Influence of Polymer Topologies on Curing Mechanism and Recyclability

Abstract

Polyurethane is widely used in various industries due to its structural strength and chemical resistance, but in particular, thermoset polyurethane has a limitation that it is almost impossible to recycle due to its crosslinked structure. Polyurethanes, despite their widespread industrial applications, present significant recycling challenges due to their thermoset nature. While recent studies have explored dynamic covalent chemistry to improve recyclability, the effect of macromolecular topology on reprocessing behavior remains underexplored. In this study, thermoplastic polyurethanes were synthesized by reacting topology-controlled polyols (branched cyclic, hyperbranched, and linear) with pentamethylene diisocyanate. The resulting polymers were characterized using swelling tests, FT-IR, TGA, and DSC, and their reprocessing behavior was investigated via DMA and UTM. Interestingly, all topologies—branched cyclic, hyperbranched, and linear—exhibited increasing brittleness upon repeated reprocessing. For branched cyclic structures, alternating transitions between intermolecular and intramolecular transcarbamoylation were observed, but their cyclic nature partially suppressed intramolecular cross-linking, resulting in relatively stable mechanical performance over multiple cycles. In contrast, hyperbranched and linear structures, which initially favored intramolecular cross-linking, gradually developed more intermolecular cross-links during reprocessing. Notably, linear samples demonstrated a greater tendency for intermolecular cross-linking than hyperbranched, attributed to their extended linear architecture. These findings highlight the crucial role of polymer topology in dictating cross-link rearrangement pathways during reprocessing, offering insights for designing recyclable polyurethanes with enhanced durability.