MISCIBILITY AND ESTERIFICATION IN THE POLY(STYRENE-C-MALEIC ANHYDRIDE) PHENOXY BLENDS

The ''miscibility'' and esterification in poly(styrene-co-maleic anhyd ride) (PSTMA)/phenoxy blends were investigated by DSC and FTIR. The bl ends prepared by casting exhibited a single composition-dependent but broad T-g during the first scanning. The broadness of the T-g transiti on range is due to the presence of microphases in the blends, which ac quired some stability because of the hydrogen-bonding interactions wit h the continuous phase. However, the blends displayed two distinct T(g )s during the second scanning, which can be attributed to phenoxy-rich and PSTMA-rich phases dispersed one in another at a scale larger than the initial one. To investigate the effect of esterification, the sam ples subjected previously to two scannings have been additionally heat -treated several times between 30 and 220 degrees C and annealed each time at 220 degrees C for increasing periods of time. During the addit ional scannings, the two T(g)s identified during the second scanning i ncreased with increasing annealing time but remained distinct. The fac t that the fraction soluble in tetrahydrofuran decreased with increasi ng annealing time indicates that crosslinking due to esterification ha s occurred in both phases. The two phases generated after the first sc anning were stabilized by the esterification reaction at the interface s. (C) 1998 John Wiley & Sons, Inc.