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In the present paper, we explore the amorphous phase behavior of poly(butylene terephthalate) (PBT)Zpolyarylate (PAr) blends, primarily using dielectric spectroscopy. Small-angle X-ray scattering experiments show clearly that the PAr resides in the interlamellar zones. We observe two dielectric relaxations associated with long-range motion for blends in which PBT has crystallized. Following from recent research on order-disorder interphases in crystalline blends, we tentatively assign the low-temperature transition to the presence of a crystal-amorphous interphase and the high-temperature relaxation to an unconstrained (mixed) amorphous phase.

The amorphous phase behavior of blends of poly(butylene terephthalate) (PBT) and polyester-ether) segmented block copolymers (PEE) was found to vary from completely immiscible to miscible, depending on the copolymer composition. The predictions of the Flory-Huggins relationship are in general agreement with the observed behavior when the interaction parameters are estimated from solubility parameters. The results of thermal analysis and small-angle X-ray scattering experiments strongly suggest that the PBT and PEE copolymers are capable of cocrystallization in the miscible blends under all crystallization conditions. The cocrystalline microstructure results from the complete miscibility and the blocky nature of the copolymer (i.e., the identical chemical and crystalline structures of the PEE hard segments and PBT). The crystallization rate of the copolymer in the miscible blends was found to be significantly enhanced due to the presence of PBT, and the resulting crystal thickness was found to be the same as that observed for PBT. Partially miscible blends of PBT with copolymers containing intermediate hard-segment concentrations formed distinguishable crystal populations, but the crystallization rate of the copolymer in these blends was also strongly influenced by the presence of PBT.

In this paper we focus on miscible blends of two engineering polymers: poly(butylene terephthalate) (PBT) and a polyarylate (PAr). The issue of transesterification in these blends will be addressed, followed by a discussion of the crystallization kinetics of PBT, poly(ethylene terephthalate) and several PBT/PAr blends. The ability to estimate polymer–polymer interaction parameters in blends from melting point depression will also be discussed. The amorphous phase behavior of the PBT/PAr blends has been explored primarily using dielectric spectroscopy. For blends in which PBT has crystallized, we observe two relaxations associated with Tg‐like motion, and this behavior is interpreted in light of our recent work on order–disorder interphases in crystalline blends.