New Insights in Structures, Properties, and Rheological Behaviors of Cationic Dyeable Polyesters

The incorporation of ionic groups (sodium sulfonate group) in cationic dyeable polyesters (CDPs) leads to alterations in melt flow behaviors and corresponding effects on the conventional production process compared with poly(ethylene terephthalate) (PET). In this study, a range of CDPs were synthesized with a wide range of sodium-5-sulfo-bis(hydroxyethyl)-isophthalate (SIPE) contents, and their structures, properties, and rheological behaviors were comprehensively investigated. The thermal stability of CDPs decreased, while the glass transition temperature initially decreased and then increased with an increase in SIPE content. Several rheological tests were performed, and the time–temperature superposition principle was utilized to give an in-depth analysis of ionic aggregations and internal structures of CDPs. A more complex rheological behavior of CDPs was observed due to the ionic aggregation effects aroused from the strong polarity of sodium sulfonate groups. Based on temperature scans, small amounts of SIPE would act as a plasticizer, reducing the complex viscosity (η*) of CDPs. As the SIPE content increased, the η* of CDPs increased, and the linear viscoelastic interval became narrower, indicative of the formation of ionic aggregates, and this structure was also verified by the results obtained from extensional rheology. Time–temperature superposition began to fail when the SIPE concentration rose further, confirming that ionic aggregation clusters emerged. This work may shed light on the understanding of design and structure–property relationships of PET ionomers.