oxide), polystyrene,and their blends

Cracks have been propagated in double-cantilever beam specimens of poly(2,6-dimethyl-1,4-phenylene oxide), polystyrene, and their blends. The plane-strain crack propagation energy varies with crack speed, distance from crack arrest following an instability, molecular weight, and blend composition. Auxiliary measurements of moduli, yield properties, and craze initiation resistances at crack tips were carried out together with microscopic studies of the crack-tip plastic zone. Fracture instabilities are rationalized in terms of the interplay of shear deformation with crazing in the crack-tip plastic zone. Negative deviations from ideal behavior in the crack propagation resistance of the blends are rationalized in terms of the concurrent negative deviation in crazing resistance which in turn is thought to be related to positive deviations in shear resistance and thus to negative volumes and heats of mixing.     

Tailored polymer electrets based on poly(2,6-dimethyl-1,4-phenylene ether) and its blends with polystyrene

Due to the establishment of common thermoplastics such as polyethylene, polypropylene and polytetrafluoroethylene as substrates for modern electrets, research in this field has seen significant progress in recent decades. However, there still is a need for new substrate materials in order to boost modern-day electret applications. Important targets for a further development are electret substrates with a tailored balance between cost and performance especially at elevated temperatures. In this study, experimental results concerning the charge storage behaviour of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) films and its blends with polystyrene (PS) are presented. As demonstrated, the good electret performance of neat PPE can be further enhanced by the addition of suitable weight fractions of PS, a synergistic electret behaviour that is related to morphological blend parameters such as the packaging density and the presence of PS micro-heterogeneities in the PPE/PS matrix. Most importantly, the results highlighted in this study clearly demonstrate the potential of blending as a promising approach towards satisfying the demands of tomorrows’ electret applications.     

Miscibility of blends of poly(2,6-dimethyl 1,4-phenylene oxide) with polystyrene-based ionomers and copolymers

Blends of poly(2,6-dimethyl 1,4-phenylene oxide) (PPhO) with the copolymer poly(styrene-co-methacrylic acid) (PS-MAA) and the ionomer poly(styrene-co-sodium methacrylate) (PS-MAA-Na), up to 10 mol% co-unit content, were investigated by dynamic mechanical thermal measurements. The PPhO/PS-MAA-Na blends are compared with PS/PS-MAA-Na blends. The blends of PPhO with PS-MAA are no longer miscible at 10 mol% acid content; this is attributed to a copolymer effect induced by the reduction of PS-PPhO interactions due to the presence of the MAA group which does not interact favorably with PPhO. The blends of PPhO with the ionomer are already immiscible at the lowest ion content studied (2.4 mol%), but become increasingly so as ion content is increased. Despite favorable PS-PPhO interactions, these blends are only a little more miscible than the PS/PS-MAA-Na blends. This is attributed to a combination of the increasing importance of the ionomer cluster phase (from which the homopolymer chains presumably are excluded) as ion content is increased, and of a copolymer effect between the homopolymers and the unclustered phase of the ionomer. These results are compared with published data indicating that blends of PPhO with another biphasic ionomer, zinc sulfonated polystyrene, are miscible. The contrasting behavior is rationalized in part by the suggestion that the copolymer effect between PPhO and the unclustered phase of the latter ionomer, but not of the former, is absent; this is related to multiplet structure and sizes. The analysis made of the above systems is extended to predict what might be the miscibility behavior between PPhO and other PS-based ionomer and related copolymer systems. © 1993 John Wiley & Sons, Inc.     

Thermal degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide)

Thermal degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide) have been examined in air in the range 100–400°. Plots of weight-average molecular weight vs time are linear, confirming random chain scission. The breakdown process has also been studied by DTA and TGA. It was concluded that thermal analysis alone was insufficient to characterize the degradation fully so the degradation products were determined qualitatively using i.r. and NMR spectroscopy. The heats of activation for the systems have been calculated and a stabilization mechanism by bis(1-phenyl-3-α-pyridyl triazeno)Cu(II) chelate has been postulated.     

Effect of POSS on morphology and properties of poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 blends

Poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 (PPO/PA6) (50/50 w) blends filled with epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) were prepared via melt-mixing. The reactions between POSS and PPO/PA6 blends were studied by Fourier transform infrared spectroscopy, end group and gel content tests. The morphology of PPO/PA6/POSS composites was observed by field emission scanning electron microscope and transmission electron microscope. As a chain extender and a crosslinking agent for PA6, POSS largely affected the morphology of the composites, which was mainly dependent on the melt-viscosity ratio and interfacial tension between the components. With increasing POSS content from 2 to 4 phr, the morphology of the composites transformed from droplet/matrix to co-continuous morphology. The PPO/PA6/POSS composites with co-continuous morphology had the better mechanical properties than those with droplet/matrix morphology. Dynamic mechanical thermal analysis showed that the addition of POSS increased the T_g of PA6.     

