Polyphenyls

This short section is concerned with molecules having two or more benzene rings that are not condensed. The rings therefore have a degree of independence from each other, and so their reduction may show some selectivity. 

Many years ago, Homer Atkins and his colleagues examined the reduction of triphenylmethane catalysed by nickel powder it went non-selectively to the tri-cyclohexylmethane. 1,3,5-Triphenylbenzene was reduced to the tri-cyclohexylcyclohexane. With phenylethanes, rates decreased slightly with increasing number of phenyl groups.  

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The main synthetic fluids used as special lubricants are esters, polyglycols, silicones, halogenated hydrocarbons and polyphenyl ethers. 

Some work has been done on the nitration of polyphenyls the case of -terphenyl presents problems in connection with isomer distributions similar to those met with that of biphenyl. 

Synthetic oils have been classified by ASTM into synthetic hydrocarbons, organic esters, others, and blends. Synthetic oils may contain the following compounds diaLkylben2enes, poly(a-olefins) polyisobutylene, cycloaUphatics, dibasic acid esters, polyol esters, phosphate esters, siUcate esters, polyglycols, polyphenyl ethers, siUcones, chlorofluorocarbon polymers, and perfluoroalkyl polyethers. 

Fig. 10. Tuning curves (41) for a continuous argon laser pumped dye laser, where A represents polyphenyl 2 B, stilbene 1 [74758-59-1] C, stilbene 3...

Alkylated aromatic lubricants, phosphate esters, polyglycols, chlorotrifluoroethylene, siUcones, and siUcates are among other synthetics that came into production during much that same period (28,29). Polyphenyl ethers and perfluoroalkyl polyethers have followed as fluids with distinctive high temperature stabiUty. Although a range of these synthetic fluids find appHcations which employ their unique individual characteristics, total production of synthetics represent only on the order of 2% of the lubricant market. Poly(a-olefin)s, esters, polyglycols, and polybutenes represent the types of primary commercial interest. 

Polyphenyl Ethers. These very stable organic stmctures have been synthesized in a search for lubricants to meet the needs of future jet engines, nuclear power plants, high temperature hydrauHc components, and high temperature greases (49). A typical formula is C H (—OC H ... 

One hquid in this class intended for aircraft engine use is described in military specification MIL-L-87100 for operation from +15 to 300°C. Limitations of this class of synthetics are pour points of +5°C and higher, relatively poor lubricity, and high cost of 265/L ( 1000 + /gal) (44). Polyphenyl ether greases are available with good radiation resistance for appHcations in the temperature range of +5 to 288°C. 

Perfluoroalkyl ether greases thickened with polytetrafluoroethylene (MIL-G-38220 and MIL-G-27617) are used from —40 to 200°C in missiles, aircraft, and appHcations where fuel, oil, and Hquid oxygen resistance is needed (55). Polyphenyl ether greases find special use from 10 to 315°C in high vacuum diffusion pumps and for radiation resistance. 

Although synthetic lubrication oil production amounts to only about 2% of the total market, volume has been increasing rapidly (67). Growth rates of the order of 20% per year for poly( a-olefin)s, 10% for polybutenes, and 8% for esters (28) reflect increasing automotive use and these increases would accelerate if synthetics were adopted for factory fill of engines by automotive manufacturers. The estimated production of poly( a-olefin)s for lubricants appears to be approximately 100,000 m /yr, esters 75,000, poly(alkylene glycol)s 42,000, polybutenes 38,000, phosphates 20,000, and dialkyl benzene 18,000 (28,67). The higher costs reflected in Table 18 (18,28) have restricted the volume of siUcones, chlorotrifluoroethylene, perfluoroalkylpolyethers, and polyphenyl ethers. 

Biphenyl (diphenyl, phenylben2ene) and terphenyl are the lowest members of a family of polyphenyls in which benzene rings are attached one to another in a chainlike manner, Many higher polyphenyls are known (1), but only biphenyl and the terphenyls are of commercial significance. Some... 

