Poly l,3-phenylene isophthalamide

Poly(l,3-phenylene isophthalamide) (polyaramide (4.64) deteriorates rapidly on exposure to terrestrial sunlight. Fibres made from this polymer suffer loss of breaking strength and become yellow [369-371, 378, 2131, 2132]. 

During UV irradiation of poly(l,3-phenylene isophthalamide) in vacuum, a chain scission of the amide link yields two radicals (4.65) and (4.66), which can either recombine directly or eliminate carbon monoxide [368-371, 1105]  

This scission reaction is accompanied by a photo-Fries rearrangement which occurs by [378]  

No photo-Fries product was detected after UV irradiation in air. The cross-linking reaction occurs only in the absence of oxygen. The photo-oxidation reaction of poly(l,3-phenylene isophthalamide) is accompanied by a rapid chain scission [369]  

The formation of nitroso (—NO), nitro (—NO2) and carboxylic (—COOH) groups has been confirmed by IR spectroscopy. 

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As mentioned earlier, amides are less reactive than esters, and diamides are even less reactive. An example of this trend is the low reactivity of the dibenzoyl amides of 1,3- and 1,4-diaminobenzene, which are model compounds for the polymers Nomex [poly(l,3-phenylene isophthalamide)] and Kevlar B [poly (1,4-phenylene terephthalamide)] [243]. 

Various investigations of the thermal degradation of wholly aromatic polyamides (aramids), such as poly(l,3-phenylene isophthalamide) (Nomex) and poly(l,4-phe-nylene terephthalamide) (Kevlar), have also been reported. - " ... 

J. R. Brown and A. J. Power, Thermal degradation of aramids Part I—Pyrolysis/gas chro-matography/mass spectrometry of poly(l,3- phenylene isophthalamide) and poly(l,4- pheny-lene isophthalamide). Polymer Degradation and Stability, 4, 379 (1982). 

The combination of photoscission, photo-oxidation, and photorearrangement means that even very high performance polymers, such as epoxy resins, aromatic polyethers polyketones, and polysulfones, and the aromatic polyamides poly(l,3-phenylene isophthalamide) and poly(l,4-phenylene terephthalamide) (Nomex and Kevlar respectively) will degrade significantly on solar exposure. For example, it has been shown (108) that poly(phenylene oxide) and polysulfone both lose about 50% of their initial tensile strength after 2 years of outdoor exposure in Queensland. 

The chemical structures of these polymers were characterized using FT-IR. Poly(1,3-phenylene isophthalamide) (PMI) and poly (2,4-difluoro-l,5-phenylene isophthalamide) (2,4-DIF-PMI) shoved N-H stretching bands at 3400-3200 cm l and C==0 stretching bands(amide I) at 1630-1650 cm-. Poly(2,4-difluoro-1,3-phenylene trimellitic amide-imide) (2,4-DIF-PMTAI) showed additional bands at 1740 and 1796 cm l corresponding to imide C==0 stretching band at 1625 cif and C-0-C stretching bands at 1255 and 1050 cm l. 

Poly(n,n -l,3-phenylene isophthalamide) Isophthaloyl chloridc- 1,3-phenyleneditimine polymei 25765-47-3 I, 3-Benzenedicarbonyl diohloride, polymer with 1, 3- benzene-diamine R (C H4Cl202- CftHsN,),... 

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