Chemical modification of poly(2,6-dimethyl-1,4-phenylene oxide) by bromination-alkynylation

The chemical modification of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by bromination of the aromatic ring, followed by displacement of bromine with substituted acetylenes, has been investigated. This pathway leads to a series of novel copolymers containing substituted alkynes on the aromatic ring. The degree of bromination and alkynylation, determined by ¹H-NMR, was in the range of 20–85 and 15–80%, respectively. ¹³C-NMR and FT-IR unambiguously elucidated the structure of the alkynylated polymers. Finally, thermal properties and permeation properties of substituted PPO to carbon dioxide, methane, oxygen, and nitrogen are reported. © 1994 John Wiley & Sons, Inc.     

Effect of bromination on the thermal properties of poly(2,6-dimethyl-1,4-phenylene oxide)

The thermal behavior of poly(2,6-dimethyl-1,4-phenyiene oxide) (PPO R resin), poly(3-bromo-2,6-dimethyl-1,4-phenylene oxide), and a series of their statistical copolymers with identical average molecular lengths has been characterized by thermogravimetry and computer-interfaced differential scanning calorimetry. The heat capacities are found to be additive with respect to the concentrations of the two components. The change in heat capacity at the glass transition ( C _p) is independent of composition for bromination of up to 75% of the repeat units. At higher bromine levels C _p decreases abruptly. This behavior is attributed to the temperature dependence of C _p for the two components. The glass transition temperature (T _g) of the copolymers varies nearly linearly with composition. A comparison of the experimental values ofT _g is made with various equations derived for statistical copolymers and homogeneous polymer blends. A modification of the Couchman equation is presented taking into account the temperature dependence ofC _p.

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Zusammenfassung Das thermische Verhalten von Poly(2.6-dimethyl-1.4-phenylenoxyd) (PPO R-Harz), Poly(3-brom-2.6-dimethyl-1.4-phenylenoxyd) und einer Reihe von statistischen Copolymeren dieser Verbindungen mit gleicher durchschnittlicher Moleküllänge wurde durch Thermogravimetrie und Differential-Scanning-Kalorimetrie mit Computerinterface charakterisiert. Die Wärmekapazitäten sind hinsichtlich der Konzentrationen der beiden Komponenten additiv. Die Veränderung in der Wärmekapazität beim Übergang zum Glas (C_p) ist unabhängig von der Zusammensetzung bei Bromierung bis zu 75% der wiederho-lungseinheiten. Bei höheren Bromierungsgraden nimmtC _p abrupt ab. Dieses Verhalten wird der Temperaturabhängigkeit vonC _p der beiden Komponenten zugeschrieben. Die Glasübergangstemperatur (T_g) der Copolymeren verändert sich nahezu linear mit der Zusammensetzung. Ein Vergleich der experimentellen Werte von T_g wird mit verschiedenen für statistische Copolymere und Mischungen homogener Polymere abgeleiteten Gleichungen ausgeführt. Eine die Temperaturabhängigkeit vonC _p berücksichtigende Modifikation der Gleichung von Couchman wird angegeben.

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, , (2,6- -1,4), (3--2,6--1,4- ) . , ë . ë (C ) 75%. C . C . T . . T . , . , C .

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This work was supported by the National Science Foundation, Polymers Program (DMR 78-15279) and the General Electric Corporate Research and Development Center. The authors are indebted to the following individuals at General Electric CRD for their experimental assistance: S. R. Weissman and P. E. Gundlach (molecular weight characterizations); D. W. Marsh (X-ray analysis); V. H. Watkins and E. L. Hall (electron microscopy); and N. A. Marotta (thermogravimetry). P. E. Donahue and E. A. Williams are gratefully acknowledged for carrying out and interpreting the NMR experiments.

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One of the authors (R. C. Bopp) would like to thank A. R. Shultz, J. T. Bendler, and D. M. White at General Electric CRD for their helpful discussions of this work and express his sincere appreciation to Professor P. R. Couchman (Rutgers University) for his illuminating discussions of the thermodynamic basis of his equation.     

Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions

Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.     

Molecular relaxation in the blends of polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) at low temperature

Molecular relaxation behavior in terms of the α, β, and γ transitions of miscible PS/PPO blends has been studied by means of DMTA and preliminary work has been carried out using DSC. From DSC and DMTA (by tan δ), the observed α relaxation (T_α or T_g) of PS, PPO, and the blends, which are intermediate between the constituents, are in good agreement with earlier reports by others. In addition, the β transition (T_β) of PS at 0.03 Hz and 1 Hz is observed at −30 and 20°C, respectively, while the γ relaxation (T_γ) is not observed at either frequency. The T_β of PPO is 30°C at 0.03 Hz and is not observed at 1 Hz, while the T_γ is −85°C at 0.03 Hz and −70°C at 1 Hz. On the other hand, blend composition-independent β or γ relaxation observed in the blends may be a consequence of the absence of intra- or intermolecular interaction between the constituents at low temperature. Thus it is suggested that at low temperature, the β relaxation of PS be influenced solely by the local motion of the phenylene ring, and that the β or γ relaxation of PPO be predominated by the local cooperative motions of several monomer units or the rotational motion of the methyl group in PPO. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1981–1986, 1998     

Electrochemical stability and transformations of fluorinated poly(2,6-dimethyl-1,4-phenylene oxide)

Fluorination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) leads to narrowing of its window of electrochemical stability in a cathodic range of potentials. It is found this is connected with appearance of both perfluorinated and incompletely fluorinated units in the polymer. The former units are liable to electrochemical reduction (at potentials <−2.0 V) followed by elimination of fluorine anions and the latter react with basic products (generated at potentials <−1.8 V) of electrochemical reduction of the background solution. In the both cases this results in appearance of conjugated multiple bonds in the fluorinated macromolecules. Quantities of these units in fluorinated PPO were determined with a help of direct and indirect electrochemical reductive degradation techniques.     

