Fourier-transform infrared (FT-IR), near-infrared (NIR)-excited FT-Raman, and FT-NIR spectra have been measured for poly(acrylic acid) (PAA) in a cast film over a temperature range of 40−140 °C, to investigate structures of hydrogen bonds and their dissociation. The CO stretching bands in the FT-IR spectra are unraveled by a prevalent multiple species model for small aliphatic acids with various kinds of associated forms of carboxylic acid groups, namely cyclic dimer, linearly associated oligomers of COOH, and free COOH groups. These different structures of hydrogen bond persist even when the temperature rises well above the glass transition temperature. The FT-Raman spectra confirm the existence of such COOH groups. Temperature-dependent intensity changes in the first overtone of an OH stretching mode of PAA reveal that the COOH groups dissociate significantly at high temperatures. We propose that the coexistence of various possible hydrogen-bond forms analogous to those in small aliphatic acids best int...

Infrared, Raman, and Near-Infrared Spectroscopic Evidence for the Coexistence of Various Hydrogen-Bond Forms in Poly(acrylic acid)

Infrared (IR) spectroscopic imaging seemingly matured as a technology in the mid-2000s, with commercially successful instrumentation and reports in numerous applications. Recent developments, however, have transformed our understanding of the recorded data, provided capability for new instrumentation, and greatly enhanced the ability to extract more useful information in less time. These developments are summarized here in three broad areas--data recording, interpretation of recorded data, and information extraction--and their critical review is employed to project emerging trends. Overall, the convergence of selected components from hardware, theory, algorithms, and applications is one trend. Instead of similar, general-purpose instrumentation, another trend is likely to be diverse and application-targeted designs of instrumentation driven by emerging component technologies. The recent renaissance in both fundamental science and instrumentation will likely spur investigations at the confluence of conventional spectroscopic analyses and optical physics for improved data interpretation. While chemometrics has dominated data processing, a trend will likely lie in the development of signal processing algorithms to optimally extract spectral and spatial information prior to conventional chemometric analyses. Finally, the sum of these recent advances is likely to provide unprecedented capability in measurement and scientific insight, which will present new opportunities for the applied spectroscopist.

https://journals.sagepub.com/doi/pdf/10.1366/12-06801

Infrared Spectroscopic Imaging: The Next Generation

Polymer blends may be defined a s physical mixtures of two or more polymers [1]. Conceptually, polymer blends are analogous to metal alloys, materials which date back to the dawn of civilization. In much the same way as the metallurgists sought to improve the chemical and physical properties of metallic materials by mixing various metals, polymer scientists have also employed this technique to produce a wide variety of useful polymeric materials. However, we must be careful not to push this analogy too far. There are many fundamental differences between these two classes of materials.

Fourier Transform Infrared Spectroscopy: Probing the Structure of Multicomponent Polymer Blends

The miscibility of poly(4-vinylphenol) (PVPh) and poly(methyl methacrylate) (PMMA) blends has been investigated by FTIR and FT-Raman spectroscopy. Although both techniques provide evidence for the ...

FTIR and FT-Raman Studies of Partially Miscible Poly(methyl methacrylate)/Poly(4-vinylphenol) Blends in Solid States

For phase-separated multicomponent polymeric systems, characterization of the interface between the components is particularly challenging. We have observed an optical effect in the infrared that can be used to image the interface specifically. This method yields images of the interfaces based on the interfaces showing apparent absorption arising from changes in refractive index at frequencies far from the specific frequencies associated with the components of the mixture. This method has been applied to multicomponent samples of polymer-dispersed liquid crystals where the nature of the interface can be specifically altered by the application of an electric potential across the sample. Effects of this optical phenomenon on spectra from such multicomponent systems are discussed, and factors that complicate quantitative analysis of data from interfacial regions have been pointed out.

FT-IR Imaging of the Interface in Multicomponent Systems Using Optical Effects Induced by Differences in Refractive Index:

Calculations of infrared difference spectra of polymer blends and pure components have been made based on models with no intermolecular bonding interactions. The results demonstrate that residual peaks can arise from optical phenomena based solely on the effects of differences in the real part of the refractive indices of the pure components. Accordingly, chemical interpretations, such as intermolecular bonding interactions, of residual difference peaks must be made with caution in blends where the real refractive indices of the components differ by several percent or more in absorption-free energy regions.

D. L. Allara

Papers

Infrared Spectra of Polymer Mixtures—Problems Caused by Dispersion Effects in Difference Spectra