Aromatic polyamides and polyimides

Kawakami Y, Yu SP, Abe T (1992) Synthesis and gas permeability of aromatic polyamide and polyimide having oligodimethylsiloxane in main chain or in side chain. Polym J (Tokyo) 24( 10) 1129... 

Chem. Descrip. N-Methyl pyrrolidone CAS 872-50-4 EINECS/ELINCS 212-828-1 Uses Solvent, cosolvent In coatings, stripping/cleaning of paints/vamishes. Industrial cleaning, mold cleaning, petrochem. processing solvent for adhesives, inks, dyes, soaps, metal complexes, agric. solvent for PVAc, PVDF, PS, vinyl copolymers, nylon and aromatic polyamides and polyimides, polyesters, acrylics, PC, cellulose derivs., syn. elastomers, waxes... 

Addition of LiCl can accelerate the polymerization. In another study 4,4 -oxydianiline (3-22) was used as the A2-component and gel formation was observed within 10-20 min even at lower concentrations. Jikei and Kakimoto reviewed the field of aromatic polyamides and polyimides in detail. 

M. Jikei, M. Kakimoto, Dendritic aromatic polyamides and polyimides, J. Polym. ScL, Part A.- Polym. Chem., 42, 1293-1309 (2004). 

C.P. Yang, J.H. Lin, Syntheses and properties of aromatic polyamides and polyimides based on 3,3-( w[4-(4-aminophenoxy)phenyl]-phthalimi-dine. Polymer 36 (13) (1995) 2607-2614. 

These polymers contain the —NH.CO— group. Originally the aliphatic polyamides were only utilized as fibres, but in recent years engineering applications of these polymers have been realized. Aromatic polyamides and polyimides as high-performance fibres are also being developed. 

Carboxyhc acids react with aryl isocyanates, at elevated temperatures to yield anhydrides. The anhydrides subsequently evolve carbon dioxide to yield amines at elevated temperatures (70—72). The aromatic amines are further converted into amides by reaction with excess anhydride. Ortho diacids, such as phthahc acid [88-99-3J, react with aryl isocyanates to yield the corresponding A/-aryl phthalimides (73). Reactions with carboxyhc acids are irreversible and commercially used to prepare polyamides and polyimides, two classes of high performance polymers for high temperature appHcations where chemical resistance is important. Base catalysis is recommended to reduce the formation of substituted urea by-products (74). 

The novel polymers (end of 1960s and early 1970s) belong mostly to the HT group and their overall utility is limited. Many appear as special fibers, like aromatic polyamides and polyesters, polyimides and Parylene. The novel structures have rings (either aromatic or heterocyclic), in the main chain (para-phenylene is preferred over meta-phenylene). Substituting C—H bonds... 

Poly(imide-co-amides) are easier to produce and to process than aromatic polyamides or polyimides. Like these, they are used in particular for electrical insulation coatings. As the ratio of imide/amide increases, the thermal stability of the copolymers increases, but the flexibility of the product deteriorates. 

Attempts of photo-dilatation and contraction of polyamide and polyimide containing stilbene in the aromatic chain backbone were made in water. It was found that poly-imide-poly(iininoisophthaloylimino-l, 3-phenylenevinylene-1,4-phenylene), if stretched under constant tension, relaxed on irradiating with UV light, and recovered to initial stress when the irradiation was stopped This type of polyimide is stable in the dark in the trans conformation which is more stretched, and transforms to the cis form which is the more coiled conformation under irradiation. Therefore, the relaxation by photoirradiation should be associated with an increase in polarity of the polymer film. 

Tg measurements have been performed on many other polymers and copolymers including phenol bark resins [71], PS [72-74], p-nitrobenzene substituted polymethacrylates [75], PC [76], polyimines [77], polyurethanes (PU) [78], Novolac resins [71], polyisoprene, polybutadiene, polychloroprene, nitrile rubber, ethylene-propylene-diene terpolymer and butyl rubber [79], bisphenol-A epoxy diacrylate-trimethylolpropane triacrylate [80], mono and dipolyphosphazenes [81], polyethylene glycol-polylactic acid entrapment polymers [82], polyether nitrile copolymers [83], polyacrylate-polyoxyethylene grafts [84], Novolak type thermosets [71], polyester carbonates [85], polyethylene naphthalene, 2,6, dicarboxylate [86], PET-polyethylene 2,6-naphthalone carboxylate blends [87], a-phenyl substituted aromatic-aliphatic polyamides [88], sodium acrylate-methyl methacrylate multiblock copolymers [89], telechelic sulfonate polyester ionomers [90], aromatic polyamides [91], polyimides [91], 4,4"-bis(4-oxyphenoxy)benzophenone diglycidyl ether - 3,4 epoxycyclohexyl methyl 3,4 epoxy cyclohexane carboxylate blends [92], PET [93], polyhydroxybutyrate [94], polyetherimides [95], macrocyclic aromatic disulfide oligomers [96], acrylics [97], PU urea elastomers [97], glass reinforced epoxy resin composites [98], PVOH [99], polymethyl methacrylate-N-phenyl maleimide, styrene copolymers [100], chiral... 

A technique of vapor deposition polymerization has recently been developed. This method was first applied successfully to synthesize thin layers of polyimide [9] and aromatic polyamide and aromatic poly(afflide-iniide) [10]. 

Chemical structure of (a) aromatic polyimides, (b) aromatic polyamides, and (c) aromatic polybenzimidazoles. 

The two-step poly(amic acid) process is the most commonly practiced procedure. In this process, a dianhydride and a diamine react at ambient temperature in a dipolar aprotic solvent such as /V,/V-dimethy1 acetamide [127-19-5] (DMAc) or /V-methy1pyrro1idinone [872-50-4] (NMP) to form apoly(amic acid), which is then cycHzed into the polyimide product. The reaction of pyromeUitic dianhydride [26265-89-4] (PMDA) and 4,4 -oxydiani1ine [101-80-4] (ODA) proceeds rapidly at room temperature to form a viscous solution of poly(amic acid) (5), which is an ortho-carboxylated aromatic polyamide. 

Polyamide or polyimide polymers are resistant to aliphatic, aromatic, and chlorinated or fluorinated hydrocarbons as well as to many acidic and basic systems but are degraded by high-temperature caustic exposures. 

The routes give, using well-known condensation and radical reactions, bakelites (I), polyazophenylenes (II), polyimides (III), polyurethanes (IV), nitro compounds and polyamides (V), aromatic polyethers and polyesters (VI), polychalcones (VII), polyphenylene sulfides (IX), ammonia lignin (X), carbon fibers (XI), silicones (XII), and phosphorus esters (XIII). In addition, radiation and chemical grafting can be used to obtain polymers of theoretical interest and practical use. Although the literature on the above subject is very large, there are comprehensive summaries available (1,28,69). 

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