The research of Vogel and Marvel truly represents a pioneering effort in the synthesis of high performance polymers. In this landmark article, they extended the knowledge of the thermal stability of im-idazole derivatives into the realm of high molecular weight, fully aromatic polybenzimidazole (PBI) polymers. They demonstrated the ability to produce high molecular weight polymers having potentially useful properties. One key to achieving a high molecular weight was the use of the phenyl ester derivative of the aromatic dioic acids. This provided superior polymer to that produced by using the free acid or the methyl ester. The commercial PBI products of today still rely on that finding. Their exploratory studies were extended through funding by the Air Force Materials Laboratory and NASA, who addressed a specific set of aerospace and defense needs. This subsequently led to some of the earlier developments of a prepolymer that could be used a8 a high temperature adhesive, a carbon foam made possible by the high carbon yield of PBI, and the development of PBI fibers. Essential to the practical utility of Vogel and Marvel's polymers was that several PBI compositions formed fully soluble, high molecular weight polymer solutions. This allowed subsequent processing into useful forms avoiding the nonprocess-able, proverbial "brick-duet," encountered with some other high performance polymers. From a commercial viewpoint, the balance of processability and polymer performance led to the selection of poly[2,2'-(rn-phenylene)-5,5'-bibenzim-idazole] as the principal product of commerce. Monomers needed to produce this PBI composition were a major concern. Diaminobenzidine (now more commonly referred to as tetraaminobiphenyl) was not commercially available and the diphenyl iso-phthalate was a limited-supply specialty chemical. Hence, dedicated facilities for manufacturing tetra-aminobiphenyl (Hoechst AG) and PBI polymer and fiber (Celanese Corporation, now Hoechst Celanese) were constructed and began operation in 1982/1983. Barring a significant discovery to reduce mono-mer costs, PBI remains a specialty polymer targeted at high performance niches. Even so, its unique performance attributes (e.g., has a glass transition temperature of 435°C; does not bum in air, contribute fuel to flames or produce much smoke; forms a tough flexible char in high yield; is hydrophdic, having high moisture regain; forms very comfortable fabrics for garments; has good chemical resistance) permita PBI to be used in a cost-effective manner in particular situations. Fire blocking of aircraft seats was among the earliest large-volume uses for PBI fiber. Currently, fire service applications are the predominant commercial area. Vogel and Marvel, in the course of their early investigations, may not have envisioned the future when people who had used PBI products in these commercial applications would have acknowledged that "PBI saved my life." They 1123

No abstract

A polybenzimidazole has been prepared from 3,3′‐diaminobenzidine and phthalic anhydride which has a high molecular weight and very good heat stability. Replacement of the hydrogen atoms on the nitrogen of the imidazole nuclei in a polybenzimidazole does not improve the heat stability as indicated by the properties of poly‐2,6‐(m‐phenylene)‐3,5‐diphenyldiimidazobenzene. Polybenzimidazoles with aliphatic units have been prepared from 3,3′‐diaminobenzidine and the diphenyl ester of succinic and glutaric acids. The diphenyl esters of oxalic and malonic acids did not yield polymers presumably because cyclic amides were formed. Further hydrolytic stability tests on polybenzimidazoles have been reported. Some model compounds have been prepared for comparison of their melting points and absorption spectra with those of the corresponding polymer.

