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.

     

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.     

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.     

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.     

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.     

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.     

Direct metalation of poly(2,6-dimethyl-1,4-phenylene ether)

Poly(2,6-dimethyl-1,4-phenylene ether) (I) was metalated with butyllithium in tetrahydrofuran and with the N,N,N′,N′-tetramethylethylenediamine complex of butyllithium in a variety of solvents. In these cases, metalation occurred at both the ring and side chain positions, the former being preferred initially. Subsequently, there was an isomerization in favor of the side chain. At 25°C, there is no significant amount of polymer scission or crosslinking during metalation, but some crosslinking occurs on derivatizing with dimethyl sulfate and trimethylchlorosilane for high extents of ring metalation. With sodium and potassium alkyls, only side-chain metalation was observed. The metalated polymer reacts as a typical organometallic, allowing polymer modification by a wide variety of reactions.     

Thermodynamic properties of poly(2,6-dimethyl-1,4-phenylene ether)

The thermodynamic properties of crystalline and amorphous poly(2,6-dimethyl-1,4-phenylene ether) (PPO

1 Registered trademark of General Electric Company.

polymer, General Electric Co.) have been studied calorimetrically between 80 and 570°K. The calculated configurational entropy of this polymer, of similar magnitude to other glass-forming liquids, is consistent with the combination of an unusually high ratio of T_g/T_m, and a low melting entropy.     

The phase behaviour of poly(styrene-co-methacrylic acid)/poly(2,6-dimethyl-1,4-phenylene oxide) by inverse gas chromatography

The miscibility behaviour of blends of poly(styrene-co-methacrylic acide) (PSMA-12) containing 12% of methacrylic acid with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at five different compositions has been studied by inverse gas chromatography (IGC). The adequacy of two types of solvents (solvents and precipitants) has been tested in order to detect the glass transition temperature, T(g). A single T(g) has been observed in PSMA-12/PPO blends containing less than 67wt% of PPO. Two glass transition temperatures appeared, however, in blends containing higher PPO content. The polymer-polymer interaction parameters have been calculated in the molten state (260-280 degrees C), their values being in good agreement with the observed phase behaviour. Moreover, the methods proposed by Farooque-Deshpande and Huang for obtaining the true polymer-polymer interaction parameters have been compared. Finally, the ability of IGC in order to determine T(g)s has been extended to a ternary system, PSMA-12/PPO/EMV4P-8 poly(ethylmethacrylate-co-4-vinylpyridine) which, depending on the composition, gives a single, two and even three T(g)s.     

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.     

Polymeric catenanes from crosslinked poly(2,6-dimethyl-1,4-phenylene oxide) and cyclic poly(dimethylsilozane)

Poly(2,6-dimethyl-1,4-phenylene oxide) has been crosslinked in the presence of large poly(dimethylsiloxane) cyclics (92 repeating units). Approximately 26% by weight of the cyclics were threaded and permanently captured by the polymer network forming a topological isomeric structure referred to as a polymeric catenane. Nonentrapped cyclics were extracted with chloroform. Chemical analyses and micrographs showed evidence for crosslinking and cyclic entrapment, while physical testing demonstrated distinct differences in physical properties such as the glass transition temperature, ultimate mechanical properties, and dynamic viscoelastic response between the crosslinked control samples, and those containing cyclic poly(dimethylsiloxane).     

Blends of organosilicon polymers with polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide)

Blends of organosilicon polymers with polystyrene, PS, and poly(2,6-dimethyl-1,4-phenylene oxide), PPE, were investigated by transmission electron microscopy and differencial scanning calorimetry. Blends with poly(tetramethylsilphenylenesiloxane), PTMPS, showed a morphology characterized by globular domains dispersed in the organic matrix. An apparent homogeneous system was observed when poly(dimethylsilphenylene), PDSP, was mixed with PPE. A crystalline phase was found in samples with a higher PDSP content. The morphology of PS/PDSP blends with low PDSP content showed a dendritic phase dispersed in the PS-rich matrix. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2609–2616, 1997     

Ion exchange membranes from poly(2,6-dimethyl-1,4-phenylene oxide) and related applications

Ion exchange membranes (IEMs) play a significant role in fields of energy and environment, for instance fuel cells, diffusion dialysis, electrodialysis, etc. The limited choice of commercially available IEMs has produced a strong demand of fabricating IEMs with improved properties via facile synthetic strategies over the past two decades. Poly(phenylene oxide) (PPO) is considered as a promising polymeric material for constructing practical IEMs, due to its advantages of good physicochemical properties, low manufacturing cost and easy post functionalization. In this review, we present the accumulated efforts in synthetic strategies towards diverse types of PPO-based IEMs. Relation between polymer structures and the resulted features is discussed in detail. Besides, applying IEMs from PPO and its derivatives in fuel cell, diffusion dialysis and electrodialysis is summarized and commented.     

