In-Situ Synchrotron X-ray Scattering Studies of the Thermally-Induced Self-Assembly of High-Performance Aromatic Copolyesters

Abstract

In-situ synchrotron small-angle X-ray scattering measurements and quantitative data analysis were used to investigate isothermal self-assembly in a series of high-performance poly(1,4-cyclohexyldimethylene-co-ethylene terephthalate)s (PCETs) enriched with 1,4-cyclohexanedimethanol (CHDM). Interestingly, the bulky CHDM units, which assumed a kinked chair conformation, formed lamellar crystals. The self-assembly process was governed by a nucleation and growth mechanism that depended on the degree of supercooling. Isothermal self-assembly occurred through a four-regime process. The structural evolution was driven mainly by a primary crystallization process, which contributed to crystal layer thickening, and in part by a secondary crystallization process during the later stages, which did not contribute to crystal layer thickness, to produce a lamellar structure. In addition to the primary crystals, highly imperfect small secondary crystals distinct from the lamellar crystals were observed to form. The secondary crystals formed only in the amorphous phases, including in the amorphous layer of the lamellar structure. Surprisingly, the minor ethylene glycol (EG) units tended to be excluded from the primary lamellar crystals.