Poly phenylene oxide s

Polyethers that form by chain-growth polymerizations of carbonyl compounds and by ring opening polymerizations of cyclic ethers and acetals are discussed in Chap. 6. In this section are discussed poly(phenylene oxide)s and phenoxy resins. 

Phenols with halogen substituents require higher temperatures. Large substituents can lead to 

The active catalyst is believed to be a basic cupric salt that forms through oxidation of cuprous chloride followed by complexation with two molecules of the amine [102]  

This is a step-growth polymerization involving phenoxy radicals. The polymer formation can be illustrated as follows  

Dissociation leads to aryloxy radicals or to two new radicals that couple. Quinone ketals are formed initially. They dissociate to yield the original aryloxy radicals and then couple [102]  

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One class of aromatic polyethers consists of polymers with only aromatic rings and ether linkages ia the backbone poly(phenylene oxide)s are examples and are the principal emphasis of this article. A second type contains a wide variety of other functional groups ia the backbone, ia addition to the aromatic units and ether linkages. Many of these polymers are covered ia other articles, based on the other fiinctionahty (see Polymers containing sulfur, POLYSULFONES). 

Many newer poly(phenylene oxide)s have been reported ia the early 1990s. Eor example, a number of poly(2,6-diphenyl-l,4-phenylene oxide)s were prepared with substituents ia the 4-positions of the pendent phenyl groups. Of particular iaterest is the 4-fluoro substitueat, which imparts a lower melting poiat, enhanced solubiUty, and a lesser tendency to crystallize than has been found for the parent material (1). 

Table 1. Thermal Properties of Poly(Phenylene Oxides)s...

The backbone of poly(phenylene oxide)s is cleaved under certain extreme reaction conditions. Lithium biphenyl reduces DMPPO to low molecular weight products in the dimer and trimer molecular weight range (20) and converts poly(2,6-diphenyl-l,4-phenylene oxide) to 3,5-diphenylphenol in 85% yield (21) (eq. 4). 

Poly(phenylene oxide)s undergo many substitution reactions (25). Reactions involving the aromatic rings and the methyl groups of DMPPO include bromination (26), displacement of the resultant bromine with phosphoms or amines (27), lithiation (28), and maleic anhydride grafting (29). Additional reactions at the open 3-position on the ring include nitration, alkylation (30), and amidation with isocyanates (31). 

Halogen Displacement. Poly(phenylene oxide)s can also be prepared from 4-halo-2,6-disubstituted phenols by displacement of the halogen to form the ether linkage (48). A trace of an oxidizing agent or free radical initiates the displacement reaction. With 4-bromo-2,6-dimethylphenol, the reaction can be represented as in equation 10 ... 

Halophenols without 2,6-disubstitution do not polymerize under oxidative displacement conditions. Oxidative side reactions at the ortho position may consume the initiator or intermpt the propagation step of the chain process. To prepare poly(phenylene oxide)s from unsubstituted 4-halophenols, it is necessary to employ the more drastic conditions of the Ullmaim ether synthesis. A cuprous chloride—pyridine complex in 1,4-dimethoxybenzene at 200°C converts the sodium salt of 4-bromophenol to poly(phenylene oxide) (1) ... 

The electrolytic oxidation was found to proceed much faster in the presence of Cu-pyridine as a redox mediator in the electrolytic cell divided with a membrane. The electrode coated with Cu/poly(4-vinylpyridine) was also effective for the oxidative polymerization, and what was more, without a partition membrane (Figure 8). Polymer-Cu complex film coated on the electrode prevented formation of the insulating film of the product polymer on the electrode surface and decreased the electrolytic potential. The oxidation using the electrode coated with a macromolecular Cu complex provides a facile method for forming poly(phenylene oxide)s. 

A. S. Hay. Poly(phenylene oxides)s and poly(arylene ether)s derived from 2,6-diaryIphenols. Prog. Polym. ScL, 24(l) 45-80, April 1999. 

The chemical structures of sulfonated poly(4-phenoxybenzoyl-l,4-phenyl-ene) (S-PPBP) (1), poly(p-xylylene) (S-PPX) (2), poly(phenylene sulfide) (S-PPS) (3), poly(phenylene oxide) (S-PPO) (4), poly(ether ether ketone) (S-PEEK) (5), poly(ether ether sulfone) (S-PEES) (6), arylsulfonated poly(ben-zimidazole) (S-PBl) (7) sulfonated polyphenylquinoxiiline (S-PPQ) (8) and sulfonated phenoxy polyperyleneimide (PSPPI) (9) are shown below. ACPs are sulfonated using common sulfonating agents [82-85]. In particular, PEEK can be sulfonated in concentrated sulfuric acid [50], chlorosulfonic acid [86], SO3 (either pure or as a mixture) [53,65,86,87], a mixture of methanesulfonic acid with concentrated sulfuric acid [88] and acetyl sulfate [89,90]. 

Poly(phenylene oxide)s also form through photodecomposition of benzene-1,4-diazooxides ... 

Zhang J, Wang H, Li X. Novel hyperbranched poly(phenylene oxide)s with phenolic terminal groups synthesis, characterization, and modification. Polymer 2006 47(5) 1511-8. 

Poly(phenylene oxide)s can also be formed by oxidative displacement of bromides from 4-bromo-2,6-dimethylphenol [102, 105]. Compounds, like potassium ferricyanide, lead oxide, or silver oxide, catalyze this reaction ... 

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