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.     

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.     

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.     

Functional polymers and sequential copolymers by phase transfer catalysis. 18. Synthesis and characterization of α,ω-bis(2,6-dimethylphenol)–poly(2,6-dimethyl-1,4-phenylene oxide) and α,ω-bis(vinylbenzyl)–poly(2,6-dimethyl-1,4-phenylene oxide) oligomers

A novel and convenient synthetic method for the preparation of α,ω-bis(2,6-dimethylphenol)–poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-2OH) is presented. It is based on the oxidative copolymerization of 2,6-dimethylphenol (DMP) with 2,2′-di(4-hydroxy-3,5-dimethylphenyl propane) (TMBPA) in a mixture of water–methanol or chlorobenzene–methanol. By using a 4/1 mole ratio of DMP to TMBPA and different solvent mixtures, it was possible to obtain bifunctional PPO-2OHs with number average molecular weights between 1000 and 5000. A phase-transfer-catalyzed etherification of PPO-2OH chain ends with a mixture of m- and p-chloromethylstyrene was used to synthesize α,ω-bis(vinylbenzyl)-poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO-2VBs). The thermal polymerization of the PPO-2VBs was studied by differential scanning calorimetry, and has demonstrated a very high thermal reactivity for this new class of reactive oligomers.     

Protection of poly(2,6-dimethyl-1,4-phenylene oxide) against u.v. irradiation

The photo-oxidative degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide) films have been examined in the temperature range 263–313 K in air with u.v. light of 253.7 nm. The changes in weight-average molecular weight, quantum efficiencies, carbonyl index, hydroperoxide concentration and i.r. spectra have been followed in the absence and presence of the stabilizer. The heats of activation of the systems have been calculated and the mechanism of stabilization has been postulated. A saturation limit in photostabilization of the polymer was achieved beyond 0.6 wt% of zinc di-n-hexyl dithiophosphate.     

Interpenetrating polymer networks of poly(2,6-dimethyl-1,4 phenylene oxide) and poly(urethane acrylate). I

Simultaneous full and pseudo- interpenetrating polymer networks of poly(2,6-dimethyl-1,4 phenylene oxide) (PPO) and a poly(urethane acrylate) (PUA) have been synthesized and characterized by differential scanning calorimetry, ultimate mechanical properties, and electron microscopy. No evidence of phase separation was detected in both the full and pseudo- PPO/PUA networks. The networks exhibited a single glass transition temperature at all the compositions studied. A maximum in tensile strength to break was observed at 25 PPO/75 PUA composition by weight percent.     

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.     

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.     

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

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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.     

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).     

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.     

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     

The Crystal Structure of 5,5′,7,7′-tetramethyl-3,3′,9-triethyl thiacarbocyanine perchlorate

The crystal structure of the title compound has been determined by X-ray crystallographic analysis from diffractometer data. The compound is found to exist in the crystalline state as the mono-cis isomer (a). The conjugated chain is in a folded configuration and the two sulfur atoms are on opposing sides. It is the first time such a mono-cis isomer has been analysed by X-ray crystallography.     

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.     

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.     

Polymer-Polymer interactions via analog calorimetry. 1—blends of polystyrene with poly(2,6-dimethyl-1,4-phenylene oxide)

Analog calorimetry is used as a tool to study the interaction of polystyrene, PS, with poly(2,6-dimethyl-1,4-phenylene oxide), PPO, and with poly(1,4-phenylene oxide). Electrostatic charge calculations were used as a guide to divide polymer repeat units and analogs into groups. A mean-field binary interaction model was used to cvaluate group interaction energies. The enthalpic interaction energy for the blend of PS-PPO obtained from this study is −1.35 ± 0.19 cal/cm₃, which is in good agreement with values obtained from neutron scattering. The results indicate that electronic rearrangements between the phenyl ring and substituted methyl groups in PPO have a large influence on the interaction with polystyrene. © 1996 John Wiley & Sons, Inc.