Fourier transform infrared temperature studies of an amorphous polyamide are presented. The results strongly suggest that prior interpretations of the changes occurring in the N-H stretching region of the spectra of polyamides and polyurethanes with temperature were greatly oversimplified. In essence, these spectral changes were interpreted to be solely due to hydrogen-bonded N-H groups transforming to "free" N-H groups. Subsequent use of these data to obtain thermodynamic parameters associated with hydrogen bond dissociation must now be considered erroneous.The primary factor not taken into account concerns the very strong dependence of the absorption coefficient with hydrogen bond strength. With increasing temperature, the average strength of the hydrogen bonds decreases, which is observed in the infrared spectrum by a shift to higher frequency. Concurrently, the absorption coefficient decreases, leading to a reduction in the absolute intensity of the hydrogen-bonded N-H band. In this study we present experimental results in the N-H stretching and amide I, II, and V regions of the infrared spectrum of an amorphous polyamide. In addition, we present a model, justified by theoretical considerations, which we believe advances our understanding of the strong dependence of absorption coefficient with the strength of the hydrogen bonds. The ramifications of this work to hydrogen-bonded polymers are discussed.
Fourier transform infrared temperature studies of two semi‐crystalline polyamides, nylon 12 and a terpolymer of nylon 6/66/610 are presented. The results obtained are consistent with those recently published from similar studies of an amorphous polyamide and nylon 11 and further bolster our general interpretation of the infrared spectra of polyamides.
The authors have an ongoing research interest in the application of Fourier transform infrared spectroscopy to the study of compatible polymer blend systems and, in particular, the role of intermolecular interactions in compatibilization. It was considered essential to obtain an independent measurement of the lower critical solution temperature (LCST) of the particular polymer blends used in our studies. Not having conventional light scattering equipment, it was decided to attempt to use our Raman spectrometer for these purposes. In this communication we describe the simple method employed and present preliminary results from three polymer blend systems. The results exceeded our expectations. The onset of phase separation is obvious, and the experimentally determined LCSTs are in accord with previously published data.
Polymer blends of an amorphous polyamide with poly(2vinyl pyridine) (P2VP) are presented. Differential scanning calorimetry results suggest that the system exists as a single phase material as evidenced by a single glass transition temperature. However, as illustrated by light scattering studies, this miscible binary mixture possesses a relatively low, lower critical solution temperature (LCST). Fourier transform infrared (FTIR) spectroscopic investigations indicate that the interactions occur in the blend between the NH group of the polyamide and the N: atom of P2VP and that the strength of the Interactions between the components is nearly identical to that occurring in the self‐association of the pure amorphous polyamide. Additionally, by monitoring the concentration of “free” carbonyl groups, a quantitative measure of the number of interactions occurring in the blend is obtained.
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