2,6-Dimethylphenol polymer

Health and Safety Factors. Animal-feeding studies of DMPPO itself have shown it to be nontoxic on ingestion. The solvents, catalyst, and monomers that are used to prepare the polymers, however, should be handled with caution. Eor example, for the preparation of DMPPO, the amines used as part of the catalyst are flammable toxic on ingestion, absorption, and inhalation and are also severe skin and respiratory irritants (see Amines). Toluene, a solvent for DMPPO, is not a highly toxic material in inhalation testing the TLV (71) is set at 375 mg/m, and the lowest toxic concentration is reported to be 100—200 ppm (72). Toxicity of 2,6-dimethylphenol is typical of alkylphenols (qv), eg, for mice, the acute dermal toxicity is LD q, 4000 mg/kg, whereas the acute oral toxicity is LD q, 980 mg/kg (73). The Noryl blends of DMPPO and polystyrene have PDA approval for reuse food apphcations. 

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. 

Dimethylphenol, synthesis of, 383 /V,/V-Dimorpholinodicthyl ether (DMDEE), 225, 230 Dinitrile-diamine polyamides, 158 Dioctyltin dilaurate, 232 Diol-functionahzed telechelic polymers, 457... 

Poly(2,6-dimethyl-l,4-oxyphenylene) (poly(phenylene oxide), PPG) is a material widely used as high-performance engineering plastics, thanks to its excellent chemical and physical properties, e.g., a high 7 (ca. 210°C) and mechanically tough property. PPO was first prepared from 2,6-dimethylphenol monomer using a copper/amine catalyst system. 2,6-Dimethylphenol was also polymerized via HRP catalysis to give a polymer exclusively consisting of 1,4-oxyphenylene unit, while small amounts of Mannich-base and 3,5,3, 5 -tetramethyl-4,4 -diphenoquinone units are always contained in the chemically prepared PPO. 

The study of the molecular weight of the intermediate course is an effective method for the classification of polymerization as chain or stepwise reaction. In Figure 3, the molecular weight of the obtained polymer is plotted against the yield, for the oxidative polymerization of dimethylphenol with the copper catalyst and for the electro-oxidative polymerization. The molecular weight rises sharply in the last stage of the reaction for the copper-catalyzed polymerization. This behavior is explained by a stepwise growth mechanism. 

Table 14. Oxidative polymerization of 2,6-dimethylphenol catalyzed by polymer-Cu complexes... 

Fig. 28. Schematic profile of polymer-Cu catalyst in steady state of oxidation of 2,6-dimethylphenol About 72 Cu ions are coordinated on a partially quaternized poly(4-vinyl-pyridine) ligand (DP = 200, Q% = 28). Fraction of Cu(II) = 0.24, fraction of substrate-coordinated Cu = 0.80...

The overall reaction rate and the rate constant of the electron-transfer step are summarized in Table 17 for the polymer-Cu-catalyzed oxidation of substrates such as 2,6-dimethylphenol (XOH) and ascorbic acid15 . The ks values for polymer-Cu-catalyzed oxidation are larger than those for monomeric-Cu-catalyzed oxidation. Particularly in the oxidative polymerization of XOH, it is obvious that the electron-transfer step is accelerated by polymer ligands, and the large value of ke is in agreement with the higher rate of polymer-Cu-catalyzed polymerization. Therefore, the... 

Using activated manganese dioxide, silver oxide, or lead dioxide as the oxidizing agents, McNelis has also obtained low molecular weight polymer from 2.6-dimethylphenol (60, 61). 

The oxidative polymerization reaction is rapid at room temperature. Oxidation of 2.6-dimethylphenol readily gives high polymer with only a minor amount of the diphenoquinone (VIII R=R1=CH3). This polymer is now being produced commercially. In general when the substituents are small (Table 4) the polymer is formed preferentially (35). If one of the substituents is as large as tert-butyl or both as large as isopropyl then the diphenoquinone is preferentially formed. 

