Simulation of the influence of the polymer conformation, orientation, crystallinity, and stretching on its IR absorption spectrum

Abstract

535.43Using cis-1,4-polyisoprene as an example, the influence of the conformation and orientation of the polymer chain on its polarization absorption spectra has been simulated. It has been shown that if a change in the orientation of the polymer chain leads to a monotonic change in the intensities of the absorption bands with their maxima positions remaining unchanged, then changes in the polymer chain conformation additionally cause a shift and the appearance of new absorption bands. According to the results of the calculation of the vibrational spectra, the inversion of the IR dichroism of the absorption bands of polymers is associated with the conformation transition. We simulate the influence on the IR absorption spectrum of the degree of crystallinity of cis-1,4-polyisoprene, in which the amorphous and amorphous-crystalline states are considered as a mixture of noninteracting polymer chains, where each state is characterized by a certain ratio of conformers. Likewise, the changes in the IR absorption spectrum of cis-1,4-polyisoprene under its stretching have been investigated.

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“…as reference), since it presents a unitary dichroic ratio independently of the polymer structure. While the peaks at 1367 cm − 1 (CH 3 deformation) and at 837 cm − 1 (= CH out of plane bending) were selected to calculate the dichroic ratio (R) in all the selected configurations, in order to investigate the orientation of the macromolecular chains of the cis-1,4-polyisoprene [18,19].…”

“…The acquired polarized ATR-IR spectra were analyzed considering the peak at 2960 cm −1 , related to the CH 3 asymmetric stretching, as reference band, since its dichroic ratio is unitary, independently of the polymer's structure [18,19]. In our case, for all samples the dichroic ratios of the peaks at 1367 cm −1 and 837 cm −1 were calculated, since, as previously mentioned, these two peaks are assigned to the CH 3 deformation and the CH out of plane bending of cis-1,4-polyisoprene, respectively.…”