In poly 2,6-dimethyl-l,4-phenylene

FIG. 26.14 Equilibrium solubilities of crazing fluids in poly(2,6-dimethyl-l,4-phenylene oxide) (Bernier and Kambour, 1968 reproduced by permission of the American Chemical Society). 

Mark and Semiyen, in a series of papers, have studied the mechanism and the effect of trapping cyclics in end-linked elatomeric networks [100-103], Sharp fractions of cyclics of polyfdimethylsiloxane) (PDMS), varying in size from 31 to 517 skeletal atoms, were mixed with linear chains for different periods of time and the linear chains were then end-linked using a tetrafunctional silane. The untrapped cyclics were extracted to determine the amount trapped. It was found that while cyclics with less than 38 skeletal atoms were not at all trapped, for n>38, the percentage of cycUcs trapped increased with size, with 94% trapped in the case of the cychc with 517 skeletal atoms. In effect, the system of trapped cycUcs in the end linked PDMS network is a polymeric catenane. It is thus possible to control the elastomeric properties of the network by incorporating the appropriate sized cyclics. This study has been extended to cyclic PDMS in poly(2,6-dimethyl-l,4-phenylene oxide) [104,105] and cyclic polyesters in PDMS [106]. 

The ESC A spectra of poly(2,6-dimethyl-l,4-phenylene oxide) photo-oxidized in oxygen are shown in Fig. 4.3. The increase in the intensity of the Oj, band with duration of photo-oxidation is accompanied by the appearance of an envelope of peaks to the high binding energy side of the main Cjj peak [585, 1701], Greater photo-oxidation of the surface can be explained by intensive oxidation of methyl group in poly(2,6-dimethyl-l,4-phenylene oxide). 

Also the polymorphic behavior of s-PS can be altered by blending, in particular with poly-2,6-dimethyl-l,4-phenylene oxide (PPO), both for the case of crystallization from the melt [104] and for the case of crystallization from the quenched amorphous phase [105]. 

In order to determine the necessity and/or the length of the spacer that is required to achieve liquid crystalline behavior from flexible vs. rigid polymers, we have introduced mesogenic units to the backbones of a rigid [poly(2,6-dimethyl-l,4-phenylene oxide) (PPO)] and a flexible [poly(epichlorohydrin) (PECH)] polymer through spacers of from 0 to 10 methylene groups via polymer analogous reactions. 

Increasing temperature shortens the induction time and increases the maximum chemiluminescence intensity in the case of chemiluminescence of PP powder (type (a), see Figure 15), whereas it increases the initial chemiluminescence intensity in the case of poly(2,6-dimethyl-l,4-phenylene oxide) (type (b), see Figure 5). This is perhaps not surprising as the rate of oxidation reaction increases with temperature as well. 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

The co-occurrence of nucleation and spinodal decomposition had been observed in the temperature quench experiment of poly(2,6-dimethyl-l,4-phenylene oxide)-toluene-caprolactam system, [64,65], in which the typical morphology formed by nucleation and growth mechanism was observed with electron-microscopy when the quench of temperature is slightly above the spinodal boundary. On the other hand, if the quench temperature is somewhat lower than the spinodal boundary, they observed interconnected structures as well as small droplets. 

The substituents in the 2- and 6-positions must not exceed a certain geometrical size. Otherwise, instead of regular -0-C- coupling leading to the po-ly(phenylene ether)s, there is simply a -C-C- coupling of the monomers to form diphenylquinones. This reaction is favored by higher temperatures. The pale-yellow coloration of poly(-2,6-dimethyl-l,4-phenylene ether) may be caused by the presence of quinones. 

Xu S, Zhao H, Tang T, Dong L, Huang B. Effect and mechanism in compatibilization of poly(styrene-l)-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide)/poly(ethylene-ran-acrylic acid) blends. Polymer 1999 40 1537-1545. 

