Miscibility enhancement of modified polystyrene blends with a liquid crystalline polymer

Polystyrene (PS) was completely immiscible with a liquid crystalline polymer (LCP), a copolyester of p-hydroxybenzoic acid and poly(ethylene terephthalate). As revealed by differential scanning calorimetry and scanning electron microscopy (SEM), chemically modified PS, sulfonated PS (SPS) and four of its salts, were miscible with the LCP. Each LCP/SPS blend had only one composition-dependent glass transition temperature (T-g), from which and from the T(g)s of the SPS compounds, the T(g)s of the LCP component were found to be almost the same via the Fox equation. SEM observation showed that LCP/SPS 75/25 blends had a homogeneous texture with no discernible dispersed particles, while LCP/SPS 25/75 blends had dispersed, nanometre-sized particles which were aggregates of SPS anions as confirmed by X-ray photoelectron spectroscopy. Characteristic absorption shifts in the Fourier transform infra-red spectra of LCP/HSPS revealed that miscibility enhancement was caused by specific interactions between the carbonyl groups of LCP and sulfonate groups of the acid form of SPS. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.