Increasing the cross-link density in a dual dissociative and associative polythiourethane covalent adaptable network improves both creep resistance and extrudability

Sergio Serna, Nathan S. Purwanto, Logan M. Fenimore, John M. Torkelson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

There have been significant, recent reports of the effects of cross-link density on the relaxation dynamics and processability of exclusively associative covalent adaptable networks (CANs), also called vitrimers. Similar characterization is lacking for the substantial number of CANs that exhibit dual associative and dissociative dynamic covalent chemistries. Polythiourethane (PTU), which is a thiol-based analogue of polyurethane, is one such polymer class that exhibits both dissociative and associative dynamic chemistries. Here, we tune the cross-link density of PTU CANs by systematic incorporation of long-chain and short-chain thiols. As would be commonly expected, relative to networks with lower cross-link density, PTU networks with higher cross-link density exhibit improved creep resistance at 60 °C and 100 °C. However, we also observe faster elevated-temperature stress relaxation with increasing cross-link density, which is attributable to the dual nature of the PTU dynamic chemistry, with the associative dynamic mechanism being increasingly favored and becoming increasingly more rapid with increasing cross-link density. Because of this shift, our PTU CAN with the highest cross-link density undergoes facile melt extrusion at 150 °C; in contrast, our PTU CAN of lowest cross-link density cannot be melt extruded. Overall, this work highlights the significance of cross-link density in networks exhibiting two or more dynamic chemistries and how that may lead to otherwise unexpected outcomes, e.g., better processability at higher cross-link density.

Original languageEnglish (US)
Article number127232
JournalPolymer
Volume306
DOIs
StatePublished - Jun 21 2024
Externally publishedYes

Keywords

  • Covalent adaptable network
  • Creep resistance
  • Cross-link density
  • Extrusion
  • Polythiourethane
  • Stress relaxation
  • Transcarbamoylation

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Materials Chemistry

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