Synthesis and degradation of cyano‐containing aramids

Abstract

Various aramids having a cyano group on the diamine ring were synthesized. Aramids containing a cyano group ortho to the amide bond underwent thermal degradation via a two step mechanism, whereas those containing a cyano group meta to the amide bond did not. The first sfep represented the loss of HCN resulting in benzoxazole polymers, which degraded further in the second stage producing high char yield at 900°C. The thermal studies of copolyamides from m-phen ylened iam ine, 2,4-d iam inobenzon if rile, and isoor terephthaloyl chloride showed that as the mole fraction of 2,4-DABN increased the initial decomposition temperature decreased, but the char yield and glass transition temperature increased gradually from the poly(l,3-phenylene isophthalamide) to the polycyanamide homopolymer. To confirm the nucleophilic displacement reaction mechanism rather than isomerization cyclization suggested by Barashkov et al. for aramids with the cyano group ortho to the amide bond, a high-temperature cell attached to a FT-lR spectrometer were employed. Model compound studies also showed evidence for the benzoxazole ring formation. 2,4-DiaminobenzonitriZe(2,4-DABN) [ 151 A mixture of 21.2 g (0.1 mol) of 2,4-dinitrobenzoic acid (Kodak Chem. Co.) and 32.0 g (0.21 mol) of benzenesulfonamide was stirred and heated in an oil bath at 205-210°C for 1 hr and then at 225°C for 1 hr and allowed to cool to room temperature under a nitrogen atmosphere. The black solution was shaken with methylene chloride and dilute NaOH solution. The brown-colored methylene chloride layer was sepa- EXPERIMENTAL PROCEDURE Monomer Synthesis 1042-7147~rn1~49-2~$12.50

A New Synthetic Route to Benzoxazole Polymer via Tandem Claisen Rearrangement

“…A novel polyamide 2 29 was synthesized by lowtemperature solution polycondensation of diamine 1 and terephthaloyl chloride, as shown in Scheme 1. The structure of this polymer was confirmed by IR, 1 H NMR, and 13 C NMR measurements. In the IR spectrum of the resulting polyamide, carbonyl absorption corresponding to an amide bond was observed at 1672 cm -1 .…”

“…30 A white powdery polybenzoxazole 4 instead of the polymer 3 was obtained by precipitation of the reaction mixture into methanol. The structure of the polybenzoxazole 4 was confirmed by IR, 1 H NMR, and 13 C NMR spectra. In the IR spectra, the carbonyl absorption for an amide bond at 1672 cm -1 observed in the precursor polyamide 2 disappeared after the thermal treatment, while a new peak corresponding to the CdN bond of oxazole rings was observed at 1626 cm -1 for the resulting benzoxazole polymer 4.…”

“…IR (KBr): 1626, 1193, 1015 cm -1 . 1 H NMR (CD3Cl): δ 1.35 (s, 18H, -C(CH3)3), 3.71 (s, 4H, -CH2-), 5.12 (s, 2H, dCH2), 7.22 (s, 2H, Ar), 7.65 (s, 2H, Ar), 8.13 (4H Ar) 13. C NMR (CD3Cl): δ 162.32, 148.88, 148.38, 145.00, 142.26, 129.91, 128.07, 124.43, 122.14, 115.16, 36.88, 35.34, 32.18.…”

Benzoxazole Resin: A Novel Class of Thermoset Polymer via Smart Benzoxazine Resin

“…While the very high rigidity of PBO molecules is responsible for the outstanding performance, it also leads to difficulties in synthesis and fabrication. The wholly aromatic PBOs suffer from various associated difficulties: (i) they are soluble only in harsh acids, such as sulfuric, methanesulfonic, triflic, and polyphosphoric acids, and complex-mediated Lewis acid/solvent systems, such as AlCl 3 /nitromethane; (ii) the decomposition temperature of PBOs is below their melting points, which impedes the melt processing of PBOs; and (iii) bis( o -aminophenol)s used as the main starting materials for most synthesis approaches of PBOs are extremely expensive. , All of these shortcomings limit the application of this highly useful class of high performance polymers. The drawbacks of the aforementioned methods for polybenzoxazole synthesis motivated us to develop a new route to solve, if not all, many of the disadvantages of the traditional approaches.…”

Thermal Conversion of Hydroxy-Containing Imides to Benzoxazoles: Polymer and Model Compound Study

“…Intramolecular nucleophilc aromatic substitution involving displacement of a cyano group, for example, by the amide oxygent resulted in formation of the benzoxazole ring. 15 This paper describes our results concerning the thermal conversion of hydroxycontaining polyimides to polybenzoazoles and model compounds to benzoxazoles.…”