The high‐strength, high‐modulus Kevlar 49 fiber is widely used today because of its superior properties. In this paper, we discuss the fundamental physicochemical nature of the commercial fiber. It is an extended chain polymer, poly(p‐phenylene terephthalamide), which is highly crystalline. Extensive analysis shows that the material composition is quite consistent from lot to lot and is low in impurities. The fiber absorbs water reversibly; the extent of absorption is related to the ash content. The well‐known interaction of the fiber with ultraviolet light is illustrated with spectra, and the thermal stability of the fiber is demonstrated with various thermal analysis techniques.

Fourier transform infrared (FTIR) spectroscopy is used to determine the cure rate of an epoxy resin consisting of Tetraglycidyl‐4,4′‐diaminodiphenyl methane (TGDDM) and diaminodiphenylsulfone (DDS). Cure rates at 120 and 160°C are shown to increase noticeably when 1% BF3–MEA is added to either TGDDM to TGDDM plus DDS. Fluoroboric acid is shown to increase the cure rates even more than the BF3–MEA. These Results combined with the NMR results in the accompanying article indicate that BF3–MEA is not a catalyst for epoxy resin cure. Instead it is rapidly hydrolyzed to fluoroboric acid which acts as the catalyst.

Fluorine‐19 NMR is used to examine the role of boron trifluoride monoethylamine (BF3–MEA) in epoxy resin cure. Spectra were first recorded in a variety of solvents suitable for dissolving different epoxy resins. All spectra contained a peak due to fluoroboric acid. Spectra of BF3–MEA in orthodichlorobenzene were then recorded at elevated temperatures. The floroboric acid peak area increased, indicating that the BF3–MEA was being hydrolyzed. Results indicate that, at temperatures above 100°C, BF3–MEA is completely hydrolyzed within 5 min to fluoroboric acid.

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