Dimethylphenol oxidative coupling

Polymerization Mechanism. The mechanism that accounts for the experimental observations of oxidative coupling of 2,6-disubstituted phenols involves an initial formation of aryloxy radicals from oxidation of the phenol with the oxidized form of the copper—amine complex or other catalytic agent. The aryloxy radicals couple to form cyclohexadienones, which undergo enolization and redistribution steps (32). The initial steps of the polymerization scheme for 2,6-dimethylphenol are as in equation 6. 

The oxidative coupling of 2,6-dimethylphenol to yield poly(phenylene oxide) represents 90—95% of the consumption of 2,6-dimethylphenol (68). The oxidation with air is catalyzed by a copper—amine complex. The poly(phenylene oxide) derived from 2,6-dimethylphenol is blended with other polymers, primarily high impact polystyrene, and the resulting alloy is widely used in housings for business machines, electronic equipment and in the manufacture of automobiles (see Polyethers, aromatic). A minor use of 2,6-dimethylphenol involves its oxidative coupling to... 

Poly(phenylene ether). The only commercially available thermoplastic poly(phenylene oxide) PPO is the polyether poly(2,6-dimethylphenol-l,4-phenylene ether) [24938-67-8]. PPO is prepared by the oxidative coupling of 2,6-dimethylphenol with a copper amine catalyst (25). Usually PPO is blended with other polymers such as polystyrene (see PoLYETPiERS, Aromatic). However, thermoplastic composites containing randomly oriented glass fibers are available. 

Figure 15.18. Oxidative coupling of dimethylphenol dimers to tetramers...

Propylene oxide is one of the raw materials used to manufacture rubbery and crystalline polyepoxides. R. J. Herold and R. A. Livigni describe propylene oxide polymerization with hexacyanometalate salt complexes as catalyst. Polyphenylene oxide is made by copper catalyzed oxidative coupling of 2,6-dimethylphenol. G. D. Cooper, J. G. Bennett, and A. Factor discuss the preparation of copolymers of PPO by oxidative coupling of dimethylphenol with methylphenylphenol and with diphenylphenol. 

This reaction has been actively studied since it was first reported by Hay in 1959 (I), but most of the extensive literature, which includes several recent reviews (2-8), deals primarily with the complex polymerization mechanism. Few copolymers have been prepared by oxidative coupling of phenols, and only one copolymer system has been examined in any detail. Copolymers of 2,6-dimethylphenol (DMP) and 2,6-diphenylphenol (DPP) have been prepared and the effect of variations in polymerization procedure on the structure and properties of the copolymers examined (4, 9) this work has now been extended to copolymers of each of these monomers with a third phenol, 2-methyl-6-phenylphenol (MPP). This paper presents a study of the DMP-MPP and MPP-DPP copolymers and a comparison with the DMP-DPP system previously reported. 

Block copolymers may also be made by condensation polymerization. Elastomer fibers are produced in a three-step operation. A primary block of a polyether or polyester of a molecular weight of 1000-3000 is prepared, capped with an aromatic diisocyanate, and then expanded with a diamine or dihydroxy compound to a multiblock copolymer of a molecular weight of 20,000. The oxidative coupling of 2,6-disubstituted phenols to PPO is also a condensation polymerization. G. D. Cooper and coworkers report the manufacture of a block copolymer of 2,6-dimethyl-phenol with 2,6-diphenylphenol. In the first step, a homopolymer of diphenylphenol is preformed by copper-amine catalyst oxidation. In the second step, oxidation of dimethylphenol in the presence of the first polymer yields the block copolymer. 

The telechelica,(i -bis(2,6-dimethylphenol)-poly(2,6-dimethylphenyl-ene oxide) (PP0-20H) [174-182] is of interest as a precursor in the synthesis of block copolymers [175] and thermally reactive oligomers [179]. The synthesis has been accomplished by five methods. The first synthetic method was the reaction of a low molecular weight PPO with one phenol chain end with 3,3, 5,5 -tetramethyl-l,4-diphenoquinone. This reaction occurred by a radical mechanism [174]. The second method was the electrophilic condensation of the phenyl chain ends of two PPO-OH molecules with formaldehyde [177,178], The third method consists of the oxidative copolymerization of 2,6-dimethylphenol with 2,2 -di(4-hydroxy-3,5-di-methylphenyl)propane [176-178]. This reaction proceeds by a radical mechanism. A fourth method was the phase transfer-catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,2-di(4-hy-droxy-3,5-dimethylphenyl)propane [181]. This reaction proceeded by a radical-anion mechanism. The fifth method developed was the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in the presence of tetramethyl bisphenol-A (TMBPA) [Eq. (57)] [182],... 

Oxidative coupling reaction of p-cresol (27) was effected with rhodium(III) complex (760) and CS2CO3 in bromobenzene (90 °C, 24 h) to give selectively 2,2 -dihydroxy-5,5 -dimethylbiphenyl (758) (51-67%). Oxidation of 2,3-dimethylphenol (761) also provided the corresponding biphenyl 762 (59%) (Scheme 150). 

Oxidative coupling of phenols was first reported by Hay and coworkers in 1959" and has since been developed to produce commercially useful polymers. In these reactions the parent compound, phenol, has a potential functionality of four, that is the two ortho and the one para position of the aromatic ring and the phenolic group. Not surprisingly, the commercially useful polymers are made from substituted phenols in which the potential functionality is reduced to two. Of these phenols 2,6-dimethylphenol or orf/zo-xylenol has been developed to a commercial polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (54). The General Electric Company sells this as a blend with polystyrene under the trade name Noryl. 

Oxidative coupling of phenols Silver carbonate precipitated on Celite is an excellent reagent for oxidative coupling of phenols thus 2,6-dimethylphenol (1) gives thep-diphenoquinone (2) in 98% yield. 

GPC (pyridine eluant (17,18)) the brown component, CuO, which initiates the oxidative coupling of 2,6-dimethylphenol (10-16), Reaction 4, has the cryoscopic properties of polymeric species with CuO units that. 

Oxidative coupling polymerization in SCCO2 has been demonstrated for the synthesis of poly(2,6-dimethylphenylene oxide) 27. The polymerization of 2,6-dimethylphenol in the presence of oxygen is conducted using CuBr as the catalyst, pyridine and a block copolymer of styrene and 1,1-dihydroperfluorooctyl acrylate (PS- -PFOA) as a stabilizer in SCCO2 (350 bar) at 40 C. The polymerization occurred via a dispersion process and produced the polymer in a 74% yield with high molecular weight (17 000) (Scheme 46). 

Poly(phenylene oxide) (19) is obtained from free-radical, step-growth, oxidative coupling of 2,6-dimethylphenol (2,6-xylenol). This involves passing oxygen into a reaction mixture containing 2,6-xylenol, cuprous chloride, and pyridine. 

Another PPO, called PPE, is produced by the oxidative coupling of a mixture of 2,6-dimethylphenol and 2,3,6-trimethylphenol. This stiff polymer, like Noryl, is available fi om General Electric. It is usually modified by blending with PS or HIPS. 

Diphenylphenol and 2,6-dimethylphenol can copolymerize by oxidative coupling. If the diphenyl derivative is polymerized first and subsequently the dimethyl derivative is added to the reaction mixture, block copolymers form. If, however, the order is reversed or both phenols are polymerized together, a random copolymer results. ... 

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