Poly(2,6-dimethyl-l,4-phenylene oxide). It is well established that PS and PPO are miscible in all proportions and that the mbber partides from HIPS are distributed uniformly throughout the new mixed matrix. 

The ability to polymerize readily via selective oxidation utilizing the abundant and cheap oxidant 02 often represents a desirable low-cost method for upgrading the value of a raw material. The most successful example is the oxidative polymerization of 2,6-dimethylphenol to yield poly(2,6-dimethyl-l,4-phenylene ether) with copper-amine catalysts under an 02 atmosphere at room temperature. Thiophenol also has a labile hydrogen but is rapidly oxidized to yield thermodynamically stable diphenyl disulfide. This formation is based on the more facilitated formation of S—S bond through radical coupling [82] in comparison with the formation of C—S—C bond through the coupling with the other molecules in the para position (Eq. 9). 

An Sjuyl-type (S l ) mechanism has been proposed in the synthesis of poly(2,6-dimethyl-l,4-phenylene ether) through the anion-radical polymerization of 4-bromo-2,6-dimethylphenoxide ions (204) under phase-transfer catalysed conditions269. Ions 204 are oxidized to give an oxygen radical 205. The propagation consists of the radical nucleophilic substitution by 205 at the ipso position of the bromine in 204 (equation 144). The anion-radical 206 thus formed eliminates a bromide ion to form a dimer phenoxy radical 207 (equation 145). A polymeric phenoxy radical results by continuation of this radical nucleophilic substitution. 

Frisch HLHMW (1991) Birefringence in Interpenetrating Polymer Networks of Poly(2,6-Dimethyl-l,4-Phenylene Dioxide)/Polydimethylsiloxane. J Poly Sci Part A Poly Chem 29 131-133... 

FIGURE 9.4 Dependence of constants (a, b, and c present Henry constant, sorption affinity constant, and Langmuir sorption capacity respectively) of the model of dual-mode sorption of hydrocarbons by glassy polyphenylene oxides on boiling temperatures of hydrocarbons Z), is pDMePO, poly-2,6-dimethyl-l,4-phenylene oxide o is pDPhPO, poly-2,6-diphenyl-l,4-phenylene oxide is pDMePO/pDPhPO copolymer (97.5/2.5% mol) v is pDMePO/pDPhPO copolymer (75/25% mol). (From analysis of results presented in Lapkin, A.A., Roschupkina, O.P., and Ilinitch, O.M., J. Membr. Sci., 141, 223, 1998.)... 

The photooxidation and photodegradation of polymers continues to attract some interest but is not as widespread as in previous years. Review articles have appeared dealing with poly(2,6-dimethyl-l,4-phenylene oxides) , photocatalyst fibres, polymers with azo links and accelerated weathering specifications. Other articles of interest include the design of an integrating sphere for repeatability in polymer ageing and the use of FTIR for monitoring the photostability of clearcoats . 

Poly(alkyl and aromatic ethers) - Using laser flash photolysis poly(2,6-dimethyl-l,4-phenylene oxide) undergoes scission at the phenolic link to give phenoxy radicals . Poly(vinyl methyl ether) has been shown to undergo a complex series of photoprocesses as shown in Scheme 2. ... 

In the case of poly (2,6-dimethyl-l,4- phenylene) photooxidation in solution produces radical-cation polymeric... 

Phenols are oxidized by NaBiO3 to polyphenylene oxides, quinones, or cyclohexa-2,4-dienone derivatives, depending on the substituents and the reaction conditions [263]. For example, 2,6-xylenol is oxidized in AcOH to afford a mixture of cyclohexa-dienone and diphenoquinone derivatives (Scheme 14.123) [264] and is oxidatively polymerized in benzene under reflux to give poly(2,6-dimethyl-l,4-phenylene) ether (Scheme 14.124) [265]. Substituted anilines and a poly(phenylene oxide) are oxidatively depolymerized by NaBiO, to afford the corresponding anils [266]. Nal iO, oxidizes olefins to vicinal hydroxy acetates or diacetates in low to moderate yield [267]. Polycyclic aromatic hydrocarbons bearing a benzylic methylene group are converted to aromatic ketones in AcOH under reflux (Scheme 14.125) [268]. 

