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.

     

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.     

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.     

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.     

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.     

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.     

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     

Thermal properties of silica/poly(2,6-dimethyl-1,4-phenylene oxide) films prepared by emulsion polymerization

Thermal properties of the silica/poly(2,6-dimethyl-1,4-phenylene oxide) films prepared via emulsion polymerized mixed matrix (EPMM) method are investigated, and the impact of the synthesis protocol on the silica content, compatibility between the organic and inorganic phases, and the thermal stability of these nanocomposites is studied. Two series of films, namely EPMM-1S and EPMM-2S, synthesized in one- and two-step process, respectively, with different combinations of surfactant and compatibilizer were prepared. The polymerization of the silica precursor in the films was confirmed by ²⁹Si nuclear magnetic resonance, and its content was investigated by inductively coupled plasma mass spectroscopy analysis. Thermal properties of the EPMM films were investigated by differential scanning calorimetry and thermogravimetric analysis. The glass transition temperature (T _g) of EPMM films was greater compared to the neat PPO film. However, an increase in T _g was not related to the concentration of silica in the film, but rather to the quality of dispersion of synthesized nanoparticles. Despite a lower inorganic loading, EPMM-1S films had a greater T _g than EPMM-2S films. On the other hand, both the decomposition temperature and the activation energy for the decomposition were directly related to the silica content in the EPMM films. In general, regardless of the synthesis protocol, the presence of compatibilizer (ethanol) leads to greater inorganic content and improved thermal properties of the EPMM films.     

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).     

Thermal and photochemical oxidation of 2,6-dimethylphenyl phenyl ether: A model for poly(2,6-dimethyl-1,4-phenylene oxide)

The oxygenation of 2,6-dimethylphenyl phenyl ether (I) at 260°C has resulted in the formation of 4-methylxanthone (II), 2-hydroxy-3-methylbenzophenone(III), 2-phenoxy-3-methylbenzaldehyde (IV), 2-phenoxy-3-methylbenzoic acid (V), 2-phenoxy-3-methylbenzyl o-cresotinate (VI), 2-phenoxy-3-methylbenzyl alcohol (VII), and 2-phenoxy-3-methylbenzyl 2-phenoxy-3-methylbenzoate (VIII), The photochemical oxidation at 75° produced compounds II, III, IV, VII, and VIII. Oxidation of poly(2,6-dimethyl 1,4-phenylene oxide) film at 200°C and photochemically at 50°C produced a carbonyl band at ca. 1730 cm^?1. The gel content of the photochemically aged film could be significantly reduced and the 1730 cm^?1 peak in the thermally aged specimen could be moved to longer wavelength by base treatment. The isolation of compound VIII in both processes with the model compound and the results with the polymer allows us to propose an ester group as a crosslinking unit in thermally and photochemically aged polymer film.     

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.     

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.     

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.     

Photosensitized and photostabilized oxidation of poly(2,6-dimethyl- 1,4-phenylene oxide) with metal isopropylxanthates

This work describes the results of the Cd(II) isopropylxanthate-stabilized and Mn(III) isopropylxanthate-sensitized photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide) film in air at low temperatures (?10 to 80°). The oxidation was followed by light scattering, potassium ferri-oxalate actinometry and by measuring gel formation. The weight-average molecular weight, degree of degradation, rate of scission of links, energy of activation and quantum yield of the process depend on several factors, e.g. temperature, xanthate concentration. Various oxygen-containing groups (hydroperoxides, carbonyls, etc.) are formed in the polymer. For the determination of the content of these groups, iodometry and spectroscopy were applied. The initially present or photo-induced hydroperoxides are directly responsible for subsequent oxidative reactions which occur during 254-nm irradiation. The absorption spectra of the degraded materials in the u.v. and i.r. regions were also studied to substantiate a possible mechanism of the oxidation process.     

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.     

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.