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     

Photostabilization of poly(2,6-dimethyl-1,4-phenylene oxide) by nickel(II)thiopicoline anilide

This work embodies the results of photostabilization of poly(2,6-dimethyl-1,4-phenylene oxide) (PDMPO) films in air at low temperature (−10 to +80°C), with an incident light intensity flux of 2·38×10⁻⁹ s⁻¹ cm⁻². The inhibitive effect of nickel(II)thiopicoline anilide on the photo-oxidative degradation was examined. The variation in weight-average molecular weight, degree of degradation, quantum yield, and carbonyl, hydroxyl and hydroperoxide contents of the polymer sample were investigated. The data obtained have been processed to calulate the heats of activation of the system. It was found that nickel(II)thiopicoline anilide showed a pronounced inhibitive effect on degradation. The presence of thiopicoline anilide also affected the infra-red spectra of the polymer.     

The high-temperature degradation of poly(2,6-dimethyl-1,4-phenylene ether)

The thermal degradation of poly(2,6-dimethyl-1,4-phenylene ether) has been investigated to 1000°C in an inert atmosphere. X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were employed to study the physical changes in the polymer, and vapor-phase chromatography, infrared spectroscopy, and mass spectrometric thermal analysis were used to elucidate the chemical aspects of the degradation process. It was found that degradation occurs in two steps: (1) a rapid exothermic process occurs between 430 and 500°C, leading to the evolution of phenolic products, water, and a black, highly crosslinked residue, and (2) a slower, char-forming process occurs above 500°C, characterized by the evolution of methane, carbon monoxide, and hydrogen. The chars formed in process 2 were found by x-ray analysis to be amorphous. The infrared spectrum of a sample heated to 510°C is nearly identical with that of the starting polymer, indicating that oxidative reactions are not important in the first process. The data for the low-temperature process are consistent with a thermal degradation scheme based on the radical-redistribution reaction of polyphenylene ethers and/or the degradation of o-benzylphenols formed by the thermal rearrangement of o-methyl diphenyl ethers. The char-forming process is best explained by simultaneous operation of the Szwarc mechanism of toluene pyrolysis, producing hydrogen and methane and reactions that cleave the aromatic rings and produce carbon monoxide.     

Mass spectral characteristics of poly(2,6-dimethyl-1,4-phenylene ether)

The mass spectral characteristics of poly(2,6-dimethyl-1,4-phenylene ether), its monomer (2,6-xylenol), and its dimer (3,5-dimethyl-4-hydroxyphenyl 2,6-xylyl ether) have been determined. The monomer and dimer show peaks for the molecular ions (122; 242 amu) and degradation patterns similar to those of o-methylaryl ethers. Loss of methyl and cleavage of the ether with transfer of an o-methyl hydrogen are observed. Metastable transitions are recorded corresponding to a loss of 15 from 122 and 56 from 107 amu (xylenol) and of 151 from 242 and 40 from 104 amu (ether). The polymer volatilizes readily at 380–400°C. (TGA shows rapid weight loss at 400°C) and gives sets of peaks at (N × 120) ± 14 up to 1080 (N = 9). The principal peak is at (N × 120) + 2, calibrated against PFA, and this is attributed to an ion of a volatilized oligomer. The oligomer is either present as such, is formed in a degradation process involving an ether redistribution, or is formed in a hydrogen transfer process in the ether cleavage reaction.     

A novel proton-conductive membrane with reduced methanol permeability prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)

A series of proton-conducting membranes were developed for direct methanol fuel cell (DMFC) applications via sulfonation of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) base membranes. Besides the low manufacture cost, the membranes exhibited an excellent control on methanol crossover and swelling, and a sound balance with high proton conductivities. These can be attributed to the inherent properties of membrane structures: (i) benzyl substitution with bromine, which imparted the membrane stronger hydrophobicity, (ii) cross-linking between BPPO chains, which enhances the dimensional stability and renders the membrane a dense texture, (iii) proper content of sulfonic acid groups, which guarantees the proton conductivity. An optimal membrane was obtained after investigating the effects of the bromination degree and sulfonation process on the performances of corresponding membranes, i.e., the membrane possesses the methanol permeability of 2.64 × 10⁻⁸ cm²/s and characteristic factor Φ value of 30 times higher than that of Nafion^® 117. The sulfonation process should be controlled within a proper period of time and in mild sulfonation conditions so as to achieve a proton conductivity higher than 0.07 S/cm for potential applications in DMFC.     

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.