Since the thermal dehydrocondensation proceeds by a free-radical mechanism (37), various radical-forrning promoters like acetone, ethanol, or methanol have been found useful in improving conversion of ben2ene to condensed polyphenyls. In the commercial dehydrocondensation process, ben2ene and some biphenyl are separated by distillation and recycled back to the dehydrocondensation step. Pure biphenyl is then collected leaving a polyphenyl residue consisting of approximately 4% o-terphenyl, 44% y -terphenyl, 25% -terphenyl, 1.5% triphenylene, and 22—27% higher polyphenyl and tars. Distillation of this residue at reduced pressure affords the mixed terphenyl isomers accompanied by a portion of the quaterphenyls present. 

Pure (9-terphenyl can be obtained by fractional distillation. To obtain high purity m- or -terphenyl, the appropriate distillation fraction has to be further purified by recrysta11i2ing, 2one refining, or other refining techniques. Currently, litde demand exists for pure isomers, and only a mixture is routinely produced. Small amounts of acetone, ethanol, or methanol are used to promote dehydrocondensation, and as a result, minor amounts of methyl- or methylene-substituted polyphenyls accompany the biphenyl and terphenyls produced. For most purposes, the level of such products (<1%) is so small that their presence can be ignored. For appHcations requiring removal of these alkyl-polyphenyl impurities, an efficient process for their oxidative destmction has been described (38). 

Historically, polychloriaated biphenyls (PCBs) and to a lesser extent polychlorinated terphenyls (PCTs) were the most important derivatives of the respective polyphenyls. When they came to be recognized as serious environmental contaminants, production ceased in the early 1970s. These products are now of significance primarily because of thek environmental aftereffects (62). Much environmental research and governmental regulations stem therefrom... 

H. Mandel, Heavy Water Organic Cooled Keactor, Physical Properties of Some Polyphenyl Coolants, A EC Report A l-CE-15, Apr. 15, 1966. 

W. H. Hedley, M. V. Milnes, and W. H. Yanko, Uiscosily and Thermal Conductivity of Polyphenyls in Eiquid and Uapor States, Final Keport IDO-11,007,... 

The mechanical properties of composites reinforced with wood fibers and PVC or PS as resin can be improved by an isocyanate treatment of those cellulose fibers [41,50] or the polymer matrix [50]. Polymethylene-polyphenyl-isocianate (PMPPIC) in pure state or solution in plasticizer can be used. PMPPIC is chemically linked to the cellulose matrix through strong covalent bonds (Fig. 8). 

Polyphenyls Polyphenylene oxide Decompose at 530°C (986°F) infusible, insoluble polymers. Decomposes close to 500°C (932°F) heat cures above 150° C (302°F) to elastomer usable heat range —135-185 C (—211-365°F). 

Polysulfone It is a high performance amorphous plastic that is tough, highly heat resistant, strong and stiff. Products are transparent and slightly clouded amber in color. Material exhibits notch sensitivity and is attacked by ketones, esters, and aromatic hydrocarbons. Other similar types in this group include polyethersulfone, polyphenyl-sulfone, and polyarylsulfone. Use includes medical equipment, solar-heating applications and other performance applications where flame retardance, autoclavability and transparency are needed. 

R3. Robinson, J. M., and Lurie, H., Critical heat flux of some polyphenyl coolants, Symp. Boiling Phenomena in Nucl. Heat Transfer 1962, Am. Inst. Chem. Eng., Preprint No. 156. 

VI. Van Gasselt, M. L. G., and Van Meel, D. A., Research on the influence of the conditions of flow, subcooling and composition, on the burnout heat flux of polyphenyl reactor cooling agents, EUR 2299e (1965). 

The only author to postulate a homolytic mechanism in the last few decades was Deng (1989). His arguments are based on the formation of small amounts of fluorinated bi- and polyphenyls in thermal fluoro-de-diazoniations and in mass-spec-trometric degradations of benzenediazonium tetrafluoroborate and its substituted derivatives. However, he does not include a critical discussion of his work. 

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