Fourier transform infra‐red spectroscopy of atactic polystyrene in the glass transition region

Abstract

AbstractFourier transform infra‐red (IR) studies on samples of atactic polystyrene with different thermal history, i.e. quenched from the melt (QM), quenched from the rubbery state (QR), slowly cooled (SC), and sub‐glass‐transition (sub‐Tg) annealed (AN), were carried out in the absorption region from 500 to 600 cm−1 with gradually increasing temperatures through the glass transition region at 100°C. The heights of the positive peak (532 cm−1) and the negative peak (566 cm−1) appearing in the temperature difference spectra, T‐60°C, are considered to be a measure of the amount of frequency shifts for the 540 cm−1 and 557 cm−1 bands in the conformationally sensitive spectral range of atactic polystyrene. These bands show a continuously increasing low‐frequency shift with increasing temperature, except for sample QM, the 557 cm−1 band of which shows an inappreciable frequency shift in the range 60 < T/°C < 100. The different temperature behaviour of these shifts for samples QM, QR, SC and AN is due to changes in their intermolecular interactions. Sub‐Tg annealing of the sample QM is shown to shift the frozen high‐temperature state of the quenched sample to the temperature‐defined equilibrium. For all samples of different thermal history the difference in their IR spectra vanish at temperatures above Tg.