Some interest continues in absorber systems. Silane and styrene monomers have been copolymerised with 2-vinylphenyl benzotriazole stabilisers in order to graft the stabilisers into the polymer chain °. When doped into plastics materials they were found to exhibit high surface activity. However, there is a conflicting report from other workers on similar structures where it is claimed that such polymeric stabilisers do not photoprotect the surface of polystyrene . Poly(2,6-dimethyl-l,4-phenylene oxide) has been effectively stabilised with an ortho-hydroxyphenyl benzotriazole stabiliser while in another study these compounds are claimed to be lost rapidly from polycarbonates . Other types... 

The photodegradation of poly(2,6-dimethyl-l,4-phenylene oxide), 1, has received considerable attention both in industrial and in academic laboratories. Workers have observed that when poly-(phenylene oxide) films are exposed to light of wavelengths greater than 300 nm in the presence of oxygen, considerable discoloration and crosslinking occur accompanied by the appearance of carbonyl and hydroxyl bands in the infrared spectrum (2-5). Most workers in the field have ascribed these results to a hydroperoxide-mediated free radical oxidation of the benzylic methyl groups (Scheme I). 

Chalk, Hay, and Hoogenboom (6, 7) using the same complex, reported lithiating poly(2,6-dimethyl-l,4-phenylene) ether and poly(2,6-diphenyl-1,4-phenylene) ether. The lithiation was done both at room temperature over a long time and at reflux for a shorter time. They reported catalyst efficiency of 17% as determined by the lithium content in the polymer. They attributed the low level of lithiation to the attack on THF by the metalating complex. 

Compatible Polyblends. When the polymeric materials are compatible in all ratios, and/or all are soluble in each other, they are generally termed polyalloys. Very few pairs of polymers are completely compatible. The best known example is the polyblend of polyCphenylene oxide) (poly-2,6-dimethyl-l,4-phenylene oxide) with high-impact polystyrene (41). which is sold under the trade name of Noryl. It is believed that the two polymers have essentially identical solubility parameters. Other examples include blends of amorphous polycaprolactone with poly(vinyl chloride) (PVC) and butadiene/acrylonitrile rubber with PVC the compatibility is a result of the "acid-base" interaction between the polar substituents (1 ). These compatible blends exhibit physical properties that are intermediate to those of the components. 

Tetramethvlbisphenol A Polycarbonate. A new polycarbonate has been introduced in Europe by Bayer AG (Figure 6). It is based on tetramethyIbisphenol A (TMBPA). The monomer is produced by condensing two molecules of 2,6-dimethylphenol, which is the monomer for General Electric s poly(2,6-dimethyl-l,4-phenylene ether) polymers, with acetone. The polycarbonate from tetramethylbisphenol A resembles the dimethylphenylene ether polymers in their unusually high T 207 C for the polycarbonate and 215 °C for the polyether. 

Poly(2,6-dimethyl-l,4-phenylene oxide) (PPO).— The photo-oxidation of this polymer has attracted some interest. Wandelt has found that the photoinitiated oxidation of PPO depends upon the mobility of one more unit in the polymer chain. A marked increase in the rate of photo-oxidation of the polymer occurs in the temperature range 45—60 °C, which corresponds with the j -relaxation phenomena. Chain mobility markedly controls the diffusion of oxygen. From detailed analysis of the products of PPO photo-oxidation the following reaction schemes have been proposed to account for hydroperoxide photolysis (Scheme 22) and quinone photoreaction with aromatic aldehydes to give aromatic esters, for example (16) (Scheme 23). The three chromophores are formed during... 

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