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.     

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.     

A novel synthetic method for preparing poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene alloy in reactor containing aqueous medium

Considering the defect of solution polymerization of 2,6-dimethylphenol (DMP), the low molecular weight of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in water and difficulty in processing of PPO, a novel one-pot synthetic method for preparing PPO/PS alloy in reactor containing aqueous medium was proposed based on green chemistry. In the presence of styrene, DMP was polymerized to form PPO, and then styrene was in situ polymerized under the initiation of dibenzoyl peroxide (BPO) and dicumyl peroxide (DCP), finally thermodynamically compatible PPO/PS alloy was prepared. It was found that the introduction of styrene during the oxidative polymerization of DMP could increase the molecular weight of PPO. When styrene content was 50 wt%, for the synthesized PPO/PS alloy the yield and the weight-average molecular weight were determined to be 95% and 1.7 × 10⁵ for PPO, 93% and 2.0 × 10⁵ for PS, respectively.     

Unperturbed dimensions of poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly(2,6-diphenyl-1,4-phenylene oxide) chains

The unperturbed chain dimensions of unfractionated poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly-(2,6-diphenyl-1,4-phenylene oxide) have been measured by combining molecular weight data from light scattering with intrinsic viscosity data in chloroform. The unperturbed chain dimensions of the former polymer were also measured directly by light scattering dissymmetry in a critical consolute solvent mixture (methyl cyclohexane: 1,4-dioxane 50:50 by volume). The results of these measurements and of measurements reported by other investigators are satisfactorily explained by postulating no dimension-expanding prejudice in azimuthal angle in chain conformers of the 2,6-substituted-1,4-phenylene oxide polymers. This corresponds to equal population of the two chain rotation energy minima at azimuthal angles 90° and 270°. Accepting this postulate, one calculates from the observed chain dimensions that the C? O? C bond angle is 118–120° in these aromatic polyethers in solution.     

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.     

Synthesis and characterization of semi- and full-interpenetrating polymer networks of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane

The synthesis and characterization of pseudo or semi- and full-interpenetrating polymer networks (IPNs) of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane were performed. We observed that in full IPNs, the elasticity of the IPN samples increased very drastically, as the composition of polydimethylsiloxane increased (i.e. 0–60%) while the tensile strength (TS) and the glass transition temperature (T_g) decreases. The pseudo IPNs appeared to consist of two phases while the full IPNs of lower siloxane content were miscible.     

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.

     

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 Synthesis of Poly(2,6-dimethyl-1,4-phenylene oxide)/Polymethylmethacrylate Alloy in Aqueous Medium via a One-Pot Method

An environmentally friendly one-pot synthetic method based on green chemistry was developed to prepare thermodynamically partially compatible poly(2,6-dimethyl-1,4-phenylene oxide)/poly(methylmethacrylate) (PPO/PMMA) alloy in water. The oxidative polymerization of 2,6-dimethylphenol in alkaline aqueous solution was firstly conducted and then methyl methacrylate (MMA) was added into the reactor before the end of polymerization. MMA could penetrate into PPO particles and then in situ reverse atom transfer radical polymerization (RATRP) of methyl methacrylate was initiated by 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride after the oxidative polymerization. Both the oxidative polymerization of 2,6-dimethylphenol and RATRP of methyl methacrylate were catalyzed by the complex of CuCl₂ and 4-dimethylaminopyridine. Finally, thermodynamically partially compatible PPO/PMMA alloy was successfully prepared which possessed a multi-layer core-shell structure with two polymers embedded in each other.     

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.     

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).     

Radiation-induced grafting of N-isopropylacrylamide onto the brominated poly(2,6-dimethyl-1,4-phenylene oxide) membranes

A novel thermo-sensitive switching membrane has been prepared by radiation-induced simultaneous grafting N-isopropylacrylamide (NIPAAm) onto brominated poly(2,6-dimethyl-1,4-phenylene oxide) BPPO. In order to attain a high grafting degree, the effects of dose, dose rate, concentration of NIPAAm, concentration of inhibitor Cu²⁺, membrane thickness and solvents were investigated. The grafting process was characterized by FTIR spectroscopy and the highest grafting degree obtained was 7.87%. The thermo-sensitive property of the grafted membrane was measured by water flux (20–48 °C). The results showed that the grafted membrane could respond instantly to environmental temperature changes, and there was a sharp change around the lower critical solution temperature as it is normally seen in PNIPAAm hydrogel.     

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.     

Polymerization by oxidative coupling. II. Co-redistribution of poly(2,6-diphenyl-1,4-phenylene ether) with phenols

Poly(2,6-diphenyl-1,4-phenylene ether) reacts with phenols in the presence of an initiator to form a mixture of low molecular weight hydroxyarylene ethers. Although the reaction is similar to the equilibration of poly(2,6-dimethyl-1,4-phenylene ether) with phenols, higher reaction temperatures and larger initiator concentrations are required. Compounds as 3,3′,5,5′-tetraphenyl-4,4′-diphenoquinone, tert-butyl perbenzoate, and benzoyl peroxide are active initiators. The structure of the polymer affects the extent to which the polymer equilibrates.     

Phase-separation phenomena in solutions of poly(2,6-dimethyl-1,4-phenylene oxide). I. Thermodynamic parameters of solutions in toluene

New experimental data have been collected on thermodynamic properties of solutions of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in toluene. The Flory–Huggins interaction parameters g have been determined from light scattering measurements. These values are in agreement with values obtained by osmotic measurements at low concentrations and they allow the calculation of a melting point curve which fits the experimental melting points. No liquid–liquid phase separation can be calculated, as was concluded in a preceding paper. Spinodals could not be detected by light scattering or DSC-measurements. This also indicates that liquid–liquid phase separation does not occur. The phase separation on cooling of a PPO-toluene solution is thus believed to be a crystallization phenomenon.     

Synthesis and characterization of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) as A blocks and tetramethyl bisphenol-A polysulfone as B blocks

α, β-Bis(hydroxyphenol) tetramethyl bisphenol-A polysulfone (PSUT) was synthesized by two different methods, one using a strong base, the other using a weak base. The bifunctional polysulfone containing tetramethyl bisphenol-A chain ends was exploited as a model telechelic that can be used for the preparation of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as A segments and PSUT as B segments. PSUT and PPO were incorporated into triblock copolymers by an oxidative coupling copolymerization of PSUT with 2,6-dimethylphenol or by the redistribution of PPO in the presence of PSUT. The mechanism of block copolymerization is discussed. DSC studies indicate that short immiscible PPO and PSUT segments incorporated into a triblock copolymer do not exhibit phase separation. Polymer blends of the PPO–PSUT–PPO triblock copolymers with PPO homopolymer were analyzed by DSC. Both miscible and phase-separated blends can be prepared depending on the molecular weight of both PPO homopolymer and of the PPO segment present in the triblock copolymer. Polymer blends of the PPO–PSUT–PPO triblock copolymer with PSUT were miscible at all compositions.     

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.     

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.