Poly 2,6-dimethyl-l,4-phenylene oxide

The photodegradation of poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) (4.5) has been extensively investigated [84, 416-419, 424-426, 1096, 1117, 1176, 1701, 1712, 1721, 1722, 1846, 1847, 1995, 2008, 2211, 2213]. This polymer shows rapid discoloration after a few weeks or months of outdoor exposure, and also after about a year indoors under a combination of fluorescent and window lighting [1722]. 

The absorption spectrum of commercial poly(2,6-dimethyl-l,4-phenylene oxide) is shown in Fig. 4.2 it increases during UV irradiation. 

This mechanism has been strongly supported by ESCA spectroscopy measurements [585, 1701], 

ESR spectroscopy has proved the formation of phenoxy radicals (4.6) however, no ESR signals have been obtained which could confirm the presence of benzyl radicals [2144, 2154], Phenoxy radicals are very stable and can exist in air for 30-35 h at room temperature. 

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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]. 

The chemical modification of poly (2,6-dimethyl-l,4-phenylene oxide) (PPO) by several polymer analogous reactions is presented. The chemical modification was accomplished by the electrophilic substitution reactions such as bromination, sulfonylation and acylation. The permeability to gases of the PPO and of the resulting modified polymers is discussed. Very good permeation properties to gases, better than for PPO were obtained for the modified structures. The thermal behavior of the substituted polymers resembled more or less the properties of the parent polymer while their solution behavior exhibited considerable differences. 

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. 

Coupling and Capping Reactions on Poly(2,6-dimethyl-l, 4-phenylene Oxide)... 

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. 

FIG. 26.13 Critical strain of poly(2,6-dimethyl-l,4-phenylene oxide) vs. solubility parameter 5 of crazing and cracking liquids. Minimum in cr occurs at 8 equal to that of the polymer. Band at top indicates critical strain of polymer in air (Bernier and Kambour, 1968 reproduced by permission of the American Chemical Society). 

Evidence from spectral studies for interactions other than the above hydrogen bonds is not very plentiful. Polystyrene/poly(2,6 dimethyl-l,4-phenylene oxide) blends have been studied by infra-red and ultraviolet spectroscopy . Interactions involving the aromatic rings of the two polymers were proposed. Studies of low molecular weight ethers with aromatic compounds have shown evidence for specific interactions and this has recently been extended to blends of polystyrene with poly(methyl vinyl ether)... 

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