In the former case the diphenoquinone is formed exclusively while in the latter case small amounts of low molecular weight polymer have been observed. As would be expected, substituents which raise the oxidation potential of the phenol retard the polymerization. Thus whereas 2.6-dimethylphenol polymerizes readily at room temperature, temperatures in the neighborhood of 60° C are required to polymerize 2-chloro-6-methylphenol at comparable rates and even higher temperatures are necessary to oxidize 2.6-dichlorophenol. 

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. 

Although redistribution and coupling can be observed separately, oxidative polymerization under ordinary conditions involves both reactions and redistribution of oligomers to form monomer followed by removal of the monomer by coupling is an important mechanism of polymer growth. Redistribution in dimethylphenol polymerizations is extremely rapid. Addition of monomer to a polymerizing solution causes an immediate drop in the solution viscosity almost to the level of the solvent, as redistribution of polymer with monomer converts the polymer already formed to a mixture of low oligomers. 

A major factor in the interaction of the two phenols during oxidation, making the dimethylphenol appear less reactive and diphenylphenol more reactive than expected, must be the monomer-polymer redistribution reaction. Redistribution of diphenylphenol with the low oligomers... 

These redistribution reactions of polymer molecules with other polymer molecules as well as with monomer, continue throughout the polymerization and should result in randomization of the polymer. Inasmuch as dimethylphenol is among the most reactive and diphenylphenol the least reactive of the phenols which have been oxidized successfully to linear high polymers, it appears likely that oxidation of any mixture of phenols will yield random copolymers. 

Solubility in Methylene Chloride. The methods described above can show the presence of blocks of DMP and blocks of DPP units, but they do not distinguish between block copolymers and blends of homopolymers. Gel permeation chromatograms of the copolymers are sharp and symmetrical, indicating that they are indeed copolymers rather than blends, but this alone is not conclusive as blends of the homopolymers do not produce binodal or badly skewed curves under the conditions used unless the two polymers differ considerably in molecular weight. A partial answer to this question is provided by the solubility behavior in methylene chloride. Dimethylphenol homopolymer dissolves readily in methylene chloride but precipitates quantitatively on standing for a short... 

Twenty percent solutions in methylene chloride of the two copolymers prepared by Procedures 1 and 2 were stable indefinitely, showing that no significant amount of dimethylphenol homopolymer was present and that the DMP blocks must be in the form of a block copolymer. Separate experiments using blends of DMP homopolymers with random copolymers or with DPP homopolymer showed that DMP homopolymer, even of very low molecular weight (DP 15), could be detected easily if present to the extent of 5% of the total polymer. 

For the stabilization of various insoluble hydrocarbon polymers in carbon dioxide, it has been found that no one surfactant works well for all systems. Therefore it has become necessary to tailor the surfactants to the specific polymerization reaction. Through variation of not only the composition of the surfactants, but also their architectures, surfactants have been molecularly-engineered to be surface active—partitioning at the interface between the growing polymer particle and the CO2 continuous phase. The surfactants utilized to date include poly(FOA) homopolymer, poly(dimethylsiloxane) homopolymer with a polymerizable endgroup, poly(styrene-b-FOA), and poly(styrene-b-dimethylsiloxane). Through the utilization of these surfactants, the successful dispersion polymerization of methyl methacrylate (MMA), styrene, and 2,6-dimethylphenol in CO2 has been demonstrated. 

Some of the peaks in the pyrogram may result from the units of the polymer that have free phenol groups, and others may result from the ether group cleavage. Some compounds such as phenol, methylphenols, and dimethylphenols may come from both sources. 

As seen from Table 9.1.10, besides 2,6-dimethylphenol and 3,5-dimethylphenol, which are expected to be generated in the pyrogram, trimethyl phenols are also present at considerable levels. Also trimethylbenzene and even tetramethylbenzene were detected in the pyrolysate. The polymer being relatively stable at elevated temperatures, the decomposition starts only above 450° C when migration of the -CHs groups seems to occur. 

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