Pressure-volume-temperature properties of blends of poly(2,6-dimethyl-1,4-phenylene ether) with polystyrene

The pressure-volume-temperature (PVT) properties of blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPO) with polystyrene (PS) have been studied experimentally in both the glassy and melt states at 0, 20, 40, 50, 60, 80, and 100% PPO content. In all compositions a strong glass transition was observed varying linearly with composition. For all but the 40% PPO composition this was the only transition, indicating molecular compatibility of the components in these blends. The 40% PPO composition showed a very weak second transition near the glass transition of pure PS. A small amount of phase separation may have occurred in this blend. The data for the glassy and melt states were fitted to an empirical equation of state based on the Tait equation. The volume of the melts at constant pressure and temperature showed a virtually linear dependence on composition. Any negative excess volume of mixing compatible with the data would have to be very small, smaller than expected from previous measurements in the glassy state. Various properties relating to the glassy and melt states and to the glass transition were evaluated and are discussed as a function of composition. It was found that most properties of the glasses could not be modeled by simple functions of composition.     

Wear and friction in glassy polymers: Microscratch on blends of polystyrene and poly (2,6-dimethyl-1,4-phenylene oxide)

The microscopic process of abrasive wear and friction in glassy polymers was studied by using a special microscratch technique. A miscible blend of polystyrene (PS) and poly(phenylene oxide) (PPO) was used. It was found that as the composition varies there seems to exist two wear regimes in the blends controlled by different breakdown mechanisms corresponding to the brittle—ductile transition. Detailed study of the contact loads and SEM micrographs indicate that abrasive wear in the glassy polymers is controlled by microcracking under the asperity contacts. The critical load τ_c for initiating microscopic cracks can be linked to the macroscopic wear via a statistical Weibull model where τ_c is taken to be the mean of a strength distribution function. On the other hand, the friction coefficient was found to be independent of the composition but to vary strongly with the contact load. It approaches zero at the extrapolated zero load, but increases rapidly and eventually levels off with contact load. This behavior can be understood by a simple frictional adhesion model in which the polymer deformation during a frictional contact is analyzed by considering the compressive plastic ploughing and shearing yielding around the asperity contact. The shear strength S_o of the polymer/asperity contacts was found to vary with the normal load. The vertical scratch hardness H_v, which characterizes the spontaneous indentation yielding on the polymer surface, was found to be independent of scratch length and depth, and indeed can be regarded as a material constant. Although both S_o and H_v can accurately describe the frictional behavior of the glassy polymers, they bear no correlation to abrasive wear in the same materials. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1295–1309, 1997     

Molecular simulation of gas permeability: poly(2,6-dimethyl-1,4-phenylene oxide)

Self-diffusion and solubility coefficients of four gas molecules (O₂, N₂, CH₄, and CO₂) in poly(2,6-dimethyl-1,4-phenylene oxide) have been investigated by means of molecular simulation using the COMPASS molecular mechanics force field. Diffusion coefficients were obtained from molecular dynamics (NVT ensemble) using up to 2 ns simulation times. Solubility coefficients were obtained by means of the Widom particle insertion method. Simulation values for O₂, N₂, and CH₄ agree reasonably well with published data. Agreement was less satisfactory for CO₂. Possible explanations for the CO₂ results are discussed on the basis of the partial immobilization model and considerations of simulation time and the size of the simulation box.     

Drawing by solid-state coextrusion of blends of atactic and isotactic polystyrene with poly(2,6-dimethyl-1,4-phenylene oxide)

Atactic polystyrene (aPS)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and isotactic polystyrene (iPS)/PPO compatible blends of varied composition were subjected to solid-state coextrusion. The efficiency of drawing, orientation, and crystallinity development were studied as a function of composition and draw ratio. The efficiency of drawing, as measured by elastic recovery, is high for coextrusion at temperatures ?40°C above the glass transition temperature of the particular blend. The maximum attainable draw ratio for the blends decreased with increasing PPO concentration; the highest blend draw ratio attained was 6.5 for 25 wt % PPO. The orientation on drawing, as measured by birefringence, increased with draw but decreased with increasing PPO component at the same draw ratio. When PPO was <50% in iPS/PPO blends, iPS crystallized on draw. The morphology of drawn blends was studied by electron microscopy and wide-angle x-ray scattering.