DYNAMIC-MECHANICAL RELAXATION AND X-RAY-SCATTERING STUDY OF POLY(BUTYLENE TEREPHTHALATE) POLYARYLATE BLENDS

Blends of poly(butylene terephthalate) and polyarylate have previously been shown to be miscible for all blend compositions in the melt stat e or in the quenched amorphous state. Recently, we showed that all com positions of these blends exhibit depression of the thermodynamic melt ing point and a negative Flory interaction parameter.1 Once PBT crysta llizes, it will form crystal lamellae consisting of pure PBT and an am orphous phase of noncrystalline PBT and PAr. The composition of the am orphous phase is the subject of the present study. Dynamic mechanical analysis shows that there exist two tan delta maxima, indicating two a morphous regions, which are assigned to a mixed amorphous phase and a region primarily consisting of amorphous PAr. The location of the PAr depends on the blend composition and was studied by small-angle X-ray scattering (SAXS). For PAr composition < 0.50, the long period of lame llar stacks, obtained from SAXS, increases as PAr composition increase s, while for PAr > 0.50, it decreases. Lamellar thickness can be estim ated from the breadth of (001) using wide-angle X-ray scattering. By c ombining the long period, lamellar thickness, and crystallinity, we de rive a general methodology to describe the morphology of the blends. O ne main conclusion of this work is that the long period is strongly af fected by the degree of undercooling. When blends of different composi tion are prepared with the same thermal history (i.e., the same T(c)), their long periods will vary due to the different degrees of undercoo ling and competition between crystallization and phase separation. Our results show that, for PBT/PAr blends, interlamellar PAr structure ho lds for blends with PAr < 0.40, while either interfibrillar or intersp herulitic structure exists for blends with PAr > 0.40.