Search

Thestructure, morphology, and thermal properties of biobased andbiodegradable poly(butylene succinate-ran-butyleneazelate) random copolyesters with a wide composition range were studied.These PBS-ran-PBAz copolymers can crystallize inthe entire composition range despite being random, displaying a eutecticpoint when their melting point is plotted as a function of composition.Wide angle X-ray scattering (WAXS) studies confirmed isodimorphicbehavior where PBS-rich copolymers crystallize with PBS type unitcells with some PBAz repeating unit inclusions and vice versa forPBAz-rich copolymers. Away from eutectic compositions the copolymersexhibit only one crystalline phase (PBS-rich or PBAz-rich crystallinephases) while at the eutectic point both phases can crystallize. Theonly double crystalline copolymer among those prepared had a compositionclose to the eutectic point of 45 mol % PBS (and 55 mol % PBAz). Thecrystallization of the two phases occurred in the same temperaturerange upon cooling from the melt at 10 °C/min in a DSC (i.e.,coincident crystallization). Self-nucleation (SN) studies of the PBS-richphase were performed. After SN, the separate crystallization of eachphase was clearly observed during cooling from the self-nucleationtemperature (i.e., PBS and PBAz-rich phases). Small angle X-ray scattering(SAXS) experiments were performed for the first time for these typesof isodimorphic copolymers. The results show that the lamellar longperiod is a strong function of composition. While limited inclusionsof PBAz units within the crystal lattice only cause a slight expansionof the PBS component unit cell, the increase of comonomer contentproduces an unexpected synergistic increase in long periods and lamellarthickness values. In the case of the only double crystalline copolymerexamined, the PBS-rich phase forms space filling spherulites (observedby polarized light optical microscopy, PLOM) at higher temperaturesthat template the superstructural morphology of the copolymer. ThesePBS-rich phase spherulites contain radial lamellar stacks whose longperiod was determined by SAXS. Upon further cooling, the PBAz-richphase crystallizes in the intraspherulitic amorphous regions withnewly formed lamellae that have their own distinct long period accordingto SAXS results. AFM observations of the PBS-rich crystalline lamellaeconfirmed the lamellar thickness and long spacings determined by SAXS.A schematic morphological model of the mixed spherulites producedby this double crystalline diblock copolymer is proposed based onthe experimental evidence collected by SAXS, PLOM, and AFM. [ABSTRACT FROM AUTHOR]