The article contains sections titled: 1. Introduction 2. Production Processes 2.1. Substitution of Hydrogen 2.2. Halogen ‐ Fluorine Exchange 2.3. Synthesis from Fluorinated Synthons 2.4. Addition of Hydrogen Fluoride to Unsaturated Bonds 2.5. Miscellaneous Methods 2.6. Purification and Analysis 3. Fluorinated Alkanes 3.1. Fluoroalkanes and Perfluoroalkanes 3.2. Chlorofluoroalkanes 3.3. Bromofluoroalkanes 3.4. Iodofluoroalkanes 4. Fluorinated Olefins 4.1. Tetrafluoroethylene 4.2. Hexafluoropropene 4.3. 1,1‐Difluoroethylene 4.4. Monofluoroethylene, Monofluoroethylene 4.5. 3,3,3‐Trifluoropropene 4.6. 3,3,3‐Trifluoro‐2‐(trifluoromethyl)‐prop‐1‐ene 4.7. Chlorofluoroolefins 5. Fluorinated Alcohols 6. Fluorinated Ethers 6.1. Perfluoroethers 6.1.1. Low Molecular Mass Perfluoroethers 6.1.2. Perfluorinated Epoxides 6.1.3. High Molecular Mass Perfluoroethers 6.2. Perfluorovinyl Ethers 6.3. Partially Fluorinated Ethers 7. Fluorinated Ketones and Aldehydes 7.1. Fluoro‐ and Chlorofluoroacetones 7.2. Perhaloacetaldehydes 7.3. Fluorinated 1,3‐Diketones 8. Fluorinated Carboxylic Acids and Fluorinated Alkanesulfonic Acids 8.1. Fluorinated Carboxylic Acids 8.1.1. FluorinatedAcetic Acids 8.1.2. Long‐Chain Perfluorocarboxylic Acids 8.1.3. Fluorinated Dicarboxylic Acids 8.1.4. Tetrafluoroethylene ‐ Perfluorovinyl Ether Copolymers with Carboxylic Acid Groups 8.2. Fluorinated Alkanesulfonic Acids 8.2.1. Perfluoroalkanesulfonic Acids 8.2.2. Fluorinated Alkanedisulfonic Acids 8.2.3. Tetrafluoroethylene ‐ Perfluorovinyl Ether Copolymers with Sulfonic Acid Groups 9. Fluorinated Tertiary Amines 10. Aromatic Compounds with Fluorinated Side‐Chains 10.1. Properties 10.2. Production 10.3. Uses 11. Ring‐Fluorinated Aromatic, Heterocyclic, and Polycyclic Compounds 11.1. Mono‐ and Difluoroaromatic Compounds 11.1.1. Properties 11.1.2. Production 11.1.3. Uses 11.2. Highly Fluorinated Aromatic Compounds 11.3. Perhaloaromatic Compounds 11.4. Fluorinated Heterocyclic and Polycyclic Compounds 11.4.1. Ring‐Fluorinated Pyridines 11.4.2. Trifluoromethylpyridines 11.4.3. Fluoropyrimidines 11.4.4. Fluorotriazines 11.4.5. Polycyclic Fluoroaromatic Compounds 12. Economic Aspects 13. Toxicology and Occupational Health 13.1. Fluorinated Alkanes 13.2. Fluorinated Olefins 13.3. Fluorinated Alcohols 13.4. Fluorinated Ketones 13.5. Fluorinated Carboxylic Acids 13.6. Other Classes

In connection with the search for new high molecular weight material8with superior properties such as stability, retention of stihess, toughness at elevated temperatures, etc., a study of the preparation of fully aromatic polybeneimidazoles haa been started.Imidazole derivatives are known to be remarkably stable compounds.'-'Many of them are resistant to the moat drastic treatments with acids and bases and are not readily attacked by oxidizing reagents. They have high melting points and are stable at elevated temperatures (43O-64S0C.).' These properties suggest that a condensation polymer characterized by the recurrence of benzimidazole nuclei would also exhibit outstanding heat stability. We were able to synthesize a variety of polybeneimidazoles by melt polycondensation of suitable aromatic tetraamines and aromatic dicarboxylic acids. DISCUSSIONA most versatile and practical synthesis of benzimidamles is provided by the interaction of an 0-phenylenediamine with a carboxylic acid.' Its applicability in polymer chemistry has recently been shown by Brinker and Robinson,L who discovered that the reaction of bis-o-diaminophenyl compounds with aliphatic dicarboxylie acids could be employed to form linear condensation polymers.The preparation of a polybenzimidazole containing only aromatic recurring units required the condensation of an aromatic tetraamine with an aromatic dicarboxylic acid or derivative thereof. The interaction of 3,3'-diaminobeneidine and lJ2,4,5-tetraaminobenzene with aromatic dibasic acids, eq.