Application of the Low Frequency Raman Spectroscopy for Studying Ultra‐High Molecular Weight Polyethylenes

Abstract

Summary:In the frequency range below $150 cm À1 , the longitudinal acoustic modes (LAM) localized along straight chain segments (SCS) of macromolecules emerge in the Raman spectra of linear semicrystalline polymers. The LAM frequency is inversely proportional to the SCS length; therefore, the LAM band contour reflects the SCS length distribution in a sample. The opportunities given one by the low-frequency Raman spectroscopy for studying the ordered structures in polyethylene are demonstrated and discussed. The illustrating material consists of both previously published and original data on nucleation and transformation of the ensemble of SCS in powder-like, gelled, and drawn ultra-high molecular weight polyethylene.

Ultrafast impulsive Raman spectroscopy across the terahertz–fingerprint region

“…One direction might be toward the field of material science, with potential applications in investigating polymers, which often have rich information in the fingerprint and low-frequency regions. 16,49 5 Appendix A: Further Results of DIVS…”

“…This can be especially valuable in fields such as pharmacology or polymer research, where the purity or localization of targets may be assessed by fingerprint spectra, while the crystalline polymorphism or the polymer stress, extent, or nature of polymerization can be probed by lowfrequency spectra. [12][13][14][15][16][17] Although there exist a multitude of techniques for capturing broadband Raman spectra across the THz-fingerprint region, they tend to be too slow for certain applications. For example, spontaneous Raman spectroscopy, a well-developed and commonly used Raman technique, can provide broadband vibrational spectra including both low-frequency and fingerprint regions but at typical spectral acquisition rates of <10 spectra∕s.…”